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A Novel Reduced-Complexity Low-Profile mm-Wave Beam Steerable Risley Prism Antenna

Low-profile mechanical beam steering concepts such as the Risley prism antenna (RPA) have become competitive candidates for next-generation millimeter-wave applications where low-cost, high-gain, and wide-angle beam steering are critical. In this paper, we present a novel beam steerable RPA at 19 GHz that advances traditional RPA configuration and further reduces the system complexity and profile. It consists of a circularly-polarized (CP) gradient-phase feed array (GPFA) and a lightweight 3D-printed CP gradient-phase transmitarray (GPTA). A novel hybrid-phasing technique is implemented to realize the GPFA. It combines short delay lines and element rotations to exclusively perturb the aperture phase of the cross-polarization component and significantly improves the axial ratio performance of the RPA. The GPTA is 3D printed using the charge-programmed multi-material process and achieved 50% weight reduction over conventional ones. The simulated RPA achieves LHCP beam-scan from broadside to 56◦ in elevation. With a 9.2 cm diameter aperture, the RPA demonstrates a broadside directivity of 22.7 dB at 19 GHz (55.6% aperture efficiency). The 3-dB directivity bandwidth for both the broadside and maximally scanned beam is greater than 9%, within which range the 3-dB axial ratio bandwidth is 6.8%.