A resonant short-circuit plunger as part of tunable waveguide-dielectric and waveguide-coaxial resonators built around cylindrical evanescent waveguides

Abstract

Subject and Purpose. Tunable resonant structures make numerous microwave devices, among which are waveguide-dielectric and waveguide-coaxial resonators (WDR and WCR) built around cylindrical evanescent waveguides and involving a resonant short-circuit (RSC) plunger for tuning purposes. The present paper seeks to study specific features of the RSC-plunger operation in the evanescent waveguide and estimate the RSC-plunger efficiency. Method and Methodology. The RSC-plunger efficiency is approximately estimated in terms of the transmission line theory. Comparative experimental verification of the Q-factor increase is provided by an example of a 3 cm WDR resonator equipped with a RSC-plunger. Results. It has been shown that relevant formulae of the transmission line theory can be extended for the RSC-plunger efficiency estimation on the TEM and H11 oscillations. A possibility has been studied of the TEM type transformation to the H11 oscillation and back when the spurious resonance of the RSC-plunger falls within the WDR (WCR) tuning range. Conclusion. Insignificance of the effect that small deviations from the numerically predicted dimensions of the RSC-plunger exert on the RSC-plunger operation efficiency has been demonstrated. The RSC-plunger efficiency and a possibility to remove the spurious resonances from the resonator tuning range have been experimentally confirmed.

Keywords

• evanescent waveguide
• q-factor
• resonant frequency
• short-circuit plunger
• waveguide-coaxial resonator
• waveguide-dielectric resonator