Design of dual-band bandpass filter using stub-loaded resonator with source-load coupling and spur-line at 2.45/5.5 GHz for WLAN applications

A microstrip-line dual-band bandpass filter using stub-loaded resonator (SLR) with good selectivity in first pass band and wide bandwidth in second pass band is proposed in this paper. By properly adjusting the gap between source-load and SLR, good return loss at lower frequencies can be achieved. To further improve the rejection level between the first pass band and second pass band, the spur-line in the coupled feeding line is etched to produce the another transmission zero at 4.3 GHz. Based on the proposed SLR, a dual-band bandpass filter with three transmission zeros is implemented. The upper stopband extends widely to 10.75 GHz to have good suppression below -20 dB.