A Differential-fed Patch Antenna with Symmetric Radiation Pattern Used for Circularly Polarized Phased Array

in this paper, we propose a low-profile differential-fed patch antenna with improved radiation pattern used for circularly polarized phased array The periodic antenna element is mainly composed of a radiation square patch, four L-shaped differential-fed probes which guarantee the symmetry of radiation pattern of antenna array, and a 3-dB branch-line coupler to obtain both right hand circular polarization (RHCP) and left hand circular polarization (LHCP). The periodic antenna element achieves a impedance bandwidth (10-dB return-loss) and circular polarization bandwidth (3-dB axial ratio) both more than 18% while scanning up to 45° by periodic boundary simulation. Moreover, the 3-dB axial-ratio beam-width (ARBW) is over 250° at boresight direction. The total thickness of the circularly polarized array is only 0.07 wavelength at the low operating frequency. A 4 × 4 antenna array is presented and the results are in a good agreement with the periodic element simulation.