Near-Field Behaviors of Intelligent Reflecting Surface: Experimental Measurements at 60GHz

In recent years, the increasing demand for communication networks has motivated research on the use of high-frequency bands. However, although the use of high-frequency bands enables high-speed and high-capacity communication, their high directionality makes it difficult for radio waves to penetrate obstacles, limiting the range of communications in an obstructed environment. To address this problem, intelligent reflecting surfaces (IRSs), which reflect radio waves in the desired direction and enable the construction of new communication paths to avoid obstacles, have attracted significant attention. Many existing studies of IRSs have adopted IRS control with beamforming, approximating radio waves as plane waves and considering only the angular component. However, radio waves can be approximated as plane waves only in the far field, distant from the IRS; plain wave approximation is not applicable to the near field, and thus, spherical waves must be assumed. As spherical waves are weakly correlated in the distance direction, we considered beamfocusing taking into account both the angular and distance components for IRS control in near-field communications. Therefore, in this study, we used a prototype IRS to measure the near-field characteristics of the IRS when using beamfocusing, and thereby evaluated its effectiveness.