Low-Profile Dual-Band Shared-Aperture Composite Antenna Array Consisting of Ka-Band Reflectarray and X-Band Phased Array for Satellite Communications

This communication proposes a low-profile dual-band shared-aperture composite antenna array with Ka-band reflectarray (RA) and X-band phased array (PA). The minimal unit of the array consists of three concentric rings. As an RA unit, the reflected phase can be controlled by varying the size of the inner two rings. The outermost ring remains constant, and each minimal $4\times 4$ units can serve as a PA unit by employing a slot-coupled feed structure. By this mean, the radiation structures of RA and PA can be constructed within a single layer of substrate. To validate this concept, an antenna prototype is designed, fabricated, and measured. The profile of the proposed antenna is $0.067~\lambda _{0}$ at 9 GHz. The measured results show that the RA has a peak gain of 31.3 dBi at 28 GHz, with a corresponding aperture efficiency of 52.5%, and a −3 dB relative gain bandwidth of 18% (24.8 to 29.7 GHz). The PA achieves a gain of 20.87 dBi (9 GHz), and the relative bandwidth is 16.35% (8.42 to 9.92 GHz) when scanned in the boresight direction. The gain loss during the scan at 45° on the E/H planes is 2.0 and 1.72 dB, respectively.