4-Port Microstrip planar resonator for multiband microwave material characterization applications

Planar microstrip resonators suitable for material characterization application are presented in this paper. The prototype consists of three resonators fed through four ports in a planar dielectric substrate without any additional resonators. The resonators are working in different frequency regions making it suitable for resonant based characterization at different frequencies using a single prototype. In this proposed work, the overall dimension of the prototype is 100mm x 50mm when fabricated in a 1.6mm thick FR4 epoxy substrate of dielectric constant 4.4 and loss tangent 0.02. The three resonators are operating within their fundamental mode at 900MHz, 1.8GHz and 2.4GHz respectively. The analysis in this work is carried out on the fundamental electrical mode for all the three resonators, but is similar for the higher order modes. The prototype is highly compact and low cost compared to the conventional cavity based resonant characterization techniques.