A novel asymmetry C-band dual-mode bandpass filter using pentagon loop resonator

A dual-mode pentagon resonator that produces asymmetrical frequency response is proposed for the first time in this paper. Unlike a typical dual mode filter, its two ports are distributed along a straight line. By changing the arrangement of perturbation, two transmission zeros (TZs) can be both in the upper stop-band or one in the lower stop band and the other in the upper stopband. The effect of cavities’ depth on odd and even modes’ splitting is also investigated. Finally, a asymmetric dual-mode filter with elliptical response is designed to verify the effectiveness of the proposed method. The pass-band of designed filter is centered at 6.41 GHz with fractional bandwidth of 7.8%, and its selectivity is improved by two transmission zeros located at 6.2 and 9.8 GHz.