On the development of compact lumped-element LCP filters

This paper presents a novel compact, UHF-band lumped element filter that shows good results versus other similar designs, with a 20% fractional bandwidth operating at 500MHz with a 17dB return loss. The circuit was designed using multilayer LCP, with a focus on minimising the footprint and the number of vias present, which was achieved by folding the design and implementing a block of shared ground vias, avoiding unwanted coupling in the process. Using a 4-pole tubular filter circuit model, the initial filter designed showed a good response and underwent a subsequent successful redesign that reduced the footprint by 60% and the number of vias by 37.5% without sacrificing the response of the filter.