Wideband bandpass filter using parallel-coupled line and step-impedance open stubs

A novel wideband bandpass filter using parallel-coupled line and step-impedance open stubs is presented in this paper for use in wideband wireless communication applications. In the proposed filter configuration, step-impedance open stubs are introduced to both sides of the parallel-coupled line in order to produce transmission zeros near the passband. As a consequence, the filter is compact in size and exhibits sharp attenuation characteristic near its passband as well as wide stopbands. On the other hand, the bandwidth of the filter is controlled by adjusting the impedance ratio of the step-impedance open stub. The filter is successfully realized in theory and verified by full wave EM simulation. Theoretical filtering responses show good agreement with the simulated results.