Tri-band microstrip BPF design using tri-section SIRs

In this paper, a new second-order tri-band BPF is proposed and designed using open-stub-embedded TSSIRs. The three operating bands are chosen to be commercially practical, with their center frequencies being 1.57 GHz (GPS LI), 2.45 GHz (ISM), and 3.5 GHz (WiMAX), respectively. The 0deg feed and the embedded open stubs are implemented in the designed tri-band BPF to produce transmission zeros at appropriate frequencies for improving passband selectivity and stopband rejection. In addition, the TSSIRs are bent into rectangular shape to reduce the circuit size; their end sections are designed in an anti-parallel fashion to produce an extra zero. The proposed tri-band BPF will first be simulated by using HFSS (a full-wave electromagnetic simulator) and then verified by measured data. The filter design and the obtained results are presented.