Compact tri-band BPF design using spur-line-loaded tri-section SIRS

[[abstract]]In this article, a new tri-band microstrip bandpass filter (BPF) is proposed. The BPF is composed of two folded, rectangular-shaped three-section SIRs (TSSIRs) whose first three resonant frequencies can be tuned to locate in the desired passbands. The BPF are 0� fed and the end sections of the TSSIRs are designed in an antiparallel fashion to produce zeros at appropriate frequencies for improving passband selectivity. In addition, by embedding spur lines and defected ground structures (DGS) in the BPF, extra transmission zeros around the first spurious passband are introduced to widen the upper stopband. The designed BPF is fabricated on an RT/Duroid 6010 substrate. The measured fractional bandwidths (minimum insertion losses) for the 1.57 GHz (GPS), 2.45 GHz (ISM), and 3.5 GHz (WiMAX) bands, respectively, are 11.5% (1 dB), 4.6% (2.19 dB), and 10.9% (1.3 dB), which agree well with those predicted by simulation. It also shows that for miniaturization purposes, the TSSIRs are made meandered to give an overall circuit size of only 23.29 � 10.94 mm2 for the designed BPF