Wideband Widebeam Circular-Polarized Antenna Using Asymmetrical Tri-Dipoles for Direct Satellite-to-Handset Communications

This article presents a compact wideband circular-polarized (CP) antenna with wide beamwidth for low-orbit direct satellite-to-handset communication. In this design, an asymmetric tri-dipole antenna is proposed and integrated onto the upper bezel of mobile terminal. The contributions of the asymmetry are with three aspects: 1) the antenna is composed of asymmetrical dipoles to generate circular polarization, i.e., a folded dipole for horizontal polarization (HP) and two bent dipoles for vertical polarization (VP); 2) the two bent dipoles are also asymmetrical to improve both impedance and axial ratio (AR) bandwidths; and 3) for each bent dipole, the two arms are asymmetrically designed to enhance the beamwidth for low-orbit range coverage. To validate, a prototype of the proposed antenna was fabricated and tested, indicating gratifying circular polarization performance of −6-dB impedance bandwidth of 680 MHz, 3-dB AR bandwidth of 140 MHz, and 3-dB beamwidth beyond 92° in a volume of
$0.88\times 0.07\times 0.005\lambda _{0}^{3}$
at the center frequency of 3.8 GHz. With the merits of compact size, wide bandwidth, and wide beamwidth, this asymmetric tri-dipole CP antenna exhibits potential for mobile terminal applications of low-orbit satellite communications.