Microstrip open-loop filter using multilayer liquid crystal polymer technology

In this paper, two compact microstrip filters using open-loop resonators are presented. The first one is a single-band filter designed at 5.2GHz with a fractional bandwidths of 7.5%, and the second one is a dual-band filter operating at 2.4GHz and 5.2GHz with fractional bandwidths of 10% and 9%, respectively. The effective sizes are reduced by using multilayer liquid crystal polymer (LCP) technology. The microstrip open-loop resonators are located on the first and the third layer, and the second layer is used as common ground plane. Couplings between resonators on different layers are obtained by the coupling slots on the common ground. Transmission zeros are generated by the cross coupling between open-loop resonators.