A planar three-section coupled-line high-selectivity wideband bandstop filter

A planar three-section coupled-line high-selectivity wideband bandstop filter (BSF) is proposed. The proposed filter topology contains three coupled-line sections (CLs) and two transmission-line sections (TLs). The four locations of transmission zeros (TZs) are obtained through the deduction of the theoretical equations, which validates the proposed topology. During circuit simulation, the effect of the Ze1 on the skirt roll-off is investigated. A highly selective wideband BSF with center frequency at 2.4 GHz, rejection level below 20 dB and attenuation rate at 278.69 dB/GHz is designed and manufactured. The theoretical and simulation results are in good agreement. Indeed, it illustrates the correctness of the theoretical analysis.