Synthesis Theory of Wideband Bandstop Filter with Controllable Equal Ripples

A wideband bandstop filter (BSF) is introduced in this letter, where multi-transmission zeros (TZs) and reflection zeros (RZs) can be designed by the proposed synthesis theory. First, we propose a series of BSFs with open stubs cascading through N section transmission lines (TLs). By finding the laws of the structure and experimental verification, we proposed a synthesis method to design wideband BSFs. By using this theory, more TZs and RZs can be created regularly. Not only that, the proposed wideband BSFs have sharp attenuations and the ripple levels can be controlled. Then, in order to decrease the size of the BSFs, new exploration and improvement were made to the structure. As a result, the size of the new BSF is smaller and the ripples are equal.