5.8-GHz circularly polarized dual-rhombic-loop traveling-wave rectifying antenna for low power-density wireless power transmission applications

This paper reports a right-hand circularly polarized (RHCP) high-efficiency traveling-wave rectifying antenna (rectenna) designed in a coplanar stripline (CPS) circuit that is etched on a Rogers Duroid 5870 substrate with epsilon(r) = 2.2 and 20-mil thickness. A 4 x 1 traveling-wave array of RHCP high-gain dual-rhombic-loop antennas (DRLAs) and a reflecting plane are used to provide highly efficient RF-to-dc conversion in the presence of lower power densities regardless of the rectenna's broadside orientation. The DRLA array has a circularly polarized antenna gain of 14.6 dB with a 2: 1 voltage standing-wave ratio bandwidth of 17% and a better than 3-dB axial ratio fractional bandwidth of 7% centered about 5.8 GHz. The rectenna achieves 82% RF-to-dc conversion efficiency at 5.8 GHz and uses a low-profile CPS band-reject filter to suppress the re-radiated second harmonic by over 14 dB. The rectenna operating at low power density should have many applications when the transmitting power is low and/or the transmission distance is long.