Phase-Corrected Near-Field Microwave Imaging via Inverse Source Reconstruction with Modulated Signals

A team led by Quanfeng Wang has introduced a novel approach to passive radar imaging that leverages everyday Wi-Fi signals instead of dedicated radar transmitters. Their method, detailed in a preprint on arXiv, uses inverse source reconstruction (ISR) to process modulated signals from non-cooperative Wi-Fi sources. The system employs a fixed reference antenna and a planar scanning probe that moves across multiple positions. By normalizing the probe measurements against the reference signal, spatial coherence is achieved, allowing a single-frequency ISR solver to generate 3D images. A key innovation is the phase correction method for combining images from different frequencies coherently, improving resolution. The researchers validated their technique in a typical office room using software-defined radios and narrowband orthogonal frequency-division multiplexing (OFDM) signals at standard Wi-Fi bands. With background subtraction, they successfully imaged a mannequin, demonstrating the system's potential for low-cost, non-intrusive imaging.

The work has significant implications for security, surveillance, and through-wall imaging. Traditional passive radar requires specialized transmitters or relies on high-power broadcast signals. By using ubiquitous Wi-Fi, this method drastically reduces hardware cost and complexity. The phase correction method ensures high-quality multi-frequency image fusion, while the ISR-based approach handles near-field scenarios common in indoor environments. Future developments could enable real-time imaging with portable scanners, making it accessible for search-and-rescue, law enforcement, or even consumer applications like smart home monitoring. The paper also notes that for narrowband signals, an incoherent imaging approach is sufficient under some conditions, simplifying deployment further.