Wideband dual mode microstrip bandpass filters using a new perturbation with notch rectangular slots

This paper presents wideband dual mode microstrip bandpass filters using a square ring resonator structure with a novel perturbation by notch rectangular slot. A rectangular slot shape perturbation is excited to degenerate a dual mode, which is made the two reject bands on each side of passband, resulting in high sharp cutoff frequency and low insertion loss. The proposed filters have been designed at a center frequency f_o of 5 GHz. It has been found that performances of the proposed filters have been improved with a bandwidth greater than 50%, a sharp cutoff frequency greater than 195 dB/GHz, an insertion loss better than 0.4 dB, a return loss more than 10 dB, and two reject bands greater than 32 dB. This proves that the new perturbations can improve the performances of the proposed filters.