Microwave oscillators incorporating high performance distributed Bragg reflector microwave resonators

We previously demonstrated a new resonator device structure that achieves Q-factors well above those currently realisable. The new structure consists of a microwave cavity, where the enclosure walls consist of distributed Bragg reflectors (DBRs) in three dimensions, made of low-loss sapphire. Theoretical analysis has demonstrated that the resonator´s performance is critically dependent upon accurate alignment of the DBR components, thereby maintaining the desired symmetry of the resonant structure. Breaking of the symmetry causes mixing of the high performance Bragg reflected mode with low-Q hybrid cavity modes. The fabrication tolerances required to achieve the expected resonator performance are met with a precise but simple alignment tool. A pair of these resonators have been built at 9.0 GHz, and have demonstrated unloaded Qs in excess of 700,000 at room temperature. These resonators are incorporated into simple two-port feedback oscillator circuits. Phase noise measurements were performed on the two free-running oscillators.