The ellipticity of radiation from polarization-agile patch antennas

Polarization-agile patch antennas comprise square or circular patches with independently biased varactor diodes connected between the patch and the ground plane, located symmetrically on each radiating edge. The feed probe is located on a bisecting diagonal line, simultaneously exciting orthogonal modes, and the phase relation between the modes, which is controlled by the varactor diode bias voltages, determines the polarization state of the radiation. This can be circular (left or right hand), linear in the /spl Theta/=0, 45, or 90 degree planes, or elliptical. Varactor diode-loaded polarization-patch antennas capable of radiating linear polarization in any one of three selectable planes, circular polarization of either sense, and elliptical polarization have been developed. Continuous independent variation of diode bias voltages affords optimisation of such parameters as axial ratio, input impedance match and resonant frequency. Radiation patterns display no undue perturbations. The authors believe this type of antenna would be suited to applications where it is necessary to discriminate between two circularly polarized channels transmitted at the same frequency.