Theoretical study of dual-resonant frequency and circular polarization of elliptical microstrip antennas

A simple and accurate technique is presented for calculating the dual-resonant frequency f/sup e.0//sub 11/ of the dominant even and odd modes and for predicting the existence of circular polarizations (CPs) of elliptical microstrip antennas (EMAs). The dual-resonant frequency f/sub 11//sup e.0/ can be achieved by feeding the elliptical patch at M or N point as presented. In this paper, to get improved dual-resonant frequency f/sub 11//sup e.0/, the effective semi-major axis u/sub ui/ is taken into account in evaluation. The elliptical microstrip antennas (EMAs) with small values of eccentricity have been employed to produce circular polarizations (CPs) with the use of single feed (M or N) point The comparison between calculated and measured dual-resonant frequency f/sub 11//sup e.0/ demonstrates that the present technique provides less than 1% errors for two different thicknesses of dielectric substrate with low relative permittivity (/spl epsiv//sub r/=2.48). Generally, the technique calculates the dual-resonant frequency f/sub 11//sup e.0/ of elliptical microstrip antennas (EMAs) as accurately as possible with the tolerance range of the antenna structure's electrical and physical parameters. The present dual-resonant frequency f/sub 11//sup e.0/ is useful for application of elliptical microstrip antenna (EMA) designs with simple closed-form formula. The existence of circular polarization can be demonstrated by axial ratio (AR) as presented.