Radar Imaging Using a Wideband Adaptive Array

Mark Curry and Yasuo Kuga
Department of Electrical Engineering
University of Washington, Box 352500
Seattle, WA 98195-2500
Email:  curryma@gte.net


Abstract The focus of this work is to investigate the application of wideband adaptive array processing techniques to an experimental imaging system. In particular we are interested in joint range-angle estimation with angular resolution improvement for small, relative to l, array antennas. Simulations and experimental results indicate that this approach shows promise for imaging and multiple target location applications.

This approach uses a standard Fourier based approach for range information and uses wideband, adaptive beamforming for the azimuth dimension. Range resolution is achieved by sequentially emitting a set of CW signals spanning a wide bandwidth. Snapshots from the receive array are then processed by a spatial resampling method to align each target’s angle of arrival, while preserving downrange phase information. For each of M transmit frequencies that are generated to achieve the desired range resolution, L closely spaced frequencies are generated to create multiple independent sets of data for covariance matrix estimation. These L frequencies result in a synthetic Doppler shift, which is applied to the target scene. Each independent data set is range compressed using an FFT. The covariance matrices are computed at each range bin from the data sets. A minimum variance angular spectrum is then computed for each range bin, yielding a range-angle plot of backscattered energy. Simulation and experimental results are used to illustrate the performance. Our prototype is a 4-element vertical dipole array for receive and a horn for the transmitter. Bandwidth is 800 MHz to 1200 MHz. The experimental system was used to locate multiple objects in a 10m by 10m area and was subjected to clutter energy from the test chamber itself. A 12-element system is currently under construction for continued research.

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