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

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.

Compact High-Selectivity Wide Stopband Microstrip Cross-Coupled Bandpass Filter With Spurline

“…Thus, different nonuniform perturbations have been incorporated by the researchers in the coupled region between the adjacent arms of the lines. In this context, spurline is one of the most attractive microstrip defects that effectively suppress the harmonics for parallelcoupled line filter [14][15] and hairpin-line filter [17][18][19]. Hence, the next objective of the present work has been set to suppress the harmonic attenuation level below 35 dB keeping the satisfactory passband response.…”