Compact ultra-wideband bandpass filter using broadside coupled hairpin structures on multilayer liquid crystal polymer substrate

A novel ultra-wideband (UWB) bandpass filter (BPF) using a broadside-coupled hairpin structure and multilayer organic liquid crystal polymer (LCP) technology is presented. To suppress stopband harmonic response, folded stepped impedance structures were adopted as hairpin resonators in the design. The proposed filter has been investigated numerically and experimentally. Multilayer LCP technology was used to implement designed UWB BPF. Good agreement between simulated and measured results of the proposed filter was observed. They show that the fabricated UWB BPF has a good performance, including a small insertion loss, a flat group delay with a variation within 0.1 ns in most of its passband, a wide stopband from 11.0 20.0 GHz with a high rejection level up to 20.0 dB, and a very compact size of 9.8 times 7.5 mm (0.36 lambdag times 0.27 lambdag, where lambdag is the guided wavelength of 50 Omega microstrip line at 6.85 GHz).