Near field imaging for conducting objects

Microwave images of conducting objects obtained from microwave diversity imaging have been interpreted and predicted. The distance between the antennas and the object is assumed in the far-field region, and the equiphase surface is therefore a plane. When the distance between the object and the antennas becomes much shorter than the distance required in the far-field condition, the equiphase surface can no longer be assumed to be a plane. The image might be blurred or distorted if commonly used reconstruction algorithms are applied. Since the equiphase surface is spherical in general, it is reasonable to reconstruct the image through a generalized spherical back-projection method. The authors describe this method and employ it to reconstruct the near-field images of conducting objects. Numerical (6 to 16 GHz) and experimental examples are given.<>