Phase-noise improvement of microwave feedback oscillator using shunt-stub-based ring resonator

This paper presents a low phase-noise feedback oscillator using a shunt-stub-based (SSB) ring resonator. Since the proposed resonator has the 2^nd and 3^rd harmonic suppression characteristics, the phase noise of the developed oscillator can be significantly improved about 10 dB at 100-kHz offset frequency as compared with that of the conventional one. To the best of our knowledge, this is the first paper to figure out the reason of this improvement using impulse sensitivity function (ISF). The calculated ISF parameters, c₂ and c₃, of the proposed configuration demonstrate that the noise portions contributed from the 2^nd and 3^rd harmonics are effectively reduced.