Structured Radio Waves for Radar Imaging

This study proposes a novel radar imaging approach utilizing structured radio waves, which are electromagnetic waves engineered with spatiotemporal control over multiple degrees of freedom, including orbital angular momentum (OAM). A pulse radar system is formulated based on the simultaneous superposition of multiple OAM modes and partial phase-front analysis of the scattered signals. The method enables the estimation of target distance, azimuth angle, and scattering characteristics, with potential extension to target height estimation. Consequently, the proposed approach may hold promises for addressing the issue of foreshortening commonly encountered in conventional radar imaging. To validate the structured radio waves generation approach, we exploited the analogy between electromagnetic and acoustic phenomena. An 8-channel circular loudspeaker array with a radius of 18.5 cm was constructed, confirming the generation of structured waves via superposed ±1 OAM modes at a carrier frequency of 587 Hz – corresponding to the 2 GHz band via scale conversion. We then demonstrated via numerical simulations that the proposed 10 GHz radar at an altitude of 500 km can reconstruct the 3D positions and radar cross sections of three-point scatterers on the ground with an error of approximately 1 %. These results highlight the feasibility of applying structured radio waves to high-resolution radar imaging, contributing to the advancement of next generation sensing technologies.