A study of narrow-band and compact size microstrip bandpass filters for wireless communications

Coupled filter design covers the odd and even wave coupling of transmission lines, which results in odd and even characteristic line impedances. Cascading the parallel coupled-line sections gives rise to bandpass filter structures. Since conventional coupled-line filter is large in size, it is not suitable for wireless communications. Hairpin- comb and zig-zag filters were introduced to solve this disadvantage. These filters have narrow-band and compact size. This paper focuses on designing hairpin-comb and zig-zag filters at 1800 MHz and comparing their performances. The results show that a hairpin-comb microstrip filter has a better performance than a zig-zag microstrip filter in three categories, namely, return loss, size, and passband bandwidth.