On the design of a re-entrant square cavity as resonator for low-frequency ESR spectroscopy

Abstract

The construction and the design equations of a microwave resonator which can be used as sample cavity in a low-frequency ESR spectrometer are described. The resonator, which has the form of a re-entrant square cavity, has a Q factor of the order of 1000 and a maximum filling factor of 0.25. The resonant frequency can be conveniently evaluated using a very simple equivalent circuit which can be adapted to any shape of resonator. Four prototypes have been built and a good match has been found between the experimental values of the resonant frequencies and the theoretical ones. This agreement has been found to be particularly good for low values of the gap thickness.