Wideband Circularly Polarized Transmitarray Antenna Based on Partially Dielectric-Loaded Parallel-Plate Waveguide for UAV Satellite Communications

This paper presents a wideband circularly polarized (CP) transmitarray antenna (TA) for unmanned aerial vehicle (UAV) satellite communications. In the unit cell (UC) design, this antenna adopts a partially dielectric-loaded parallel-plate waveguide (PPW) structure. Two propagating modes, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\rm {TEM}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\rm {TE_{1}}$</tex-math></inline-formula>, in such a UC are excited to form the two orthogonal components required by CP radiation, while, the heights of the dielectric and PPW are varied to realize 360<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> continuous phase shift and 90<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> differential phase between the two components. Based on this UC, a transmitting surface (TS) with 3-bit phase quantization is then proposed. Owing to the wide passband and low dispersion characteristics of the UC, the proposed TS exhibits wideband property. Meanwhile, the PPW structure is possible to handle higher power than those conventional designs, compensating for the atmospheric attenuation in UAV-satellite communications. To match with the TS in terms of bandwidth and realize a compact configuration, a planar 2×2 slot-coupled patch array is proposed as the feeding source. It adopts differential feeding network and symmetric structure to attain a stable phase center, and demonstrates a comparable aperture efficiency to that of a standard 10-dBi horn used case. To validate the design idea, a prototype with a 9×9 TS is fabricated and measured. The experimental results show that the proposed antenna achieves a wide 3-dB axial ratio bandwidth (ARBW) of 31<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> (8.5-11.6GHz) and the 3-dB gain bandwidth is 34.1<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> (8.5-12.0GHz).