Ultra-low Phase Noise RF Oscillator Using High-Q Quad Spiral Resonator

In this paper a 14.4 GHz ultra-low phase noise oscillator is introduced based on a simple; previously designed; high-Q quad spiral microstrip resonator. The low cost X-band ATF13786 GaAs (Gallium Arsenide) MESFET (Metal semiconductor field effect transistor) is used as the active device. The circuit is designed with an appropriate positive feedback and optimized output circuit with low insertion loss coupled line coupler. The designed circuit is simulated using the EM-Circuit-Co Simulation in the ADS (Advanced Design System) tool resulting in an oscillation at 14.44 GHz with an output power of 7.82 dBm. The oscillator is then fabricated and measured. A great agreement is found between simulation and measurements with a 0.2% shift in the oscillation frequency. The fabricated circuit gives an oscillation at 14.4 GHz with an output power of 10.6dBm. The circuit gives a very low phase noise of -110dBc/Hz @ 100kHz offset, and -130 dBc/Hz @ 1 MHz offset. The figure of merit (FoM) is calculated to be -197.5 dB. The total power consumed in the oscillator circuit is calculated as 460 μW. A comparison is done between this proposed oscillator and the recent published work in a close frequency range. The oscillator shows at least 20 dB improvement in the FoM. Up to authors knowledge, this proposed oscillator is very useful in many applications such as 5G backhaul systems.