Design of metamaterial stepped-impedance microwave LPFs

In this paper, stepped-impedance microwave low-pass filters (LPFs) are presented. A conventional stepped-impedance LPF with cutoff frequency (fc) of 1.9GHz is proposed. Replacing rectangular split ring resonator (SRR) structure instead of low-impedance lines in conventional design to get compact, low insertion loss (IL), sharp cutoff, and high selectivity LPF. The effect of etching rectangular complementary split ring resonators (CSRRs) or etching square CSRRs in the ground of microstrip line to get new metamaterial microwave LPFs is also presented. The new filters have better results compared to conventional filter. The simulated results indicate that the proposed filters achieve a flat pass-band without ripples, corresponding to numbers of unit cells of CSRR structures. Reduction in size up to 29% of the filter has been achieved by using square CSRRs. The group delay values of LPFs approximate to 0.5 ns in the pass-band interval in all designs. Numerical results for the stepped-impedance microwave LPFs are obtained. The filters are then simulated by the computer aided design software (Ansoft HFSS) commonly used in microwave applications which has been implemented on the Roger RO3210 substrate with dielectric constant er = 10.2, substrate height h = 1.27mm, and thickness of microstrip conductor t = 0.035mm.