Double-Layer SIW Filters with Higher-Order Mode Suppression

Abstract

Two substrate integrated waveguide (SIW) filters based on a double-layer configuration are presented in this paper. The first one has good performance with wide stopband rejection beyond 20 GHz. The method for higher-order mode suppression is illustrated in detail. To achieve higher selectivity, a second filter with cross coupling is introduced, which could also be considered as a four-stage filter with both electric and magnetic coupling. Transmission zeros (TZs) on both sides of the passband can be produced to enhance the filter selectivity. By varying the electric coupling coefficient, the distance between these two TZs could be easily adjusted, which can be used to control the filter selectivity and out-of-band rejection. The proposed two filters were fabricated and measured. Good agreement has been observed. They both exhibit outstanding performance including high Q, low-loss, and wide stopband rejection. A compact size has also been achieved simultaneously.