Modeling of perforated SIW structures and their application to the design of step-impedance microwave filters

A new topology of stepped impedance filters in substrate integrated waveguide (SIW) technology is presented in this paper. The filters are based on the reduction of the effective dielectric permittivity on certain waveguide sections which are below cutoff in the pass-band of the filter. Two different techniques for reducing the substrate permittivity have been analyzed and compared. In the first one, the impedance inverters have been achieved by inserting cylindrical air holes to lower the substrate permittivity. A second implementation of high-impedance SIW sections is investigated in this paper, which consists of the insertion of centered rectangular air boxes. The impedance inverter characteristics are investigated. Finally, following the described techniques for reducing the substrate permittivity, two filters have been designed and fabricated to demonstrate the feasibility of the proposed method.