A wave interference filtering section that consists of three stubs of different lengths, each with an individual stopband of its own\ncentral frequency, is reported here for the design of band-stop filters (BSFs) with ultra-wide and sharp stopbands as well as large\nattenuation characteristics. The superposition of the individual stopbands provides the coverage over an ultra-wide frequency\nrange. Equations and guidelines are presented for the application of a new wave interference technique to adjust the rejection\nlevel and width of its stopband. Based on that, an electrically tunable ultra-wide stopband BSF using a liquid crystal (LC) material\nfor ultra-wideband (UWB) applications is designed. Careful treatment of the bent stubs, including impedance matching of the\nmain microstrip line and bent stubs together with that of the SMA connectors and impedance adaptors, was carried out for the\ncompactness and minimum insertion and reflection losses. The experimental results of the fabricated device agree very well with\nthat of the simulation.Thecentre rejection frequency asmeasured can be tuned between 4.434 and 4.814GHz when a biased voltage\nof 0ââ?¬â??20Vrms is used. The 3 dB and 25 dB stopband bandwidths were 4.86GHz and 2.51GHz, respectively, which are larger than\nthat of other recently reported LC based tunable BSFs.
Loading....