Equivalent circuit model of a coaxial excited microstrip-fed quasi-lumped element resonator antenna array

An approximate lumped-parameter equivalent circuit model of the quasi-lumped element resonator antenna array is presented. The array consists of six series resonant circuits of frequency-independent elements, each with an interdigital finger capacitor (IDC), and shorted across by a parallel narrow strip inductor. Each resonator exhibits an aperture size of 0.207λ_g × 0.2λ_g at a centre frequency of 5.8 GHz, with entire array size of 2.857λ_g × 1.07λ_g. The resulting design is fed by a microstrip line and excited by a coaxial feed probe. A simple equivalent circuit model representing the six resonant circuits as well as the coaxial feed probe circuit, using the magnetic-frill model approach but with the simplest uniform-current model is described to predict the characteristics of the proposed resonator (and by extension, the proposed array), the effects of the coaxial probe and the microstrip feed line. Simulated data obtained from a full wave analysis using finite integration technique commercial solver is compared with the Agilent advanced design system results of the equivalent circuit. The derived equivalent circuit model was validated both analytically and by numerical simulations.