Impacts of Wall–Target Interaction on Matched Illumination Waveforms for TWRI

The impacts of wall–target interaction on matched illumination waveforms for through-the-wall radar imaging are examined via finite-difference time-domain simulation. Returns from various wall–target scenarios are considered as a function of the target-to-wall separation in order to examine the effectiveness of the so-called primary-wave target response in the matched illumination implementation. The primary-wave target response is shown to effectively maximize the signal-to-interference-and-noise ratio (SINR) in through-wall radar applications where the wall–target interaction is minor, and the primary-wave response closely resembles the full-wave target response, which contains all wall–target interactions. The ability of the primary-wave target response to maximize the SINR can be degraded by relatively minor errors in the wall–target transfer function caused by the incomplete wall–target physics inherent to the scheme. In such cases, the resulting matched illumination waveform spectrum is generally characterized by narrowband energy concentrated at suboptimal frequencies.

I. Introduction

Surveillance and reconnaissance of targets is vitally important to both military and civil applications. A particularly challenging problem is encountered when the target is within an enclosed structure such as a building. For this problem, radar systems are employed, which attempt to image the scene behind the wall. However, this is a challenging problem due to the attenuation and dispersive effects of the wall. As the transmission pulse propagates through the wall, the target return signature is obscured. In addition, as with any radar problem, it is desirable to enhance our return signal by mitigating noise and clutter. Recently, matched illumination waveform design has been used by researchers to mitigate clutter and noise in radar systems and has recently been applied to through-the-wall radar imaging (TWRI) [1]– [6]. Deriving an optimal transmission pulse that accounts for the wall while enhancing the signal-to-interference-and-noise ratio (SINR) is needed for more successful target classification and discrimination.