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Military Microwaves Supplement
I went to work at Hughes Aircraft in March 1962 and worked as a microwave engineer until the early 80's when I made a bit of a career change to Program Management. As a Program Manager I worked mostly communications and radar programs and some classified programs. Since the interest here seems to be in the early days of the microwave industry in Southern California, I will focus on the period from 1962 to about 1980 at Hughes Aircraft when I was involved in developing microwave hardware for various radar and communications systems, including satellite communications systems for Hughes Fullerton. Most of this work was in the area of solid-state microwave amplifiers and so that will be the focus of this summary. No tube stuff here. But I will include a short discussion of the "tools of the trade" for microwave engineers in the 60's and early 70's, a period when those tools were undergoing a very rapid evolution. And for completeness I'll provide a list of the major Hughes programs for this time period and a list of people that could be contacted for additional information about the microwave oriented programs at Hughes' Ground Systems Group.
Early 60's microwave amplifier technology.
When I started at Hughes in 1962 the available solid-state amplifier technologies were masers, which I worked on at the Hughes Research Labs, tunnel diode amplifiers and parametric amplifiers. Maser technology was eventually transferred to Hughes Fullerton where we built masers for NRL, Lincoln Labs and Boeing. The designs we used were based on coupled cavity resonators, small ferrite isolators, magnetrons for the "pumping" function and superconducting lead as a magnetic shield for the maser electronics. These amplifiers were cooled to liquid helium temperatures ( a few degrees Kelvin) in order to achieve what are still, in all likelihood, world record low noise temperatures of the order of 10 degrees Kelvin.
Tunnel Diode Amplifiers (TDAs) were the amplifier of choice for low noise amplifier (LNA) applications in the early 60's. These amplifiers utilized the negative resistance characteristic of microwave tunnel diodes to provide power gain when operated as a one-port device in conjunction with a ferrite circulator in a reflection amplifier configuration. Tunnel diode amplifiers were first used at Hughes, at least in large numbers, in the ADAR radar. This was a very state of the art (bleeding edge might be a better term) hemispherical shaped phased array radar that was perhaps the first of the many predecessors to the current very large scale phased-array based National Missile Defense (NMD) Ground Based Radar (GBR). We developed TDAs for various other Hughes systems including the Mark 1B Satellite Communications System and the AN/SSC-3, one of the earliest shipboard satellite communications systems.
Parametric amplifiers (paramps) were also in fashion in this timeframe and were competitive with TDAs performance-wise if not in terms of complexity and cost. They utilized varactor (variable capacitance) diodes and had the advantage that they could be cryogenically cooled to achieve noise temperatures that approached, but could not quite reach maser-like performance. Cost-wise, however, they were a much better choice than masers and eventually displaced them in the market for ultra-low-noise amplifiers.
In the late 60's and early 70's there were technological developments which revolutionized both low noise and high power microwave amplifier development. These technologies were the alumina substrate based microstrip circuit and low noise and, somewhat later, high power bipolar transistor technology. Avantek was one of the first companies to really exploit low noise transistor technology and were a major competitor to in-house development of LNAs at Hughes. HP was one of the early sources for low noise and medium power microwave bipolar transistors and we used HP devices in virtually all of the low noise amplifier designs that we did at GSG. Despite the competition from Avantek and others we did develop a number of LNAs for Hughes radars. These include the 33-IV upgrade to the Navy's first and possibly the world's first operational phased array radar that had been developed by Hughes Fullerton in the late 50's and early 60's. This radar, the AN/SPS-33 was installed on the Navy's first nuclear powered carrier, the U.S.S Enterprise, and on the U.S.S Long Beach, a nuclear powered guided missile cruiser. The family tree for the Navy's current Aegis shipboard radar system is traceable directly to the AN/SPS-33 system. You can find information on the 33 radar in Wikipedia's SCANFAR article. We also developed the LNA for the Navy's still operational AN/SPS-52 shipboard radar.
In the 70's the major programs that I worked on were JTIDS, the AN/SPS-37 Artillery Locating Radar and the Navy's Marisat and Leasat satellites. The JTIDS system provided a spread spectrum, frequency hopping, encrypted air-to-air and air-to-ground communications capability for the Boeing 707 based AWACS Radar system. The major microwave developments for the JTIDS system were the Low Power Amplifier (LPA) and the High Power Amplifier (HPA). In combination these amplifiers provided a fully solid-state one kilowatt high duty cycle transmitter for the JTIDS system. The key building blocks for the HPA were the Class C amplifier modules that utilized internally matched silicon RF power transistors manufactured by the Microwave Semiconductor Corp. (MSC). We also developed the Low Power Amplifier that served as the driver for the tube-based AN/TPQ-37 Artillery Locating Radar. We developed receivers and various passive components in support of Hughes' Space and Communications Division in the early and late 70's for the Marisat and Leasat programs. The design of most of the Marisat components and subsystems represented a step backwards in technology for the Fullerton group due to the conservative design rules established by Space and Comm. For example, amplifiers were constructed in sheet metal housings with point to point wiring and then filled with plastic foam to provide robust shock and vibration performance. Basically 50's technology. But it worked. The payoff from this approach, which required that proven manufacturing technology, materials and processes be used in all designs, was superb reliability. Things evolved a bit for the Leasat program where we started to utilize more up to date stripline and microstrip technologies. But even then, the design rules established by Space and Communications Division remained extremely conservative.
Other Hughes Activities.
As noted above, Hughes Fullerton was one of the first companies developing phased array radars and I suspect that in 60's timeframe we were the technology leader in that field. Important related microwave developments that were ongoing at Hughes in the 60's and 70's included array antenna design, high and low power filter, diplexer, duplexer, rotary joint and ferrite and PIN diode phase shifter development.
Tools of the Trade.
As a point of reference it worthwhile looking back at the tools available to microwave engineers in the early 60's. We used slide rules for most calculations. If we really needed accuracy we used a gee-whiz Friden mechanical calculator. If the program could afford it, we submitted stacks of cards to IBM computers for processing FORTRAN programs that typically ran over night. This was typically reserved for the computation of the performance of various phased array configurations and the design of microwave filters. It was expensive and slow but it was all we had.
Nobody typed. The term "word processing" hadn't been invented yet so we had to write out our reports by hand and, if lucky, we had a secretary to type them up for us. We used a T-Square, plastic triangles and a drafting board to make our drawings on erasable velum paper. We used Xacto knives and Rubylith to lay out the masks for etching stripe-line circuits. We were still using that technique when me started to develop microstrip circuitry in late 60's.
Test equipment was in the dark ages. We had pretty good Tektronix scopes but we used single frequency HP generators and slotted lines to make impedance measurements that we hand-plotted on Smith Charts. Believe it or not, that's the way we designed Tunnel Diode Amplifiers in the early 60's.
It was the age of cut and try.
We made reasonable estimates of the performance of the devices we were designing and then tweaked the circuits by various means until we got the performance we were after. This changed rapidly in the late 60's and early 70's. Hughes signed up for GE time sharing services and we started running BASIC programs from punched paper tape to compute the performance of what became our next big thing: bipolar RF low noise amplifiers. We developed amplifier circuits using home-brewed CAD based on optimization routines, circuit models and transistor data measured on that wonder of wonders we called "The Hollytron". The Hollytron (Al Holly's baby) was our first real HP network analyzer and it revolutionized linear RF transistor amplifier design. As time went on smaller versions of this original network analyzer migrated to our labs and became part of the standard set of microwave test equipment. And our home-brewed CAD eventually gave way to the hot new (at the time) commercial microwave computer-aided-design software from COMPACT and, later on, from EEsof. Another major "revolution" was the introduction of the HP-35 hand calculator in the early 70's. Finally, the slide rule could be put away for good.
Major Programs at Hughes Fullerton.
Here's my list. Mostly 60's, 70's and 80's programs. It's not complete but it's the ones I remember:
• Navy Radars: AN/SPS-33 phased array radar, AN/SPS-32 phased array radar, AN/SPS-52, IPD/TAS.
• Army Tactical Radars: AN/TPQ-36 X-Band Mortar Locating Radar, AN/TPQ-37 S-Band Artillery Locating Radar.
• Other radars: Project 863 airborne radar, Florida Radar.
• Air Defense Radars: ADAR (early 60's), HADR (Hughes Air Defense Radar - late 80's early 90's).
• Electronic Warfare: AN/SLQ-17.
• Communications: Mark 1B (AN/MSC-46 Satellite Communications System), AN/SSC-3 (Shipboard Satellite Communications System), PLRS (Position Locating and Reporting System - pre GPS), EPLRS (added data handing to PLRS), JTIDS (AWACS communications system), MISR (covert millimeter wave communications for Ft. Monmouth), PRC-104 HF Radio, STAJ (Short Term Anti-Jam frequency hopping version of the PRC-104).