Dual-band bandpass filter using multimode square ring loaded resonators

A novel microstrip dual-band bandpass filter (BPF) with multimode square ring loaded resonators (SRLRs) is proposed in this article. The improved SRLR is loaded by a meander ring stub and a stepped-impedance resonator for compactness to realize the dual-band performances. Even- and odd-mode method is applied to explain mode splitting characteristics. Moreover, another mode in the second passband is generated by adding a half-wavelength U-shaped resonator. This resonator also introduces cross-coupling between feed lines so that an additional transmission zero is produced, which enhance the selectivity. The dual-band BPF operating at 2.4 and 3.5 GHz for WLAN and WIMAX applications is designed and fabricated. Measurement results agree well with the simulated results. (c) 2013 Wiley Periodicals, Inc.