COMPACT TWO-LAYER MICROSTRIP BANDPASS FILTERS USING BROADSIDE-COUPLED RESONATORS

This paper presents a design methodology for realizing broadside-coupled microstrip bandpass fllters on multilayer substrates to reduce the size of the fllter. The new fllter conflguration consists of broadside coupled split-ring resonators on two layers backed by a ground plane. With the proposed new method, miniaturization to a greater extent can be achieved compared to the conventional method of realizing microstrip multilayer fllters. In addition, coupling apertures in the ground plane used to achieve coupling among the resonators in conventional multilayer structures are eliminated. The proposed design is more ∞exible compared to traditional multilayer fllters. Layers can be easily added to increase the fllter order. To demonstrate the method, a miniaturized two-layered bandpass fllter centered at 728MHz with low insertion loss is implemented and investigated. Miniaturization of more than 25% is achieved compared to the conventional broadside coupled structure and more than 40% miniaturization compared to the edge coupled structure. The new microstrip fllter discussed in this paper can be realized using simple fabrication techniques.