A wide rejection bandwidth bandpass filter with stepped‐impedance hairpin resonator and interlaced coupled‐line

In this paper, a wide rejection bandwidth bandpass filter with stepped-impedance hairpin (SIH) resonator and interlaced coupled-line was proposed. With the former, its elliptic-function low-pass response was adopted to steepen the upper roll off characteristic and flatten the rejection level; the latter was utilized to broaden the rejection bandwidth by shifting the transmission zero. Measured results show that the filter with interlaced length λ2 mm has suppressed the second harmonic response from −19 to −53 dB when compared to three stages conventional parallel coupled-line filter. Moreover, the upper rejection bandwidth was expanded from 3.2 to 4.5 GHz when the interlaced coupled-line was increased from 0 to 3 mm, which stands for 40% improvement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 542–545, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22194