Investigations on a Novel Folded Ring Resonator Antenna With Multiband Characteristics

A novel loop antenna based on the volumetric folded ring resonator (FRR) structure is proposed. It is shown that the FRR antenna can be represented by an equivalent circuit model for approximate analysis with sufficient accuracy. Two practical implementations are presented: The first version is a single FRR antenna embedded in a dielectric substrate and excited by a 50 coaxial feed line. Parametric studies of the structural parameters are presented showing three resonances that can be impedance matched achieving positive gain. In the second implementation, the FRR is embedded in a slotted ground plane for improved matching and radiation performance. Two bands, one at 3.6 GHz and another between 4.75 GHz and 5.8 GHz, are matched to better than S₁₁ = -10 dB and maintain a constant 2.5 dBi gain with >; 90% radiation efficiency. The simulated reflection coefficient and gain radiation patterns agree well with measurements.