A wideband bandstop filter with two independently controllable equal-ripple levels

In this letter, a novel wideband bandstop filter with controllable equal-ripple response is newly presented. The proposed topology consists of two cascaded transmission lines and three open-circuited stubs, where, one two-section OS is shunted between two transmission lines, two three-section OSs are shunted at two output ports, respectively. By using the proposed design approach, both passband and stopband provide controllable equal-ripple responses independently, where there are five transmission zeros and six reflection zeros in a single period of frequency domain. For demonstration, an experimental BSF centered at 2 GHz with 20-dB FBW 129.5% and 30-dB stopband rejection is designed and fabricated. The simulations and measurements agree with the design theory very well.