Quasi-Elliptic UWB Bandpass Filter Using Multilayer Liquid Crystal Polymer Technology

A novel ultra-wideband (UWB) bandpass filter (BPF) with quasi-elliptic response using non-uniform periodical structures is presented. In the design, a periodical unit structure is proposed and studied, which can provide transmission zeros at both lower and upper stopbands to improve the selectivity. The proposed periodical unit structure consists of broadside coupling patches, slotted ground and embedded quarter-wavelength resonator. It can be implemented using a multilayer structure with a compact size. A high selectivity UWB BPF with multiple transmission zeros can be designed by cascading a few proposed non-uniform periodical units. As a demonstration, a UWB BPF with five periodical units is developed by full-wave simulation. Multilayer liquid crystal polymer technology is used to implement the designed prototype. The predicted results are verified by the experiments, which show that the fabricated filter has an ultra wide fractional bandwidth, a wide stopband and a high selectivity with quasi-elliptic response. The proposed filter is attractive for UWB communication and radar systems.