Ultra-wideband (UWB) Bandpass Filter with Cascaded Lowpass Filter on Multilayer Liquid-Crystal Polymer (LCP) Substrate

An ultra-wideband (UWB) bandpass filter with extended upper-stopband on multilayer liquid-crystal-polymer (LCP) substrate is presented in this paper. The proposed filter is designed to select the frequency band from 1.0 to 20 GHz. The filter consists of two parallel-coupled stub-loaded resonators separated by a composite lowpass filter. The composite lowpass filter is implemented to obtain a very wide rejection band. The proposed filter is fabricated using multilayer LCP technology. Excellent agreement between expected and measured results of the filter is obtained. The measurement results show that the fabricated filter has a fractional bandwidth of 180% and a very low insertion loss of less than 0.6 dB at center frequency of 10.5 GHz. The measured filter has a wide stopband and an excellent rejection level higher than 40 dB.