Anti-Interference DoA Estimation for LFM Radar Signals Using Space-Time-Modulated Metasurfaces

In this work, we present an anti-interference direction of arrival (DoA) estimation system based on a space-time-modulated metasurface (STM-MTS). The proposed system, composed by a 1-bit STM-MTS and a single receiving antenna, can accurately estimate DoA of a linearly frequency modulated (LFM) plane wave in the presence of several other LFM interfering wave. The STM-MTS generates a set of scattered harmonics, whose components are related to the space-time modulation scheme of the metasurface and the specific incident angle. However, once the signal bandwidth exceeds the modulation frequency, the aliased spectrum cannot be directly utilized for DoA estimation. To solve the problem, we analytically establish the desired relationship between the spectrum and the pulse compressed time signal by using a matched filter. Furthermore, due to the presence of the interfering signal, we introduce a properly designed separation procedure to extend the anti-interference feature to metasurface-based DoA estimation system, allowing to obtain the intended time-domain LFM signal for which the DoA can be estimated via multiple signal classification (MUSIC) algorithm applied to harmonic component distribution. Both simulated and measured results demonstrate the effectiveness of anti-interference DoA estimation. The absolute errors in the DoA estimation are less than 2° within the incident range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$[-50^{\circ },+50^{\circ }]$ </tex-math></inline-formula>, demonstrating the accuracy of the proposed anti-interference DoA estimation system based on STM-MTSs.