Analysis of Antenna Radiation Characteristics Using a Hybrid Ray Tracing Algorithm for Indoor WiFi Energy-Harvesting Rectennas

In this paper, the radiation features of indoor WiFi energy-harvesting antennas are analyzed, and the design guidelines that enhance receiving power are proposed. It is acknowledged that an RF energy-harvesting antenna is desired to depict circular polarization (CP) and omnidirectional patterns, as ambient sources are omnipresent; however, the polarization and half-power beamwidth (HPBW) of the antenna are inconclusive in earlier studies. To clarify the requirement of the radiation characteristics for indoor environments, the receiving performance of six antennas with different HPBWs and polarizations is analyzed. The research methodology is a hybrid ray tracing algorithm that integrates image and shootingand-bouncing-ray methods. These antennas are placed at different locations in a room, and the orientations are evenly and uniformly sampled. The receiving performance of each antenna is cast into cumulative density functions, which clarify the antenna that provides the maximum amount of successful receptions at specified energy-harvesting sensitivity. The simulated results are verified by performing the measurement. Surprisingly, the results indicate that CP and omnidirectional patterns cannot offer the most favorable receiving performance. In contrast, linear polarization and narrow HPBWs with high gain are desired in most of the scenarios, even though the directions of signal arrival have been uniformly sampled.