Low pass filters with finite transmission zeros in evanescent modes

摘要

A waveguide lowpass filter operates in at least two evanescent modes. The filter has successive ridges with a space between said ridges. The ridges are associated with parallel capacitance and a space between them is associated with series inductance in the TE.sub.10 mode. Each ridge is top-loaded so that series capacitance can occur in a TM.sub.11 mode in parallel to said series inductance. The filters of the present invention can be made smaller than previous evanescent lowpass filters and can achieve improved results.