Wide band, high rejection and miniaturized fifth order bandpass filter on LCP low cost organic substrate

This paper deals with miniaturized and wide band bandpass filter. This filter is based on an original topology based on series and parallel resonators. Series resonators are realized using open-ended coupled lines and parallel resonator is implemented using an open-ended stub. This hybrid topology based on two kinds of stub leads to a twice more compact 5th order design compared to the conventional 5th order approach. Moreover, the use of resonators presenting different periodic behaviors implies additional transmission zeros and so, enhances the rejection of the filter. Liquid crystal polymer (LCP) is chosen by considering its low cost, good and stable RF performance over the frequency of interest and its ability to act both as a substrate and a package to obtain wide band filter. So, the combined use of this technology and this topology leads to a filter that presents very good electrical performances in a reduced occupied area. A compact wideband filter (2.38-4.2 GHz) with insertion loss of 1.2 dB and rejection has been designed by using a full-wave analysis and measurements are presented.