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CHAPTER 14

OPERATING PRINCIPLES OF A HEMISPHERICALSCAN RADAR AN/SPS-42 (PART I)

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INTRODUCTION

A hemispherical scan radar system presentsthree-dimensional target information. Theground range (distance) and azimuth (bearing)and elevation (height), of a target are displayedon plan position indicators and the elevation andslant range are displayed on range-height indi­cators.

A representative hemispherical scan radarsystem presently in naval use is the Radar SetAN/SPS-42 (fig. 14-1). The circuits of theAN/SPS-42 are used in discussing the operat­ing principles of a hemispherical scan radar.

Recent changes in the AN/SPS-42 led to thedevelopment of the AN/SPS-39 . The latterequipment underwent a change to become theAN/SPS-39A. The first change from the AN/SPS-42 to the AN/SPS-39 is significant in thatit modified the basic elevation scanning proc­ess. The change to the AN/SPS-39A was aphysical change in the various units in the sys­tem but did not change the functional or circuitoperation of the radar set.

The treatment of the AN/SPS-42 is containedin two parts. Part I (this chapter) considers themajor circuits involved in producing the r-fpulse envelope which is radiated by the radarantenna. Part II (chapter 15) presents a dis­cussion of the major receiving and display cir­cuits. Block diagrams are used to illustratefunctional operation.

GENERAL DESCRIPTION

Radar Set AN/SPS-42 provides three-dimen­sional target position data under all weatherconditions, at ranges up 160 miles, in 360 0

azimuth and up to 75,000 feet in elevation. Asis true of all radar systems, the AN/SPS-42consists basically of a single antenna, a trans­mitter, and a receiver indicator and synchro­nizer (fig. 14-2). The presentation of range,azimuth, and elevation information for all

311

targets in the field of scan is accomplished bydetecting the video echo pulse in the receivingfunction and displaying the information on thescreen of a cathode-ray tube located in the in­dicating function.

The azimuth scanning is performed by theantenna. The antenna is motor driven at 4.8,11, 15, or 30 revolutions per minute (rpm). Theelevation scanning is accomplished electroni­cally by changing the frequency of the transmit­ted radar beam in discrete increments.

A synchronizing function provides mastertiming triggers necessary to coordinate the op­eration of all units in the Radar Set AN/SPS-42.

From a stable attitude of the antenna, theradiated beam scans in elevation from approxi­mately 48 0 to 3/4 0 above the horizontal plane in26 steps, each step having a discrete scan fre­quency. To permit stabilization of the elevation­scan pattern in space irrespective of pitch androll of the ship, additional frequencies are avail­able to compensate for radar-beam positionsabove 48 0 and below the horizontal plane. Theseadditional frequencies are used to cancel out theeffects of the pitch and roll motions of the shipso that the indicator displays the correct infor­mation.

Radio-frequency energy in the range from2910 to 3090 me is generated and supplied bythe transmitter circuits to the antenna. Eachapplied frequency causes the radar beam to beradiated at a different elevation angle. The se­lection of a frequency to provide the proper ele­vation angle is performed by the frequency­selection channel in the transmitting function.This channel receives gate pulses from thesynchronizing function to control the radiationfrequency . An increase in the radiation fre­quency lowers the radar beam and a decrease infrequency raises the radar beam in the elevationscan.

The frequency-generating system in the trans­mitting section consists of three banks of oscil­lators, frequency multipliers, and amplifiers.

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312 CIRCUITRY OF SIDPBOARD ELECTRONICS EQUIPMENT

ANTENNA

11JT RANSM ITTINGTRANSMITTED RF (2 9 10 TO 3090 tv1C IN 25 STEPS)

FUN CTION RECEIVED RF(VARI ABLE

. It \~~FREQUENC Y) LOCAL OSCILLATOR RF

~FREQUENCYSELECTING

UCHANNEL ANTENNA(OMNI)

SYNCHRONIZI NGTRIGGER OMNI

LOCALRETURN

OS CILLATORSIGNAL

SID E LOBE

SYNCHRONIZ ING RECEIVING SUPPRESSIONIF

(SLS)F UNCTION FUN CT IO N SIGNALS

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ANTEN NA SYNCHRONIZING VIDEO

ELEVATION TRIGGER

(~) SIGNALS AN TE NNA ANTEN NA AZ I MUTH SIG NAL

PO S ITION I NG AZIMUTH ERROR SI GNA L

ANTENNA FU NCTI ONINDI CATING AZI MUTH SIGNAL

FUN CTION GROUNDRANGE

COORDINATES

i WAVEFORM..ROLL , PITCH CONVE RTIN G

AND O.SC SLANT RANGE FUNCTIONDATA COORDINAT ES

TESTING

FUNCTI ONSHIP'S

__ OPERATING POWER TO ALL GROUPSPOWER

PRIMARY - -..t POWER DISTRIBUTIONCONTROL

440V 60 CPS 3~ FUNC TION __ SIGNALS TOTE ST S IGNALS 11 5V 60 CPS 14>

FROM ALL GROUPS

ALL GROUPS

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Figure 14-2.-Simplified block diagram of Radar Set ANjSPS-42.

The oscillators receive binary gates from flip­flop circuits in the synchronizing section.These gates combine the oscillator outputs inaccordance with the computer programming toproduce the various output frequencies of theradar transmitter .

The target video signal returned to the an ­tenna is applied to the receiving function. Afteramplification in the r ec eiver, the video signal

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is supplied to the indi cating function which usestwo types of indicators (fig. 14-1). One of theseis a plan position indicator (PPI) and displaysthe azimuth and range of the various targets.The other is a range height indicator (RHI), anddisplays target data in slant range, altitude, andelevation angle. The PPI indicates target posi­tion with reference to either true north (true bear­ing ) or to own ship's course (relative bearing). o

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 313

The radar set is provided with operatingpower from the ship's primary power source.This power is delivered at 440 volts, 60 cps,3~ and at 115 volts, 60 cps, single phase to thepower distribution circuits, which, in turn, sup­ply the entire radar system.

The radar system consists of nine systemfunctions (fig. 14-2). Seven of these functionsare shown in more detail in figure 14-3. Func­tion, as applied in this discussion, refers to agroup of electronic circuit sections, channels,and stages combined to produce a specializedradar operation. The seven functions shownare: antenna positioning, testing, receiving,ind icating, power distribution, transmitting, andsynchronizing. The other two functions (treatedlater) which make up the total of nine functionsare the side lobe suppression (SLS) and wave­form converting functions (fig. 14-2).

Each function (fig. 14-3) performs a specificoperation which will be discussed fully later.A brief description of each function is given inthe following paragraphs to show the purposeand relationship of the various functions, andshould be considered introductory to the speci­fic performance.

The purpose of the synchronizing function isto provide master timing triggers and controlsignals necessary to coordinate the operation oftransmitting, receiving, indicating, and testingfunctions.

The transmitting function generates a seriesof precise frequencies between 2910 and 3090megacycles, which are transmitted as one­megawatt r-f pulses during the transmittingperiod. The pulse width of the transmitted r-fenergy may be either 1 or 4 microseconds induration as determined by the radar operatingmode. During the receiving period, the trans­mitting function supplies the local oscillatorsignal to the receiving function.

The transmitting function consists of threechannels, namely, the r-f channel, the modula­tor channel, and the power supply channel (notshown). The microwave circuits, i.e. , the r-finput waveguide and mixer circuits, are alsocontained in the transmitting function.

The r-Lchannel comprises a frequency se­lection channel. This circuit contains a fre­quency counter which controls the frequency ofthe transmitted radar beam. Reference to thisfrequency counter (not shown) and its effect onthe transmitter output is repeated several timesthroughout this chapter.

The r-f channel provides the necessarypower amplification for a low-level r-f signalgenerated in an oscillator-amplifier section

similar to that in the transmitting functionalsection of the Radar Set AN/SPS-29. The actionis treated in chapter 12 of this training course.The modulator channel gates high-power r-famplifiers in the r-f channel during the trans­mitting period. The power supply channel (notshown) supplies the necessary d-c potentialsfor the generation of the transmitted pulse.

The receiving function of the AN/SPS-42consists of three major parts , exclusive of theantenna. These are the i-f amplifier channel,the clutter gate channel, and the moving targetindicator (MTI) channel.

The receiving function provides the detectionand amplification of target echoes. Echoes re­ceived at the antenna are routed through themicrowave circuits in the transmitting functionto a crystal mixer assembly similar to that inthe Radar Set AN/SPS-lOD discussed in chapter10 of this text. The echo pulses are heterodynedwith a local oscillator signal in the microwavecircuits to produce a 12-mc i-f signal. Thissignal is amplified and fed to the i-f amplifierchannel in the receiving function.

The i-f s ignal is detected and the resultantvideo is routed to a clutter gate channel and toa moving target indicator (MTI) channel. Eachof these are video channels which operate underspecific conditions.

The clutter gate makes possible the detectionof moving targets located amidst large targets,such as clouds and sea return, which wouldotherwise be lost. The MTI unit is designed tocompare the video returns from two successivetransmitter pulses at the same beam position.

The clutter gate is essentially an electronicswitch which normally channels the video signalto the radar indicators. Under certain condi­tions, however, the clutter gate automaticallysuppresses the clutter gate normal video chan­nel to the indicators and gates on the movingtarget indicator video channel. This action pro­vides MTI video to the radar indicators. If allof the requirements for MTI presentation arenot met, the clutter gate channel will suppressthe output of the MTI video channel, and gate onthe clutter gate normal channel.

The moving target indicator presentationshows only those targets that are in motion inthe midst of clutter. Signals from stationarytargets in clutter are removed from the returnby memory circuits.

The purpose of the antenna positioning func­tion is to control the azimuth rotation of theradar antenna. Control of the antenna speedis accomplished either automatically or manu­ally.

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314 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

When the antenna positioning function is inthe automatic mode of operation the antennawill rotate at a specific rate of speed as deter­mined by the setting of antenna control switcheson an electrical test panel (not shown), a radarset control (fig. 14-1), or the radar test setgroup. In the automatic mode the antenna maybe operated at one of four speeds that are au­tomatically controlled by a closed loop servo­amplifier system (fig. 14-3). The normal op­erating speed is 15 rpm. The other threespeeds are 11.5 rpm for MTIoperation, 4.8rpm for coincident video operation, and 30 rpmfor antenna testing. In the manual mode of op­eration, antenna speed and positioning are con­trolled by a hand-operated tachometer genera­tor.

The indicating function displays airbornetargets on the screens of cathode-ray tubes sothat the position of the various targets may bedetermined in terms of azimuth, height, andrange. The cathode-ray presentation is dis­played at the radar set console (fig. 14-1). Twocathode-ray indicators are used. One of .theindicators, azimuth-range indicator, displaysthe target information in the form of groundrange versus azimuth bearing. The other indi­cator, the range-height indicator, displays thetarget information in the form of slant rangeversus height.

The range-height indicator (fig. 14-3) re­ceives its video input directly from the re­ceiver while the video to the azimuth-range in­dicator is routed through the IFF equipment.The azimuth-range indicator presents targetinformation in true or relative bearing.

The indicating function receives synchroniz­ing triggers from the synchronizing function toinitiate and terminate the indicator sweeps.

The indicating function contains a data sta­bilization section which supplies space stabi­lized information to the target positioningcircuits of the two indicators. The space sta­bilization signals compensate for pitch and rollof the ship before application to the target po­sitioning circuits.

The purpose of the power distribution func­tion is the production, distribution, and controlof a-c and d-c power within Radar Set AN/SPS-42. utility functions such as heaters,blowers, and delay and interlock circuits arealso part of the power distribution function.

The power distribution function obtainsthree-phase, 440-v, 60-cps power, and single­phase 115-v, 60-cps power from the ship'sprimary power source. Output power is appliedto the various functions of the radar system.

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The radar set console and the antenna pedes­tal space heaters are remotely located from theradar room. These units therefore obtainsingle-phase, 115-v a-c power directly from theship's primary power source.

The testing function (fig. 14-3) provides ameans of checking the operation of Radar SetAN/SPS-42, and aids in the isolation of malfunc­tions within the radar system. This is accom­plished by routing samples of the major signalsand voltages from various functions to a testinstrumentation console, and checking their op­eration characteristics. The instrumentationconsole consists of the radar test set group(fig. 14-1) and associated oscilloscopes.

Contained in the meter monitoring and oscil­loscope monitoring section of the testing func­tion is an r-f power monitoring channel, a volt­age standing wave ratio measuring channel, anantenna speed monitoring channel, and twomonitoring oscilloscopes. The circuit to betested is selected by the operator. Testing thevarious functions of Radar Set AN/SPS-42 maybe accomplished without interfering with thenormal operation of the radar system.

The waveform converting and side lobe sup­pression functions are not shown in figure 14-3.The relationship of these functions to the var­ious other functions in the radar system istreated in chapter 15 of this text. The side lobesuppression (SLS) function detects and elimi­nates return echoes originating outside the mainlobe beam of the radar antenna. The SLS cir­cuit also prevents enemy jamming signals fromdisrupting the indicator displays.

A signal from an omnidirectional antenna isutilized to provtde a reference signal with whichthe radar return signal from the main antennais compared. When the signal from the omni­directional antenna is greater than that from theradar antenna, an undesirable signal is presentand an SLS gate is generated which reduces theradar receiver gain during the time that theobjectionable return is being received.

The purpose of the waveform convertingfunction is to convert ground range target in­formation to slant range target information.

SYNCHRONIZING FUNCTION

As forestated, the synchronizing functiongenerates the timing and control signals forRadar Set AN/SPS-42. The timing and controlsignals program and coordinate the operation ofthe indicating, receiving, transmitting, and test­ing functions. The synchronizing function pro­vides the necessary timing and control signals

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 315

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for four possible modes of operation: Normal,Normal-MTI, Coincident Video (CV), and CV­MTI. The specific operation achieved in eachof these modes is discussed later in this chap­ter.

The synchronizing function (fig. 14-3) isseparated into two main channels; the timingchannel and the elscan computer-programmerchannel. The channels of the synchronizingfunction provide separation of the two types ofsignals produced by the synchronizing function;Le., timing pulses and control gates.

The timing channel provides the timing trig­ger s necessary to coordinate the operation ofthe radar system. These triggers synchronizethe operation of the testing function , initiate thetransmission of r-f energy, turn the receiveron and off, and initiate and terminate the indi­cator sweeps.

The elscan computer-programmer channelprovides control gates to the receiving, indicat­ing, and transmitting functions. The controlga tes are employed to select the transmitterfrequency , and, by means of the frequency, tocontrol the elevation angle beam position of theradiated energy. The control gates also posi­tion the indicator sweeps so that they coincidewith the radiated beam position, and prov idespecial commands to the receiving functionduring MTI or CV operation. The elscancomputer-programmer channel is divided intothe beam positioning subchannel and the MTI -CVsubchannel.

The synchronizing function is a digital com­puter with built-in logic circuits. The produc­tion of binary gates and timing triggers is con­trolled by these logic circuits. Relays andswitches, which are activated when the operatorselects any of the four modes of radar opera­tion, permit the built-in logic to be modified forthe particular mode selected.

The basic theory of computer operation ispresented in the training course, Basic Elec­tronics, NavPers 10087-A. However, a briefintroduction of computer logic is given here.This information will be helpful in understand­ing the functional operation of the synchronizingfunction which follows.

LOGICAL ALGEBRA

Logical algebra is a branch of algebra thatexpresses formal logic in equation form. Theuse of logical algebra greatly facilitates theanalysis of logic circuits such as those em­ployed in the synchronizing function. Inputsignals applied to these logic circuits produce

logic signal outputs. A logical equation is con­structed as follows: The output signal is ex­pressed in terms of the input signals and theoperations performed upon these input signalsby the logic circuits. Each signal is a variablewhich is expressed by suitable algebraic nota­tion. These variables are then combined byoperational symbols similar to the additionand multiplication signs of ordinary algebra toform a logical equation.

The advantage in writing logic signals (sig­nals produced by logic circuits) in equationform is derived from the fact that the equationcan easily be converted into a circuit which isable to produce the output signal expressed bythe equation.

As applied to the synchronizing function,logical algebra is restricted to devices whichare always in either of two possible states. Thetwo states can be called the on and off states,the transmission and hindering states, and 1 ando states, or the true and false states. The logiccircuits employed in the synchronizing functionconsist of AND gates, OR gates, transmissiongates, transistor inverters, and flip-flops . TheAND, OR, and transmission gates are composedof semiconductor diodes and behave essentiallyas single throw (ON-OFF) switches.

Flip-flops are multivibrators whose squarewave outputs are in either of two possible volt­age states. The flip-flop behaves as two singlethrow switches acting in opposition to eachother (t.e., if one switch is turned ON the otheris turned OFF). The transistor inverter pro­duces the inverse of the signal applied to it.

Throughout the synchronizing function, logics ignals will be described as being in either the1 state or the 0 state. In the 1 state, the signalvoltage ranges from 0 to +4 volts, the valuebeing dependent upon the particular signal in­volved. In the 0 state, the signal voltage rangesfrom -15 to -18 volts, again depending on theparticular signal. Timing triggers, i .e., clockpulses, are excluded from the logic signal cate­gory and are described as being either presentor not present.

All logical equations essentially answer thequestion "When is the output signal in the 1state?" To determine the answer to this ques­tion, write the equation of the circuit, express­ing each input signal in algebraic notation; re­place each variable by its value, either 1 or 0;and perform the algebraic operations indicatedby the equation.

Three logical operations are possible withtwo-state devices; logical addition (the OR op­

. eration), logical multiplication (the AND

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316 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

operation), and negation. The terms additionand multiplication, as they are used in logicalalgebra, have no equivalent in ordinary algebra.

The OR operation is symbolized by the plussign. A typical equation in which the OR opera­tion is performed is A + B = C. In words, thisis expressed as "If either variable A or B isequal to 1, or if both variables are equal to 1,the output (variable C) is equal to 1." A simplecircuit which performs the OR operation con­sists of two switches in parallel between the in­put and output terminals of the circuit. If eitherswitch is closed, the circuit is completed and aninput signal is passed. If both switches areclosed, the input signal is still passed. Therules of OR operation (logical addition) arewritten as:

o + 0 = 01 + 0 = 10+1 11 + 1 == 1

The AND operation is symbolized in thesame way that multiplication is symbolized inordinary algebra. A typical equation involvingthe AND operation is AB = C. In words, this isexpressed as "If, and only if, both variable Aand variable B are equal to 1, the output (vari­able C) is equal to 1." A simple circuit whichperforms the AND operation consists of twoswitches in series between the input and outputterminals of the circuit. Only when bothswitches are closed can an input signal bepassed. The rules of AND operation (logicalmultiplication) are written as follows:

1 x 0 0o x 1 0o x 0 01 xII

Negation is the act of taking the complementof a variable, and is symbolized by placing abar over the variable which is negated. If var­iable A is in the 1 state, its negation, A, is inthe 0 state. Conversely, if A = 0, A = 1. Thenegation of A is A which can also be expressedas A. A simple circuit which performs this op­eration consists of two switches mechanicallylinked so that if switch A is closed, switch A isopened.

LOGIC CIRCUITS

To perform the operations required by log­ical algebra, physical devices are utilized. A

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circuit composed of these devices can be syn­thesized directly from the logic equation of theoutput signal which is to be produced. A diodeAND gate circuit, or a transmission AND gatecircuit (passing a pulse to gate a circuit) satis­fies the conditions for the AND operation sign;a diode OR gate or a transmission OR gate re­places the OR operation sign; a flip-flop or atransistor amplifier (inverter) replaces thenegation sign. These six circuit elements canbe combined in any manner that may be requiredto reproduce any logic equation incorporatingthe operations of multiplication, addition, andnegation.

AND Gate

An AND gate circuit (fig. 14-4, A) consistsof two or more semiconductor diodes connectedin such a way that the signal inputs to both diodesare in the 1 state when the output of the ANDgate is in the 1 state. The voltage state of theoutput, C, is determined by the conduction stateof input diodes CRI and CR2. The input voltageat points A and B can be either -18 volts (theo state) or +2 volts (the 1 state). If both inputsare in the 1 state, both diodes are forwardbiased and conducting. Neglecting the forwardvoltage drop across the diodes, the voltage atpoint C is also in the 1 state (+2 v). If eitherinput A or input B is in the 0 state, (he inputdiode to which the -18 volts is applied is for­ward biased. The drop across that diode isstill negligible, and the -18 volts at point Cback-biases the other input diode. The voltageat point C is therefore in the 0 state (-18 v),

An AND gate can be constructed for anynumber of input signals. Each input signal musthave its own input diode. Regardless of thenumber of inputs, it is still true that if anyoneof them is in the 0 state, the voltage at point Cis in the 0 state. The truth table (operationtable) summarizes the possible combinations ofA and B. In each row of the table, the A and Bentries produce the C entry. This table is sim­ply a formalized way of writing the rules oflogical multiplication.

Transmission AND Gate

The transmission AND gate (fig. 14-4, B) isa modified AND gate used to control the passageof a timing trigger to the input of a flip-flop orblocking oscillator. A and B (enabling gates)are applied to the cathodes of input diodes (fig.14-4, B). The timing pulse (T p ) is applied tothe cathode of diode CR3. Diode CR4 is always

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 317

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6 70 778 0 - 6 3 - 2 1 CONFIDENTIAL

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318 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

conducting through Rl, R2, and the B supply .This diode is essentially a short connectingpoints C and D.

If either input A or input B is in the 0 state,the voltage at point C is -18 volts to ground.Neglecting the voltage drop across CR4, pointD is also at -18 volts to ground. If the -15 volttiming pulse is present at the cathode of CR3,this diode is back-biased by the voltage at pointD, and the trigger is not permitted to pass.

If both A and B are in the 1 state, CRI andCR2 are back-biased 2 volts making the voltageat point C zero with respect to ground. DiodeCR4 is still forward biased, placing point D atzero volts to ground, and diode CR3 is forwardbiased if the -15 volt timing pulse is applied.The timing pulse therefore passes through diodeCR3 to the output.

The transmission AND gate can be built forany number of enabling gates. Each enablinggate must have its own input diode. All of theenabling gates must be in the 1 state in orderfor the timing trigger to be passed. The equa­tion for the transmission AND gate is writtenas T p (A~). In words, this is stated as "Timingpulse T p IS passed when and only when both Aand B are in the 1 state."

One form of the transmission AND gate (fig.14-4, C) provides a transmission gate whichpasses triggers only when the enabling gate isin state O. When gate A is in state 1, diodeCRI is forward biased, the trigger pulse isshorted to ground through d-c blocking capaci­tor C1 and diode CRl, and no trigger appearsat the output "C" of the transmission gate.When gate A is in state 0, diode CRI is backbiased, the trigger is not shorted to ground,but appears at the "C" of the transmission gatecircuit.

OR Gate

An OR circuit (fig. 14-5, A) consists of twoor more semiconductor diodes connected insuch a way that if anyone of the input signalsis in the 1 state, the output of the OR gate at"C" is in the 1 state. If input A is +2 volts andinput B is -18 volts, CD diode CRI is forwardbiased. Because the forward voltage dropacross CRI is negligible, point C is also at +2volts which back-biases diode CR2, and the -18volts at point B is dropped across the high-backresistance of CR2. Point C is, therefore, in the1 state. This condition also exists in @ whenA is -18 volts and B is +2 volts. If both A andBare +2 volts, @, both diodes are forwardbiased and point C is still in the 1 state. If both

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A and B are in the 0 state, @, C will be in theo state because with B- at -20 volts and thedrop across R, 2 volts, point C is -18 volts toground. There is no voltage across the diodesin this condition because both sides of eachdiode are -18 volts to ground. The truth tablesummarizes the possible combinations of A andB.

Transmission OR Circuit

The transmission OR circuit (fig. 14-5, B) isa modified OR circuit that is used to control thepassage of a timing trigger to the input of aflip-flop or blocking oscillator. The operationof the transmission OR gate is similar to thetransmission AND gate. If either the A or theB input is in the 1 state, CD point C is nearground potential and diode CR3 is forward biasedwhen the timing pulse is applied. When the A orB input is in the 1 state, the timing pulse thenpasses through diode CR3 to the output. Theexpression for the transmission OR gate iswritten as (A + B) T. In words, this is stated:"Timing pulse T p is passed when either A orB, or both, are in the 1 state." When both Aand B are in the 0 state, @ CRI and CR2 couplethe -18 volts to the anode of CR3, biasing thisdiode beyond cutoff and no timing pulse appearsat point "C."

Flip-Flop

Several flip-flop configurations are used inthe synchronizing function; however, their basicoperation is the same. The flip-flop (fig. 14-6 , A)produces two outputs, each of which is the nega­tion of the other. Basically, the flip-flop iscomposed of a cathode follower output stage anda bistable multivibrator stage contained in aduo-triode tube (VIA and VIB). Both tube sec­tions of the multivibrator receive input signals,and both sections produce outputs. The plateoutput signals of the flip-flop are cathode­follower coupled to the output.

The two input signals are generally calledthe J and K inputs, and the outputs are generallydesignated Q and Q. The J and K inputs consistof negative-going triggers whose passage to thegrids of the multivibrator stage is usually con­trolled by a transmission gate. The Q and Qoutput signals are square waves.

Assume that the A section of the multivibra­tor is initially conducting, the B section is cutoff, and the J input trigger is applied to the Asection. Since the J input is a negative trigger,it drives the A section into cutoff. The

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. 1) 319

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B'CR '

+ov

.-- sov

CR2 A BC "," A + - -1811+

, o ,~"o"

av

F2V:i "," B

avLOAD ov

+ =IBV" 0"

I~ON2 V

DiODE S

CD0 CR,

t- OV

.s --

-=- 1[",e + -zv --=- IBV--

i+ i+ 15 V

AB C

0 ' I A B r,22 v , 0 - 15v

( zv CD2V.

LOAD

:ed)r

CDto CR t

A CRI

ov

ic CR2 A B C

0 0 0

A)2V

a. - lavl LOAD

+ +

ld 2V_

U'BV

20V'==:

+JCDs, TRUTH TABLE

.!... ~ £.o 0 0o I I

I 0 ,

r I I

a V~-A-~ - STATE I

INPUT A.=..!lli ~ l.--l l-- STAT E 0I 1 II I I

ov~ - -~-ST .~TE '

INPUT e -; LJu 1\ _STATE 0

I I I I I I II I I 1 I I I _ STATE 1

OOTPUT C - STATE 0

WAv E FORMS rOR O F! CIRCUIT

B'

WAvEF ORMS FOR TRANSM ISSION OR CIRCUIT

Tp LJlJl.J1J1JNEGATIvE

p ULSES

OV~- STATE I

INPUT A -18V : L-J~L -STll.lE aI I

all T2V1

~ _ sre r s I

Ir,!PUT B~ I -STA-:-E aI I I

OUTPUT C : I INEGATIVE! rl r---1 r- tB V

PULSES u u u

+

f'~~ '"." -50111

A -

,------0 "0 "o v ov

,8 CR2

1/.0 " o v o v

I S~ONDIODE S -

3 2 V~c., 'BV - -0 C -- . - -

r~-+ - -

18V TO 3 11

- -~

+ - OV ~APAC ITOR)- LOAD- --=- 1611 -=- 1511-

T+CHARGE:

~P~TH ,

A B Tp 7~'-

0 0 0 x.. \~ 18v --=--CD -

"-.~~._,. _ .

-T

2V

LOAO

AB C, I I

~ ovC

BCR2

~ OV +2 2V

·1 .-

B -2v l

- - -+ - -- ~18V -

l'20 V -

+T

d-CD

. 2V

.1yitIe

Ie

s

A B

r, 032, 248

Ftgure 14-5.-0R gate logic ci r cuits.

CONFIDENTIAL

CONFIDENTIAL

320 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

NOTE:DOTT ED INPUT PULSES INDI CATE THATTHE OUTPUTS ARE AS SHOWN WHETH EROR NOT A PUL SE IS PRESENT

INPUT JNEGATIVE ~ r---PULSES (TOVIA) I I 1 1

II IIU o..J

INPUT KN£GATIVE~~PUlS ESllU v IB) , I I I

, t IIU U

l TO10JJS ,1 TO IOu 'VIA OFF

STATE I

VIA ON VIA ONOUT PUT a STATE 0

_-OFF; f----ON~ - OFF- -VIB OFF

STATE IOUTPuT 0 VIS OFF . / If

VIB ONSTATE 0

FLI P- FLOP "O FF" CONDITI ON

~IP - FLOP " ON" CONDITION

"I " STATE " 0 " STATE

0 GJ-G Q

J K

OFF ON

A BI-STABLE MULTI VIBRATOR ON

" 0 " STATE " , " STATE

Q GJ---G. Q

J K

ON OFF

a 81- STA8LE MULTlVI8 RATOR OFF

032. 249

Figure 14-6.-Basic flip-flop circuit.

positive-going Q output is taken from the plateof the A section and is in th e 1 sta te. In thiscondition, when the A section is cut off and theQ output is equal to 1, the flip -flop is sa id tobe tur ned ON (fig. 14-6 , A).

As the A section goes to cu toff (fig. 14-6, A)a r egene rative action causes the B section toconduct, and the Q output therefore is ne gative­going (the 0 state). If another nega t ive tr iggeris applied to the J side, no change takes placein th e state of the flip-flop since the A sectionis already cut off. However, a ne gative triggerapplied to the K side drives the B section intocutoff (fig. 14-6, B), and the regenerative actioncauses the A section to conduct. In this condi­tion, when Q = 0 and Q = 1, the flip-flop is saidto be turned OFF. .

If triggers are appli ed to both the J and Ksides simultaneously (flip-flop ON), the K tr ig­ger starts the B section towa r d cu toff and apositive signal is coupled to the grid of the Asection. After the short duration trigger pulseshave disappeared, the B section still continuestoward cutoff due to A section beginning to con­duct and coupling a negative signal to the gr idof section B. When the flip-flop stabilizes, theB section is cut off and section A is conducting(flip-flop OFF). Approximately 5 to 10 micro­seconds are required, following the applicationof an input tr igger, before the flip-flop becomes

CONFIDENTIAL

stabilized in a new state. This is an importantconsideration in the ope r ation of the synchroniz­ing function since any flip-flop is still in its olds ta te whil e the short dur ation input t r igger pulseis present. The ope r ation of the flip-flop issummarized in table 14-1.

Table 14-1. -Flip-Flop Operation.

I NPUTF LI P- F L O P FLIP- FLOP

STAT E P R IO R STATE AFTERT RIGGE RT O TRIGG E R TRIGGER

J ON ONJ OFF ONK OFF OFFK O N OF F

J&K ON OF FSimul -

tan eouslyJ &K OFF ON

Simul-tane ously

Transistor Inverter

The transis tor invert er (fig. 14-7, A) pro­duces a s ingle output which is the negation of theinput signal. The input s ignal is applied to thebase of the PNP transistor. If th e input s ignal ,A, is in the 1 state (base emitter reverse biased),the tr ansis tor is cut off and the collector poten­tial becomes nega tive, producing a negative­going output s ignal , A = 0, at the collector.Conversely, if input A is in the 0 state , thetransistor is forwa rd biased and condu cts, pro­ducing a positive-going outpu t A = 1.

AND-OR Gate

An AND-OR gate (fig. 14-7, B) consists oftwo or mo re AND gates the outputs of which arecombined by an OR gate to produce a logicalAND-OR func tion. The logical equation of theAND-OR gate is AB + CD = E.

BINARY-NUMBER SYSTEM

There are two systems of number represen­ta tion in computers: a decimal-number systemand a binar y-number system. The decimal­number system represents number s as a sumof powers of ten, where each power of ten isweighted by a digit between zero and 9 inclusive.When a decimal is written, only the wei ght tobe attached to the var ious powers is noted. Thedig it immediately to the left of the decimal point

J;

,If

'II

CONFIDENTIAL

Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 321

T RANS I STO R IN VERTE R

FREQUENCY COUNTER

The frequency counter is located in the syn­chronizing function (fig. 14-3) and consists ofseven bistable Eccles-Jordan flip-flop circuitseach similar to that shown in figure 14-6. Theseven flip-flops operate together to form a bi­nary counter which reproduces any decimalnumber between 0 and 127 in binary form.

The state of the frequency counters at anygiven time can be represented by a seven digitbinary number. The highest binary count is thebinary number 1111111 which is equivalent to127 in the decimal system. The next lowercount corresponds to 1111110 or 126 in the dec­imal system.

The least significant digit of the binary num­ber is the right-hand digit. A change from 1 tooor 0 to 1 in the right-hand digit of the binarynumber represents a change of 1 in the leastsignificant digit of the decimal number equiv­alent. This change of 1 acts on the frequencycounter to cause a change of 1.5 me in thetransmitter frequency and a change of approxi­mately 3/4 0 in the beam angle.

The most significant digit of a seven digit thebinary number is the left-hand digit. A changefrom 1 to 0 or 0 to 1 in this digit represents achange of 64 in the decimal number equivalent.This corresponds to a change of 96 me in thetransmitter frequency.and approximately 48° inbeam angle.

In order for the flip-flop to count in a binaryfashion, the state of the least significant flip­flop must control the state of the next-to-leastsignificant flip-flop. In a similar manner thestates of the two least significant flip-flops mustcontrol the state of the third least significantflip-flop, and so on, until finally the state ofthe most significant flip-flop is controlled bythe states of the other six flip-flops. This con­trol of the state of each flip-flop is acheived bya frequency counter flip-flop transmission gatecircuit which controls the passage of programtrigger pulse, Tp ' to the various grids of theflip-flop circuits.

The frequency counter can perform threetypes of binary counting operations, the particu­lar counting operation performed being deter­mined by the states of the enabling gates appliedto the frequency counter flip-flop transmission

CONFIDENTIAL

It is thus apparent, using the binary system,that any number can be expressed by a series ofhigh and low voltages corresponding respectivelyto 1 and 0 states or can be stored in a devicesuch as a flip-flop which has two stable states.

032 .250

AB+C D =E

t ..t . J " ,

,~ c..1 3 2. I/.,

=1110000

6'l3U~ o( 1-

Figure 14-7.-Transistor inverter ,and AND-OR Gates.

" A NO" - " OR " GA T ES

= 16 + 8 + 0 + 2 + 1

112 = 1 x 10 2 + 1 x 10 1 + 2 x 10 0

27 2 x 10 1 + 7 x 10 0

B

o

A

A

B

c

L-__~1\111-------

= 1 1 0 1 1 in the binary system

112 = 1 x 2 6 + 1 x 2 5 + 1 x 24 + 0 x 2 3 + 0 x 2 2

The binary-number system represents num­bers as a sum of powers of two. The weightsconsist entirely of zero or one , that is, thepower is either present or it is not present.For example:

is the weight of ten to the zero power, and thenext digit to the left of the first digit is theweight of ten to the one power and so on. Forexample:

II

·tJ,

,

JI

"

.'

e

Ie

d),

e

ent

n

CONFIDENTIAL

322 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

gates. The three possible counting operationsare: countdown in steps of one decimal digit(1.5 me), countdown in steps of four decimaldigits (6.0 mc), and reset in steps of 64 decimaldigits (96 mc).

The one-digit countdown operation is usedonly on the lower beam positions where 1.5megacycle steps are taken as previously dis­cussed. The four-digit countdown operation isused only on the upper beam positions where 6megacycle steps are taken.

The 64-digit reset is used for two purposes:to change the counter position by 64 countersteps when the radar beam comes within 3/4°of the horizontal plane, and to change the COWl­

ter position to 63 or 127 in the event of exces­sive tilt.

THE ELSCAN COMPUTER PROGRAM

The elevation scan (elscan) computer pro­grammer (fig. 14-3) controls and coordinatesthe operation of Radar Set AN/SPS-42 througha 26-beam (normal) or 29-beam (coincidentvideo) elevation scan cycle. At each beam po­sition, the elscan program provides commandsignals required by the transmitting, receiving,and indicating functions, Special command sig­nals are supplied for each of the four possiblemodes of operation (normal, normal-MTI, coin­cident video CV, and CV-MTI) which define theparticular mode selected by the operator. Thefunctional operation of the radar system in eachof the operating modes is explained later.

The elscan beam covers approximately 48°in azimuth height. From 48° to 21° during nor­mal operation, the elscan range is limited toabout 34.4 nautical miles (fig. 14-8), From 21 °to about 3/4° above the horizon, the range is in­creased to 160 miles', During coincident videooperation, the beam range is 60 nautical milesfor the entire 48° scan (not shown).

The range is determined by short and longdelay lines which are selected automaticallyduring normal operation to produce the 34.4­and 160-mile beam ranges described above.The 160-mile range can be reduced to 60 milesby the operator.

In a complete elscan cycle, the radar beamis positioned in steps through an elevation sweepof approximately 48° (fig. 14-8). Each positionof the beam corresponds to a different trans­mitted frequency. A frequency change of 2megacycles per second in the transmitted fre­quency changes the beam elevation angle byapproximately one degree. The radar antennais designed so that an increase in frequencylowers the beam elevation with respect to thehorizontal plane and a decrease in frequencyraises the beam. The period of one elscancycle is approximately 27,900 J.1.s ; or 35.8 cyclesper second.

Binary frequency counter gates from thesynchronizing function (fig. 14-3) are applied tor-f exciter stages in the transmitting functionto control the transmitted frequency. The fre­quency counter is capable of controlling thetransmitter output frequency in 128 discretesteps of 1.5 megacycles each. Each frequencystep corresponds to a change in beam angle ofapproxtmately 3/4 degree. During a completeelscan cycle in any of the four modes, 64 ofthese binary counter steps are used, correspond­ing to a frequency range of 96 megacycles and aswept angle in elevation from the axis of the topbeam to the axis of the bottom beam of approxi­mately 48°, providing vertical angular surveil­lance volume of approximately 50 degrees .

ELSCAN TERMINOLOGY ANDTIMING SIGNALS

An early trigger pulse (T e ) (fig. 14-9) isprocessed in the elscan computer programmer

1

.1

75'OOOFT----1

ALTITUDE LINE

SURFACE OF THE SEA

1------------------ 160 MI - - --- - - - - - - - - - - - -

032.251Figure 14-8. -Sectional view of radar beam search volume.

CONFIDENTIAL

s

CONFIDENTIAL

Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 323.INDICATOR

SWEEP T IME IIII

t s rt~~~ nI [_.-, ~ ..I,

Tm ( ·16.5 ", s )

s

TRANSMIT

/BEAM 23

uT RANSM ITBEA M 24

u

RECEIVER ON

T RANSMITBEA M 25

II

____---,1

U f. 12~I )lsoc

1--75 II )lSo-;-J

IRADAR TRANSMISSION FOR:9EAM I

POSIT ION 25 BEGINSHERE - -_nI

TpCLOCK PULSE

TmMASTER TRIGGER

?

s

sIII

t2 nl....- nl....-__----l..

I

Tmd(T;.,_m_._12..:..)I~se;.;,c.:..) nL.. ;.-__nL. nL.. ..J,

INIT IATESSWEEP TIME

Irr..:..e.~1::::2)J:..:so:.;:c.:..) nTed -

TERM INATES SWEEP TIME

NOTE: TIME INTERVALS NOT DRAWN TO SCALE

032 .252Figure 14-9.-Sequence of basic timing signals .

channel to generate the programmer clock pulse(Tp). Te and T p are co incident in time and itis understood throughout this discussion thatthe clock pulse is generated whenever the earlytrigger is generated. The clock pulse is usedto trigger the frequency counter circuits in theelscan computer programmer and the MTI cir­cuits in the receiving function. The early tr ig­ger initiates flyback time or dead time whichis defined as the interval during which the in­dicator sweeps back to the starting position.During this interval the receivers and thetransmitters are all turned off.

Seventy-five microseconds after the earlytrigger time (t), the master trigger (T m) is gen­erated at t l' terminating the dead time intervaland turning on the transmitter (transmit time).At T m + 6.5 microseconds, the receiver isturned on. At Tm + 12 microseconds, the indi­cator sweeps start, beginning the indicatorsweep time. When the range/altitude limitof the sweep is reached (the limit of the

surveillance volume), the next early trigger isproduced which causes the generation of a T ed(delayed early trigger). This trigger is pro­duced 12 jJ.s after the early trigger to terminatesweep time and start a new dead time interval.At early trigger time, the regenerated earlytrigger T initiates a count by the frequencycounters (if the programmer logic so requires)and the r-f exciter output frequency is therebychanged in preparation for the next transmittime.

The Normal Elscan

As stated earlier, the normal elscan cycle(fig. 14-8) consists of 25 discrete elevationsteps extending from about 48 0 above the hori­zontal plane (beam position 26) down to 3/40

above the horizontal plane and a return step orelscan reset making a total of 26 steps. Theradar surveillance volume is limited to a maxi­mum range of 160 nautical miles or an altitude

( .

CONFIDENTIAL

CONFIDENTIAL

324 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

of 75,000 feet; the one occurring first being thelimiting factor. The ranging function is accom­plished by ranging circuits in the synchronizingfunction which automatically terminate thetransmission after the 160-mile or 75,OOO-footlimit is reached.

Initially, the frequency counter system in thesynchronizing function is set at 96 megacyclesbelow the position 1 beam frequency (fig. 14-10,A). This frequency is equivalent to a 64 fre­quency counter step change from th e counterposition for the (position 1) beam. Radar trans­mission for beam position 26 begins at mastertrigger time t 1 (fig. 14-9). When the surveil­lance altitude reaches 75,000 feet , the rangingcircuits produce the next early trigger and in­dicator sweep time is terminated at t 2 •

At the next ea rly trigger time, t 3 (fig. 14-9),the frequency counter (which controls the trans­mit frequency) is stepped down four countersteps. Th is action causes the transmitted fre­quency to be increased by 6 megacycles to beamposition 24 (fig. 14-10, A). At master triggertime t 4 (fig. 14-9), the frequency for beam po­sition 24 is transmitted, and the same processis continued until beam position 13 is reached.

While beam position 13 is being transmitted,initiated at t 13 (fig. 14-10, B) a step size com­parator circuit begins to supply the signal C3= 1. This state 1 condition indicates that thene xt lower frequency interval between trans­m itted frequencies is to be 1.5 megacycles (one

counter step) and that the beam is to be lowered3/4 degree. When the next early trigger occurs(t 14)' the frequency counter steps down onecounter step to beam position 12. From beamposition 12 to beam position 1, the frequencycounter is stepped down in one-counter step in­tervals at each early trigger time.

When beam position 1 is reached, a horizonflip-flop circuit is supplying the signal Cl = 1wh ich indicates that the radar beam is betweenthe horizontal plane and the horizontal planeplus 3/4 degree. At the next early trigger (t 2 6 ) ,

which is generat ed by the ranging circuits afterthe sweep has reached 160 miles, the frequencycounter is instructed to reset and steps up 64counter steps from the bottom beam positionto beam position 26. A new elscan then beginswhich is like the preceding one .

Normal-MTI Mode

During MTI operation, the echo pattern re­sulting from one radar scan is compared withthe echo pattern obtained in a second scan whi chimmediately follows the first. Echoes whichappear at the same position in both scans arecancelled and do not appear on the radar indi­cator. Thus, the observed pattern shows onlymoving targets.

The normal-MTI elscan program is like thenormal elscan except for the repetition rateof the bottom four scans of the beam. The

D I RECT l o r~ OF ANTENNA ROTATION

),..1,

RESETBEAM BEAM

POSITiO N 2 POSITI ON I

Ij

B NORMAL TIMING DIAGRAM

BEGIN 3/ 4 DEGREE STEPS9 314 DEGREES ABOVE

HORIZON

LOWEST TRANSMIT TE D FREOUENCY(9 6 MEGACy CLES BELOW BOT TOM

FREOUENCY)

24 SEAM POSIT lm J 2 5

~3 DEGREE STEPS

22

RADARsETiANlSPS·1l..-:

- -- -.:::\.\=-: ~~"\

SURf ACE OF '-.:,THE SEA~

HIGHEST TRANSMITTED FREQUENCY

A CROSS- SECTION OF NORMAL ELSCAN BEAM PATT ERN

032.253Figure 14-1O.-Elevation scan positions.

CONFIDENTIAL I,.

CONFIDENTIAL

Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 325

~d

~s

.-

),ry

~h

transmitted frequency is stepped, as before, at6 megacycles (3°) per beam position on the top13 positions and 1. 5 megacycles per beam po­sition on the bottom 12 positions. After the 60miles (short) or 160 miles (long) sweep limitis reached, as selected by the operator, theranging circuits will terminate the sweep timein all beam positions except after the first scanof the bottom four positions.

The bottom four beam positions consist of anMTI pair, which is formed by providing twotransmissions on each beam position. The rep­etition rate of the early trigger for the bottomfour beam positions is controlled alternately bya delay line (not shown) in the MTI unit con­tained in the receiving function, and by the rang­ing circuits contained in the synchronizing func­tion. Either a long delay line (for 160-milerange operation) or a short delay line (for 60­mile operation) can be selected by the operator.A frequency count at the transmitter is made atevery other (alternate) early trigger time.

The early trigger which terminates the firstperiod of an MTI pair is generated by.a trigger

from the delay line. The second period is ter­minated by allowing the ranging circuits to gen­erate the early trigger. A frequency count isaccomplished at the second early trigger time.

When beam position 5 is reached at S5 (fig.14-11) an MTI comparator (located in the MTIchannel of figure 14-3) supplies the signal C2= 1, which indicates that MTI operation is tobegin on the next beam position. At the nextearly trigger time, t 2 2 , the frequency counteris stepped down one counter step to beam posi­tion 4. At this early trigger time, the first pe­riod of the MTI pair on beam 4 is started bygating on MTI flip-flop E1 which goes to thestate El = 1 and E1 =0 a few microsecondsafter early trigger time tn' This action per­mits the generation of gate pulse Tv' which inturn causes the generation of T c2'

Gate pulse T c2 is sent to a delay line (notshown) at first period early trigger time on thebottom four beam positions. After 2053 micro­seconds (long range), T c2 is reproduced at theend of the delay line as the MTI trigger(T mt).

Tm'i 'j

C2 r.p/

STATE I

STATE 0

STATE I

STATE 0

STATE I

STATE 0

STATE I

STATE I

STATE 0

STATE 0

BEAM POSITION 5 BEAM POSITION 4 BEAM POSITION 3,2 OR I

r---..A~-~y A y A \

LFIRST PERloofSECONO PERIOO+FIRST PERloofSECONO PERIOO----JI 2053""oc 2053 ""oc 2053 psoc 20~3 psec ITe s-Jl'-- T.;..::2~2n n n n rL

I I I I II I I I I

MI ~L-- .- --;. ~------+-------l-

II I I I 1

I I I

Tv 'ro' --In n n n rLVID~~;TEn~ --!n rn75~S h ~75~5 h

)--I I 1 I 1n'-----__-----11 LI I I 1

E I ("rj ...Jv 1\ V t\, v-I I I I '-- -J1

I I I I II I I II I I 1 I

Ei 'r'j-------;,' I l I IA 1/ ~ !/ ~GENERATED BY EI I I r I

FLIP - FLOP I I

PREVENTS THE EARLY TRIGGER I I IPULSE (Te) FROM AFFECTING A I 'I 1 'FREQUENCY COUNTER STEP I I I I

Te2 "r'j .In ! n : rLI I 1'--------,-------,r---2053.J1,oc=:n I n II I I I II Iii II I I I

E2 'r'j--------l:--------.J~ENERATED BY E2 ~'- __'vr---------~FLIP - FLOP

••I

o

I

o

Io

I

o

NOTE: TIME INTERVALS NOT DRAWN TO SCALE

032,254

Figure 14-11.-Normal MTI timing diagram.

CONFIDENTIAL

CONFIDENTIAL

326 CIRCillTRY OF SHIPBOARD ELECTRONICS EQUIPMENT

The generation of the MTI trigger terminatesthe first period sweep time in beam position 4and starts the second period of the MTI pair byturning on MTI flip-flop E2 (E2 = 0) and turningoff flip-flop E1 (E1 = 0, E1 = 1) a few micro­seconds after early trigger time. A frequencycount is prevented at the end of the first trans­mission on beam position 4 by E1 = 0 althoughan early trigger is generated.

The second early trigger, which starts thesecond period after 2053 ue, causes the genera­tion of a second Tv pulse. At 75 microsecondsafter early trigger time, the master trigger(Tm) for the second period on beam position 4is generated. The delay line pulse, T c 2 ' is notintroduced to the delay line in the second pe­riod of beam position 4 because E1 (the inhibit­ing pulse) is still in the 1 state and blocks T c 2

generation at second early trigger time. Be­cause of this action, the second period is ter­minated by the ranging circuits which generatethe next early trigger after the maximum rangeis reached. A frequency count is permitted atthe second early trigger by E1 = 1, and thecounter steps the frequency 1. 5 megacycles tobeam position 3 where a new MTI pair is gen­erated. This procedure is followed down tobeam position 1.

After both periods of the MTI pair on beamposition 1 are completed, reset occurs as inthe normal elscan program. The MTI videogate, T v' is sent to the clutter gate channel inthe receiving function (fig. 14-3) at the begin­ning of each period of an MTI pair. This pulseturns on the MTI video channel during the first50 miles of sweep time for each period so thatmoving targets amid sea return clutter can bedetected.

The signal E2 = 1 is sent to the MTI unitduring the second transmission period where itpermits MTI cancellation to occur during thesecond period of an MTI pair.

Coincident Video Mode

When coincidence video (VC) is selected, anyrandom pulse jamming is eliminated. In CVoperation, the radar transmits twice on everybeam position. The echo return from the firsttransmission is delayed for one transmissionperiod and is compared in time with the unde­layed second echo return. In order to obtainan output from a pulse coincident video sys­tem, the radar echo return must be present atthe same range on each of the two successivetransmissions of a beam position. When CVhas been selected, pulse coincident video is

CONFIDENTIAL

substituted for normal video in the clutter gatechannel.

The coincident video (CV) mode is selectedby the operator. In the CV mode, there are 29beam positions starting with the 29th beam whichis approximately 48° above the horizontal plane.As in the normal mode, 64 counter intervalsare required for a complete elscan. The extrathree beam positions are obtained by startingthe 1.5 megacycle frequency steps at beam po­sition 17 instead of beam position 13. Twotransmissions per beam are maintained through­out the CV elscan program and the range islimited to 60 miles.

The repetition rate of the early trigger (fig.14-12) is controlled alternately by the delaylines in the MTI unit and by the ranging circuits.A frequency count is made at every other earlytrigger time .

The early trigger which terminates the firstperiod of a transmission pair is generated by atrigger from either the long or short delay line.No frequency count is permitted at this earlytrigger time. The second period is terminatedby permitting ranging to generate the earlytrigger . A frequency count is made at this earlytrigger time.

The radar transmission for beam position 29is initiated by T e' This pulse passes throughgates and causes the production of trigger Tel'which is fed to the short delay line. After 819microseconds, T c1 is produced at the end of thedelay line as the MTI trigger (Tm t i)'

The MTI tr igger causes the generation of thenext early trigger , which terminated the firstperiod, and initiates the second period a fewmicroseconds after early trigger time . Thesecond transmission on beam position 29 begins.A frequency count is prevented at this earlytrigger time by E1 = O. Normal ranging occursduring the second period and terminates thesecond period sweep time by generating thenext early trigger. A frequency count takesplace at th is early trigger time and the frequencycounter in the transmitting function steps thebeam down to position 28.

This procedure is followed until beam posi­tion 17 is reached where the step size compara­tor for the frequency counter generates a gate(C3 = 1), indicating that the next frequency in­terval is 1.5 megacycles. At the early triggertime which terminates the second period on beamposition 17, the frequency counter which controlsthe transmitter output frequency is stepped downone counter step to beam position 16.

The early trigger at beam position 16 causesthe generation of gate pulse Tv which, in turn,

...,i

CONFIDENTIAL

Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 {PT. 1)327

y

BEAM POSITIONS IB THROUGH 29 BEAM POSITION 17 BEAM POSITION 16 BEAM POSITIONS 15 THROUGH I(~__~A A'-__~y~__---,A'-__~y A~__~\

,)

SECONDPERIOD

2053.p sec

FIRSTPERIOD.

2053.,usee

III

h<-------t-II I

/4-20 5 3=1l.,.usee

'--__....1__ L..-__+-_....I.,I

SECONDPERIOD

2053.,usee

III

..----\~'---__fIIII

FIRSTPERIOD

2053.,usee

FIRSTPERIOD

819~ec

SECONDPERIOD

819,.usee

FIRSTPERIOD

819 .c-sec

TC2 I,-')---.!----+----++---+----

C3 1,-<)----:------..---------:1

ISECONDPERIOD

I Bl9.,usee

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NOTE: TIME INTERVALS NOT DRAWN TO SCALE

032.255Figure 14-12.-CV and CV-MTI timing diagram.

y

S

1

produces T c2' The latter pulse is sent to thelong delay line and is reproduced at the end ofthe delay line 2053 JJ.s later. The gate pulse asit leaves the delay line is referred to as theMTI trigger (Tm t i)' This pulse causes the gen­eration of the next early trigger which termi­nates the first period of the transmission pairand initiates the second period on beam posi­tion 16.

The second period is terminated by allowingranging to occur as was done on the upper 13beam positions. This procedure is followeddown to beam position 1. After both transmis­sions on beam position 1 are completed, thecounter is reset to beam position 29.

CV-MTI Mode

The CV-MTI mode is like the CV mode ex­cept that MTI scanning occurs in a portion ofeach elscan cycle. You will recall that in thenormal MTI mode, the MTI scanning was ac­tive only on the bottom four beam positions.The MTI scan is not active at all in the normalCV mode. Thus, as might be expected, theCV-MTI mode combines both CV and MTI by

permitting CV operation on the top 12 beam po­sitions and MTI operation on the bottom 17 beampositions.

SPACE-STABILIZATION GEOMETRY

The radar antenna is mounted on a platformparallel with the ship's deck plane. As the shippitches and rolls, the attitude of the antennavaries accordingly. Unless compensated for,these motions appear on the radar indicator andcould possibly be interpreted falsely as targetmotions. For instance, when the ship's bowpitches 10° down, a target directly ahead at 20°from the horizontal plane will be displayed asthough it were at an elevation of 30° from thehorizon. In order to make proper correctionsfor such errors, the ship's motions are elec­tronically subtracted from the signal data priorto display on the indicators. This electronicmethod is quicker, simpler, and more accuratethan providing an electronmechanical servosystem to stabilize the radar antenna platform.

The space-stabilization geometry refers tothe accurate relationships of the various anglesgiving rise to the signal data displayed on the

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328 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

zp

,1.,

y

N

STARBOARD

B

90° a

y(STARBOARDDIRECTION)

Z (SPACE VERTICAL)

TARGET

~

ZU)

u

OSC

x

I,

032.256

Figure 14-13.-Radar beam stabilization geometry.

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 329

'.

indicator s . These relationships include the po­sition of the radar beam with respect to theship's deck, the attitude of the ship's deck withrespect to the horizontal plane, and the angleof the ship's course with respect to the merid­ian. They are expressed as equations involvingthe position coordinates of the radar beam, thedeck attitude, and the ship's bearing. Refer­ring to figure 14-13 , A, X represents a linethrough the bow of the ship and corresponds tothe ship's direction of motion (heading). Theline Y is drawn at right angles to line X andrepresents the ship's starboard direction. BothX and Yare in a horizontal plane. The line Zis drawn perpendicular to both the X and Y linesand represents the space vertical in the figure.The space position of the radar beam can bespecified by a vector (a quantity having a direc­tion and magnitude) whose components are X,Y, and Z.

When the ship is motionless, i. e . , when it isnot moving forward, pitching, or rolling, targetrange and bearing information can be displayed

CRT

y+10 VOLTS

on the radar indicator in coordinates designatedby X, Y, and Z. The target position on the indi­cator is formed by vectorially combining the in­formation forwarded to the X-axis of the cathode­ray tube with that of the Y-axis. For example,if the PPI scope receives a target signal of +15volts at its X-axis and +10 volts at its Y-axis ,the resultant position of the target will appearat T on the screen as shown in figure 14-14, A.The vectorial summation is presented in figure14-14, B.

The data stabilization section performs vec­torial operations on target signals specified byX, Y, and Z coordinates when the ship is motion­less. As shown in figure 14-13, B, referencevoltage VR represents a unit length on the radarbeam projected at an elevation angle of E (epsi­lon) with respect to the horizontal plane OMQB.The angle E is called the space elevation angle,which represents the angle between the radarbeam and the horizontal plane. The verticalcomponent Z of the unit beam length VR will

N

E

S

w

®

T

O"-------------------tl.- x+1 5 VOLTS

®032.257

Figure 14-14.-Target position information.

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330 CIRCUITRY OF SffiPBOARD ELECTRONICS EQUIPMENT

then be VR sin E, the vertical distance betweenthe target and the horizontal plane.

Relative Bearing Components

The projection of the radar beam vector VRon the horizontal plane is shown as ~ (fig .14-13), which is equal to VR cos E. The projec­tion of~ or VR cos E, through angle o (alpha),the space azimuth angle in the horizontal plane,on the X-axis yields the X component equal to~ cos a , or VR cos E cos a, which representsan azimuthal vector quantity in the direction ofthe ship's motion. Similarly, the projection ofOQ on the Y axis gives the component OQ s in a,or VR cos E sin a. Thus, X, Y, and Z compo­nents represent direction cosines and are pro-jected at right angles to each other . Thesecomponents spec ify the radar beam directionwith respect to the heading of the sh ip and henceare called the relative bearing components.

With a motionless ship, the component X =VR cos E cos a represents the ship's coursedirection, Y = VR cos E sin a represents thestarboard direction of the ship, and Z = VR sinE represents the direction perpendicular to theship's deck or parallel to the ship's mast. Theangles a and E are measured by the antennaposition and the synchronizing function, respec­tively . However, when the ship is in motion,these angles are no longer measured directly.Consequently, the data-stabilization function isused to compensate for the signal errors. Thesesignal errors are the direction cosines of thequantities representing the angles provided bythe ship 'S motion and antenna attitude.

True Bearing Components

The direction of the radar beam can also bespecified with respect to the meridian line(U-axis) , latitude line (V-axts), and the spacevertical (Z-axis). This relation is illustratedin figure 14-15, in which the ship's heading isrepresented by X and its starboard direction byY. The own ship's course angle y (gamma) ismeasured clockwise, on the horizontal plane,between the meridian N (true north) and theship's heading X.

To determine the radar-beam direction withrespect to the earth coordinates or the truenorth N, the X and Y axes are rotated electroni­cally counterclockwise through angle y by thedata-stabilization function so that the X and Yaxes coincide with U and V axes, respectively.Thus the U component is equal to VR cos E cos(a + y) or VR cos E sin [90-(Qi + y)). The

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components VR sin E and VR cos E remain thesame as for the relative coordinates. Sincethese three components U, V, and Z specify thedirection of the radar beam with respect to truenorth, they are called the true coordinates . Thedesired coordinates can be Selected by means ofthe true-relative switch in the data-stabilizationsection.

Pitch and Roll Compensation

Pitch and roll compensation is applied byshifting the bottom beam frequency as the anglebetween the axis of the radar antenna and thehorizon plane varies with pitch and roll. Dueto the small angular change in the aspect of theship during a single elscan cycle (27,958 j.1.s),the correction takes the form of a 1.5 megacycle(one counter step of 3/4 0

) frequency shift forapproximately one elscan cycle out of every 20to 50 cycles.

The correction rate depends upon the pitchand roll rate. By shifting the bottom beam fre­quency up or down, the entire elscan pattern isshifted up or down since all other beam positionfrequencies are referenced to the bottom beamposition (reset ini t ia ted from this beam posi­tion). The necessity for a compensation issensed essentially by the horizon comparatorand its associated horizon flip-flop. Pitch androll information is compared in the horizoncomparator with a fixed voltage which is anal­ogous to the horizon plus 3/4 degree.

Because reset does not occur until the signalC1 = 1 from the horizon flip -flop is produced,the frequency counter continues to step the radarbeam down only so long as this signal is notpresent. Thus, if pitch and roll occurs, it willoccasionally require, in the case of a normalelscan, 25 or 27 beam steps depending upon thedirection of motion of the ship, to reach horizonplus 3/4 degree. If theship is pitching up, forinstance, an extra beam position is occasionallyrequired before the horizon comparator detectsthat the beam is within 3/4 0 of the horizon. Ifthe ship is pitching down, on the other hand, only25 beam positions are occasionally required be­fore C1 = 1. The horizon comparator thereforeshifts the horizon frequency by forcing the fre­quency counter to count down until horizon plus3/4 0 is reached.

Due to the slow rate of change in the ship'saspect relative to the elscan rate, the correc­tion will never involve more than one beamstep of 3/4 0 in a single elscan cycle, and thecorrection therefore is made in 3/4-degree in­crements.

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 331

N

VR COS , cos 0<

<=-- -l-- - ""<-- --___... x (OSC)

y

(STARB OAR D DIR ECTIO N)

zIf)

9 0°

Z

~~'?;"'-

~~ N~<::J~

VR COS E COS oc:

VR COS , cos.. x( OSC )

r032 .2 58

Figure 14-15.-Ship's heading and attitude geometry.

'I

In the event of excessive pitch or roll(greater than ± 20°), a full elscan program can­not be covered since some of the frequenciesrequired for such an elscan program are aboveor below those selectable by the frequencycounters, When the excessive tilt gate sensesthis condition, it generates the signals Q = 1and Q = 0 which reset the frequency counter to63 counter steps above position zero (3100.5megacycles) if the horizon cannot be reached,or to position 127 (2910 megacycles) if a beamelevation of 48° cannot be obtained. This actionensures that the full elscan program will befollowed. Radar echoes will not be accuratelydisplayed when the roll or pitch of the ship isin excess of limits of the elscan program.

TRANSMITTING FUNCTION

The transmitting function of the AN/SPS-42consists of an oscillator-amplifier type system.

(Another oscillator-amplifier system in theAN/SPS-29 radar system was discussed inchapters 12 and 13 of this training course.) Theoscillator amplifier (fig. 14-16) generates a lowlevel r-f energy pulse which is amplified andused for detecting and locating surface and air­borne targets . The system transmits the r-fenergy from the radar antenna at a nominalpeak power of 1 megawatt and at frequenciesbetween 2910 and 3090 megacycles. The trans­mitted energy is a pencil beam which scans asearch volume of 360 ° in azimuth and 48 ° inelevation. This function comprises a radio­frequency (r-f) channel, a modulator channel,and a power supply channel.

The transmitted energy is generated in ther-f channel. This channel consists of an oscil­lator amplifier, an r-f driver amplifier, and amicrowave section. The oscillator amplifiergenerates continuous-wave energy which is

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CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

TO M IXER I NRECEIV IN GFUN CTI ON

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332

FR OMSYNCHRO NIZING

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032. 25 9

Figur e 14-16.-Tr ansmitting function, block diagram.

modulated in the driver and final amplifiers bygates received from the modulator channel.The oscillator amplifier output is amplified bya fac tor of 1 billion to produce a peak poweroutput fr om the final a mpli fier of 1 me gawatt.

The r-f energy is supplied to the antennathrough a microwave s ection and is r adiatedinto space at elevation angles dependent on thestep frequencies of the r adiation. The frequencyof the radiated r-f energy is controlled by theelscan computer-programmer in the synchro­nizing function.

The radar set is capable of scanning in ele­vation by programming 128 discrete step fre ­quencies. Each of these frequenc ies alters thewavefront of the radiated ene r gy, therebychanging the elevation position of the radarbeam in steps. The radar beam is raised or

lowered by respectively decreasing or increas­ing the fr equency of the r adiated ener gy fr omthe antenna . Because the antenna scans in twocoordinates of azimuth (bearing and height) , theresultant sc anned field is a thr ee- dimensionalsearch volume in space around the ship.

MODULATOR CHANNEL

Modulating pulses for the r-f driver amplifier(fig. 14-16) and the r-f final amplifier in the r-fchannel are generated in time coincidence bytwo separ ate modulators contained in the modu­lator channel. The action is s imilar to the mod­ula tion process used in Radar Set AN/SPS-29,which is discussed in chapters 12 and 13 of this text.

Both of the modulators are triggered simul­taneously by each master trigger pulse (Tm )

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 333

~r

f

1-

rt,

\

I

which is supplied from the synchronizing func­tion. Due to a difference in time duration ofthe two modulating pulses, a variable delay line(not shown) at the input of the driver amplifiermodulator permits delay of the output triggerfrom this circuit, thereby permitting an opti­mum coincidence of outputs from the two modu­lator sections.

The r-f driver amplifier contains two travel­ing wave tubes (TWT) which are described later .When triggered, the driver-amplifier modulatordelivers a high voltage negative pulse to eachtraveling wave tube in the r-f driver amplifier.Delay lines in the modulator permit selectionof pulse widths of either 1 microsecond or 5microseconds. The minimum time duration ofthe transmitted r-f energy, therefore, is deter­mined by the driver-amplifier modulator.

The final-amplifier modulator also generatesa high voltage negative pulse for each triggerinput. This pulse is applied to the klystronfinal amplifier in the r-f channel. The pulse isgenerated by discharging a 4-microsecondpulse-forming network through the primary ofa pulse transformer. The secondary of thetransformer furnishes -90 kilovolts to the cath­ode of the klystron during the pulse transmittime. The maximum time duration of the trans­mitted r-f energy is thus established at 4 micro­seconds by the final amplifier modulator.

R-F CHANNEL

The r-f channel produces pulses of S-bandr-f energy between 2910 and 3090 megacyclesonce during each operating cycle of the radarsystem in response to binary control signalsfrom the frequency-selection channel. TheseS-band pulses are radiated from the frequency­scanning antenna into space at programmedangles of elevation, and may have a time dura­tion of either 1 microsecond or 4 microsecondsas selected by the operator.

The oscillator-amplifier also produces theheterodyning signal required for the receptionof target echoes. During the receive period ofeach operating cycle, a voltage is generated bythe r-f channel which causes the oscillator­amplifier output frequency to be increased ordecreased by 12 megacycles. This signal issupplied as the local oscillator signal to thereceiving function.

The r-f channel may be consrdered as amaster oscillator-power amplifier type trans­m itter containing four major functional groups:a continuous-wave oscillator amplifier (r--fexciter), a pulsed r-f driver amplifier, a pulsed

6 70 77 8 0 -63 -2.Z

r-f final amplifier, and microwave circuits to­gether with the antenna. An output signal fromthe oscillator amplifier appears continuously atthe input of the pulsed r-f driver amplifier. Theexact frequency of this signal (between 2910 and3090 mc) is determined by gating signals fromthe synchronizing function. The r-f driver am­plifier and r-f final amplifier produce an outputonly when they are supplied with high voltagepulses from their respective modulators.

Under conditions of no pitch and roll of theship, the first transmission in the elscan cycle(which is the highest transmitted elevation scan)takes place on 2955 megacycles. This frequencycorresponds to a counter state of 97, which is30 counter states down from the top state of 127.If pitch and roll do exist, the beam positionnumber (and its corresponding elevation angle)move up and down to compensate for the move­ments of the ship.

For example, if the combined pitch and rollof the ship are such that the plane of the deckmakes an angle of 20° below the horizon, thefirst beam position (normally beam position 97)will move up 30 counter states to become coun­ter state 127. Because this position now rep­resents the first transmitted beam position, allof the other beam positions will move up anequal number of counter states. Thus, the final(bottom) counter state will be 127 - 64 = 63, andthe elscan beam angle is maintained between48 ° maximum and 3/4° minimum above thehorizon.

Oscillator Amplifier

The oscillator amplifier (fig. 14-17) consistsof the following sections: two matrices (A andB), three banks of oscillator units (A, B, and C) ,two mixers, a doubler-limiter, and a frequencymultiplier. The two matrices supply theSWitching voltages necessary to gate on oneselected A, B, and C crystal-controlled oscil­lator unit in the respective oscillator bank.

The output frequencies of the three selectedoscillator units are mixed and filtered to pro­duce a resultant r-f signal which has a frequencyequal to A - B - C. Through the doubler-limiterand frequency-multiplier units, the A - B - Csignal is amplitude limited and frequency mul­tiplied to produce an output which has a constantamplitude and a frequency of 64 x (A - B - C).

Each of the oscillator banks A and C containeight oscillator units, and B contains two oscil­lator units. Thus, 8 x 2 x 8 different combina­tions , or 128 resultant frequencies, are possiblein the range of 2910 to 3090 megacycles.

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334 CIRCUITRY OF SmPBOARD ELECTRONICS EQUIPMENT

The two diode matrices (A and B) are iden­tical. Each consists of nine d-e amplifiers andeight AND gates. One d-e amplifier of eachmatrix is used for switching oscillator unitsBl and B2. The remaining eight d-c amplifiersof each matrix are individually controlled by anassociated AND gate, and are used for gatingoscillator units Al through A8, and Cl throughC8.

Fourteen binary gating signals that originatein the synchronizing function are used by thematrices in selecting the three oscillator unitsA, B, and C. Each of the gating s ignals has twostates: a high binary state represented by 2volts, and a low binary state represented by-15 volts.

R-f Driver Amplifier

The r-f driver amplifier (fig . 14-17) providesan intermediate level of power amplificationfor the r-f energy generated in the oscillatoramplifier. The power divider at the input con­sists of two quarter-wave coaxial matchingtransformers (not shown) that have a commonr-f input c: nnection, Each of these transform­ers is connected to a 50-ohm coax ial cablewhich terminates in a 50-ohm load. However ,the power output ratio is 2: 1. Two-thirds ofthe input power is supplied to the r-f mixer inthe receiving func tion as the loc al oscillatorsignal, and the other one-third is routed to theinput of the first traveling wave tube (TWT No.1).

The r-f driver amplifier contains two trav­eling wave tubes (TWTs) which provide ampli­fication of the oscillator amplifier output to anominal one-kilowatt level. The output of thesecond TWT, after passing through an atten­uator and two directional couplers, is used todrive the final klystron amplifier.

R-f Final Amplifier

The r-f final amplifier provides amplifica­tion of the pulsed r-f output from the r-fdriver amplifier to a nominal one-megawattpeak-power level. The major component ofthe r-f final amplifier is the klystron whichsupplies its amplified r-f output through themicrowave circuits to the radar antenna whereit is radiated into space.

The klystron, in order to produce an r-f out­put pulse, requires an r-f driving pulse and anegative modulating pulse. The r-f driverpulse is applied to the klystron signal inputcavity from the r-f driver amplifier, while the

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negative modulating pulse is applied to theklystron cathode from the final amplifier mod­ulator.

The klystron in the final amplifier is ofbroadband design for operation in the S-bandregion. The klystron is provided with an elec­tron gun at one end and a collector at the otherend . Between the electron gun and the collectorare six cascaded cavities, which are stagger­tuned for operation over the range of frequen­cies between 2910 and 3090 me . Electronsflowing from the cathode to the collector forma beam which passes through each cavity. Thecathode is pulsed with a potential of -90 kv. Anelectromagnetic focusing coil for each cavityconfines the electron beam to the center of thecavity.

R-f input pulses from the r-f driver ampli­fier are fed into the input cavity by means of aprobe. This energy interacts with the electronbeam passing through the input cavity, alter­nately accelerating and retarding the electronsto produce a modulated electron beam. Thiselectron beam further interacts with the suc­ceeding cavities so that increasingly morebeam energy is transferred into the cavities asthe beam progresses toward the collector. Inthis manner the r-f energy is amplified as ittraverses the cavities, and becomes maximumin the last cavity . Energy from the last cavityis coupled into the transmission system througha dielectric window from the klystron whichopens into the antenna microwave circuits.

The electron tube liquid cooler supplies aflow of coolant to the electromagnet, body, andcollector of the klystron to maintain a safeoperating temperature. The coolant fluid iscirculated through the system by means of amotor-driven pump. A pressure relief valveconnected across the pump prevents rupture ofthe interconnecting hoses in case the coolantflow is blocked while the pump is operating.

Thermal and flow switches are incorporatedin each of the coolant distribution branches forklystron protection. In the event that the fluidflow through a branch falls below a set limit,the flow switch in that branch cuts off the highvoltage to the klystron. If the coolant tempera­ture in a branch exceeds a set limit, the thermo­switch in that branch cuts off the klystron highvoltage.

TRAVELING WAVE TUBE

The traveling wave tube (fig. 14-17) is a de­vice which provides signal amplification by theinteraction between an electromagnetic wave

....MM

M-D

I

o

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 335

and a beam of electrons within a TWT helix.This inter action results in a transfer of energyfrom the electron beam to the electromagneticcomponents of the input signals, which arepropagated down the helix to the output cavityof the tube. Thus, a small r-f input results ina large r-f output over a wide frequency band.The action is described below. Magnetic focus­ing is used to confine the electron beam to thecenter of the helix as closely as possible.

A simplified diagram of a traveling wavetube is shown in figure 14-18. The r-f energyto be amplified is delivered to the input helix5 of the TWT by means of coaxial tubing 12.The energy is then coupled from input helix 5to TWT helix 6, where it is propagated withinthe tube toward output helix 7.

In the presence of a negative modulatingpulse at the cathode 9, the TWT conducts andbecomes an amplifier. The electrons emittedby the cathode are accelerated and focused toform a narrow beam which travels axiallythrough the center of TWT helix 6 toward col­lector 11. The focusing action creates a pe­riodic magnetic field around the TWT to pre­vent dispersion of the electron beam.

The electron beam within helix 6 interactswith the r-f energy propagating relatively slowlyalong the helix. As the beam progresses throughhelix 6, electron bunching, which occurs as aresult of the interaction, results in a transferof energy from the electron beam to helix 6.Because of a small velocity difference betweenthe electrons which comprise the beam and ther-f energy traveling down the helix, the two ar­rive near the end of the helix out-of-phase. Atthis point, the r-f energy in the output helix 7increases as it absorbs energy from the elec­tron bunches. The electron beam continuesthrough the TWT to the collector 11, where theremaining energy of the beam is dissipated asheat by cooling fins 8. A blower (not shown) issupplied to remove heat.

The r-f energy from the driver amplifier isalmost completely attenuated by an r - f attenua­tor (fig. 14-17) when the two TWTs are not con­ducting.

Output from the first TWT is routed througha directional coupler to the second TWT , whichis like the first. The cathode modulating pulserequired to key-on the traveling wave tubes isgenerated in the modulator channel and applied

2 3

4 10

9

12

5 6 1

13 11

8

I. GLASS ENVELOPE2. SUPPORTING ROD3 CERAMIC INSULATOR4. HEATER5. RF INPUT HELIX6. HELIX7. RF OUTPUT HELIX

8 COOLING FINS9. CATHODE10. GRID

II. COLLECTOR12. INPUT COAXIAL TUBING13. OUTPUT COAX IAL TUBINGo TUBE PIN CONNECTIONS

032.261

Figure 14-18.-Traveling wave tube, structural drawing.

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336 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

simultaneously to both TWT cathodes. Thesetwo stages therefore produce simultaneous r-fpulsed outputs.

The output from the second TWT is appliedthrough directional couplers and an attenuatorto the r-f final amplifier klystron. The direc­tional couplers provide small amounts of r-fenergy from various points in the r-f driveramplifier to the testing function.

Microwave Circuits and Antenna

S-band energy in the frequency range from2910 to 3090 me is supplied to the radar an­tenna by means of the waveguide microwavecircuits (fig. 14-17). The energy is concen­trated into a narrow beam at the antenna andradiated into space at an elevation angle de­pendent on the instantaneous S-band frequency.The azimuth angle of the transmitted energy isdetermined by the angular position of the an­tenna with respect to ship's bow (relative bear­ing) or true north (true bearing).

The duplexer portion of the microwave cir­cuits permits the use of the same antenna fortransmission and reception of the radar signal.The duplexer consists of two hybrid couplers,an antitransmtt-r ecetve (ATR) section, an atten­uator, and a transmit-receive (TR) section.The duplexer acts as a high speed electronicswitch whose operation is controlled by pulsesof S-band energy from the r-f channel.

During transmission, the duplexer routesthe r-f output of the transmitter to the antennaand blocks the input to the receiver. During recep­tion, the duplexer routes the target-reflectedenergy from the antenna to the receiver andisolates the receiver from the transmitter.

The hybrid couplers of the duplexer providethe switching and isolating functions duringtransmission and reception. R-f energy fromthe transmitter is divided into two equal-powercomponents by hybrid coupler 1, and routedthrough the ATR section of the duplexer. Afterpassing through the ATR section, the two com­ponents are combined by hybrid coupler 2 androuted to the antenna.

The action is as follows. The hybrid cou­plers (fig. 14-19) are four terminal structures,and consist essentially of two parallel sectionsof waveguide. These waveguide sections arejoined at their narrow dimension by an openingreferred to as the interaction space. R-f energyfrom the klystron final amplifier is injected intoNo. 1 terminal of hybrid coupler 1, and dividesequally between the two opposite terminals (Le.,terminals 2 and 4), with little or no energy sup­plied to the adjacent terminal 3.

Because of the greater distance that the r-fenergy travels diagonally through the interac­tion space to terminal 4, the phase of the energyat terminal 4 of coupler 1 is 90° lagging withrespect to the energy at terminal 2. Negligibleenergy is coupled to terminal 3, the adajcentarm of the coupler.

The ATR tubes are resonant-cavity, gas­filled tubes with a window in one side. The ATRtubes are electrically placed in series with thewaveguide by substituting each window for aportion of the broad side of the waveguidewall.

Two ATR tubes are used in each of the twopaths through the ATR section. One tube hasa design frequency range of 2900 to 3000 mc ,while the second has a design frequency rangeof 3000 to 3090 mc. Thus, the total range of

TOCRYSTALMIXER INRECEIVER

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032.262

Figure 14-19. -Microwave circuits, simplified diagram.

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 337

gyto

'.,1-

'R

N:R

frequencies over which the ATR tubes can op­erate effectively is 2900 to 3090 me .

R-f energy from hybrid coupler 1 causesionization of the gas in the ATR tubes, El andE3, during the transmit period. Ionization ofthe gas then causes short circuits to be re­flected across the windows of each ATR tube.The waveguide walls therefore appear to thesignal to be continuous, and the r-f energy isallowed to pass through coupler 1 without re­flection or attenuation.

After passing through the second ATR sec­tion (E2 and E4 are ionized), the r-f energy isapplied to input terminals 2 and 4 of hybridcoupler 2. As mentioned before, the phase ofthe energy applied at terminal 4 is 90 0 laggingwith respect to the energy applied at terminal2.

From arms 2 and 4 of hybrid coupler 2, ther-f energy reaches a second interaction space.Because of the greater distance it travelsthrough the interaction space, energy from arm4 arrives at arm 3 (of hybrid coupler 2) dis­placed by 90 0 from arm 4 and therefore 1800

from arm 2. Therefore, the two r-f componentsare almost entirely canceled, and only a smallamount of this energy will be coupled from arm3 to the receiver input during transmission.

However, the r-f energy which follows thepath 1 to 4 in hybrid coupler 1, and 4 to 1 incoupler 2 arrives at the antenna input in phasewith the energy traveling path 1 to 2 in coupler1 and 2 to 1 in coupler 2. This action causesthe r-f energies to add at terminal 1 of hybridcoupler 2 in route to the antenna. Thus, theduplexer introduces very little loss in thetransmitter output.

The TR tube is a resonant-cavity, gas-filledtube which is used to protect the receiver crys­tal mixer during transmission. Like the ATRtubes, the TR tube is an electronic switch whichis capable of open ing and closing the circuit atthe radar pulse-repetition rate. The TR tubeis placed in shunt with the waveguide sectionwhich supplies r-f energy to the receiver crys­tal mixer.

Because of the inability of the waveguide tomaintain exact matching over the range of op­erating frequencies, a small amount of thetransmitted r-f energy is coupled to the TRtube from terminal 3 of hybrid coupler 2. Thisenergy causes the TR tube to ionize and estab­lish a short circuit across the waveguide. Thus,transmitted energy that leaks through hybridcoupler 2 is blocked from the receiver input.

A keep-alive voltage of 700 volts maintainsa source of ions to assist in ionizing the TR

tube at the instant the radar pulse begins. Thisvoltage permits rapid ionization during trans­mission, but is sufficiently low to prevent ion­ization of the tube during reception. Thus , re­ceived echo signals pass into the receiver.

During reception, the ATR tubes are deion­ized, and their windows appear as discontinui­ties in the waveguide walls. Received energyfrom targets is therefore blocked and cannotpass into the transmitter.

ANTENNA

The antenna is mounted on a pedestal (14-1) ,which permits rotating of the antenna and scan­ning of the beam through 360 0 of azimuth. Thetransmitting and receiving elements of the an­tenna consist of a vertical linear array of ra­diators and a parabolic reflector.

Energy from the klystron r-f final amplifier(fig. 14-17) is fed through the microwave cir­cuits to the antenna (fig. 14-20). The r-f energyis radiated by an array of slots, directed to aparabolic-cylinder-section reflector (fig. 14-1)by means of directing vanes, and reflected intospace by the parabolic reflector. The reflectorand array are inclined from the vertical by anangle such that a line through the broadsideaxis of the assembly forms an angle of + 25 0

with respect to the deck.The frequency scanning technique is employed

to permit variable positioning of the radiatedbeam in the vertical plane. With this technique,the elevation angle of the radiated beam isaltered by changing the frequency of the energysupplied to the antenna. A series of at leasttwenty-five different frequencies thus resultsin scanning of the beam through 48° of elevation.

Because scanning in the vertical plane is ac­complished electronically, it is not necessaryto move the antenna in the vertical plane. Thus,mechanical stabilization of the antenna plat­form is not required. Both the position of thetransmitted beam in space and the indicator­presentations are stabilized electronically.

In order to use the vertical electronic scan­ning principle effectively, and to obtain a highdegree of resolution in azimuth, the radiatedenergy is directed within narrow angular limits.The antenna vertical array of radiating ele­ments limit the vertical beamwidth, and theparabolic cylinder section reflector limits thehorizontal beamwidth. The resultant pencil­shaped beam is narrow in both planes. Theradiated beam is 3.0 0 wide in the vertical planeand 2.4 0 wide in the horizontal plane.

CONFIDENTIAL

CONFIDENTIAL

338 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

FIBERGLASS RADOME

cv

I

c I

~'RECTlN~-.

VERTI CAL ARRAYWAVEGUIDE SECTION

, ,

I

REFLECTOR --1I

I

WAVEGUIDE --+----l

WAVEGUIDE 180 0 ·----------1H~

END CASTIN G

TO R-F ATTE NUATOR ----a~;:;?~~~

R·F IN PUT FROM _--I---<~

KLYST RON (FIG.14 - 17)V IA WAVEGUIDE

AND ROTARY COUPL ER

032.263

Figure 14-20.-Radar antenna sinuous feed assembly.

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 339

The vertical array of radiators is formed byfolding the waveguide transmission line back andforth on itself. This forms what is known as a" s inuous feed ." R-f energy is supplied to theupper end of the sinuous feed from the klystronr-f amplifier via the waveguide transmissionline and rotary coupler. The feed consists of44 straight waveguide elements joined at theirends by 180 0 end cas tings.

Vertical slot radiators are cut in the narrowdimension on each side of a straight waveguideelement, and are covered by a Fiberglas radometo permit the waveguide to be pressurized. Twometallic directing vanes, which extend the lengthof the array, are positioned so that the r-f en­ergy radiated from the slots is directed to theparabolic reflector . The sinuous feed is ter­minated at its lower end in a load which absorbsthe r-f energy not radiated from the antenna,thus preventing reflections of the energy withinthe feed.

The conductance of a slot at the frequencybeing transmitted is a measure of the power thatit radiates. It is related to the angle of inclina­tion of the plane of the slot from a perpendicularto the waveguide axis increasing as the angleincreases. In order that equal power be radi­ated from the first and last slots of the array,the conductance of the last slot must be consid­erably greater than that of the first slot. There­fore , the slot inclination is increased pro­gressively along the array from the minimumconductance near the input.

The reason for the slot configuration can beexplained as follows: If all of the slots wereinclined at the same angle, thus having the samevalue of slot conductance , the greater part ofthe r -f energy would be r adiated from the firstfew slots near the input of the array . Thus ver ylitUe energy would be available for radiationnear the end of the array.

The vertical angle of inclination of the slotsin relation to the narrow side of ,the waveguidekeeps the antenna elevation side lobes at -20 dbor less , relative to the main lobe. The slotsexist on both sides of the waveguide. The pairsof slots on opposite narrow sides of the rec­tangular waveguide are crossed so that thebeams from the two halves of the reflector willbe in phase in the horizontal plane.

The method of forming the radiated patternis illustrated in figure 14-21. .Alt hough 44 pairsof slot radiators are used in the sinuous feed,only three slots are represented. In the expla­nation, it may prove helpful to consider each

slot radiator as the equivalent of a small dipoleantenna.

When the distance between energy maxima isequal to the slot spacing A (fig. 14-22), the en­ergy pattern moving down the sinuous feedreaches its maximum value at the same timefor each slot. Thus, each slot radiates a wave­front at the same time. The radiated wavefrontsreinforce or form the beam maximum in a di­rection broadside to the array of slots. How­ever, when the distance between energy maximadiffers from the spacing between slots, wave­fronts are radiated by the slots at differenttimes. Figure 14-22 illustrates a case in whichthe distance between energy maxima A is greaterthan the slot spacing, and the beam elevation isthus altered. The amount this distance isgreater than the spacing is a function of the fre­quency of the energizing wave. For example , asthe r-f energy moves down the waveguide thecrest of the wave reaches slot 1 first , slot 2later, and slot 3 last.

The three wavefronts are reinfor-ced to formthe beam maximum at an angle ex above thebroadside position (N) of the array.

In a like fashion, when the distance betweenenergy peaks is less than the slot spacing, theradiated wavefronts are reinforced to form thebeam maximum at an angle below the broadsideposition (N) (not shown).

The distance between peaks in the energypattern may be increased or decreased in ac­cordance with the frequency of the energy fed tothe slots. When the frequency is decreased thewavelength increases, and hence the distance be­tween the peaks increases with a correspondingincrease in beam elevation. When the frequencyis increased the wavelength decreases, and hencethe peak-to-peak distance of the wavefront de­creases. This action lowers the beam elevation.The overall effect is that an increase of fre­quency causes the beam to scan away from thefed end, while a decrease of frequency causesthe beam to scan toward the fed end.

From the foregoing discussion it should beunderstood that by changing the transmitter fre­quency in steps, the position of the radiatedbeam can be made to step in angular incrementsrelative to the broadside position. The broad­side position of the beam occurs at a frequencyof 3000 megacycles.

The microwave circuits and antenna, as theyare related to the receiving function , are treatedin chapter 15 of this text along with all of theremaining functions of the AN/SPCl-42.

CONFIDENTIAL

CONFIDENTIAL

340 CIRCUITRY OF SHIPBOARD ELECTRONICS EQUIPMENT

1

I~ WAVEGUIDE PRIMARY FEED

o::J)

'"o....oz

o...'"Z'";vG>-<.......o~ \ ..,.- - - - - - - - - - RADIATED WAVEFRONTS

.....-----*-.....------4-.....-----~~----------- ... BROADSIDERAD IATEO

BEAM MAXIMUM

""'---- RAOIATED WAVEFRONTS AT tl

RADIATED WAVEFRONTS AT t2

RADIATED WAVEFRONTS AT t 3

RADIATORS ARE FED IN PHASE .

RADIATOR SPACING:),./2.

1,2,3, REPRESENT SLOT RADIATORS .

032.264

Figure 14-21.-Formation of broadside beam, simplified diagram, side elevation.

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Chapter 14-0PERATING PRINCIPLES OF A SCAN RADAR, AN/SPS-42 (PT. I) 341

!--------------------WAVEGUIDE PRIMARY FEED

RADIATEDBEAM MAXIMUM

RADIATOR SPACING: ~12 .

~2,3. REPRESENT SLOT RADIATORS.

1-----RADIATED WAVEFRONTS

.1fI:::::.---+-+---Pr---~'--Hr__--__+____1i__4----------- N

BEAM POSITION ATBROADSIDE FREQUENCY

1032 .265

Figure 14-22.-Formation of the elevation beam.

CONFIDENTIAL

CONFIDENTIAL

E

2

Figure 14-1.-Radar Set An/SPS-42, relationship of units.

~__R,-~ DIRECTI..

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032.244

CONFIDENTIAL

POWERSUPPLY GROUP

~L- I"~~

CONVERTER­DUPLEXER GROUP

RADAR TEST SET GROUP

ELECTRONTUBE

LIQUIDCOOLER

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RADAR SET CONTROL

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WAVE FORM CONVERTER GROUP

SLANT RANGE SIGNALFOR USE AS NEEDED

CONFIDENTIAL

II SYNCHRONIZING FUNCTIONL .J

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032.2.6

Figure 14-3.-Overall system, block diagram.

CONFIDENTIAL

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CONFIDENTIAL

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032.260Figure 14-17.-R-f channel, block diagram.

CONFIDENTIAL

. :_:._.: \. .~ . . "- ' .- - -._- -- ' . - - " - - -

I

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