Realizability analysis of wideband non-equiripple bandpass filters using parallel-coupled lines

In this paper, the realizability of wideband non-equiripple bandpass filter using parallel-coupled lines is extensively investigated. Through the direct synthesis approach for non-equiripple responses, the required characteristic impedances of each involved line sections are explicitly determined. The realizable range of filtering bandwidth is then investigated based on the obtained impedance values. Under the restriction in fabrication and material, the required physical dimensions of the parallel-coupled line section are finally discussed.