# Dual-Band RF Wireless Power Transfer System with a Shared-Aperture Dual-Band Tx Array Antenna
## 3 Experimental Results of RF Wireless Power Transmission
### Single-Band RF WPT Experiment
#### 3.1.1 WPT Experiment (1): Varying the Transmission Distance  
First, as shown in Figure 14, the Rx antenna, which is either the 2.4 GHz patch antenna in Figure 2(a) or the 5.8 GHz patch antenna in Figure 2(b), was located in front of the Tx. With a change of the transmission distance between the Tx and Rx from 1 m to 3.92 m, the received power was measured. When RF power of 2.482 GHz was transmitted to the Rx, as shown in Figure 1(a), which is located at the front of the Tx, the results of the measured received power by the Rx antenna according to the distance are shown in Figure 1(a) and Table 2. Here, the power transmitted by each 2.4 GHz radiating element in the Tx array is equal to 25 dBm and the total transmitted power is 40 dBm (=10 W) for 2.482 GHz. The distance of 1-3.92 m at 2.482 GHz is within the Fresnel area (0.85-6.12 m) based on the 2.4 GHz thinned array. To operate beam-forming and beam-focusing, the phases of the excited signal of each radiating element are adjusted by the GUI. According to the experimental results, as the distance was increased, there was no significant difference in the received power by beam-forming (in this case, the excited phase is the in-phase) or beam-focusing (applied excited phase calculated by Equation (3)). However, as the distance between the Tx and the Rx decreased, the received power by beam-focusing was prominently higher than that by beam-forming. In particular, when the beam is focused to a point at a distance of 1 m, the measured received power was approximately 0.7 dBm higher than when beam-forming was applied.  
Figure 14: RF WPT experimental set-up (1): according to the transmission distance.  
Figure 15: Measured and calculated results of the received power according to the transmission distance: (**a**) 2.482 GHz; (**b**) 5.73 GHz.  
When the 5.8 GHz Rx shown in Figure 2b is located at the front of the Tx, Figure 15b and Table 3 present the results of an experiment in which 5.73 GHz wireless power is transmitted to the Rx. The magnitude of the power radiated by each 5.8 GHz radiating element in the Tx array is equal to 25 dBm and the total transmitted power is 40 dBm (=10 W) at 5.73 GHz. The distance of 1-3.92 m at 5.73 GHz is within the Fresnel area (0.57-4.84 m) based on the 5.8 GHz thinned array. In this experiment, when the excited phase for beam-focusing was applied in the Tx array, the received power was measured and found to be higher by approximately 0.25 dBm compared to that when applying the beamforming method, on average. Consequently, the measured results of the received power were in good agreement with the results calculated using Equation (4), indicating that the implemented WPT system was appropriately established and that the WPT experiment was conducted well. According to the measured results of the received power by applying the beam-focusing, the WPT efficiencies at the 2.482 GHz and 5.73 GHz are distributed as 2.985-0.224% and 0.841-0.050%, respectively, when the distance varies from 1 m to 3.92 m. It is believed that a slight measurement arose due to the indoor experimental environment and the inaccuracy of the Rx position.