Measurement of Doppler Frequency Shift and Angle of Arrival With Rydberg Atom-Based Sensors

Doppler frequency shift (DFS) and angle of arrival (AOA) measurements play a crucial role in modern radar, aviation, and satellite communication systems. Rydberg atom-based receivers are renowned for the high sensitivity, wide operating frequency range, and immunity to electromagnetic interference in microwave electric field sensing. In this work, the concept of electromagnetically induced transparency (EIT) with Rydberg atoms, along with heterodyne mixing techniques, is employed to accurately measure both the DFS and AOA of microwave field within a unified experimental system. The proposed scheme utilizes the dual-coupled beams in the Rydberg atom vapor cell to reduce experimental errors and improve the measurement accuracy. The experimental results indicate that within the frequency measurement range from 11 to 18 GHz, the experimental error in measuring the DFS of different Rydberg states is within +/- 0.5 Hz, showcasing the wideband tunability of the system. Moreover, the AOA measurement for the echo signal reveals that the measurement error is less than 0.5 degrees within the range from -30 degrees to 35 degrees. This research shows the first instance of simultaneously measuring DFS and AOA within the same Rydberg atom system. Additionally, by introducing the concept of "relative frequency zero point" in DFS measurement for the first time, the differentiation of the direction of the DFS can be identified. Furthermore, the accuracy of AOA measurement based on Rydberg atoms has been further improved in this research. Overall, this research provides a novel approach for measuring DFS and AOA using Rydberg atomic system.