Phase noise of a microstrip microwave oscillator with varactor frequency tuning 6–12 GHz

This work presents the results of a study of the microwave oscillator's active device biasing influence on the oscillator phase noise. The paper considers a hybrid voltage-controlled oscillator (VCO) with an octave frequency tuning (6–12 GHz), based on a low-noise SiGe-heterojunction transistor. The simulation of the VCO in the AWR Design Environment (AWR DE) allowed one to evaluate the choice of the transistor operating point influence on the oscillator phase noise. Based on the data obtained, an experimental study of the fluctuation characteristics of several samples of the hybrid microwave VCOs, differing in the operating mode of the active devices, was carried out. The results of the research carried out make it possible to determine a number of conditions (the value of the collector current, the ratio between the currents of the transistor base and the resistive divider, determining the mode of the active device), which provide the best oscillator characteristics. It is shown that the smallest average level of the phase noise power spectral density is –95 dBc/Hz at 100 kHz offset from the carrier with a minimum change in its level in the tuning range within $\pm$ 2.5 dB.