Direction finding systems
First Claim
1. A direction finding system responsive to a band of frequencies includingat least three antennas disposed so as to define an array of antennas equally spaced about the periphery of a circle having a diameter less than a proportion of half the wavelength of the highest frequency of said band,a respective wideband receiver connected to each said antenna and adapted to produce a digital output representative of the signal received by said antenna,means for deriving from said digital output a signal in digital form representing the spectrum of said received signal,means for deriving from said signal spectrum of each said received signal the phase (φ
- (m,ω
)) of any signal received by the antennas at each of a plurality of sample frequencies (ω
) relative to a virtual reference, andmeans for calculating for each said sample frequency (ω
) a spatial Fourier series (ρ
(ω
)) of said phases, where ##EQU11## in which M is the number of antennas in said array, and m is an index which takes the values 0 to M-1 to represent each said antenna in turn, and deriving from said spatial Fourier series the bearing of any source transmitting at each said sample frequency.
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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 π/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.
43 Citations
5 Claims
-
1. A direction finding system responsive to a band of frequencies including
at least three antennas disposed so as to define an array of antennas equally spaced about the periphery of a circle having a diameter less than a proportion of half the wavelength of the highest frequency of said band, a respective wideband receiver connected to each said antenna and adapted to produce a digital output representative of the signal received by said antenna, means for deriving from said digital output a signal in digital form representing the spectrum of said received signal, means for deriving from said signal spectrum of each said received signal the phase (φ - (m,ω
)) of any signal received by the antennas at each of a plurality of sample frequencies (ω
) relative to a virtual reference, andmeans for calculating for each said sample frequency (ω
) a spatial Fourier series (ρ
(ω
)) of said phases, where ##EQU11## in which M is the number of antennas in said array, and m is an index which takes the values 0 to M-1 to represent each said antenna in turn, and deriving from said spatial Fourier series the bearing of any source transmitting at each said sample frequency. - View Dependent Claims (2, 3, 4)
- (m,ω
-
5. A method of processing the signals received in a wideband, narrow aperture direction finding system by each antenna of a uniform circular array of antennas, comprising the steps of receiving and digitising the signal received by each antenna,
performing a discrete Fourier Transform on each received signal, taking for each of a plurality of sample frequencies (ω - ) the arctan of the real and imaginary parts of the Fourier transform to provide the relative phase (φ
(m,ω
)) of any signal received by each antenna at each frequency (ω
),taking the spatial Fourier series (ρ
(ω
)) of the relative phases at each sample frequency, where ##EQU12## in which M is the number of antennas in said array, and m is an index which takes the values 0 to M-1 to represent each said antenna in turn, andproducing the bearing of any received signal as π
/2 minus the arctan of the real and imaginary parts taken to a suitable modulus of said spatial Fourier series for each sample frequency.
- ) the arctan of the real and imaginary parts of the Fourier transform to provide the relative phase (φ
Specification