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Scattering characteristics of a waveguide section with a pair of antipodal posts are studied. The section is formed by two short rectangular inserts arranged in antipodal position in a cross section of a rectangular waveguide. Influence of changing the posts' dimensions on the section frequency response is numerically investigated. A pole generation mechanism is examined within the concept of the spectral theory of open waveguide resonators. Attenuation pole generation is demonstrated over the single-mode range and in a wide multi-mode range. It is shown that "spectral" estimations of the pole frequency and bandwidth are more precise than ones obtained within the ordinary 'modal' approach. High-accuracy estimation is demonstrated in a wide frequency range.

waveguide filter; natural oscillations; attenuation pole; trapped mode resonance