A Compact Multi-Layered Ultra-Wideband Bandpass Filter With Plural Transmission Zeros and Improved Out-of-Passbands

This paper proposes a novel ultra-wideband (UWB) bandpass filter (BPF) with a shielded multi-layered (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 the scattering characteristics of the filter with a finite element method (FEM), an equivalent circuit analysis and experiments. In the FEM analysis, this filter exhibits a UWB performance from 1.61 GHz to 4.16 GHz, a bandwidth that corresponds to RBW_-3dB = 88.4%. In this passband, maximum ripple is around 1.2 dB , and minimum insertion loss is 0.08 dB. These theoretical predictions agree with the experimental results within an acceptable range of errors. Further, 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 insight into the filter mechanism