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Abstract

A DF system using a circular array of three to eight antennas, analyses the received signals digitally by first calculating at (8) the Fourier transform of the received signals to obtain frequency information and deriving at (10) from the Fourier transform the relative phases of the received signals at each of a number of spaced sample frequencies. This phase information is then fed to a stage (12) which takes the spatial Fourier series of the phases from which the required bearing information is derived as .pi./2 minus the arctan of the ratio of the real and imaginary parts of the Fourier series taken to suitable moduli. For a four antenna array the diameter of the circular array is constrained to be less than half of the wavelength at the highest frequency of interest. For a three antenna array, the diameter is constrained to be less than one third the wavelength at the highest frequency of interest in order that the analysis should yield accurate and unambiguous bearing outputs.

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First Claim