Miniaturized Dual-Mode Dual-Band BPF Using a Single Square Patch Loaded Stepped-Impedance Square Open Loop Resonator

摘要

This letter presents a dual-mode dual-band Bandpass Filter (BPF) using a single Square Patch Loaded Stepped-Impedance Square Open Loop Resonator (SPLSISOLR). The first four Transmission Poles (TPs) of SPLSISOLR can be tuned freely. A pair of high-impedance microstrip lines coupled with the resonator are employed to excite these four TPs to build up a dual-mode dual-band BPF, with two TPs in each passbands. The tapped point of the 50 Q feeding lines can be freely sliding on the high impedance microstrip lines, which increases the design freedom of external quality factor of two passbands. To validate the proposed method, a dual-band filter centered at 1.79/5.42 GHz with -3 dB fractional bandwidth of 4.5%/22.5% and compact size of 0.15 lambda(g) x 0.144 lambda(g) are designed. The fabricated filter has the merits of high band-to-band isolation, wide stopband, DC block and simple design procedure.