Basic Evaluation of Service Link Antenna for Footprint Fixation in HAPS System

High altitude platform station (HAPS) has attracted significant attention as a new communication platform for disaster countermeasures because it can cover an ultra-wide area at once as well as enable direct communication with terrestrial mobile terminals. In the HAPS system, it is necessary to form multiple cells to accommodate high communication traffic at service area. For a multi-cell configuration, HAPS has a problem that the service area (footprint) projected on the ground is displaced as the platform moves, which results in frequent handovers and degradation of the communication quality. If the coverage area is more than a 50 km radius, it is difficult for the conventional planar array antennas to overcome this problem. To address this issue, we proposed a footprint fixation control method using a cylindrical array antenna. Because the antenna consists of a circular array in the horizontal plane and a linear array in the vertical plane, it can three-dimensionally control the beam; hence, it can easily compensate for footprint displacement even in the coverage area of 100 km radius. In this paper, we report on a prototype development of service link antenna system based on the proposed method and show that the proposed footprint fixation control can be achieved using real equipment from the measurement results of the beam pattern and the verification of dynamic beam steering control.