Resonances in a semiinfinite waveguide with iris in relation to the excitation of higher-order modes

New types of resonances were discovered in a structure comprising a short-circuited waveguide and a capacitive iris in the case when the distance between the iris and the short is in the order of several hundredths of the waveguide wavelength. The existence of these resonances is explained by the excitation of high-order modes in the iris aperture. It was found that a more complicated shape of the iris aperture results in the frequency characteristic of the electromagnetic structure considered becoming similar to that of a band-pass filter. This fact is explained by the enrichment of the spectrum of high-order modes.