Superresolution Source Location with Planar Arrays

■ The challenge of precision source location with a radio-frequency antenna array has existed from the beginnings of radiometry and has continued in modern applications with planar antenna arrays. Early work in this field was limited to estimating single source directions in one dimension with systems like crossed-loop radiometers. Currently, more advanced systems attempt to estimate azimuth and elevation by using two-dimensional arrays. Monopulse techniques have been extended to two-dimensional arrays to provide a computationally efficient method for estimating the azimuth and elevation of a single source from a planar array, but all monopulse techniques fail if there is appreciable interference close to the source. In this situation, adaptive array (superresolution) processing techniques are needed for direction estimation. This article discusses the results of a study on the proper way to design an adaptive planar array with a constrained antenna aperture. We consider the segmentation of the antenna aperture, the polarization of the antenna segments, and the algorithms used to process the signals received from the antenna. In particular, we concentrate on interference that is within one Rayleigh beamwidth of the source. The interference can be highly localized in space, as in a single direct-path interferer, or diffuse in space (possibly due to multipath). We present results of tests conducted with a segmented antenna array, along with simulations and analytical bounds, that guide us in designing a sourcelocation system.