Spatial coding with curved wavefronts

Curved wavefronts of unfocused beams can be viewed as spatial codes that can be decoded to produce high quality images. The decoding process can be performed by spatial matched or Wiener filtering methods that are a generalization of synthetic receive processing for large apertures rather than small elements. Advantages of this technique over dynamic receive processing include potentially greater echo signal-to-noise ratio and improved spatial resolution. An analytical treatment of weakly focused Gaussian apodized beams shows that the spatial bandwidth is approximately constant with depth. Experiments and simulations illustrate the efficacy of spatial coding.