4x4 Circularly Polarized Antenna Array for Ambient RF Energy Harvesting

This paper presents a planar circularly polarized (CP) 4x4 antenna array for RF energy harvesting applications. The single element is a coplanar waveguide (CPW) slot antenna. A sequentially rotated feed network is introduced for generating CP 2x2 array and achieved a phase excitation of 0 degrees, 89.39 degrees, 178.6 degrees, and 271 degrees. This 2x2 planar antenna array is repeated three times to produce CP 4x4 antenna array that equally feeds the four groups of 2x2 arrays. A microstrip to CPW transition by via holes is used for connecting the Wilkinson microstrip lines to CPW antenna elements. Four lobes at +45 degrees, +135 degrees, -45 degrees, and -135 degrees, respectively can be noticed and other interlaced beams with lower magnitudes are evolved. The array ARBW (for AR < 3 dB) is extended from 1.3 GHz to 2.83 GHz (with bandwidth of 1.53 GHz).