Innovative Filters in Partially Air-Filled in Substrate Integrated Waveguide Technology

This paper presents a novel class of substrate integrated waveguide filters, based on partially air-filled rectangular cavities. These partially-air filled cavity implements a doublet, that exhibits a frequency response with two poles and two transmission zeros. Two different topologies are proposed: in the first one, the partially air-filled region is located in the center of the rectangular cavity and this allows to locate two zeros below the pass band; in the second topology, two partially air-filled regions are located at the sides of the rectangular cavity and this allows to locate arbitrarily the two zeros, either both below, or both above, or one below and one above the pass band. Prototypes of the two topologies have been designed and experimentally verified