Modeling and optimization of circularly-polarized patch antennas using the lumped element equivalent circuit approach

This paper describes the application of lumped element equivalent circuit approach to the modeling of a capacitive-loaded circularly-polarized microstrip patch antenna. This is achieved by using vector fitting to properly fit frequency domain scattering parameter data to a rational function approximation. Then, the parameter coefficients from the approximate function are used to calculate the passive elements of the lumped equivalent circuit. The circular polarization is achieved by a combination of lumped capacitor loading at the ends of the antenna and feeding along either diagonal of the patch to produce left-hand or right-hand circular polarization. This technique is intended to give a designer an idea on the value of capacitance needed to achieve circular polarization and to facilitate the optimization process. The method is benchmarked for antennas for Bluetooth applications.