Reduction of the Coupling to External Sources and Modes of Propagation by a Nearly Confocal Resonator

This paper presents a numerical and experimental study of a nearly confocal resonator with spherical mirrors at 12 GHz. The geometry was chosen in order to have a large quality factor for the diffraction losses, and thereby a weak coupling to external parasitic TE and TM modes, that propagate in a pipe on which the resonator may be installed. In turn, this allows a significant improvement of its signal-to-noise ratio, e.g., when used as a beam monitor.