A compact ultra-wideband circularly polarized antenna array for vehicular communications

In this paper, a new compact ultrawideband (UWB) circularly polarized (CP) antenna array for vehicular communications is proposed. The antenna array consists of a 2 × 2 sequentially rotated T-shaped cross dipole, four parasitic elements, and a feeding network. By loading the T-shaped cross dipoles with parasitic rectangular elements with cut corners, the bandwidth can be expanded. On this basis, the radiation pattern can be improved by the topology with sequential rotation of four T-shaped cross-dipole antennas, and the axial ratio (AR) bandwidth of the antenna also can be further enhanced. In addition, due to the special topology that the vertical arms of all T-shaped cross dipoles are all oriented toward the center of the antenna array, the gain of proposed antenna is improved while the size of the antenna is almost the same as the traditional cross dipole. Simulated and measured results show that the proposed antenna has good CP characteristics, an impedance bandwidth for S11 <-10 dB of about 106.1% (3.26:1, 1.57-5.12 GHz) and the 3-dB AR bandwidth of about 104.1% (3.17:1, 1.57-4.98 GHz), a wide 3-dB gain bandwidth of 73.3% as well as the peak gain of 8.6 dBic at 3.5 GHz. The overall size of antenna is 0.56λ × 0.56λ × 0.12λ (λ refers to the wavelength of the lowest operating frequency in free space). The good performance of this compact UWB CP antenna array is promising for applications in vehicular communications.