Constant gamma varactor diodes used in broad band microwave VCO's are considered. The use of these diodes is seen as a possible way of overcoming degradation of the slew rate, settling time, and FM noise. The capacitance ratio of currently available diodes is about 10:1, resulting in very wide tuning ranges. The performance of an 8.5 - 12.0 GHz oscillator shows a tuning linearity of 1% and a post tuning drift of less than 3 MHz from 10 microsec to 1 millisec when tuned between any two frequencies. Slew rates in excess of 200 GHz/microsec have been observed. GaAs hyper-abrupt constant gamma diodes were tested and compared to Si abrupt-doped diodes in an X-band oscillator. The measurements on the oscillator showed a drastic improvement in linearity when using the former. The frequency stability is equal to or better than that obtained with abrupt diodes, due to the lower loss in GaAs over Si. The advantages of using hyper-abrupt GaAs varactors may be offset, however, by the additional cost for succeeding amplifier stages.
Military Microwaves '80; Proceedings of the Second Conference
- Pub Date:
- Microwave Oscillators;
- Varactor Diodes;
- Gallium Arsenides;
- Noise Reduction;
- Electronics and Electrical Engineering