Omnidirectional Circularly Polarized Antenna Based On Crossed Dipoles

In this letter, an omnidirectional circularly polarized (CP) antenna based on crossed dipoles is proposed. The proposed antenna is composed of four planar crossed dipoles of a square array as radiation elements and a broadband microstrip feeding structure composed of baluns and matching networks. Each crossed dipole element is composed of a horizontal dipole and a vertical dipole. 90 degrees phase difference between them are naturally guaranteed. With a size of 0.5 lambda(0)*0.5 lambda 0*0.47 lambda(0), the antenna exhibits a -10-dB impedance bandwidth of 15.9% (ranges from 1.45 to 1.7 GHz) and a 3-dB axial-ratio (AR) bandwidth of 11.5% (ranges from 1.47 to 1.65GHz) in the azimuthal plane. At the frequency of 1.575 GHz, the measured average axial ratio and left-hand CP (LHCP) gain are 1.5 dB and 0.84 dBi, respectively, in the azimuthal plane.