Stopband Characteristics Improvement of Waveguide Planar E-plane Filters

Abstract: The development results of new waveguide planar filters with high selectivity are presented in this article. New bandpass filters (BPF) based on folded metal structures have poles of attenuation characteristics near the filter passband and they are focused on selectivity improvement. Filters are designed in a fully symmetrical topology, which improves performance reproducibility, manufacturability, and reduces manufacturing cost. The proposed BPFs on metal-dielectric structures are based on stepped impedance resonators (SIR) with preservation of the “in-line” topology. They allow us to expand the stopband to the boundaries of the waveguide operating passband and significantly increase the insertion loss level in comparison with the original filters based on homogeneous resonators. In this case, the typical filter linear dimension reduction is about of 30%. Also we show, that the proposed filters form the attenuation characteristic pole far from the filter passband, which makes it possible to achieve a high rejection level with a small number of resonators. The measured characteristics of the filter prototypes are in good agreement with simulation results. © 2021, Pleiades Publishing, Ltd.