Fabry–Perot Resonators

The characteristics and the main applications of Fabry–Perot (FP) resonators are described at microwave frequencies, referring to a well‐documented state of the art. This article is organized in three sections. In the first, we present the basic properties of plane‐parallel FP interferometers using the traditional ray approach. Their performance is defined mainly in terms of power reflectivity of both partially transparent mirrors. Nevertheless many microwave and millimeter‐wave FP cavities employ metallic strip gratings or meshes as reflecting parts. The impact of the dispersive characteristics of these mirrors is investigated in details in Section 2. For that purpose, we first study the scattering parameters of inductive and capacitive meshes using transmission‐line models and compare them to rigorous numerical results. Then we analyze the influence of the grid geometries on the performance of plane‐parallel FP cavities (frequency responses, resonant frequencies, half‐power bandwidth, and insertion loss). Finally design rules and multilayer FP structures with metallic or dielectric mirrors are briefly considered. Various applications are discussed in Section 3: (1) frequency filters and diplexers, (2) directive antennas and multibeam and frequency beam scanning antennas, (3) open resonators with spherical mirrors for dielectric measurement, and (4) quasioptical power combiners and oscillators.