Printed dipole-like antennas with modified groundplane for wideband circular polarization

Small printed dipole-like antennas which provide circular polarization with wide axial-ratio bandwidths are presented. The first antenna is an asymmetrical dipole with a slitted ground plane which is fed by an L-shaped microstrip feedline using a via. The other antenna employs a pair of asymmetrical dipole arms which are located on opposite sides of the substrate and fed by a stepped microstrip line which connects to the shorter dipole arm. It also employs groundplane slits. By utilizing the combined orthogonal surface currents along the asymmetric arms and the microstrip line structure, circular polarization is realized. Measurements show the printed dipole antenna with a via can achieve a 23% axial-ratio bandwidth whereas the antenna without via can achieve 33.5% axial-ratio bandwidth.