Design Of Low Phase Noise Feedback-Type Harmonic Oscillator Using Siw-Cmsrr Diplexer

An X-band low phase noise feedback-type harmonic oscillator based on diplexer is proposed in this paper. Due to the compact size and high frequency selectivity, the substrate integrated waveguide (SIW) structure loaded with complementary multiple split-ring resonators (CMSRR) is adopted to design the diplexer which behaves as a fundamental frequency stabilization and second harmonic extraction elements simultaneously in oscillator. The principle of diplexer achieves a high isolation between the main feedback-loop circuit and the external load. In order to validate the proposed structure, an X-band prototype is designed and measured. The simulated frequency pulling effect of harmonic oscillator is decreased significantly compared to the fundamental frequency oscillator counterpart based on SIW-CMSRR filter. The measured results show that, the suppression fundamental frequency component is -27.9 dBc in harmonic oscillator, and the phase noise is -114.2 dBc/Hz at 100 kHz offset frequency from 9.31 GHz carrier, which is 2.6 dB better than the output of fundamental frequency oscillator followed by an ideal frequency doubler.