Low Probability of Intercept DoA Estimation Using Space-Time-Modulated Metasurfaces

This article presents a method that integrates direction-of-arrival (DoA) estimation with low probability of intercept (LPI) based on a space-time-modulated metasurface (STM-MTS). The proposed method operates by modulating an unknown incident signal with a composite coding strategy that combines a pseudorandom sequence with a designed STM matrix. This modulation spreads the energy of the scattered wave, significantly reducing its power spectral density. A cooperative receiver, possessing the corresponding pseudorandom key, can decode the scattered signal in the frequency domain to recover the harmonic distribution for DoA estimation using the multiple signal classification (MUSIC) algorithm. In contrast, an uncooperative receiver cannot perform signal despreading due to the unknown sequence, resulting in effective LPI performance. Both simulated and measured results demonstrated the effectiveness of the method, showing a reduction in the amplitude of the spread-spectrum (SS) signal by 80% and DoA estimation errors less than 2° within an incident angle range of [−60°, +60°].