A New Microwave Amplifier for Multichannel FM Signals Using a Synchronized Oscillator

Because of the excellent results of the noise-loading test on an IMPATT oscillator that is phase-locked to an external FM driving signal, a new microwave amplifier for multichannel FM signals using a synchronized oscillator is proposed. An IMPATT oscillator, injection-synchronized with an FM signal, is regarded as an amplifier and its noise characteristics for multichannel signals are evaluated with the noise-loading method as recommended by the International Radio Consultative Committee. The results show that when this oscillator satisfies the noise characteristics for 960 telephone message channels, it assures a gain of approximately 15 dB at 11 GHz, and in this sense, this oscillator can be regarded as an amplifier for multimessage channels. The degradation of SNR of this amplifier is less than 2 dB. This excellent result is obtained because of the following. In the video band, the modulation suppression of an FM driving signal in the injection-synchronized oscillator, such as the IMPATT, is very small, while the oscillator noise, which dominates the entire output characteristic, is considerably reduced by the synchronizing action of the oscillator. This amplification continues up to the high-frequency range in which this principle of operation applies.