# A Dual-Polarized Omnidirectional Rectenna Array for RF Energy Harvesting Harvesting
## 4 Discussion of the Proposed Rectenna Array  
The schematic of the proposed rectenna array is shown in Figure 14. The vertically polarized antenna subarray and the horizontally polarized antenna subarray are connected to two Wilkinson power dividers. Then, the RF powers of two different polarizations are fed equally into the two identical rectifiers through a 3-dB hybrid coupler, which finally converge at a resistive load to form the rectenna array. Both rectifiers are the same as the one in Figure 6. The resistance of the resistive load is 950 \(\Omega\), which is half the one of a single rectifier. Following the topology in Figure 14, the proposed rectenna array was fabricated. The photograph of the fabricated rectenna array is provided in Figure 15.  
The performances of the proposed rectenna array are simulated and measured under the illumination of EM waves with different incident directions and different polarizations. Figure 16a shows the simulation environment of the rectenna array for harvesting omnidirectional RF energy with different polarizations. The transmitting antenna starts from the horizontal azimuth angle of \(0^{\circ}\) and turns \(15^{\circ}\) counterclockwise each time. For the polarization, three cases of horizontal polarization, vertical polarization, and superposition of both horizontal and vertical polarizations are investigated. During the rotation of the transmitting antenna, the number of antenna elements that can receive RF power at each angle is almost always fixed due to the structural symmetry of the rectenna array. In addition, the whole process of omnidirectional RF harvesting can be simplified and analyzed by the cases of incident azimuth angles from \(0^{\circ}\) and \(45^{\circ}\). Using the software Ansys HFSS, power reception under different scenarios was simulated, and the transmission coefficients obtained from the simulation can be used to calculate the power ratio received by each port of the dual-polarized omnidirectional antenna array under different conditions. Then the software ADS is used to co-simulate the RF power-combining network and rectifier array. By adjusting the power ratio of the input source, the PCE in each corresponding state can be obtained. Figure 14: Schematic of the proposed rectenna array. Figure 15: Photograph of the fabricated rectenna array. Figure 16b illustrates the test environment of the proposed rectenna array for RF energy harvesting. During the measurement, an RF signal generator is connected to a power amplifier, and the amplified RF power is transmitted through double-ridge horn antenna points to the rectenna array to be tested. The gain of the horn used in the measurement is 14.5 dBi at 2.45 GHz. The distance between the transmitting horn antenna and the rectenna array is set to 2 m, which satisfies the far-field condition. A standard gain antenna is first placed at the receiving position, and the power density of the incident EM wave at the receiving position can be determined by measuring the received power using a spectrum analyzer. Then the rectenna array is placed on the rotary table at the receiving position. The angle of incidence can be adjusted by controlling the rotary table, and the polarization direction angles of the incident wave can be changed by adjusting the double-ridge horn antenna. A digital multimeter is used to measure the voltage on the load of the rectenna array so that the output DC power can be calculated. During the measurement, when the output power of the amplifier is 32.5 dBm, the corresponding power density at the receiving position is 100 \(\mu\)W/cm\({}^{2}\). When the output power of the amplifier is increased to 35.5 dBm, the corresponding power density at the receiving position is 200 \(\mu\)W/cm\({}^{2}\). The horizontally polarized reception, vertically polarized reception, and both horizontally and vertically polarized reception correspond to the cases when the polarization direction angle is at 0\({}^{\circ}\), 90\({}^{\circ}\), and 45\({}^{\circ}\) with the horizontal plane, respectively.