K -Band Substrate-Integrated Waveguide Filter Using TM21 Mode With Enhanced Stopband Attenuation

In this letter, we present a method for enhancing the stopband attenuation performance of a K -band TM21mode filter using substrate-integrated waveguide resonators. To improve the stopband response, we suppress and move spurious resonant peaks and produce transmission zeros. The step-by-step procedure of the proposed three-step method is shown in detail. The measurements show that when using the presented method, the filters exhibit better stopband performances than those in which the presented steps are not followed.