Low-Cost Conformal Transmit-Reflect-Array Antenna for Unmanned Aerial Vehicle Relay Communications

An ultrathin conformal transmit-reflect-array antenna (TRA) featuring an aperture thickness of $0.047\lambda _{0}$ ( $\lambda _{0}$ denotes the free-space wavelength at 28 GHz) and a single-layer substrate structure is presented. The proposed transmit-reflect (TR) aperture consists of a transmission Huygens’ element (TE) and a reflection element (RE) arranged in an alternating configuration, both of which are ultrathin and miniaturized. The TE achieves tri-mode degeneracy by employing two distinct degeneracy approaches, aiming to enable broadband operation in an ultrathin miniaturized state. The RE is derived from a modified configuration of the TE. Furthermore, we introduce a straightforward method for calculating the conformal TR aperture compensation phase, applicable to concave cylindrical, planar, and convex cylindrical geometries. This phase calculation method is based on the geometrical optics theory, decomposing the compensated phase of a cylindrical aperture into a linear superposition of multiple virtual steps. Moreover, this approach avoids complex derivations involving 3-D surfaces and vector inner products by focusing solely on 2-D planar triangulations. Finally, based on the proposed elements and phase compensation equations, a conformal TRA prototype is designed and the effect of alternating element arrangement on the aperture performance is analyzed. The ultrathin and miniaturized design of the TE and RE effectively mitigates errors arising from aperture bending and periodic sparse arrangement, resulting in the conformal TRA prototype achieving aperture efficiencies exceeding 35%. The proposed conformal TRA possesses the advantages of a lightweight, cost-effective, and simple structure to cater to unmanned aerial vehicle (UAV) relay communication requirements.