Comparative Study on High Gain Planar Circularly Polarized Antenna with Different Directors

A comparative study on high-gain planar circularly polarized antenna with different directors, e.g., linear strip, annular ring, and polygon sheet, is presented. The initial radiator is composed of two L-shaped metallic strips, and fed across the strip corners. An optional disc reflector is used to improve radiation pattern and directivity. The center frequency of the antenna operation band is fixed at 3.25 GHz with at least 6.00% axial ratio bandwidth (<;3 dB). The simulated antenna gains with and without reflector are 7.93 dB and 2.88 dB, respectively. In order to further enhance the gain, different shaped directors are added in sequence above the initial radiator, at a fix height of 27 mm (about one quarter wavelength at the center frequency). By optimizing the size of each director, we can obtain their best performances for comparative study. It is observed that the shape of the director has slight influence on antenna parameters such as gain and axial ratio bandwidth. In detail, the simulated gains of the antennas with different directors are all around 9.00 dB with 6.08%-8.26% axial ratio bandwidth (<;3 dB). Particularly, the antenna with a disc shaped director reaches the highest gain of 9.30 dB. Besides, it is observed that the axial ratio bandwidth is inversely proportional to the antenna gain according to the simulated data.