A 1-Watt, 6-Gigahertz IMPATT Amplifier for Short-Haul Radio Applications

The IMPATT diode has been developed to the point where several watts of cw power can be generated reliably in the microwave frequency range. This negative-resistance device used in conjunction with a circulator comprises a reflection amplifier suitable as the power amplifier in a microwave communications transmitter. In the present application, the diode operates in the injection-locked oscillator mode. It was demonstrated by Tatsuguchi, Dietrich, and Swan that such an amplifier using a single silicon IMPATT diode could meet the basic performance objectives of a typical short-haul radio-relay system. 1 The amplifier operates with a nominal gain of 20 dB and a noise figure of less than 52 dB. The corresponding system performance is better than 22 dBrncO per hop for a 1200-circuit message load. The amplifier's system performance is found to be dominated by thermal noise, with intermodulation distortion negligible. The dc-to-rf efficiency is 4 percent. 721 To be useful to the system, the amplifier package also contains rf samplers and detectors necessary to monitor the rf input and output power levels. The input power-monitor circuit furnishes the input information for a power-supply squelch circuit. If the input rf level drops low enough so that the locking bandwidth of the amplifier becomes small, the power supply is turned off, preventing the IMPATT oscillator from free-running out of the assigned frequency range. The dc power is automatically restored when the input rf level returns to normal.