Ultra-wideband bandpass filters using multilayer slot coupled transitions

New Ultra-Wideband (UWB) bandpass filters are proposed and tested. The filters are composed of two microstrip Conductor-Backed Co-Planar Waveguide (CBCPW) transitions and a multiple-mode resonator, constituted by a line section. The both cases, where the line section is a microstrip or a CBCPW are tested. First, simulated and experimental results for the transition are presented, showing that a wide operating band is obtained. Then, the results for the proposed filters that use this transition structure are presented. Simulated and measured data show that the filters can provide an operating band from 3.1 GHz to 10. 6 GHz (-10 dB bandwidth), which is suitable for ultra-wideband systems. The group delay is about 0.3 ns over the most central band and less than 0.45 ns all over the operating band. In addition, using an optimization procedure, a bandwidth of 15 GHz can be achieved with the proposed filter which is more than what was fixed by Federal Communications Commission (FCC) for UWB radio systems. Moreover, a filter constituted by combining the two proposed filters was also designed and fabricated, to improve further the band rejection.