Highly tuneable X-band Bragg resonator - initial results

This paper describes the design and measurement of a broad tuning aperiodic Bragg resonator at X-band. The resonator utilizes an aperiodic arrangement of non (λ_g/4) low loss alumina plates (ε_r=9.75, loss tangent of ~1 to 2×10^-5) mounted in a cylindrical metal waveguide. The initial results demonstrate a spurious free tuning range of 100MHz. The insertion loss, S₂₁, varies from -5.6dB to -4dB while the unloaded Q varies from 40,000 to 60,000 over the tuning range. The loaded Q varied from 20,000 to 23,000. It is also possible to tune over a range of 400MHz with similar unloaded Qs up to 64,000, but on occasion the required TE₀₁₁ mode passes through several lower Q modes which therefore degrades the unloaded Q of the wanted mode.