Design and Measurement of 3D Flexible Antenna Diversity for Ambient RF Energy Scavenging in Indoor Scenarios

Ambient radiofrequency (RF) energy scavenging has been recently addressed with a wide range of studies to provide alternative powering for low-power applications. However, due to the low power level of the ambient electromagnetic field, the efficiency of the latter systems is still below expectations. Multipath in the environment may be considered and antenna diversity is then a solution for quasi-omnidirectional RF reception to reach a higher probability of receiving energy in a realistic situation. A 3D flexible antenna diversity, which can be integrated into the rectangular packaging, is proposed in order to take advantage of system packaging form. The angle and polarization diversity antenna was designed on flexible substrate in order to achieve the flexibility and low-cost. This design overcomes the low performance of the substrate while maintaining a compact, high isolation, and good radiation efficiency of the antenna. An indoor experimental setup was carried out to compare different rectenna configurations. The measurement results validate the principle and demonstrate the performance of the 3D flexible diversity system. The probability measurements were carried out under precise conditions in indoor scenarios and the results in comparison with statistic models confirmed the performance of the system in such low power conditions.