Design of cross-coupled dual-band bandpass filter using stub-loaded open-loop resonators with different bandwidth ratios

Abstract

Two cross-coupled dual-band bandpass filters (BPF) using stub-loaded open-loop (SLOL) resonators are presented in this paper. The required coupling coefficients for the two desired frequencies can be achieved by adjusting the relative coupling position and the spacing between SLOL resonators. In addition, the loaded-stub also affects the coupling between the resonators. To validate this concept, two dual-band BPF with different bandwidth ratios are designed and implemented. The measured 3 dB fractional bandwidths are 4.9/4.8 and 8.2/3.8%, respectively. The results are in good agreement with those of the simulation. Furthermore, the proposed filter has two transmission zeros at each band and exhibits high skirt selectivity.