2×2 Circularly Polarized Antenna Array with Equal Phases for RF Energy Harvesting in IoT System

This paper presents a 2×2 planar circularly polarized (CP) antenna array for RF energy harvesting in IoT system applications. The single element is a slot antenna with coplanar waveguide (CPW) feed line. It consists of a main slot radiator, a grounded-L strip, a stepped impedance matching stub, two chamfered corners, and an asymmetric U-shaped strip acting as a perturbed element. A voltage doubler rectifier is designed and assembled with the slot antenna to complete a rectenna structure. Then, the 2×2 planar antenna array is designed based on the CPW feed antenna element. The array is fed by a corporate feeding network with equal phase feeding behaviour and all the elements are oriented to the same direction. A microstrip to CPW transition by via holes is used for connecting the microstrip Wilkinson power divider to CPW feed antenna elements. A prototype of the proposed array is fabricated and measured. Good agreement is obtained between measured and simulated reflection coefficients. Front and back radiation is noticed and two main lobes at 0° and 180° are depicted. The array axial ratio bandwidth (ARBW), for AR < 3 dB, is about 180 MHz. The gain, directivity, and radiation efficiency of the array are 6.605 dBi, 9.604 dBi, and 50.12 %, respectively at 2.45 GHz. The RF power received by the proposed array is about −9.37 dBm at 2.445 GHz which greatly exceeds the single element harvested power.