The Pioneering of the MERA Program

Tom M. Hyltin, Life Fellow

Abstract--A review of the contributions of the AirForces MERA (Molecular Electronics for RadarApplications) program, performed by TexasInstruments. Under this program the first solidstate 9GHz. phased array module was developed,604 of these modules were manufactured toproduce an operating phased array radar. Also,as a part of this program the first silicon and thefirst gallium arsenide monolithic microwavecircuits were developed.

Index Terms-Microwave Circuits, PhasedArray Radar, Microstrip Circuits

It all began very innocently. A new R&Dmanager at Texas Instruments suggested that somework be done on microwave solid state. Atheoretician, K. L. Kotzebue, and a microwaveperson, myself, were brought in to do something.The only solid state device available for microwaveuse was the varactor diode, so our program developedlow noise parametric amplifiers and varactorfrequency multipliers1

• Texas Instrumentssemiconductor people provided us a few devices astime permitted. Interest by management was limited,to say the least.

By 1959 silicon transistors were availablethat provided 100 milliwatts or so at a hundred MHz.Using these devices as a power source, the firstcrystal controlled, solid state microwave source wasdeveloped and reported in technical journals by theauthor and Mr. Kotzebue2

• Interest somewhatincreased and provided work for two or threeengineers.

Groundwork for another piece of thisbreakthrough effort was being laid by the Air ForceAvionics Lab in Daytbn, Ohio. There, Dick Albertsand Bill Edwards were pioneering the use of therecently developed integrated circuits in airbornecomputers and other avionics equipment. The successof their programs generated confidence within the AirForce that allowed them to fund additionalspeculative development efforts In integratedelectronics.

In 1964 Dick Alberts' section receivedprogram approval and requested proposals for aprogram to increase the usage of integrated circuitsand improve the reliability of airborne radar systems.

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The program was called Molecular Electronics forRadar Applications. They were fishing for ideas toincrease the usage of integrated circuits in amplifiers,processors, and power supplies, but no one expectedany change in microwave power' generation, beamsteering, and other microwave parts of the system.

Under much urging by me, TexasInstruments management agreed to pr<1pose not whatthe Air Force had expected, but a completely newapproach. Solid state modules would be developed tobuild an active-element phased array radar. An arraywould be configured with 604 modules, eachproducing one watt peak power. This limited peakpower would be "augmented" by the use of thenstate-of-the-art chirp pulse compression. At that timeabout 125: 1 compression was attainable, andtheoretically would bring the effective peak power to75 kilowatts.

Without a doubt the program would havebeen less speculative and more reasonable at one oreven two GHz. Texas Instruments built a few 1.2GHz. modules, Figure 1, to assist in finding otherpossible funding sources and found that there was noequivalent group of sports (with money) in themilitary at that time to fund such a program. We hadto do the program a 9 GHz. or not at all. Interest ofmanagement became intense.

In 1964 a few transistors were available thatwould produce only a tenth of a watt at 2.25 GHz., sosemiconductor diode multipliers had to be used to getto 9 GHz. Transistors had to be scaled and redesignedto increase power output by a factor of twenty in ashort time, and the power generation chain, receiver,phase shifters, and digital control had to be mounted ina space smaller than 10 cubic centimeters - a real mind­boggIer in 1964.

In the proposal we mentioned monolithicmicrowave circuits and referenced transmission linemeasurements that the author had made and reported onsemi-insulating gallium arsenide and high resistivitysilicon33

• But later, when we took a closer look at ourreal capabilities, the use of thin film on aluminasubstrates as explored by Britton Vincent4, a speaker tofollow, was the only real chance for a successfulprogram. We were doubly blessed by having a skilledthin film fabrication engineer and facility available to

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us. They did capacitors, resistors and all otherfabrication tricks as required by our designs, A moduleconfiguration, shown in Figure 2, was developed thatwas compatible with technology constraints, and circuitand device development was begun.

The decision was made to move Mr. Vincentand myself into the Semiconductor R&D group (toprovide seamless program integration.) The effect wasthat of kids moving into a candy store. RogerWebster's group in the Texas InstrumentsSemiconductor Research Laborptory had a wealth ofsemiconductor technology, and it was all available to uson a priority basis.

Within one year they produced all thenecessary devices - four or five new microwavetransistors, beam leaded frequency multiplier diodes,beam lead switching diodes, and beam lead mixerdiodes. None of these devices had ever been builtbefore. It was a phenomenal job.

Circuitry work was being done in parallelwith device development so a breadboard module couldbe demonstrated as early as possible. Some ten minutesbefore the scheduled demonstration before Air Forcerepresentatives our engineers found the last problems inthe breadboard module, and it began to work. From thattime on all people involved in the MERA programbelieved it had a place in destiny.

In another year the module was operating infinal configuration. Figure 3 shows one side of themodule with the transmitter power chain, frequencymultiplier, T-R switch, balanced mixer, and i.£amplifier. Figure 4 is the reverse side of the moduleshowing the dual digital phase shifter, digital control,and local oscillator amplifier. Even 43 years later thetechnology we used still looks modem.

Manufacturing of the 604 modules began.When we had a few we built a subarray, as shown inFigures 5, and when the final system housing becameavailable we began using it, Figure 6. As we built moremodules it became a larger array - Figure7. Thesubarray testing program served two purposes. Theyallayed persistent fears within the Air Force that theyhad taken too big a step, and they allowed TexasInstrument engineers to gain experience with the careand feeding of solid state modules. Finally, with 604modules, the radar-looked as shown in Figure 8.

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The MERA Program was not just the modulesand the array. All of the systems units, as shown inFigure 9, were produced by Texas InstrumentsEquipment Group under the leadership of Grant Doveand Glenn Bandy. They produced many subsystemsthat we were not smart enough to specify, but weremade to work anyhow.

After several demonstrations of the completedradar, there was some talk about putting this delicate,temperamental system into an airplane and flying it, butcooler heads prevailed, and it was subiected to a testprogram, to obtain antenna patterns, etc, Figure 10.This part of the program began only two years after thefirst module began operating.

As an early part of our module developmenteffort, work was begun on monolithic microwavecircuits. The capability of transistors in the microwaveregion was extremely limited so circuits for monolithicexperimentation were carefully chosen. The firstmonolithic microwave circuit ever operated is shown inFigure 11. It is an X-Band T-R switch in silicon that AlErtel and the author developed using a uniqueswitching diode design5. Other monolithic circuitsdeveloped on the MERA program included a 500 MHztuned amplifier6

, Figure 12, and an X-Band balancedmixer?, Figure 13. Due to fundamental limitations ofhigh resistivity silicon, especially in a high temperatureenvironment, none of these had even the potential forthe performance we could achieve with hybridconstruction on alumina substrates, and none wereincluded in the final radar.

On another contract we explored the use ofsemi-insulating gallium arsenide as a microwavesubstrate material. The microwave characteristics werefound to be excellent, but only very few diode devicesand no microwave transistors were available at thattime. Under the sponsorship of another Air Forcecontract the author proposed a monolithic 94 GHz.balanced mixer and local oscillator, that was executedby Dr. Shing Ma08

• Figure 14 shows the first galliumarsenide monolithic microwave circuit to be operated.

The years of the MERA program were a timeof rapid expansion in our knowledge and technicalcapabilities. Texas Instruments put together anoutstanding interdisciplinary group for the execution ofthis program. Special mention should be made ofBritton Vincent for his friendship and manycontributions as well as Roger Webster and Glenn

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Bandy who were strong leaders as well as good friendsto me and to this program from the first day onward.There were many other people who made significantcontributions to the program, too many to mention. Itwas exciting and fun to be there and playa part in thiseffort.

Very rarely in science and engineering arethe beginnings of a new technology a clearly definedoccurrence. However, for microwave monolithic andthin film circuits and solid state radar there was such asingular starting point. The seed? had it's beginnings in1958 when Texas Instruments began research workon microwave applications of semiconductors and theresults of this work continue to bear fruit.

References

1. Hyltin, Tom M., "The Performance of HarmonicGenerators Using Varactor Diodes" 1961 WinterConvention on Military Electronics.

2. Hyltin, Tom M. And K. L. Kotzebue, "A SolidState Microwave Source from Reactance DiodeHarmonic Generators," IRE Transactions on MTT,MTT-9, Number 1, January, 1961

3. Hyltin, Tom M., "Microstrip Transmission onSemiconductor Dielectrics," IEEE Transactions onMTT, Vol. MTT-13, Number 6, November 1965.

4. Vincent, B. T. Jr., "Ceramic Microstrip forMicrowave Hybrid Integrated Circuitry," 1966 G­MTT Symposium Digest, May 1966

5. Ertel, A., "A 9 Ghz. Silicon Monolithic IntegratedTIR Switching Circuit," International ElectronDevices Meeting, October, 1966, Published in theProceedings

6. Johnson, G. D., W. H. Tulloch, and Frank Opp,"An Integrated 500 MHz. IF Amplifier, "International Solid State Circuits Conference,February, 1966.

7. Portnoy, W. M. and Tom M. Hyltin, "An X-BandBalanced Mixer Integrated Circuit,"International Solid State Circuits Conference,

February, 1966.

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8. Mao, S., S. Jones, and G. D. Vendelin,"Millimeter-Wave Integrated Circuits", IEEE Trans.On MTT, Vol. MTT-16, No.7, July 1968.

Figures

Figure 1, 1.2 GHz. Demonstration Radar Module

1-+----------------1- Il1O_I

Figure 2, Module Block Diagram

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Fig. 9. FullMERARadarSystem

Fig. 10. MERARadar atAntpma Range

Fig. 12. 500 MHz.Monolithic TunedAmplifier

Fig. 11. SiliconMonolithic90Hz. T-R Switch

Fig. 13. 9 GHz.Silicon MonolithicMixer

: Fig. 14.94 Ohz.Monolithic L.D.-Mixershowing component parts

Fig. 3. TransmitterSide of Modulewith T-R Switch,Balanced Mixer andIF Amp.

Fig. 4. Phase ShifterSide ofModule withL.O. Amplifier andMultiplier

Fig. 7. 130 Modules inArray

Fig. 5. Sixteen Module MiniTest Array

Fig. 5. Sixteen Module MiniTest Array

Fig. 8. Complete Array with604 Modules

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