Design Of Circularly Polarized Rectenna For RF Energy Harvesting System

Radio frequency(RF)energy harvesting technology can convert RF energy in free space into DC power,and supply power to some low power and small devices continually.This technology has the advantages of environmental protection,low cost,and can be widely applied in wireless sensor network(WSN),Internet of Things(Io T)and other fields.It is accomplished by rectennas for RF energy harvesting.Aiming at the RF energy with unknown polarization direction in free space,a compact omnidirectional circularly polarized(CP)antenna and a wide-band circularly polarized recttenna are studied and realized in this paper.Firstly,a novel omnidirectional circularly polarized receiving antenna loaded with complementary V-shaped slits is presented.It is etched on a single-layer substrate with a patch and ground plane,which is connecting through vias,forming vertical polarization wave.By arranging the complementary V-shaped slits on two sides,horizontally polarized electric field is generated.As a result,the circular polarization performance can be realized.Meanwhile,by loading complementary V-shaped slits,the redundant arc branches of the antenna are avoided and the presented antenna achieves a compact dimension.The bandwidth of antenna is 5.66-5.84 GHz and the 3 d B axis ratio bandwidth is 10.52%(5.4-6.0 GHz),covering 5.8 GHz ISM band.In addition,the antenna can radiate omnidirectional circularly polarized waves in the range from 0? to 360?,therefore it can be used in RFID,WLAN,mobile communications and other systems.Secondly,a wideband circularly polarized dipole rectenna is designed,which consists of a CP dipole receiving antenna and a rectifier.Firstly,an off-center-fed dipole antenna with wide bandwidth is designed.By employing two pairs of branches with different lengths,a wider bandwidth is obtained.The realized antenna operates in 3.36-5.92 GHz and has a peak gain of 5.86 d Bi at 5.36 GHz.Rectifier applies simple topology structure to achieve high efficiency in wideband frequency(3.3-6.0 GHz),among which the matching network adopts simple T-shaped microstrip.The rectenna is fabricated and tested,resulting that it can output 572 m V when the power is 5 d Bm,and the maximum efficiency is 40.5%.A good agreement is obtained between the simulated and measured results.