Propagation of the H10 mode in a rectangular waveguide with a dielectric discontinuity

The transmission of the H10 wave through a waveguide-capillary cavity in the form of a section of a rectangular waveguide with a square liquid-filled capillary inside is studied theoretically. The capillary passes through the center of the waveguide perpendicularly to its wide walls. The problem is solved by constructing the mirror images of the capillary on the narrow walls of the waveguide with subsequent consideration of the diffraction of the Brillouin components of the H10 waveguide mode by a periodic “array of capillaries.” It is shown that a resonance minimum in the frequency dependence of the energy coefficient of transmission of the H10 wave through the waveguide-capillary cavity can be explained by the destructive interference of diffraction harmonics propagating in antiphase. The experimentally found existence of the capillary optimum dimension at which the resonance minimum is the most pronounced is corroborated analytically.