Development of 38GHz-band wireless communication system using high altitude platform station (HAPS) for 5G network--study on array feeder with lens antenna in ground stations--

Abstract

HAPS (High-Altitude Platform Station) is expected to extend the communication coverage in the beyond 5G era. This paper treats a HAPS backhaul system using 38GHz band. HAPS moves around at stratosphere of about 20km altitude and tries to make beams toward fixed locations on the earth by beamforming. An antenna system on ground stations needs to capture and track HAPS direction with aperture antenna, feeder part and capturing/tracking part. We adopt a method to combine lens antenna and array feeder with mechanically driven gimbal that controls the whole system. Array feeder executes precise tracking within +/-10 degrees of HAPS moving from the antenna radiated direction while mechanically driven gimbal executes tracking over +/-10 degrees. To enhance aperture efficiency and suppress radiation to outside of the lens, this paper proposes wavefront shaping by phased array feeder. Computer simulation shows that our proposed wavefront shaping can enhance antenna gain through aperture efficiency enhancement. Thanks to high and flat gain within the lens radius, it can suppress unnecessary radiation to outside of the lens, and it can widen beam control region with small array feeder.