Synthesis of Wideband Parallel-Coupled Line Bandpass Filters With Non-Equiripple Responses

This letter proposes a synthesis of wideband parallel-coupled line bandpass filters with controllable non-equiripple frequency responses. Different from the traditional Chebyshev transfer function filters, the reflection lobes of the proposed non-equiripple filters can be redistributed within the operating passband. As a result, the proposed filters have a reduced sensitivity to manufacturing errors and exhibit good tolerance control for maximum in-band reflection loss. By deriving the transfer functions, a synthesis approach with a set of nonlinear equations can be established according to the specifications such as the bandwidth and predetermined reflection lobes. Without performing any post optimization in the full-wave simulation, the non-equiripple synthesized results have less sensitivity in comparison with those obtained from traditional Chebyshev transfer functions with equiripple frequency responses.