Multilayer dual-mode dual-band bandpass filter

This paper presents a single ring resonator using multilayer technique for dual-band bandpass filter. The resonator is composed of two resonators with each one having a quarter-wavelength coupled-line connected in series to a transmission line. The two resonators are arranged in parallel to form a single ring dual-band bandpass filter topology. The controlling impedance parameters of this ring are Z_r for the transmission line and even- and odd-mode characteristic impedances i.e. Z_oe and Z_oo for the coupled-lines. Observations on the controlling parameters are conducted to investigate the effect of each parameters in terms of bandwidth, matching level and the transmission zeros. For validation, the filter is realized using multilayer technique, designed at 2 GHz on FR-4 microstrip substrate. The results exhibited good isolation between the two passbands with centered transmission zero attenuated above 40 dB while the centered frequencies were found at 1.59 GHz in the first passband and 2.41 GHz in the second passband. The simulated and measured result is presented throughout this paper to validate the concept.