Three dimensional RF tomography using sparse waveforms

Image quality in tomographic imaging is improved with the bandwidth of the probing waveform. As bandwidth is increased the spatial extent of the point spread function is increasingly reduced, contributing to improved contrast. This mitigates the influence of bright scatterers in the scene, improving the contrast of the image. Additionally, symmetric scatterers (spheres, cylinders, etc) are more accurately reconstructed. Spectrum availability, particularly at UHF and below, where improved penetration of obscuring media such as foliage is realized, inhibits the use of large instantaneous bandwidth waveforms. Tomographic apertures using narrowband waveforms exhibit sub-wavelength resolution but have more modest sidelobes. Sparse waveforms are considered to reduce spectral occupancy while maintaining point spread function sidelobes and resolution. This paper investigates the adaptation of several waveform-trajectory concepts from magnetic resonance imaging to monostatic, tomographic imaging. Image properties of angle-frequency trajectories termed “rosette” and “spiral” as well as a random frequency waveform are evaluated (resolution, peak and average sidelobe levels) against a pulsed waveform of the same total bandwidth.