Suppression of spurious modes for performance enhancement of hybrid planar/NRD-guide integrated circuits

A technique for suppressing spurious modes is presented with experimental and analysis results. It is simple and very effective in rejecting spurious modes for performance enhancement of hybrid planar/NRD-guide integrated circuits. As a practical example, a millimetre-wave planar/NRD-guide filter is designed to evaluate features of the proposed technique, which yields good results. It is found through preliminary analysis and experiments that the rejection of all spurious modes (including TE and LSE modes) can be better than -35 dB for a single microstrip-to-NRD-guide transition over the broadband frequency range of interest, and performance can be further enhanced using optimised design procedures. This new technique provides an alternative solution to the inherent problem of spurious modes occurring (especially TE modes) in the standard NRD-guide circuit design.