NASA Technical Memorandum 87201

Technology Achievements andProjections for CommunicationSatellites of the Future

James W. BagwellLewis Research CenterCleveland, Ohio

f N A S A - I M - 8 7 2 0 1 ) 1 E C H N C L O G Y A C H I E V E M E N T S A N DPROJECTIONS BOS C C H H D I i l C A T I O H SATELLITES OFTHE F U T U R E ( N A S A ) 13 P HC A C 2 / M F A

N86-H595

G3/32 05273

Prepared for the1 1th Communications Satellite Systems Conferencesponsored by the American Institute of Aeronautics and AstronauticsSan Diego, California, March 16-20, 1986

NASA

https://ntrs.nasa.gov/search.jsp?R=19860008125 2020-07-16T23:34:01+00:00Z

TECHNOLOGY ACHIEVEMENTS AND PROJECTIONS FOR COMMUNICATION SATELLITES OF THE FUTURE

James W. BagwellNational Aeronautics and Space Administration

Lewis Research CenterCleveland, Ohio 44135

Abstract

Over the past five years, NASA has conductedan extensive program to advance the state-of-the-art- in communication satellite technology. NASAis preparing to conduct a flight experiment in1989 to verify the-performance of this technology.Shortly thereafter, we should see the communica-tions satellite industry begin to use this tech-nology and enter into a new era of satellitecommunications including services in a new commu-nications band, 30/20 GHz.

What new capabilities and services does thisNASA developed technology enable? What does thefuture hold for even better systems and servicesand what technology barriers must be overcome toenable these to happen? This paper addressesthese questions by describing the accomplishmentsof the NASA sponsored technology program over thepast five years and projecting possible technologyadvancements over the next 10 yr. A systems scen-ario for the year 2000 using this technology isdescribed. The projected capabilities and systemsdescribed herein are based on technology advance-ments alone, without consideration for competingterrestrial technologies or market demand. Theseand other factors may affect the rate of develop-ment and characteristics of future satellite com-munications systems.

Multibeam systems of the future using mono-lithic microwave integrated circuits to providephase control and power gain are contrasted withdiscrete microwave power amplifiers from 10 to75 W and their associated waveguide feeds, phaseshifters and power splitters. Challenging newenabling technology areas include advanced electro-optical control and signal feeds. Large scaleMMIC',s will be used incorporating on chip controlinterfaces, latching, and phase and amplitude con-trol with power levels of a few watts each. Beamforming algorithms for 80° to 90° wide angle scan-ning and precise beam forming under wide rangingenvironments will be required.

Satellite systems using these dynamicallyreconfigured multibeam antenna systems will demandgreater degrees of beam interconnectivity. Multi-band and multiservice users will be interconnectdthrough the same space platform. Monolithicswitching arrays operating over a wide range of RFand IF frequencies are contrasted with current IFswitch technology implemented discretely. Size,weight, and performance improvements by an orderof magnitude are projected.

Un-board message processing will advance tothe state where it will be fully autonomous incor-porating in-band signaling, very high speed switch-ing and routing, and universal demodulation. Thesewill be contrasted with the current technology tobe demonstrated on the Advanced CommunicationsTechnology Satellite in 1989, using separateorderwire signaling, single format demodulationand complex high power message storage systems.

Very high speed, low power, radiation tolerantsemiconductor technologies will be required forimplementing the advanced architectural concepts.

A system scenario of the future may likelyinclude a wide array of user terminal types manu-factured for mass market consumer sales plus .building block components for existing terminalupgrades. Equal access services will be generallyavailable from customer owned terminal equipment.New satellite and Earth station technologies;willbe both adaptive and programmable to minimizeobsolescence and better assure compatibility ofexisting and emerging services. . :

Introduction . -

NASA's program in communication satellitesbegan early in the nation's space program. Everymajor advance in satellite operation has beenpreceded by a significant technology development .by NASA. Having had its communications R&D pro-gram reduced to a low ebb for approximately fiveyears during the latter part of the 1970's,. NASAnow finds itself again making major advances incommunication satellite technology. The capabili-ties these advances have enabled to date are ,impressive,.but the prospect for the future iseven brighter. The possibilities are just hintedat in NASA's current and planned activities. Thefuture undoubtedly holds many things yet unforeseenand unimagined. The technology advances required-are realizable, but attention must be given to -identification of the most promising and affordableideas.

Background History

From its beginning years, NASA was lookingtoward the exploitation of the unique characteris-tics of space. It all began with the launching ofEcho in in the early 1960's, a large balloon inspace from which radio signals could be reflectedback to Earth. This led, in 1963, to the launch-ing of the first active transponder satellite, aspinner. This was followed by a.series of experi-mental spinning satellites, Syncoms. These earlydemonstrations, led to the launch in 1965 of acommercial Syncom look-alike, the Early Bird (orIntelsat I). In 1966 NASA again took the lead insatellite communications technology with thelaunching of a series of Applications TechnologySatellites, ATS. ATS 1 to 5 featured a despunantenna and a C-band transponder in addition totransponders at VHF and L-band. These early ATSsatellites triggered the development of .the wholeseries of commercial satellites beginning with theINTELSAT 3 series and including. WESTAR, COMSTAR,TELSTAR, SATCOM, and now GALAXY. In 1974, NASAlaunched the first in a series,of 3-axis stabi-lized satellites in ATS-6. This too fostered awhole series of 3-axis stabilized commercialsatellites to follow. These included INSAT-,ARABSAT, and TDRSS.

As always, NASA had its eyes on the futureand foresaw the.need'for communication satellitescapable of high-radiated-RF-power. To this endthe Communications Technology Satellite, CTS, wasjointly developed with the Canadian government.This project sought to advance the technology ofboth space and ground-based components and systemscapable of high power in space and lower cost inthe ground segment. This satellite, launched in1975, for the first time, introduced satellitecommunication in the Ku-band. Again, as predicted,commercial ventures picked up on NASA's lead andbegan a series of Ku-band satellites in 1980 withthe launching of SBS followed, up to the present,with SPACENET and SATCOM with more yet to come.In the meantime, unfortunately, National prioritiesand a mistaken appraisal of the capabilities ofU.S. industry to assume the long range, high risktechnology development sponsored by NASA, causedNASA's R&D in communication satellites to be sig-nificantly cut back in 1973. With NASA pursuingan aggressive manned space program, the continueddevelopment of the advanced technology crucial tothe future of the emerging satellite communicationsindustry in the U.S. fell solely to a still matur-ing industry. However, this was not the caseoverseas. European and Japanese companies saw theopportunity and began to move out with communica-tions R&D sponsored, in part, by their respectivegovernments.

With the use of satellites for domestic voice,data, and video traffic increasing at a rate likelyto exceed the capacity of the C and Ku bands withina decade the attention of the U.S. government wasdrawn to finding a solution. This prospect, cou-pled with the emerging problem of internationaltechnology and trade disparities was recognized in1978 and President Carter saw fit to reinstatefederal sponsorship of commercial communicationsatellite technology. This directive (PD-42 inOctober 1978) was quickly followed by an aggressivenew NASA program in advanced R&D in satellite com-munication with the initiation of a 5 yr technologyprogram aimed at opening the Ka-band to commercialuse along with new on-board technologies of multi-beam antennas and satellite switching andprocessing.

Advanced Technology Program Overview

Over the past six years NASA has been pursuinga comprehensive, coordinated program in multibeamcommunications satellite' technology as describedin Ref. 1. Although aimed at enabling use of theKa band of frequencies, specifically 30/20 GHz,the technology program included numerous elementsof multibeam, processing, and 'switching technolo-gies which are truly frequency independent. 'Theoverall goal of the advanced communications satel-lite technology program is to develop and introducenew technologies to an extent that al1 excessiverisks have been removed or reduced to a suffi-ciently low level that the commercial satelliteindustry will not hesitate to use them when theneed arises. To date, this technology program hascompleted development of the wide array of func-tional components and subsystems shown in Table 1-.These developments-were conducted by the companiesshown under NASA'sponsorship and now are beingtested^-S ancj integrated-into a communicationsystem test bed at NASA. When completed in 1987,this test bed, functionally depicted in Fig. 1 anddescribed in Ref. 2, will be capable of emulating

a satellite based communications network includingground terminals and the intervening RF paths.Ground testing of this sort is believed to beadequate in removing excessive risk to using newtechnology in many instances. Where this approachis not sufficient, a flight experiment program isconducted to remove or further reduce the remainingrisk factors. This is currently the case in theadvanced technology program and hence, the initi-ation of the Advanced Communications TechnologySatellite (ACTS) Project. The goal of the ACTSproject is to further reduce or remove the risksassociated with the use of multiple scanning andfixed beam antenna systems and the many elementsof on-board processing and routing needed tointerconnect the multiple beams. Performing thisflight experiment at Ka-band serves the additionalpurpose of verifying successful operation in thenew band. Following its launching in 1989 and atwo year experiment period to follow thereafter,it is expected that development and deployment ofcommercial Ka band satellites will begin.

In the meantime, the advanced technologydevelopment- program is continuing to identify newgoals and objectives and pursue a course aimed atfurther accomplishments of significance in thefuture. In the paragraphs to follow, many of theaccomplishments to date will be described alongwith planned extensions and new technologyinitiatives.

Low Noise Receivers

The development of 30 GHz, low noise, satel-lite' based receivers was undertaken with dual con-tract awards. Both pursued an approach using animage enhanced mixer design believing'it to bepremature to attempt a design using 30 GHz FETLNA's. Both achieved all performance goals exceptthat the noise figures exceeded 5 dB. In thiscase, available technology has already surpassedthis goal. The ACTS flight experiment will employlow noise receivers with, a noise figure of 5.0 dBusing FET LNA's. Microwave monolithic integratedcircuit (MMIC) receivers at 30 GHz are currentlyunder development. The configuration of a typicalreceive module is shown in Fig. 2. These aretargeted for phased array antenna use which willbe described later. The anticipated noise figurefor these is 5.0 dB.

Recently the development of a 20 GHz low noisereceiver for ground station use was undertaken.This is a mostly monolithic receiver with goals oflow cost design and a noise figure of 3.5 dB. Itis anticipated that the use of monolithic tech-niques will allow for substantial reduction in thecost of 20 GHz ground terminal receivers whenmanufactured in quantity. It is likely that mono-lithic 30 GHz'receivers along with emerging phasedarray antenna technologies will minimize the useof single on-board receiver applications in thefuture.

High Power Amplifiers

Both tube and solid state amplifiers at vari-ous frequencies have been under development formany years! The satellite industry is alreadyemploying solid state amplifiers at C-band and maysoon do so at Ku-band. Since a characteristic of-solid state devices is decreasing output power andefficiency with increasing frequency, the

demonstrated performance to date at 20 Ghz hasbeen poor. First attempts at solid state ampli-fiers resulted in 15.8>W. at 13 percent efficiencyfor an IMPATT amplifier"and 8.2 W at 8.5 percentefficiency for a GaAs FET amplifier.' Combinerefficiency appears adequate but the combination oflarge numbers of devices results in a decrease inbandwidth..- The bandwidth achieved for the IMPATTamplifier was less than 100 MHz and for the GaAsFET amplifier 1.7 GHz both less than the desiredgoals of 500 MHz and 2.5 GHz respectively.

Higher power devices would require fewer incombination for the same power output. A follow-ondevice development program has resulted in IMPATTdevices at 4.3 W and 19 percent efficiency andGaAs FETs at 1.0 W and 23 percent efficiency witha 1.5 GHz bandwidth. A further effort to get a2 W FET led to a device with only 18 percent effi-

< ciency and a 1.0 GHz bandwidth.

At the same time, TWT development has beenproceeding with continued modest gains in perform-ance which already exceeds solid state performanceby nearly a factor of two. Tubes with 50 to 75 Woutput at 60 percent efficiency with 2 GHz band-width are being projected combining the new tech-niques, of diamond supported helices, graphitedepressed collectors and variable pitch helicies.Reliability, once the great risk of TWT amplifiers,has been greatly improved in recent years with thedevelopment of M-type dispenser cathodes and open-to-vacuum construction techniques. The M-typecathode,has demonstrated a 10 yr lifetime potentialon life test. While high voltages will always posea reliability threat, open to vacuum constructionand fault tolerant design have greatly reduced thepotential for failure. While tubes remain theperformance choice at higher power levels, thesolid state amplifier as a tube replacement at20 GHz appears probable up to approximately 20 W.

In the future, NASA will continue to improveTWT performance to meet or exceed the projectedgoals! On the other hand solid state devicesappear to be reaching the point where performancegains are diminishing. Thus NASA's developmentefforts in solid-state in the future will befocussed to a large extent on MMIC power modulesfor phased array antenna applications. Figure 3shows a possib.le configuration for a typical MMICpower module including an integral phase shifter.

In the area of ground station power amplifiersefficiency is not nearly as important a factor asis cost. Current tubes of the coupled cavity orhelix design are very costly to fabricate. Newdesign techniques such as the tunnel ladder tech-nique are being pursued as a means of reducingmanufacturing costs. Meanwhile, NASA had sponsoreda 30 GHz solid state amplifier using silicon tech-nology. The amplifier produced 20 W at 9 percentefficiency and 260 MHz (1 dB) bandwidth. Hereagain, solid state amplifiers will likely grow todominate the lower power applications and becauseof the lesser sensitivity to efficiency, likely beapplied at higher power levels than its spacebornecounterpart.

Multibeam Antenna^

The primary new technology begun in 1980 wasthat of the multibeam antenna. Using clusters ofwaveguide fed horns both fixed and scanning spot

beams were developed. The fixed spot beams werepositioned to provide spatial separation betweenareas of high communications traffic density. Toprovide coverage over the less-dense areas of cbnusthe scanning spot beams were employed, providingtime separation between covered areas. Addingpolarization to these techniques allowed inter-ference free spots to be even more closely spacedresulting in as much as 12 times frequency reuseacross CONUS.

Two parallel contracts were awarded for thedevelopment of the first satellite antennas to .incorporate a combination^f scanning and fixed •beams. Both contractors considered it prematureto attempt a development using MMIC device tech-nology and thereby constrained their efforts tocorporate feeds using waveguide power dividers andphase shifters. The complexity of a typical three-beam horn cluster is shown in Fig. 4. Even thoughonly small subsets of an operational six scanningbeam, 18 fixed beam system were built, consider-able difficulties were encountered in the fabrica-tion of the complex waveguide structures. .It was .generally agreed that, although the required per-formance was obtained, fabrication of an opera-tional sized system was impractical.

As previously stated, solid-state poweramplifiers to feed these multibeam antennas have .required large numbers of low power, 1 to 2 W,devices to be combined thereby diminishing overallperformance and efficiency. A typical power 'amplifier would then be connected through powerdividers and phase shifters to a multi-horncluster for proper beam forming. Each horn mightrequire only 1 to 2 W for adequate performance inrain-free conditions. If a separate amplifier ofthis power could be developed to directly feed theradiating horn or alternately perform as a direct'radiating element then the complexities and lossesof the waveguide beamforming network and the mis-matches of the combiners within the power ampli-fier could be avoided. These losses are brokenoutin Fig. 5 It was on these premises that researchin MMIC power and receive modules was begun.Although multiple contracts were awarded in theearly 1980's for both 20 GHz power modules and30 GHz low noise amplifiers, both incorporatingvariable phase shifters, it wasn't until 1985 thatsuccessful module performance was demonstrated.The concept for using such modules in an antennais shown in Fig. 6'. An experimental array antennausing the 20 GHz power modules is now under con-struction with construction of 30 GHz receive feedsystem scheduled to begin in 1986.

Once the ability to exercise virtually infi-nite control over the formed beam is realized,then additional capabilities accrue to thedesigner. Most exciting of these is the possi-bility of correcting beam anomalies created by amechanically or thermally distorted reflector.The effects of such distortion are graphicallyshown in Fig. 7. By either measuring the antennadistortion or sensing the beam distortion theon-board antenna controller can be programmed toimpose corrections to the phase and amplitude ofeach radiat.ing element to restore proper beam per-formance. The use of this technique will enhancethe performance of larger, deployable antennas onthe spacecraft. These larger antennas could thenlead to the use of lower frequencies and/orsmaller spot beams.

On-Board Switching -'.

Once having developed the concept of multipleantenna beams for both up and down links it.becameobvious that new methods had to be devised tointerconnect these beams in the proper order. The.first of these techniques took the form of dynamic'matrix IF switches. Again, two parallel contractswere awarded both pursuing the common approach ofcoupled, crossbar matrix switching using dual FETswitches at each crosspoint. Differences wereprincipally in the areas of packaging and circuitlayout. 20. by 20 matrix switches were requiredfor POC demonstration with a growth'potential to100 by 100. Because of cost, the crosspoints wereonly partially populated with couplers and activeswitching elements. A picture of one such'switchmatrix is shown in Fig. 8. The 's'ize of such aswitch assembly approached 2000 in^ includingswitch drivers. Though the best design practiceswere used these discretely implemented switcheswere bulky and imposed path losses from 13 to27 dB or varied over a 10 dB range in a singleswitch matrix. It was therefore concluded that a100 by 100 matrix was impractical by these orsimilar techniques using discrete parts.

To solve these problems, NASA is sponsoring atechnology development effort to implement a switchmatrix in MMIC. The first of these is targeted atproducing a 10 by 10 IF switch matrix with 0 dBinsertion loss. Fabrication of such a designappears possible on a 1/2 by 1/2 in. MMIC sub-strate. Additional work has recently begun usingthe same approach but at 20 GHz. Such a switchwould require only a single down conversion from30 to 20 GHz thereby 'eliminating the upconverterwhich would normally follow tne matrix switch.With the availability of a basic 10 by 10 buildingblock in MMIC, the expansion to 100 by 100 shouldeasily follow.

On-Board Processing and Routing

The second multioeam interconnection techniqueto be developed was the baseband processor. Thisinitial development embodied the followed capabil-ities: demodulation, decoding, store and forward,routing, encoding, and modulation^ The proof-of-concept system could accommodate burst rates from27.5 to 550 Mbps. Internal message storage used120 nsec CMOS memories thereby necessitating theuse of 64 bit serial to parallel and parallel toserial converters to accommodate the slow memories.Burst demodulators were developed using a combina-tion of discrete and LSI techniques 'implementing aminimum shift keying (MSK) concept. Coding wasimplemented in LSI with a single CMOS decoder chipproviding 10.2 dB gain at 13.75 MBPS using a 1/2rate, constraint length 5 convolutional code.

This first attempt at a full-up basebandprocessor served to baseline the necessary tech-nologies. As a result:, demodulators, decoders,rad hard memories, support circuits, and architec-ture have been identified as needing furtherinvestigation and technology'improvement. NASAhas undertaken' the development of GaAs parallel toseri'al and serial to parallel converters at rates"in excess of 550'Mbps with a required power goalto be 250 mW, one fourth that 'of the ECL previouslyused. This development is hoped to be only a stopgap measure until 'faster-memories can be developed..Memory access times of 5 nsec or less would be '

highly~desirable. Should a memory of this speedbecome available it makes possible developing aprocessor architecture without converters previ-ously needed to slow data accesses to the memories.

Another problem arises as more and more mes-sage processing, control, and intelligence are.placed on-board the satellite. Most of thesefunctions become feasible only if. LSI or VLSItechniques are employed. An operational system inpresent day technology would consume almost 1 kW.Thus, a low power semiconductor technology is alsodesirable. Both higher speed and lower power canbe achieved with smaller feature sizes (0.25 to0.5 ym) but care must be taken to avoid increas-ing susceptibility to radiation induced SEU.

An area yet to be seriously penetrated bytechnology is modulation and coding especially forhigh rate bursted data. In a typical advancedsatellite communications scenario using time divi-sion, multiple access (TDMA) techniques networktiming and synchronization must be maintained towithin a fraction of a microsecond. Bursts ofdata arriving at the satellite from many differentground terminals are noncoherent, and low overheaddata acquisition techniques must be developed.Systems are being conceived for the future where1 Gbps burst rates may be desired. Given theenvironmental factors such as rain and its effectsat the higher frequency bands being chosen, theserequirements pose many problems for the developerof modems and coding. Since one of the reasons .for moving to higher frequencies, such as the Kaband, is greater bandwidth to alleviate frequencycongestion, higher modulation efficiencies arealso desirable.

In an attempt at addressing this problem,NASA has recently begun a series of technologycontracts aimed at developing advanced modems.These efforts have been divided into two categor-ies, ground terminal and satellite modems, eachwith their own distinct requirements. Parallelcontracts are being pursued in each area with com-mon goals of 200 Mbps minimum with a minimum effi-ciency of 2 bps/Hz. Satellite modems are, inaddition, to be small and power efficient whilethe ground terminal modems are to have the poten-tial of low cost implementation. . Each contract isto result in demonstrable proof-of-concept hard- .ware. A subsequent effort is planned where one ormore of the developed modems will be extended toVLSI implementation. The next stage in developingthis technology will be to include techniques foraccepting many different modulation formats, theuniversal modem. This feature will be extremelyuseful for satellite modems, allowing ground sta-tions using many .different types of modulation toaccess the same satellite.

In consideration of the aforementioned tech-nology plans and needs, it appears appropriatethat renewed attention be given 'also to new archi-tectural concepts which could take advantage ofthe increased capabilities which will emerge. Asnew technologies permit higher performance compo-nents to be developed less parallelism should berequired to handle the anticipated high data rates.In-band signaling should be realized in place ofthe separate, displaced in time, orderwire methodnow being employed. Worthy of consideration,also, may be the single string implementation ofan independent function, such as an individual

input/output channel interconnected only via therouting switch. This modular approach may permittechnology to advance apart from an orderly growthin capacity dictated by traffic demand.

Functions and Service Possibilities of the Future

In the preceding paragraphs some of the futuretechnology trends have been identified. These, inturn, will open the door to functionally improvedcommunication, satellites and new services availableto the public. These technologies, in combination,will permit the development of a complete spacebased communications message center. It will bemultifrequency and multiservice. It will be ableto provide full interconnectivity between conusbeams and regional spot beams, large trunking usersand small customers premise terminals. It willrelay information from other satellites and space

.based platforms such as space station. Fullyadaptable, fault tolerant-systems will provideobsolescence free long life. Terminal sizes willrange from an affordable 1 to 2 m terminal capableof a T-l rate at a small business site to a largeterminal at a regional trunking hub. Such a com-munications platform of itself or in conjunctionwith other platforms will be capable of integratingpersonal/mobile communications into the network.

The extent to which these and other servicesyet unforeseen will develop is uncertain. Therewill be continued competition with existing andemerging terrestrial communications systems suchas fiber optics. Each will assume a complimentaryrole as new information systems and communicationsneeds impose new and expanding service demands onthe communications industry. Developing nationswith their cultural differences, unique geography,and individual communication needs will contributeto an expanding world market.

Summary of Required Technology

Multibeam antennas and higher frequencieswill provide solutions to the problems of frequencyand orbit congestion in the future. Beam inter-connection technologies of switching, processing,and routing will allow for the interconnection oflarge quantities of users in geographically diverseareas. All of these features point to a trend ofincreased on-board functions, a direct and possiblyextensive departure from the bent-pipe transpondersystems currently being employed. All of thesedepend on some major technology advancements in

the next five to ten years. VLSI and MMIC circuitswill be extensively required. Highly reliable andfault tolerant, these circuits must assume physicaland functional sizes larger than those availabletoday.

Just now emerging from the research lab, new.optical technologies may eventually solve some ofthe current problems in semiconductor performanceand displace conventional techniques now beingworked on. Their .immunity to noise...and radiationcoupled with their wide bandwidth capability makethem ideal candidates for the transmission, pro-cessing, switching, and routing functions outlinedabove. Although the possibilities are exciting,much work remains to be done. The technologies tosupport terrestrial fiber optics and satellitebased optical systems may in fact have much incommon, advances in one thereby benefiting theother. . . ,

With Government funding in key areas, U.S.industry remains in the competition, but has by nomeans overcome its foreign competitors. The rightdecisions to pursue selected high risk technologiesremains NASA's priority in enabling U.S. industryto contend in the ever expanding domestic andforeign marketplaces.

Reference

1. Santarpia, D.E. and Bagwell, J.W., "Status ofNASA's Muitibeam Communications TechnologyProgram," EASCON '83; Proceedings of theSixteenth Annual Electronics and AerospaceConference and Exhibition, IEEE, New York,"1983, pp. 53-68.

2. Bagwell, 0., "A System for the Simulation andEvaluation of Satellite CommunicationNetworks," Communication Satellite SystemsConference. 10th, AIAA, 1984. pp. 172-180.

3. Conroy, M.J., "Test Results for 27.5- to 30-GHzCommunications Satellite Receivers," NASATM-83662, 1984.

4. Shalkhauser, K.A., "Test Results for 20-GHzGaAs FET Spacecraft Power Amplifier," NASATM-87072, 1985.

5. Sanders, A., "20 x 20 High Speed MicrowaveMatrix Switches," NASA TM-83775, 1984.

TABLE I. - COMPONENTS DEVELOPED TO POC UNDER NASA•TECHNOLOGY DEVELOPMENT PROGRAM

Technology Contractors

Low noise 30 GHz receiverIF Switch matrix20 GHz Impatt transmitter20 GHz GaAs FET transmitter20 GHz multimode TWTPower processor for multimode TWTBaseband processor.30 GHz Solid state transmitterLow cost ground terminal antennas

LNR,. ITTFord Aerospace, GELNR, TRWTRW, TIHughesTRWMotorolaTRW ' 'Scientific Atlanta

EXPERIMENTCONTROL &MONITORING

t \USERSIMUL

GROUNDTERM

TRANSPONDER

NETWORKCONTROL

Figure 1. - Hardware simulation of communication network.

LOGIC IN

RF

7 mm

O>IF—^ 01OUT

DC IN REF.

Figure 2. - 30 GHz Monolithic receive module.

5 BIT PHASE SHIFTER 1 WATT VARIABLE POWER AMPLIFIER

PHASE CONTROL LOGIC

BIT NO. 5180°

BIT NO. 490°

RFINPUT

INPUTBUFFERSTAGE

BIT NO.111.25°

BUFFERSTAGE

BIT N0.345°

±LBIT NO. 2

22.5°

POWER CONTROL LOGIC

DRIVERSTAGE

0.1 WATTDGFET

I I

% WATTDG FET

''/4 WATT •DUAL GATE IDG)

FET

0.1 WATTDG FET

V4 WATTDG FET

0.1 WATTDG FET

JLL

Vi WATTDG FET

POWERSPLITTER

0.1 WATTDG FET

14 WATTDG FET

Figure 3. - 20 GHz GaAs Monolithic transmit module.

.POOR QUALITY

Figure 4. -30GHz, 3 beam horn cluster.

MODULE LOSS 57 W

•: : y <q?r URFOyi

10W

RFOUT10W

BFN LOSS 10 W

TWTLOSS60W JV

HV SUPPLY LOSS 10W

BFN SWITCHING 25W ; v : V:V: :•

Figure 5. - Comparison of technologies used to produce directed RF power radiation.

20 GHz MONOLITHICTRANSMIT MODULE

RF

VARIABLEPHASESHIFTERPHASE LOGIN IN VARIABLE

GAINAMPLIFIER

SCANNING SPOTBEAM ANTENNA

MULTIPLESCANNINGBEAMFEED-^

PARABOLICMAIN REFLECTOR

SCANNING SPOT BEAMMMIC FEED SYSTEM

PARABOLICSUBREFLECTORSPACE-FED

ACTIVE (LENS)ARRAY

Figure 6. - Multiple Scanning Spot Beam antenna concept.

OR,'SfKAL mcc JoOF POOR QUALITY

DISTORTEDANTENNASTRUCTURE-

-DOWNLINKANTENNA

AMONOLITHIC\/ FEEDJAV ARRAY

ADVANCED COMMUNICATIONSSPACECRAFT

UNDISTORTED BEAM-'

FAR FIELD ANTENNA PATTERN

Figure 7. - Effects of reflection distortion on an antenna beam.

C-83-4606

Figure 8. - Proof-of-concept 20x20 matrix switch.

1. Report No.

NASA TM-87201

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle 5. Report Date

Technology Achievements and Projections forCommunication Satellites of the Future 6. Performing Organization Code

650-60-207. Author(s)

James W. Bagwell

8. Performing Organization Report No.

E-2856

10. Work Unit No.

9. Performing Organization Name and Address

National Aeronautics and Space AdministrationLewis Research CenterCleveland, Ohio 44135

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

National Aeronautics and Space AdministrationWashington, D.C. 20546

13. Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared for the llth Communications Satellite Systems Conference, sponsored bythe American Institute of Aeronautics and Astronautics, San Diego, California,March 16-20, 1986.

16. Abstract

Over the past five years, NASA has conducted an extensive program to advance thestate-of-the-art in communication satellite technology. NASA is preparing toconduct a flight experiment in 1989 to verify the performance of this technology.Shortly thereafter, we should see the communications satellite industry begin touse this technology and enter into a new era of satellite communications includ-ing services in a new communications band, 30/20 GHz. What new capabilities andservices does this NASA developed technology enable? What does the future holdfor even better systems and services and what technology barriers must be over-come to enable these to happen? This paper addresses these questions by des-cribing the accomplishments of the NASA sponsored technology program over thepast five years and projecting possible technology advancements over the next10 yr. A systems scenario for the year 2000 using this technology is described.The projected capabilities and systems described herein are based on technologyadvancements alone, without consideration for competing terrestrial technologiesor market demand. These and other factors may affect the rate of developmentand characteristics of future satellite communications systems.

1 7. Key Words (Suggested by Author(s))

Antennas; Onboard processing;Transmitters; Receivers

19. Security Classif. (of this report)

Unclassified

18. Distribution Statement

Unclassified - unlimitedSTAR Category 32

20. Security Classif. (of this page)

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