Fully Digital Phased Array Harmonic Radar for Detecting Concealed Electronic Devices

This paper presents the design and performance evaluation of a fully integrated digital phased array-based nonlinear radar system. The proposed system employs a bi-static structure, where the transmitter and receiver are physically separated. The transmitter operates at 3-3.2 GHz, while the receiver is designed to capture the second harmonic responses at 6-6.4 GHz. The system consists of 64 channels for both transmission and reception, enabling electronic beam steering through phase shift control. To enhance the beamforming accuracy, a novel transmitter calibration method utilizing an oscilloscope instead of a network analyzer was implemented. The method simplifies synchronization requirements while maintaining precise phase alignment. Performance evaluation of the radar system was conducted through experimental validation in both free-space and concealed conditions, using arbitrary commercial electronic devices as targets. The experimental validation results demonstrated an average range error of 32.3 cm with a range resolution of 37.5 cm. Additionally, multi-target detection was performed using beamforming techniques. In free-space conditions, the radar achieved accurate target localization with angular errors below 1 degrees. In concealed conditions, nonlinear reflections introduced minor localization errors due to clutter. Despite these challenges, the system successfully detected multiple targets by employing a clustering method. To the best of our knowledge, the system presented here is the first demonstration of a fully integrated digital phased array-based nonlinear radar in the open literature.