Miniaturization of substrate integrated waveguide filters using novel compact metamaterial unit-cells based on SIR technique

In this paper, three novel compact metamaterial unit-cells are proposed. The proposed unit-cells are based on the concept of the stepped-impedance resonator (SIR) technique which are used to miniaturize the physical size of the conventional complementary split ring resonators (CSRRs). The proposed metamaterial unit-cells consists of two modified rings so that in these unit-cells, the slot lines in the conventional CSRRs are replaced by the stepped-impedance slot lines. The electrical size of the proposed unit-cells called the SIR-CSRR are larger than the conventional CSRR. To investigate the performance of the proposed SIR-CSRR unit-cells in the size reduction, three substrate integrated waveguide filters loaded by SIR-CSRR unit-cells with different configurations are designed. By loading the SIR-CSRRs on the surface of the waveguide, an additional forward-wave passband propagating below the initial cut-off frequency of the waveguide is produced. Consequently, by using the proposed SIR-CSRR unit-cells instead of the conventional CSRRs, miniaturization with arbitrary ratio are achieved. In order to validate the proposed miniaturization technique, the designed filters are fabricated and measurement results are provided. Good agreement between simulation and measurement results are achieved.