Acquisition system employing circular array

Claim 1

A direction-finding antenna system for determining the signal direction from which signals from a signal source are received, the system comprising: A. first and second concentric circular arrays, each array having N equally spaced antenna elements, where N is an even number greater than two, the first and second arrays being angularly offset by 180°/N; B. a processing circuit, connected to receive the signals from each of the antenna elements of the first and second arrays, for generating an ensemble of composite n-pole signals, n=2, . . . N2, N, by: (i) generating a first N-pole signal by adding the signals from alternate elements of the first array and subtracting the signals from the remainder of the elements of the first array; (ii) generating a second N-pole signal by adding signals from alternate elements of the second array and subtracting the signals from the remainder of the elements of the second array; (iii) shifting the second N-pole signal in phase by 90° and adding it to the first N-pole signal to generate a composite N-pole signal, in response to a single plane-wave signal with a wavelength substantially greater than twice the spacing between the elements, whose phase angle with respect to the phase center of the array is N/2 times the bearing angle of the plane-wave signal; and (iv) combining signals from the antenna elements to generate, in response to a single plane-wave signal with a wavelength substantially greater than twice the spacing between the elements, composite n-pole signals, n=2, . . . , N-2, N the phase angles of the composite n-pole signals being n/2 times the bearing angle of the plane-wave signal, whereby the ensemble of composite n-pole signals, in response to a single plane-wave signal with a wavelength substantially greater than twice the spacing between the elements, has a spatial frequency proportional to the bearing angle of the plane wave; and C. a spatial-Fourier-transform device, connected to receive the ensemble of composite n-pole signals and having a plurality of output terminals, for providing at its output ports a spatial Fourier transform of the ensemble of composite N-pole signals, thereby indicating the bearing angles of incoming plane waves by the positions of maxima in the spatial Fourier transform.

Claim 5

A method of determining the bearing angle of a plane-wave signal received by a circular array of 2N equally spaced antenna elements whose spacing is substantially less than a quarter wavelength of the plane-wave signal, where N is an even number greater than 2, the array thereby including first and second concentric circular subarrays angularly offset from each other by 180°/N, each subarray having N equally spaced antenna elements, the method comprising the steps of: A. generating an ensemble of composite n-pole signals, n=2, . . . , N, by: (i) generating a first N-pole signal by adding the signals from alternate elements of the first subarray and subtracting the signals from the remainder of the elements of the first subarray; (ii) generating a second N-pole signal by adding signals from alternate elements of the second subarray and subtracting the signals from the remainder of the elements of the second subarray; (iii) shifting the second N-pole signal in phase by 90° and adding it to the first N-pole signal to generate a composite N-pole signal, in response to the plane-wave signal, whose phase angle with respect to the phase center of the array is N/2 times the bearing angle of the plane-wave signal; and (iv) combining signals from the antenna elements to generate, in response to the plane-wave signal, composite n-pole signals, n=2, . . . , N-2, N the phase angles of the composite n-pole signals being n/2 times the bearing angle of the plane-wave signal, whereby the ensemble of composite n-pole signals, in response to a single plane-wave signal with a wavelength substantially greater than twice the spacing between the elements, has a spatial frequency proportional to the bearing angle of the plane wave; and B. performing a spatial Fourier transformation on the ensemble of composite N-pole signals, thereby indicating the bearing angles of incoming plane waves by the positions of maxima in the resulting spatial Fourier transform.

Claim 6

A method of determining the bearing angle of a plane-wave signal received by a circular array of 2N equally spaced antenna elements whose spacing is substantially less than a quarter wavelength of the plane-wave signal, where N is an even number greater than 2, the array thereby including first and second concentric circular subarrays angularly offset from each other by 180°/N, each subarray having N equally spaced antenna elements, the method comprising the steps of: A. generating an ensemble of composite n-pole signals, n=2, . . . , N, by: (i) generating a first N-pole signal by adding the signals from alternate elements of the first subarray and subtracting the signals from the remainder of the elements of the first subarray; (ii) generating a second N-pole signal by adding signals from alternate elements of the second subarray and subtracting the signals from the remainder of the elements of the second subarray; (iii) shifting the second N-pole signal in phase by 90° and adding it to the first N-pole signal to generate a composite N-pole signal, in response to the plane-wave signal, whose phase angle with respect to the phase center of the array is N/2 times the bearing angle of the plane-wave signal; and (iv) combining signals from the antenna elements to generate, in response to the plane-wave signal, composite n-pole signals, n=2, . . . , N-2, N the phase angles of the composite n-pole signals being n/2 times the bearing angle of the plane-wave signal, whereby the ensemble of composite n-pole signals, in response to a single plane-wave signal with a wavelength substantially greater than twice the spacing between the elements, has a spatial frequency proportional to the bearing angle of the plane wave; and B. performing a spatial Fourier transformation on the ensemble of composite N-pole signals, thereby indicating the bearing angles of incoming plane waves by the positions of maxima in the resulting spatial Fourier transform.