Miniaturized half-mode substrate integrated waveguide diplexer based on SIR–CSRR unit-cell

Abstract

A miniaturized diplexer based on half-mode substrate integrated waveguide (HMSIW) technology by loading a novel metamaterial unit-cell is proposed. The stepped-impedance resonator (SIR) technique has been used in order to miniaturize the physical size of the conventional complementary split ring resonators (CSRRs). The proposed metamaterial unit-cell, which is called SIR–CSRR, consists of two modified rings which the stepped-impedance slot lines are utilized instead of the conventional slot lines in the CSRRs. The proposed diplexer has been designed by cascading two bandpass filters with different center frequencies. The HMSIW bandpass filters are implemented by etching two SIR–CSRR unit-cells with different sizes. The design procedure is based on the theory of evanescent mode propagation which the SIR–CSRR unit-cells behave as an electric dipoles. A forward-wave passband below the intrinsic cutoff frequency of the HMSIW structure has been achieved by loading the SIR–CSRR unit-cells on the metal surface of the HMSIW structure. This proposed diplexer represent high selectivity and compact size by using of the sub-wavelength resonators. The designed diplexer has been fabricated and experimental verification have been provided. The measured results are in a good agreement with the simulated ones. The total size of the proposed diplexer is about 0.27λg × 0.11λg. The proposed diplexer show significant advantages in terms of size reduction, low loss, high selectivity, high Q-factor, easy bandpass frequency shifting, easy fabrication and, easy integration with other planar microwave circuits.