Novel Sapphire Directional Filters for Ultra Low Phase Noise Applications

Traveling wave (TW) sapphire whispering gallery resonator (WGR) is considered to be a very attractive device for low phase noise microwave frequency sources. However, it was found that TW WGR with distributed excitation is very sensible to the parameters of the coupling and excitation of the pure TW in high-Q WGR is a big challenge. This paper deals with a novel sapphire TW WGR based on orthogonal lumped coupling probes and 3-db quadrature directional couplers. A general theoretical background of the proposed TW WGR as well as its 3D finite element analysis and experimental results are presented. Finally a novel ultra low phase noise oscillator configuration based on the TW WGR directional filter is proposed.