A Low Phase Noise Planar Oscillator Using Compact Quarter-Wavelength Step-Impedance Resonators with Mixed Electrical and Magnetic Coupling

Abstract

In this letter, a low phase noise oscillator using a compact SIR EMC filter as frequency stabilization element is presented. The proposed filter is composed of a pair of compact quarter-wavelength step-impedance resonators(SIR) with mixed electrical and magnetic coupling(EMC). Due to introducing EMC between two resonators, a transmission zero(TZ) closed to the upper passband is realized and the upper-passband of the filter exhibits sharp selectivity characteristic. It achieves high group delay peak and high quality(Q) factor close to TZ. Therefore, the phase noise(PN) of microwave planar oscillator using this proposed filter can be reduced significantly at the oscillation frequency close to the high group delay peak frequency. To prove the method mentioned above, an S-band planar oscillator using the proposed filter with compact size is designed and fabricated. The measured results show that the designed oscillation frequency is 2.493GHz with 6.1dBm output power and its PN is −125.6 and −141.1 dBc/Hz at 100 kHz and 1 MHz offset frequency, respectively. The figure of merit of the oscillator at 100kHz offset frequency is −198.5 dBc/Hz.