Spurline-embedded compact hairpin-line bandpass filters for wide harmonic suppression

Abstract

Abstract The current paper describes the design of a fourth-order compact narrow-band hairpin-line bandpass filter centered at 2.5 GHz and enhanced stopband suppression ~38 dB required for wireless local area network (IEEE802.11b). The size reduction of 24% has been achieved for a conventional hairpin-line filter with a second-order inward folding of the open-end arms with an improvement in the skirt characteristics. However, the folding mechanism has been overshadowed by the presence of spurious harmonics with an attenuation level of <10 dB. Subsequently, L-shaped spurlines with optimum dimensions have been incorporated in the coupled arms of the folded hairpin-line cells. Three fourth-order filters have been designed with the incorporation of spurlines in different coupling regions, fabricated, and tested experimentally. Accordingly, an extended stopband with a rejection level of 38 dB up to 4.48f0 and a size reduction of 18% over the conventional hairpin-line filter has been achieved.