THREE-DIMENSIONAL IMAGING FROM COMPACT-RANGE DATA

摘要

The collection of radar scattering data necessary for imaging targets with three-dimensional resolution requires frequency diversity, combined with angular diversity over two orthogonal axes fixed to the target Although the necessary data can easily be collected using modern instrumentation systems when the target is outfitted with an embedded two-axis rotator, some applications preclude the intrusion of the rotator. This paper describes an alternative method for obtaining the required data which uses conventional target rotation in the azimuth plane, combined with a linear displacement of the compact range feed along the vertical axis of the collimator's focal plane. Frequency diversity is provided by a stepped-frequency radar and angular diversities in the horizontal and vertical directions are provided by the target rotation and vertical feed displacement, respectively. The data-collection scheme samples a wedge-shaped volume of the target spatial spectrum (k-space) with radial and angular extents determined by the bandwidth and target rotation relative to the radar axis. A three-dimensional image is formed by processing a three-dimensional array of data, typically consisting of 128×128×128 data samples.rnThe paper describes the experimental set-up used to collect Ku-band data and presents two- and three-dimensional images obtained from the data. Considerations of the following issues are addressed in the paper.rn1. Aberrations resulting from displacing the feed from the collimator focal point.rn2. Control of the linear feed displacement, target rotation, and radar operation to automate the data collection.rn3. Methods for calibrating and aligning the data.rn4. Signal processing methods which combine wideband, ISAR and spotlight SAR processing for three-dimensional applications.rn5. Clutter suppression using zero-Doppler filtering.