High-Q Tuneable 10-GHz Bragg Resonator for Oscillator Applications

This paper describes the design, simulation, and measurement of a tuneable 9.365-GHz aperiodic Bragg resonator. The resonator utilizes an aperiodic arrangement of non (λ/4) low-loss alumina plates (ε
_r
= 9.75, loss tangent of ≈1 × 10
^-5
to 2 × 10
^-5
) mounted in a cylindrical metal waveguide. Tuning is achieved by varying the length of the center section of the cavity. A multi-element bellows/probe assembly is presented. A tuning range of 130 MHz (1.39%) is demonstrated. The insertion loss S21 varies from -2.84 to -12.03 dB while the unloaded Q varies from 43788 to 122550 over this tuning range. At 10 of the 13 measurement points, the unloaded Q exceeds 100000, and the insertion loss is above -7 dB. Two modeling techniques are discussed; these include a simple ABCD circuit model for rapid simulation and optimization and a 2.5-D field solver, which is used to plot the field distribution inside the cavity.