Low phase‐noise X‐band oscillator based on elliptic filter and branchline coupler

Abstract

This paper presents a procedure for designing of a very low phase-noise (LPN) X-band planar microwave oscillator based on a closely packed four-pole elliptic band-pass filter as a frequency stabilisation section. The elliptic band-pass filter as improving phase-noise is realised, and branchline coupler as a key factor in the feedback loop is introduced. The design method to obtain LPN applications for optimum performance is presented. As a proof of concept, the X-band oscillator employing a packaged GaAs FET transistor is designed and measured. The oscillator, operating at 8.172 GHz, exhibits a measured phase-noise of −160 dBc/Hz at 1-MHz frequency offset with 4 dBm output power. To the best of authors’ knowledge, this oscillator indicates the lowest phase-noise in the class of published X-band planar oscillators, to date.