Compact UWB filter with notched band and improved out-of-band performance

A compact ultra-wideband (UWB) bandpass filter (BPF) with notched band and improved out-of-band performance is presented. In the design, A UWB bandpass filter is built up using the hybrid microstrip and coplanar waveguide (CPW) structure. Open stubs are embedded on the bottom of filter to realize the narrow band which is to reject the undesired wireless local-area network (WLAN) radio signals. The center and bandwidth of the notched band can be controlled by adjusting the length and width of the stubs. A cross-shape patch is constructed to implement transmission zeros in the upper out-of-band so as to suppress the first spurious passband. The proposed UWB filter has the merits of compact size, flat group delay, good insertion/return loss, and good selectivity.