Reduced phase noise of a varactor tunable oscillator: numerical calculations and experimental results

The signal and phase noise properties of two planar integrated tunable GaAs-MESFET oscillators with different resonator circuits at the gate terminal of the transistor are investigated using nonlinear calculation methods. The phase noise is calculated in the time domain by perturbation methods. The single sideband phase noise of a varactor-tunable microwave oscillator is reduced significantly to a value of -95 dBc/Hz, at an offset frequency of 100 kHz using a coupled microstrip line at the gate terminal of the transistor for determining the oscillation frequency. The measured output power of the oscillator is bout 12 dBm. In spite of the higher quality factor of this resonator circuit compared to that of a single microstrip line, a tuning bandwidth of more than 20% is achieved.<>