Compact Wideband 5G SIW Bandpass Filter with Enhanced Selectivity Using Mixed-Coupling Butterfly CSRRs

Abstract

In this work, a novel integrated waveguide bandpass filter for 5G applications is presented. The proposed compact filter is loaded by mixed coupling butterfly shaped complementary split ring resonators (B-CSRRs). Initially, the design exhibited only one transmission zero at higher stop-band. Thus, an asymmetric etched slot has been inserted between the split of each face-to-face B-CSRRs to produce an induced mixed coupling, thereby allowing the emergence of an additional transmission zero at lower stop-band. To further improve the selectivity factor, a second-order SIW filter using two-mixed coupling face-to-face B-CSRRs, separated by a Plus shaped Ring Slot Resonator was designed. The measured results show good performance, including low insertion loss of 1.46 dB, high selectivity factor of 55.75%, compact size of 0.107 〖λ_g〗^2 (with g the guided wave at the center frequency fc = 4.60 GHz), and high fractional bandwidth of 13.70% (i.e., 4.28-4.91 GHz). By covering the N79 5G band with a minimum attenuation of 40 dB from dc to 3.74 GHz and a minimum attenuation of 20 dB from 5.15 to 9.43 GHz, the proposed filter can be used for sub-6GHz 5G applications, as it prevents the interference between the N79 band and WiFi 5 GHz.