Design of bandstop filters using cylindrical metallic posts

The paper presents the design, implementation and measured performance of waveguide band-reject filters based on partial height cylindrical metallic posts. The posts are inserted in a uniform waveguide in which the dominant TE₁₀ is propagating. Each post provides an attenuation pole at a frequency which is adjusted mainly by its height. The offset of the post from the center of the waveguide is used to control the strength of the coupling between the waveguide mode and the post. Optimization is used to correct for dispersion effects and the fact the attenuation pole and the coupling coefficients are slightly affected by the offset and the height of the post, respectively. Measured performance of a 3^rd order band-reject filter with metallic posts shows very good agreement with computed results once losses are taken into account.