Microwave low phase noise oscillators using T-shaped stepped-impedance-resonator filters

Low phase noise microwave oscillators using T-shaped step-impedance-resonator (TSIR) filters are proposed and experimentally verified. Instead of using a high-quality factor resonator to design an oscillator, the TSIR filter is embedded into the feedback loop as a frequency stabilisation element. As the oscillator is designed at the group-delay-peak frequency of the filter, one can improve the phase-noise performance. Moreover, to miniaturise the oscillator circuit size, the TSIR filter can be further evolved into a compact net-type filter by the folding technique. The developed oscillators using TSIR filters at 1 and 5.2 GHz have the measured phase noises of -131 and -132 dBc/Hz at 1 MHz offset frequency, respectively. On the other hand, as compared with oscillators using TSIR filters, using a net-type TSIR filter to develop the filter-based oscillator at 1 GHz can achieve a 38% circuit size reduction and a 4-dB phase noise improvement at 1 MHz offset frequency.