Estimating angle of arrival with non-uniformly spaced array

The present direction-finding equipment has insufficient accuracy and resolution, so that accurate evaluation of the direction of arrival and the position cannot be carried out. Although each radar signal has a narrow bandwidth, the entire bandwidth for various radars used exceeds four octaves. In order to search all of these, equipment for each bandwidth is used at present so that the entire frequency range is covered. However, it is more effective from the standpoint of equipment size and cost to cover the entire spectrum with a single kind of equipment. It is desirable to realize high-accuracy high-resolution direction finding over a broad bandwidth. In realization, broadband antennas are used, and high-gain antennas are also needed in a low-SIN environment. Since the dimensions of high-gain and broadband antennas are large, an array configuration with a half-wave spacing may not physically be possible. Thus, the array spacing becomes more than a half-wavelength. If the range of direction estimation is -90 to +90 degrees, the phase difference exceeds 360 degrees so that ambiguity occurs. As a method to resolve this ambiguity problem, a nonuniformly spaced array is effective. In this paper, the array conditions for a nonuniformly spaced array are determined in the case of one arriving wave. Next, the case of several arriving waves is discussed and the array conditions for several arriving waves are derived. (C) 2001 Scripta Technica.