Dual Pass Band Filter using Quad Stub Loaded Uniform Impedance Resonator

A low loss, highly selective and miniaturized dual pass band filter for the wireless (WiMAX, WLAN) application is proposed in this paper. The filter is designed with Multimode resonators, constructed with Uniform Impedance Resonator (UIR) and multiple open stubs. Two different coupling schemes (electronic and magnetic) are observed for the said dual pass bands. A detail analysis about the dimension of the resonators, resonating conditions and frequency calculations are presented in this paper. The dual pass bands are achieved at 3.45 GHz and 5.4 GHz with minimum pass band insertion loss (|IL|) 0.1 and 0.18 dB and the pass band Fractional Band widths (FBW) 4% and 8% respectively. With proper optimizations, Transmission Zeros (TZ) are achieved on both sides of the dual pass bands and the spurious pass band are kept around -20dB level and hence good selectivity is achieved. The overall size of the filter is optimized for the best possible results in terms of Insertion Loss, Return Loss and selectivity, is found to be (24.2 x 21)mm = (0.28 x 0.24)λg = 0.06 λg2.