Three-Dimensional Millimeter-Wave Imaging Using Active Incoherent Fourier Processing and Pulse Compression

We present a novel three-dimensional (3D) imaging approach that combines two-dimensional spatial Fourier-domain imaging techniques with traditional radar pulse compression to recover both cross-range and down-range scene information. The imaging system employs four transmitters, three of which emit spatially and temporally incoherent noise signals, while the fourth transmits a known linear frequency modulated (LFM) pulsed signal. The spatial incoherence of the noise signals enables sampling of the 2D spatial Fourier spectrum of the scene from which two-dimensional cross-range (azimuth and elevation) images can be formed via interferometric processing. Simultaneously, the LFM signal enables high-resolution downrange imaging through matched filtering. The received signals consist of a superposition of the noise sources and the known pulse allowing for joint recovery of all three dimensions. We describe the system architecture and waveform design, and demonstrate the imaging technique using both simulations with a linear array and experimental data from a 38 GHz active incoherent millimeter-wave imaging system with 23-element randomized array. Results show the reconstruction of targets in three dimensions.

Additive Frequency Diverse Active Incoherent Millimeter-Wave Imaging

We present an approach for improving spatial frequency sampling in active incoherent millimeter-wave (AIM) imaging systems using frequency diversity. AIM imaging relies on active transmission of spatio-temporally incoherent signals to illuminate a scene, from which interferometric Fourier-domain imaging can be implemented using a sparse receiving antenna array. One of the benefits of Fourier domain imaging is the sparsity of the receiving array, which can form images with equivalent resolution to traditional filled beamsteering arrays, but with a small fraction of the elements. The hardware reduction afforded by the sparse array often leads to an undersampled Fourier space, where even though image formation is possible, the image reconstruction may be degraded when viewing complex objects. To address this challenge without requiring additional receiver channels, we explore the use of frequency diversity in the illuminating and receiving systems. Fourier domain spatial frequency samples are determined by the electrical spacing and rotation of the receiving elements, thus by changing the frequency the sampled spatial frequencies also change. We implement an additive technique where the spatial frequency samples are summed prior to Fourier transform image formation. Importantly, because the system is active, a consistent signal-to-noise ratio is maintained across all frequencies, which may not be possible in traditional passive Fourier-domain imagers.