A compact multilayered bandpass filter with transmission zeros for UWB applications

This paper proposes a novel ultra-wideband (UWB) bandpass filter (BPF) with a shielded multilayered (ML) structure. Compared with recently proposed planar UWB BPFs based on a microstrip line configuration, this filter can be made more compact and can reduce the interference to other circuit components. We have studied scattering characteristics of the filter by a finite element method (FEM), an equivalent circuit analysis and experiments. In the FEM analysis, this filter shows a UWB performance from 1.61 GHz to 4.11 GHz, which bandwidth corresponds to RBW/sub -3dB/ = 87.4%. In this passband, the maximum ripple is 0.86 dB and the minimum insertion loss is 0.11 dB. These theoretical predictions show good agreement with the experimental results. Further, a measured group delay is moderate around the center passband with a typical value of 0.4 ns. An equivalent circuit model is also developed to gain a useful insight into the filter mechanism.