Analysis and design of a sharp-rejection wideband bandstop filter with multi-transmission zeros and reflection zeros

Analysis and design of a wideband bandstop filter with multi-transmission zeros (TZs) and reflection zeros (RZs) are presented. The proposed topology consists of N-1 shunt open-circuited stubs (OCSs) cascaded through N-sections of transmission lines, and two M-sections of OCSs are shunted at two output ports, respectively. After complicated mathematical analysis, the numbers of TZs and RZs are determined by section numbers M and N. By using the proposed algorithm, equal ripples with controllable ripple levels can be realized in the passband. Although the ripples in the stopband have different levels, each ripple level can be designed independently. As the proposed algorithm can design the positions of TZs and RZs, upper and lower attenuation rates can be increased dramatically. Therefore, compared with former works, the proposed work provides enhanced sharp-rejection and simultaneously maintains wide stopband performance. For verification, two experimental circuits are fabricated, and the proposed design theory and algorithm are well verified by the measured frequency response.