Design of Wideband Circularly Polarized Crossed-Dipole Antenna Using Parasitic Modified Patches

In this paper, a wideband circularly polarized (CP) crossed-dipole antenna is presented by using parasitic modified patches. Four polygonal metal patches are sequentially rotated around the crossed dipoles. By tuning the electromagnetic coupling characteristic between the patches and the crossed dipoles, the axial-ratio bandwidth (ARBW) of the lower frequency band can be enhanced significantly. Furthermore, four slots are etched on the parasitic patches in a sequential rotation way, modifying the current distribution. Therefore, an extra CP mode produces at the higher band. A wide 3-dB ARBW is realized by combing three CP modes, including the basic CP mode of the cross dipole at the middle frequency band. A prototype of the proposed broadband CP antenna was manufactured and measured to verify the design principle. The measurement results illustrate that the antenna has a wide 10-dB return loss bandwidth of 99.2% (1.24-3.68 GHz) and a broad 3-dB ARBW of 72.7% (1.41-3.02 GHz) for right-hand circular polarization (RHCP). Besides, stable gain and unidirectional radiation patterns are also obtained over the entire band of operation.