Transmission resonance through small apertures in conducting screen

Two kinds of transmission-resonant structure are described: transmission-resonant aperture type and transmission-resonant cavity type. The transmission cross sections at resonance are found to be (2G/4π)λ² [m²] (G:gain) for both structures. It is also seen that a single transmission-resonant aperture structure, like a ridged circular aperture, can be synthesized with input and output coupling irises when the distance between them forms a transmission-resonant cavity structure.