A Bidirectional 2-D Beam-Scanning Circularly Polarized Array Antenna Based on Risley Prism at the Ka Band

Previously reported Risley Prism array antennas achieve beam scanning only within a single hemisphere, resulting in limited coverage. To overcome this, this letter presents a novel Risley Prism-based array enabling low-loss, bidirectional two-dimensional circularly polarized (CP) beam scanning. By mechanically rotating the upper and lower circularly polarization-sensitive transmission–reflection-integrated metasurfaces (UCTRM and LCTRM), right-handed CP (RHCP) scanning is realized in the upper hemisphere with an elevation range of 0<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>–40<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> and full 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> azimuth. Simultaneously, left-handed CP (LHCP) scanning is achieved in the lower hemisphere with the same range. A prototype was designed, fabricated, and tested. Measurements confirm a peak gain of 22.6 dBic, a maximum aperture efficiency of 18.3%, a 3-dB gain bandwidth over 14.3%, and a 3-dB axial ratio bandwidth exceeding 32.4% in both hemispheres. The proposed design effectively overcomes the coverage limitations of conventional Risley Prism antennas, enabling seamless CP beam scanning in full space and showing strong potential for satellite and wireless backhaul applications.