Stripline Resonator Loaded Compact SIW Filters With Wide Suppression and Flexible Response

Abstract

A novel method to design substrate integrated waveguide (SIW) filters with odd-order response is presented in this letter. By combining SIW and stripline technologies, a fully closed, third-order filter consisting of two SIW resonators and one stripline resonator is proposed. The stripline resonator provides a coupling path for the TE101 mode to form a passband, while the couplings for TE102 and TE201 modes are very weak, resulting in the suppression of their propagation. The principle for higher order mode suppression is carefully illustrated. On the basis of this filter, another two filters are designed by introducing different cross couplings, which generate extra transmission zeros (TZs) to enhance the selectivity. These two filters exhibit flexible response with controllable TZs. All these three filters are fabricated and measured. The measured results are in good agreement with the simulation, which validates the proposed design methodology and the idea of incorporating the stripline resonator into the SIW. They demonstrate a low insertion loss, high selectivity, and wide stopband. In addition, the proposed filters are featured by a reduced size due to the applications of the double-layer structure and miniaturized stripline resonators.