Bandpass filter with enhanced selectivity and stopband performance on multilayer LCP substrate

In this paper, a Ku-band bandpass filter (BPF) with enhanced selectivity and stopband suppression on three-layer liquid crystal polymer (LCP) substrate are presented. H-shape resonators and half wavelength resonators are used. Resonators on the same layer are without coupling and resonators on the different layers are with broadside coupling. Two open-circuited stubs are integrated with the H-shape resonator on the middle layer, so two transmission zeros (TZs) are generated to improve selectivity and stopband performance. Prototype filter with the center frequency of 16.4 GHz is designed, fabricated and measured. Measured results show that the selectivity is enhanced by introducing two TZs and the stopband is from 22.5 GHz to 50 GHz with suppression of more than 28 dB.