DOAEstimation Based on Equivalent Harmonic for Space-Time Coding Metasurface

To address the high hardware complexity of traditional DOA estimation systems and the performance degradation caused by harmonic aliasing in wideband scenarios for existing space-time coding metasurface methods, this paper proposes a wideband direction finding method based on equivalent harmonics. The proposed method employs a 1-bit transmissive space-time coding metasurface as a single-channel receiving aperture to perform periodic phase modulation on wideband LFM signals. By applying matched filtering to achieve pulse compression, the wideband energy is focused into a narrow pulse sequence in the time domain. Equivalent harmonic coefficients are extracted from the compressed pulses, and the mapping relationship between these coefficients and incident angles is established, extending frequency-domain harmonic analysis to the pulse compression domain. This effectively overcomes the constraint of spectral aliasing on harmonic extraction for wideband signals. The conditions for time-domain equivalent harmonic non-aliasing and the applicable bandwidth bounds are theoretically derived. Simulation results demonstrate that the proposed algorithm achieves higher estimation accuracy compared to sparse reconstruction-based algorithms in low signal-to-noise ratio scenarios.