Determining angle of arrival of radio frequency fields using subwavelength, amplitude-only measurements of standing waves in a Rydberg atom sensor

Deep subwavelength RF imaging with atomic Rydberg sensors has overcome fundamental limitations of traditional
antennas and enabled ultra-wideband detection of omni-directional time varying fields all in a compact
form factor. However, in most applications, Rydberg sensors require the use of a secondary strong RF reference
field to serve as a phase reference. Here, we demonstrate a new type of Rydberg sensor for Angle-of-Arrival
(AoA) sensing which utilizes subwavelength imaging of standing wave fields. By placing a metallic plate within
the Rydberg cell, we can determine the AoA independent of the strength of incoming RF field and without requiring
a secondary strong RF phase reference field. We perform precision AoA measurements with a robotic
antenna positioning system for 4.2, 5.0, and 5.7 GHz signals and demonstrate a 1.7◦ polar angular resolution
from 0◦ to 60◦ AoA and 4.1◦ over all possible angles.