Robust Sky-directional Circularly-Polarized Smartphone Antenna for Satellite Communication

Antenna radiation pattern is critical for the reliability of satellite communications. In this letter, a skyward circularly polarized (CP) antenna is proposed, which integrates part of the metallic frame and a quarter-wavelength patch positioned at the top of the ground plane, serving as an electric dipole and a magnetic dipole, respectively. Feeding is applied to the low-profile patch while the frame is coupled excited by the strips extended from the patch. The combination of electric currents from the coupled-fed metal frame and magnetic currents from the patch circumvents the traditional CP generation in the frame. Therefore, CP radiation toward the sky can be achieved based on thin frames. Besides, the proposed coupling scheme enables control over both the phase difference and amplitude ratio of orthogonal modes. This eliminates traditional bulky 90-degree phase shifting line and renders it compatible with the stringent clearance (<1.5mm) constraints of smartphones. Moreover, the proposed CP antenna is robust to the hand loading due to the excited differential mode. The proposed electro-magnetic antenna provides right hand circularly polarized (RHCP) gain of 2.1 dBic at the sky direction at 2.49 GHz, with a beamwidth of 76°and 210° on two principle planes. A prototype of the proposed antenna was fabricated and measured, showing an operating band from 2.47 GHz to 2.52 GHz, fully covering the downlink S-band (2483.5-2500 MHz) of the BeiDou Navigation Satellite System. The proposed antenna shows great potential in satellite communications for smartphones.