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

TL;DR

This paper introduces a 3D near-field microwave imaging method using inverse source reconstruction with modulated signals, phase correction, and incoherent approaches, validated in an office environment with Wi-Fi signals.

Contribution

It presents a novel ISR-based microwave imaging technique with phase correction for multi-frequency signals, validated through practical experiments.

Findings

Successful imaging of a mannequin in an office room using Wi-Fi signals.

Phase correction improves image coherence across multiple frequencies.

Incoherent imaging suffices for narrowband signals in realistic scenarios.

Abstract

An inverse source reconstruction (ISR) based 3-D near-field (NF) passive radar microwave imaging method utilizing modulated signals is presented. The modulated signals from a non-cooperative transmitter are scattered by the targets of interest and captured by a fixed reference antenna together with an NF scanning probe at different positions. By normalizing with the reference signals, spatial coherence of the NF observations is obtained, and a single-frequency inverse source solver is subsequently utilized for ISR and image generation. A corresponding phase correction method is proposed for the coherent superposition of multi-frequency images and verified through simulations. In addition, it is shown that for realistic narrowband signals, an incoherent imaging approach is sufficient. The presented technical scheme is validated using a planar scanning system in a typical office room, where software-defined radios are employed for the transmitting and receiving of narrowband orthogonal frequency-division multiplexing signals at Wi-Fi operating frequencies. With the aid of background subtraction and reference signals, images of a mannequin placed in the office room are successfully obtained.