Compact Wide Stopband Ultra Wideband Bandpass Filter Using Multilayer Liquid Crystal Polymer Technology

Abstract

Novel ultra-wideband (UWB) bandpass filters (BPFs) are proposed based on broadside coupled capacitive-loaded transmission line resonators (C-L TLR) in this letter. By utilizing the wideband harmonic suppression behavior of C-L TLR, the proposed UWB BPFs were designed with wide stopband and implemented using multilayer organic liquid crystal polymer (LCP) technology. As demonstrations, a vialess five-pole BPF was designed first, and then by adopting shunt short-circuited microstrip stubs at input/output ports, a compact UWB BPF was designed to meet FCC-defined UWB indoor mask. The proposed UWB BPFs were fabricated using multilayer LCP technology. Good agreements between simulated and measured results of fabricated filters were observed. The measured results show that the fabricated BPFs have good selectivity, wide stopband and high rejection level. The fabricated UWB BPFs have compact sizes of 15.15 mm by 4.7 mm about 0.55 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g0</sub> by 0.17 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g0</sub> and 9.6 mm by 9.2 mm about 0.35 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g0</sub> by 0.33 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g0</sub> respectively, where lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g0</sub> is the guided wavelength of 50 Omega microstrip line at 6.85 GHz. They are attractive for UWB communications and radar systems.