Abstract
A modified quarter-wavelength stepped-impedance resonator (SIR) is proposed and analyzed in this article. In the modified SIR, the low characteristic impedance stub of a conventional SIR is replaced by a closed rectangular loop. Based on the modified SIRs, a compact third-order bandpass filter (BPF) with multiple transmission zeros is presented. The filter consists of two novel SIRs and one half-wavelength embedded spiral-line resonator locating in the closed rectangular loops. Mixed-cross (M–C) coupling and source–load (S–L) coupling are introduced to the filter. Owing to the M–C coupling and S–L coupling, multiple transmission zeros and the suppression of harmonics can be obtained in the stopband for the enhanced frequency selectivity. A new BPF centered at 2.4 GHz with 25% fractional band width for wireless local area networks application has been designed, fabricated and measured to verify the validity of the above method.
Disclosure statement
No potential conflict of interest was reported by the authors.