Compact Wideband Bandstop Filter With Five Transmission Zeros

A compact parallel-coupled transmission line section, connected at their both ends, is presented to obtain multiple transmission zeros. As much as five transmission zeros can be obtained. The zeros can be arranged to design a sharp rejection wideband bandstop filter (BSF). A lossless transmission line model is used to analyze the structure and hence to obtain closed form expressions for the -parameters and design graphs to facilitate the filter synthesis procedure. Theoretical predictions are validated by fabricating a BSF in microstrip line technology. The single filter unit provides 29 dB stopband over a fractional bandwidth of 60% at the mid-band frequency of 1.47 GHz.