Low-profile Dual-band Shared-aperture Composite Antenna Array consisting of Ka-band Reflectarray and X-band Phased Array for Satellite Communication

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 a 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 4x4 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 λ 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 degrees on the E/H planes is 2.0 dB and 1.72 dB, respectively.