Improved second harmonic suppression in a compact coupled-line bandpass filter with triangular corrugations

This paper presents the design of a miniaturized coupled-line bandpass filter centered at 5.25 GHz with a fractional bandwidth of 20% for wireless local area network applications. Size reduction has been achieved by incorporating two different approaches in which symmetrical folding techniques have been employed. Periodic triangular corrugations have been introduced in the coupled edges of line for compensating the asymmetry in even- and odd-mode phase velocities . Accordingly, two different filter structures have been designed and optimized: folded V-shaped with five corrugations and in-line W-shaped with four corrugations. Second harmonic suppression of 62 and 30 dB and size reduction of 62 and 74% are achieved for folded and in-line filter respectively.