A low phase noise microwave oscillator based on a planar microstrip spiral resonator

This paper presents a novel, compact size, high-Q planar microstrip dual spiral resonator needed to lower the phase noise of microwave oscillators. The resonator is designed using low-loss RF duroid substrate. Simulation results show the proposed resonator has a loaded quality factor of 395 and a calculated unloaded quality factor of 1050, at its 9 GHz resonance frequency. The implemented resonator is used to design a low phase noise X-band oscillator. Based on series feedback topology, the designed oscillator uses Hewlett Packard ATF-13786 low phase noise Gallium Arsenide Schottky barrier-gate field effect transistor as the active device. The simulated oscillator phase noise is better than -130dBc at 100 kHz offset in a 1 Hz bandwidth, due to use of the high-Q resonator. The oscillator higher-order harmonics are less than -24 dBc, which verifies the operation of the proposed dual spiral resonator. The whole hybrid circuit is designed, optimized and fabricated. The resonator measurement results are in good agreement with simulations.