A high-Q electronically tunable evanescent-mode double-ridged rectangular waveguide resonator

This paper presents a novel concept to tune the resonant frequency of an evanescent-mode double-ridged rectangular waveguide resonator, while maintaining a high-Q in the tuned frequency range. The waveguide is loaded with a tuning element fabricated on the Rogers RT/duroid^reg5880 substrate, and equivalent to a variable capacitor. It is shown that, by positioning multiples of this tuning element inside the double-ridged waveguide, one can increase the number of achievable resonant frequencies. The tuning element can also be dimensioned properly for a prescribed frequency shift. To prove the introduced concept, a resonator was fabricated with a tuning element capable of generating three resonant frequencies (3.646 GHz, 3.775 GHz and 3.921 GHz respectively), while maintaining a high unloaded Q (884, 967, and 980 respectively).