Compact dual bandpass filter for terrestrial radio and GSM applications

A Compact Dual Band-Bandpass Filter (DB-BPF) with wide stopband rejection is proposed in this article. The basic tools used in the structure are Short Circuited Stepped Impedance Resonators (SCSIR), Open Stub Resonators (OSR). First, a Single Band-Bandpass Filter (SB-BPF) is designed with wide stopband rejection, and then it is modified to DB-BPF. Both the SB-BPF and DB-BPFs have similar type of construction except for an additional SCSIRs used in DB filter. The structure of the filters, use the source-load coupling and OSR to generate transmission zeros, which suppresses harmonics and achieves wide stopband. The use of SCSIRs make the SB and DB bandpass filters size compact to 0.099 lambda(g)x0.094 lambda(g) and 0.118 lambda(g)x0.092 lambda(g), where lambda(g) is guided wavelength with a wide stopband upto 6.85f(0) with 22 dB suppression for SB-BPF and 2.78f(1)/7.57f(0) with 22 dB suppression for DB-BPF, where f(0) and f(1) are centre frequencies of first and second passbands respectively.