Circular Polarized Ground Radiation Antenna for Mobile Applications

Here, we propose a ground radiation antenna (GradiAnt) with circular polarization (CP) by applying the ground-mode tuning (GMT) technique to the ground plane. We demonstrate that a GradiAnt at an arbitrary location of the ground plane can simultaneously excite two orthogonal modes of the same magnitude, and the phase difference between the two modes can be adjusted via GMT to achieve CP in mobile antennas. The proposed GradiAnt can be viewed as a combination of an electric coupler (J-type) and magnetic coupler (M-type) to the modes of the ground plane, and both modes can be excited to the same amplitude by tuning the coupling-type. GMT, applied to the ground modes using inductor-connected metal strips, can generate a 90° phase difference between the two modes of the ground plane. The proposed antenna design generates a 6 dB axial ratio bandwidth of 140 MHz from 2.38 to 2.52 GHz in the +z-direction. Right-hand CP and left-hand CP in the +z-direction and -z-direction, respectively, are obtained. The tuning mechanism is presented, and measurements are taken to validate the proposed technique.