Resonator-Embedded Four-Pole Cross-Coupled Dual-Band Microstrip Bandpass Filters

In this paper, two dual-band bandpass filters using resonator-embedded four-pole cross-coupled structure for GSM900/1800 and WLAN (2.4/5.2 GHz) are proposed. A resonator-embedded cross-coupled filter constructed by stepped-impedance hairpin resonators and miniaturized hairpin resonators, is presented. Based on resonance characteristics of the resonator-embedded cross-coupled filter, so that its second pass-band can be tuned, relative to the fundamental frequency f₀, by its structure parameters. Two topologies are presented with their associated design techniques. The first one consists of stepped-impedance hairpin resonators which the value of impedance ratio is R< 1 and miniaturized hairpin resonators. The another one is based on the two harmonics of a uniform transmission line filter and miniaturized hairpin resonators. All theoretical analysis and design procedures are discussed in detail