THE FACE OF ELECTRICAL ENGINEERING has dramatically changed over the years. Today, for example, US engineering firms count more minorities and engineers from foreign countries among their ranks. While women are still few in number, female engineers are claiming more prominent positions. Although this evolution has seemed gradual, the trends at times stood out very clearly. In December 1979, for example, the MicroWaves cover story discussed how tough it was to be an engineer in Britain.
At that time, the British electronics industrylargely the birthplace of microwave technologyverged "on a major reorganization that threatened to alter the future of many top-notch companies." Ferranti was expected to be sold to investors outside of the electronics industry at any moment. Plessey had been openly courted by Racal for a possible acquisition/merger. Decca was in dire financial straits, while EMI had reported a 58% drop in profits. The two latter firms were expected to be taken over the following year by a stronger UK manufacturer.
Yet the report also noted that this atmosphere had seemed to make British engineers both tougher and more resourceful. In March 1979, for example, more than three million telephone calls per week were made to and from Britain. Of those, 60% were handled by satellite. With intercontinental telephone traffic expected to grow at a rapid rate, system engineers were preparing to develop high-frequency electronics for new 11- and 14-GHz spacecraft. They also were finding ways to improve existing 4- and 6-GHz systems.
For instance, Chelmsford's Marconi Communications Systems Ltd. was tasked with re-engineering the three older Goonhilly earth stations. It also equipped a new earth station complex in Madley, west of London. The oldest Goonhilly station dated back to the early '60s, when it served as a relay site for Telstar experiments. In 1979, Marconi was faced with reducing the size of ground-station equipment to squeeze more channel banks into existing facilities. It also had to improve the linearity characteristics of output amplifiers and add dual polarization so that frequency reuse could be employed with Intelsat V.
As summarized by Tom Clark, who worked in the Post Office earth station planning and provisioning division, "We're putting eight receivers in a rack where there used to be four, turning to synthesizers rather than crystal sources, and upgrading with double up- and downconversion techniques throughout." The industry also was moving away from single, high-power amplifiers and using several lower-power amplifiers instead. Clark noted, "We're developing low-loss combiners to funnel the outputs of up to 12 klystrons into a single aerial feed."
A waveguide combiner network, which was designed by Marconi for the Madley site, combined the power of as many as 12 klystronseach producing 3 kW over a 40-MHz bandwidth. The resulting uplink spanned 5.93 to 6.42 GHz. This 700-lb. diplexing network handled a very large power load with greater than 40-dB channel-to-channel isolation and return loss beyond 20 dB. It exhibited insertion loss below 1 dB.
The commutator-type power combiner was built on the principles of a waveguide phase-difference network. The design relied on the differential phase shift between two parallel transmission-line paths, which were linked by directional couplers. Due to the absence of a high-Q filter, it provided much higher power-handling capability and typically lower loss than other types of devices. The result was distributed losses overall rather than localized "hot-spot" heat losses.
This article is rather heartening in today's times, when many feel that technical innovation has largely left the US. Where there is strong engineering history and that passion is passed on, innovation will continue. Today's microwave engineers follow in Marconi's footsteps, making tradeoffs and optimizing designs. In doing so, they make possible future capabilities in communications, defense, and many other market segments.