New Configurations to Reduce Converted FM Noise in FET Oscillators

To fulfill the low near carrier FM noise characteristic required by the future FET oscillators, new structures have to be looked for. This paper presents three new different methods to improve FM noise characteristics in microwave FET oscillators. - A push-push multiplier topology and a special low frequency circuit which reduce the converted noise around 2nd harmonic has been designed A noise figure of ¿95 dBc/Hz at 10 KHz off carrier has been observed around 21 GHz. The measured frequency drift with temperature is equal to 30 ppm (0-50°C). -Microwave separation of the amplification and of the limitation functions of an oscillator has provided a roughly 15 dB improvement of the FM noise at 10.5 GHz. - Appropriate low frequency circuit is the basis of the third principle envisaged. At 11 GHz a 12 dB FM noise improvement has been mesured at 1 KHz off carrier.