An iterative synthesis scheme for wideband filter based on parallel-coupled three-line

An improved equivalent circuit for parallel-coupled three-line is derived by taking the cross-coupling between non-adjacent lines into consideration. Since the cross-coupling between non-adjacent lines is also dependent on that between adjacent lines, a novel successive iteration synthesis scheme is correspondingly proposed to synthesize the filter. As an example, a two-section three-line filter with a BW of 2.8-5.2GHz are synthesized, simulated and experimentally realized, respectively. The results obtained by our synthesis theory compare very well with those by simulation and experiment, while the model neglecting the cross-coupling between non-adjacent lines shows a 17% error in bandwidth estimation.