Open Resonators Excited by Wave Beams

We study open resonators on the basis of the scattering theory. In particular, we develop the theory of an open resonator with a dielectric plate. This theory makes it possible to find the eigenfrequencies of such a system and their dependences on various parameters. Dispersion due to the dielectric plate is determined. The theory developed can be used as a basis for the method of measuring extremely small dielectric losses in the short-wavelength part of the millimeter-wave band. We also analyze the properties of a two-mirror resonator as a reflective filter and formulate the quality requirements for the exciting beam.