Dual-wideband bandpass filter using a parallel-coupled SIR and open-ended stubs

A dual-wideband filter is designed by the combination of a UWB(ultra-wideband) bandpass filter (BPF) with a bandstop filter (BSF). Firstly, a UWB BPF composed of a three-coupled-line-based stepped-impedance-resonator (SIR) and two open-ended stubs are designed in terms of a wideband filter design/synthesis theory. Secondly, a BSF consisting of a SIR and open-circuited stubs is designed to replace the transmission-line-part in the middle of BPF. Using the dimensions values of the designed BPF and BSF as initials, the dual-wideband filter is optimized by an EM simulation. As a design example, a dual-wideband filter used for UWB system is designed, simulated and experimentally-realized to have two passbands of 3.4-4.8GHz and 7.27-10.25GHz following the proposed design procedure. The measured transmission characteristics of the filter agree with the simulated ones.