Compact Microstrip Bandpass Filter Improved by DMS and Ring Resonator

In this paper, complementary split ring resonators (CSRRs) as band-stop elements are used in combination with coupled microstrip lines as high and low pass elements to design and fabricate very compact bandpass filter (BPF) having controllable characteristics. The proposed filter provides several advantages such as compactness (occupying area less than 0.1 lambda(g) x 0.1 lambda(g) in which lambda(g) is calculated at center frequency of pass band), sharp rejection, suitable insertion loss (IL 3-dB bandwidth of roughly 2 GHz from 0.7 GHz to 2.7 GHz, i.e., more than 115% FBW), good return loss (RL less than -8.5 dB in all of the bandwidth) and low cost. Defected Microstrip and Ring Resonator Structures have been used for eliminating the created spurious pass band in upper frequencies. The simulation results have been done with full-wave softwares, i.e., CST MWS and ANSYS HFSS by time and frequency domain solvers, respectively. Also, the equivalent lossless lumped circuit of total structure has been obtained and simulated by ADS software. These simulated results show good agreements with experimental ones.