Ch8-9 Radar Transmitter & Receiver

1

1 Hankuk Aviation Univ.레이다 공학

Lecture 8 : Radar Transmitters and Antenna

Objective- 레이다 송신기의 구성과 원리 이해

- 송신기 종류에 따른 특성 이해

- 안테나의 원리와 종류에 따른 특성 이해

주요 내용- 8.1 Transmitter Introduction and Functions- 8.2 Klystron Transmitters- 8.3 Traveling Wave Tube (TWT) Transmitters- 8.4 Crossed-Field Amplifier (CFA) Transmitters- 8.5 Magnetron Transmitter- 8.6 Solid State Transmitter- 8.7 Modulator- 8.8 High-Voltage Power Supplies- 8.9 Transmitter Vacuum and Cooling Systems- 8.10 Transmitter Monitoring and Testing- 8.11 Transmitter Parameters- 8.12 Microwave Components- 8.13 Waveguide- 8.14 Radar Antenna- 8.15 Sidelobe Suppression Technique- 8.16 Reference


8.1 Transmitter Introduction and Functions

Radar Transmitter- Functions

generate the EM signal for target illumination.tow type : coherent amp & non-coherent amp

- Block Diagram

<Radar Transmitter Generic Diagram>

2



Transmitter Type

- O-type : linear beam - M/W amplifying tubes,klystrons,traveling wave tubes, twystrons

- M-type : crossed-field – M/W amplifying tubes, crossed-field amp(CFAs), magnetrons

- Solid-state m/w amp



Transmitter Characteristics

< Transmitter Characteristics >

3


M/W Tubes & ComponentsM/W tubes (8.2) Klystron transmitter.

(8.3) Traveling wave tube(TWT) transmitter.(8.4) Crossed-field amp(CFA) transmitter.(8.5) Magnetron transmitter.(8.6) Solid state transmitter.(8.7) Modulator.(8.8) High voltage power supplier.(8.9) Transmitter vacuum and cooling systems.(8.10) Transmitter Monitoring and testing.

M/W component (8.11) Duplexer, Signal limiter, Magic tee, Rotary joints,

isolator, Directional coupler. Wave guide ∝ freq. band


8.6 Solid State Transmitter

Characteristics- The advantages of solid-state devices over vacuum tubes are

well known and include lower voltage requirements and highreliability

- Their primary disadvantages are low power output per deviceand relatively poor operation at higher microwave frequencies

- Radar transmitters made up of solid-state devices are reservedfor the lower frequency bands and contain many devices operating in parallel

4



Many different types of solid state device- Bipolar junction transistors (BJTs)

conventional junction (NPN and PNP) transistors used primarilyas amplifiers

- Field-effect transistors (FETs)are primarily amplifiers

- Transferred-electron devices (TEDs) are forward-biased semiconductor devices

- Avalanche transit-time (ATT) devices are complex diodes operating in reverse breakdown

Solid-state devices can make up the entire transmitter in radars



Solid-state transmitter configurations

< Solid-State Transmitter Configurations >

5



The block diagram of a transmit/receive activearray module patterned after PAVE PAWS

< A Typical Transceiver Module (modeled after PAVE PAWS) >


8.10 Transmitter Monitoring and Testing

Test and Monitoring

< Typical Transmitter Test and Monitoring >

6


8.11 Transmit Parameter

Power- It is measured by sampling a fraction of the power output and

using an RF power meter

(dB)sensor meter theport to monitoring thefrom loss the L 3) Ch. sec - (dBfactor correction cycleduty the dccf

(dBm) readingmeter power (Average) the P (dBm)power speak r tranmitte the P

(dB)L dccf(dB) (dBm)P (dBm)P

C

M

T

CMT

====

++=

Frequency- It is made more difficult by pulsing

Counters : CW signals, the most accurate meterAbsorption wavemeters : Pulsed signals, less accurate,

harder to use than counter



Pulse width and shape- Waveform monitors sample RF from the transmitter,

demodulate it, and display the envelope on an oscilloscope.One class of detector often used is square-law detector.

Spectrum- It tells much about how well the transmitter is operating- The spectrum depends on the wave being transmitted

(Hertz) lobe spectralmain theofbandwidth null-to-null : B (seconds) width pulseCW gated the:

2/B

N-N

N-N

ττ =

< Gated CW Spectra >

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VSWR and Return Loss- Reflections are measured using a dual directional coupler,

giving an attenuated sample of the forward power andsampling the reflected wave

|)| - (1 / |)| (1 voltageminimum / the voltagemaximum the

Ratio) WaveStanding (Voltage VSWR oltageincident v / the voltagereflected the t)Coefficienn (Reflectio

ΓΓ+==

−=Γ−

Transmitter, Modulator, and HVPS DC andPulse monitoring - Most transmitters have built-in test points to be used for

monitoring and testing DC and DC pulse voltages and currents


8.14 Radar Antennas

Parameters- Radiation pattern & directivity- Beamwidth & length efficiency- Aperture : effective area & efficiency- Gain & Efficiency.- Sidelobe definition & effects.- Field zones / Polarization

Functions- Act as a transducer & impedance match between Tx and

propagation-medium & between the medium and receiver- Provide gain & steer the Tx power to the desired angular

position

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Radiation PatternRadiation pattern

2λ=lengthdipole

‧Communications

‧Secondary radar

‧ECM

‧Radar target

‧Clutter

‧Square of one-way pattern

(Gain 3dB B/W 6dB B/W)

(Sidelobe lower double)


Antenna Effective Length

( )antennaoflengtheffectiveDwhere

D

radiansD

eff

eff

effdB

=

⎟⎠⎞

⎜⎝⎛=

=

(deg)180

)(3

λπ

λθ

9


Effective Area & Beam Shape

( ) (deg)180,)(

,

)()(3

)()(3

)()()()()()(

πλθλθ

ηη

AZeffAZ

AZeffAZ

ELELLELeffAZAZLAZeff

DradiansD

DDDD

==

==


Antenna Sidelobe EffectSidelobes & sidelobe effects

대책 : Ultra low sidelobe ant.

sidelobe signal suppression tech.

SLB sidelobe blanking.

CSLC coherent sidelobe cancellation.

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8.14 Radar Antennas

Antenna Field Zone- Flatness : for practical purpose,

less than of curvature.

-Fan field : longest distance to any point

on plane of ant.must be

less than

- Near field : range less than far field range.

16λ

16R λ+

48

16162

4

162

2

2

2

222

2

22

2

2

DR

RRRD

RRD

DRFF

=

++=+

⎟⎠⎞

⎜⎝⎛ +=+⎟

⎠⎞

⎜⎝⎛

=

λ

λλ

λλ

λ22DR =

< Near-and Far-Field Waves >

< Geometry for Solving Far-Field Distance >


8.14 Radar Antennas

Arrays of Discrete Elements- Arrays

Linear array – one element dimensionPlanar array – two element array dimensionConformal array- conforms to the shape of object(mounted the nose of a/c or missile)

- Array & continuous antenna - Same shape, D, area, illumination function, frequency- Element pacing < 2

λ

< Array/Continuous Antenna Equivalence >

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8.14 Radar Antennas

- Beam pattern of array

< Array Multiplication Principle >


8.14 Radar AntennaRadar Antenna Configurations

<Radar Antenna Types>

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8.14 Radar AntennaReflector Antennas

(a) Focal point feed reflector antenna- The focal point feed reflector antenna uses as a reflector a parabola of rotation with the feed at the paraboloid’s focus.

- Illumination is set by the feed antenna’s beam pattern only ->Difficult to control- Aperture blockage -> Depend on Feed and its supports

<Focal Point Feed Reflector Antenna>


8.14 Radar AntennaReflector Antennas

(b) Offset Feed Antenna- The offset feed reflector is a focal point feed antenna with part of - the reflector remove. - Purpose -> Reduce or eliminate aperture blockage- Illumination control -> Difficult

(c) Cassegrain Reflector Antenna- The cassegrain reflector system uses two reflectors, the primary being a parabloid and the secondary being an hyperboloid.

- Illumination control -> Difficult , Very large aperture blockage- The aperture Blockage -> Large

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8.14 Radar Antennas

- Array of angular offset

< Array Beam Formation

- Equal Phase Element >

eistancdextraforphaseS

anglesteering

SS2pointnobservatiothetoarraytheofplanethefrom

elementadjacentbetweenestancdiindifferenceSr

:2

sin

sin360sin

:sin

πφΔλθ

θλ

θλπφΔ

θΔ

=

==

=


8.14 Phase-Steered ArrayElectronically Phase – Steered Arrays

ⓐ Conventional Array with Phase Shifter ⓑ Space-Fed Lens Array

ⓒ Reflector Array

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8.15 Sidelobe Suppression TechniqueLow sidelobe antenna

- Illumination function -> Critical(Array antenna -> Good control of illumination)

- Aperture blockage -> Avoid

<Sidelobe Blanking Principle>

<Sidelobe Blanking System>

Sidelobe Blanking (SLB)


8.15 Sidelobe Suppression TechniqueCoherent Sidelobe Cancellation (CSLC)

<Coherent Sidelobe Cancellation Principle>

<CSLC System>

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8.16 Reference[1] Radar Transmitters by G. W. Ewell, McGraw-Hill, 1981

[2] Microwave Tubes by A. S. Gilmour, Artech House, 1986

[3] Passive and Active Microwave Circuits by J. Helszajin, John Wiley & Sons, 1978

[4] Transmission Lines and Waveguide by L. V. Blake, John Wiley & Sons, 1969

[5] Antenna Engineering Handbook by R. C. Johnson and H. Jasik, McGraw-Hill, 1984

[6] Antenna Theory and Design by W. L. Stutzman and G. A. Thiele, John Wiley &Sons, 1981

[7] Aspects of Modern Radar by E. Brookner, Artech House, 1988

[8] Fields and Waves in Modern Radio by S. Ramo and J. R. Whinnery, John Wiley& Sons, 1953


Lecture 9 : Receiver & DisplayObjective - 레이다 수신기의 구성과 원리 이해- 수신기 종류에 따른 특성 이해- 디스플레이의 종류와 특성 이해

주요 내용- 9.1 Receiver- 9.2 Receiver Type- 9.3 RF Processor- 9.4 RF Attenuator & Filter , Amplifier- 9.5 Mixer- 9.6 Local oscillator- 9.7 AFC & COHO- 9.8 IF Amplifier- 9.9 Demodulator- 9.10 Radar Receiver Example- 9.11 Display- 9.12 Reference

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9.1 ReceiverReceiver

• GeneralRadar echo signal from antenna: -20dBm ~ -100dBm- very low amplitude of

for minimal detectable targetThus, its amplitude must be increased by the receiver amp.

<Basic Functional Receiver Block Diagram>


9.2 Receiver Type

<Crystal Video Receiver>

<Homodyne Receiver>

*Crystal Video Receiver- Early receiver type.- Amplified & immediately

converted to baseband freq.- Advantage : Simple

Inexpensive- Disadvantage : Overwhelming

standpoint*Homodyne Receiver- Amplified & immediately

converted in a mixer basebandfrequency

- Advantage : Simple- Disadvantage : Poor sensitivity

Inability, Difficult to suppressinterference

Receiver Type

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9.2 Receiver Type - Superheterodyne Receiver

Superheterodyne Receiver

<Superheterodyne Receiver>

<Image-Reject Filter>

* Superheterodyne Receiver- Main signal amplification & filtering at an intermediate frequency

- Easier & better filter & amplifierdesign

- Advantage: Simply changing the frequency

* Image response-> Suppress for two reason

1) A second receiver bandwidth’sworth of noise (SNR reduce)

2) Another bandwidth(ECM-Image jamming)


9.2 Receiver Type - Superheterodyne ReceiverSuperheterodyne Receiver Type

<Double-Conversion Superheterodyne Receiver> <Triple-Conversion Superheterodyne Receiver>

Intermediate frequency -> too high -> Design of the IF amp. & filter is complicated-> For this reason, multiple-conversion superheterodyne receiver were

developed

18


9.3 RF Processor

<RF Processor>

( / ) / at the input of sys( / ) / at the output of sys

S N in S NFS N out S N

= =

* Noise Figure / Noise Factor: noise figure is a measure of how much noise is added by the system

* Noise Figure (a) system temperature (b) Ant. Trans line(c) Receiver equivalent temp

RF Processor


Noise Factor of Multi-Stage Amplifier

The overall nose factor is

stagenththeofgaintheGstagenththeoffactornoisetheF

ratiopowerfactornoiseoveralltheFGGFGFFF

n

n

T

===

−+−+−+=)(

)110(....)]/()1[(]/)1[( 213121

<Noise Factor in Multi-Stage Amplifiers>

9.3 RF Processor

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9.10 Radar Receiver Example

Search Receiver

<Search Receiver 1> <Search Receiver 2>


9.11 Radar DisplayRadar Display Summary

(1) A-scope : range vs amplitude(linear or log)(2) A/R scope : tracking radar(3) R-scope : tracking radar range gate

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9.11 Radar Display – B Type

(4) B- scope : airborne, rectangular display target amplitude brightness of the spot.commonly used air-to-air combat display.

(5) B-Prime scope : az. vs closing velocity


9.11 Azimuth vs Elevation Display

(6) C- scope : rectangular or circular display(7) D- scope : azimuth vs elevation

F- scope : basically a tracking error scope

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9.11 PPI & RHI

RHI(Range Height Indicator)

(8) PPI : Plan Position Indicator, or P-scope(9) RHI : Range-Height Indicator


9.12 Reference[1] J.B. Tsui, Microwave Receivers with Electronic Warfare Applications, New York

: Jonhn Wiley & Sons, 1986.

[2] S.J.Erst, Receiving System Design, Norwood MA : Artech House, 1984

[3] J.W.Taylor Jr., Ch.3 in M.I.Skolnik, Radar Handbook, 2nd ed., New York :: McGraw-Hill, 1990.

[4] S.Y.Liao,Microwave Devices and Circuits, Englewood Cliffs NJ : Prentice Hall, 1980

[5] J.W.Taylor, Jr.and J.Mattern, Ch.5 in M.I.Skolnik, Radar Handbook, 1st ed.,New York: McGraw-Hill, 1970.

[6] “IEEE Standard Radar Definitions,” IEEE Standard 686-82, New York : TheInstitute of Electrical and Electronics Engineers, 1982.

Documents

Ch8-9 Radar Transmitter & Receiver