A Filter Synthesis Procedure for Slow Wave Substrate-Integrated Waveguide Based on a Distribution of Blind Via Holes

In this paper, a design methodology for miniaturized cavity filters in a slow wave substrate-integrated waveguide technology is presented. It is applied in the context of ladder coupling scheme with a slow wave effect produced by a periodic arrangement of blind via holes. By taking into account the intrinsic periodicity of the structure during the synthesis, this paper aims at achieving a better filter response in terms of bandwidth and return loss, as well as providing a systematic approach for the via holes arrangement. In addition, a segmentation technique combined with the use of polynomial fittings is introduced to provide a fast and accurate design. As an illustration, a bandpass filter of 1-GHz bandwidth centered at 11 GHz is designed, fabricated, and measured. A good agreement between simulations and measurements is obtained.