Development of the FET Microwave Transmitter We have developed a microwave transmission system which uses a phased-array antenna connected directly to a power amplifier and a digital phase shifter. The power amplifiers uses F-class type GaAs-FETs. Efficiency of the amplifier is already greater than 50%. To facilitate controlling the beam without any phase ambiguity, a new two-tone pilot signal system has been developed. A retrodirective antenna system [9] seems to be the most effective technique for accurately pointing a microwave beam towards a receiving site. To overcome the well-known drawbacks of a conventional retrodirective antenna, we have developed a new two-tone pilot signal system which can determine the phases of the transmitting microwave with no phase ambiguity. A brief block diagram of the two-tone pilot signal system is shown in Fig. 1. Figure 2 shows the pointing errors of the transmitting microwave using the two- tone system. They remain below one degree if the average of seven phase conjugate circuits is used, while using a single pilot system will have an error which increases with increasing path difference.
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