Design of low phase-noise oscillator and voltage-controlled oscillator using microstrip trisection bandpass filter

In this letter, a low phase-noise oscillator using a microsrtip trisection bandpass filter is designed, fabricated, and experimentally verified. The trisection filter is mainly treated as a frequency stabilization element, and then embedded into the feedback loop of the oscillator. As the oscillation frequency is designed at group delay peak of the filter near the passband edge, the phase noise of the oscillator can be significantly reduced. In addition, by attaching a varactor on one of the resonators of the trisection filter, the developed oscillator can be easily extended to a voltage-controlled oscillator (VCO). In this letter, the oscillation frequency of the oscillator is designed at 2.46 GHz, and the measured phase noise is -144.47 dBc/Hz at 1 MHz offset frequency. Moreover, the developed VCO has a frequency turning range from 2.497 to 2.537 GHz. Over this frequency range, the measured phase noise is from -127.47 to -138.17 dBc/Hz at 1 MHz offset frequency.