Compact dual-mode dual-band bandpass filter with wide stopband for WLAN applications

A compact dual-mode dual-band bandpass filter (BPF) for WLAN applications is presented. On the basis of a primary passband formed by a ring resonator, a second passband is introduced by taking advantage of its tightly coupled input and output structures. Therefore, a dual-band performance is achieved without increasing the overall circuit size. Shorting vias and spurlines are adopted separately to realise the dual-mode excitation of each passband. Finally, a compact dual-mode BPF centred at 2.4 and 5.2 GHz is designed and fabricated, along with four transmission zeros, leading to sharp skirts and a wide stopband. Experimental results reveal good agreement with simulation results.