A Beamforming Antenna using Analog Phase Shifter for 5.7GHz RF Wireless Power Transfer System

This article presents a prototype of a beamforming antenna integrated with a reflective phase shifter used for wireless power transfer at 5.7 GHz. Following the fabrication of discrete components-the Wilkinson splitter, a reflective phase shifter, and a square microstrip antenna-on an FR-4 board, we integrate them as a phased array antenna and assess the characteristics of beam steering. The Wilkinson splitter exhibited a 2 dB attenuation beyond the ideal threshold. Despite the intention to secure a 135-degree phase shift for beam direction control within +/- 45 degrees using the reflective phase shifter employing a 90-degree hybrid and a varactor, the achieved phase shift plateaued at 46 degrees, enabling a maximum steering of +/- 15 degrees. The authors clarify the relationship between the applied voltage value for the varactor and the quantities of phase shift in this experiment. A 4-element square microstrip array antenna is capable to maintain an S-11 of -10 dB or lower in the 5.7 GHz band. The proposed phased array antenna is an integration of them, and its radiation pattern is measured by setting the quantity of the phase shifts obtained by the preceding experiment. The measurement results, unfortunately differs from our expected one at this stage.