Compact dual-band filter using quadruple-mode resonator for WLANs

This paper presents the design and implementation of a dual-band bandpass filter using a new quadruple-mode resonator. The two passbands are centered at 2.4 GHz and 5.2 GHz. The proposed resonator has two even mode and two odd mode resonant frequencies. Each passband is realized using one odd mode and one even mode frequencies. Two half-wavelength C-shaped resonators are used to provide sufficient external quality factor value for both passbands. The stopband performance of the filter is improved by using stepped impedance resonator to push the harmonics of the first passband from 3 to 3.3 times the center frequency of the first passband. The simulated and measured results of the two dual-band bandpass filters show good agreement.