Highly efficient C-band circularly polarized rectifying antenna array for wireless microwave power transmission

This paper reports a new circularly polarized (CP) high-gain, high-efficiency rectifying antenna (rectenna) array designed in a coplanar stripline (CPS) circuit. The array can maintain a constant dc output voltage regardless of its broadside orientation. The array is etched on Rogers Duroid 5870 substrate with ε_r=2.33 and 10 mil thickness. High-gain dual rhombic loop antennas and a reflecting plane are used in order to reduce the total number of rectenna elements necessary to cover a fixed area. Each antenna has a CP antenna gain of 11 dB and a better than 1 dB axial ratio fractional bandwidth of 4.7%. The single element rectenna achieves 81% RF-to-dc coversion efficiency at 5.71 GHz and uses a CPS band-reject filter (BRF) to suppress the reradiated harmonics by more than 19 dB. At 5.61 GHz, using an array loading of 150 Ω, a 3 × 3 rectenna array produces 0.86 W of dc output power with an RF-to-dc conversion efficiency of 78% and an axial ratio of 0.25 dB for an incident CP power density of 7.6 mW/cm².