A design of high-Q dielectric resonators for MIC applications

A radiation-suppressed dielectric resonator with a semispherical metal cap loaded over a semispherical, high-constant dielectric is theoretically studied and the resonant frequency and unloaded Q are calculated. It is established that this resonator operates in the dielectric resonator mode when the metal cap is small and changes to the hollow cavity mode when the cap size is increased over a certain value. Thus, if the cap size is chosen in the range where the resonator operates in the dielectric resonator mode, the resonant frequency becomes almost constant independent of the metal cap size and a high unloaded Q is achieved. These results are confirmed by experiment. The temperature variation rate of the resonant frequency of a resonator on alumina substrate is quantitatively studied, and it is found that the effect of the outer model cap and the substrate on the frequency variation rate is small.