A Modified Dual-Mode Ultra-Wideband Bandpass Filter Fabricated On Ultra Thin Liquid Crystal Polymer Substrate

This paper presents a dual-mode ultra-wideband bandpass filter with two transmission zeros and a low insertion-loss on ultra thin (100 mu m) liquid crystal polymer (LCP) substrate. The UWB BPF mainly comprises one wavelength (lambda g) square ring resonator with two orthogonally separated I/O ports that are direct-taped to feed electromagnetic (EM) energy. By tuning the sizes of apertures of the ring-like perturbation element attached at the corner of the ring resonator, the even and the mode EM energies are excited to produce a wideband performance. Additionally, a pair of transmission zeros are generated to improve the selectivity of the proposed BPF. The designed BPF was fabricated on a 100 mu m thick LCP substrate and measured by using probe and vector network analyzer. Measurement results show that the fabricated filter exhibits an ultra wide passband from 3 GHz to 5.08 GHz and a low insertion loss of 1.6 dB over the passband. Good agreement between simulation and measurement results is presented.