Microwave oscillators incorporating high performance distributedBragg reflector microwave resonators

摘要

We previously demonstrated a new resonator device structure thatnachieves Q-factors well above those currently realisable. The newnstructure consists of a microwave cavity, where the enclosure wallsnconsist of distributed Bragg reflectors (DBRs) in three dimensions, madenof low-loss sapphire. Theoretical analysis has demonstrated that thenresonator's performance is critically dependent upon accurate alignmentnof the DBR components, thereby maintaining the desired symmetry of thenresonant structure. Breaking of the symmetry causes mixing of the highnperformance Bragg reflected mode with low-Q hybrid cavity modes. Thenfabrication tolerances required to achieve the expected resonatornperformance are met with a precise but simple alignment tool. A pair ofnthese resonators have been built at 9.0 GHz, and have demonstratednunloaded Qs in excess of 700,000 at room temperature. These resonatorsnare incorporated into simple two-port feedback oscillator circuits.nPhase noise measurements were performed on the two free-runningnoscillators