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 0.099λg×0.094λg and 0.118λg×0.092λg, where λg is guided wavelength with a wide stopband upto 6.85f0 with 22 dB suppression for SB-BPF and 2.78f1/7.57f0 with 22 dB suppression for DB-BPF, where f0 and f1 are centre frequencies of first and second passbands respectively.