FFT-based aperture monitor for scanning phased arrays
First Claim
1. The method of monitoring the performance of a scanning phased array antenna to identify faults in said antenna, said antenna having a plurality of radiating elements and plurality of phase shifters associated with said elements to control the direction of a beam of energy transmitted by said radiating elements, said antenna scanning between the maximum angles of +θ
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o and -θ
o, θ
being the angle between the axis of said beam and the normal to the axis of the array of said antenna, comprising;
collecting, from a single detector of signals transmitted by said antenna, at equal increments of arcsin θ
, a plurality of signal samples;
analyzing said collected samples by means of a Fourier transform to provide a sequence of data indicating the amplitude and phase of the signal radiated by each of said antenna radiating elements when the beam of said antenna was directed toward said detector; and
comparing the data of said sequence with known values of the amplitude and phase of the signal radiated by each of the radiating elements of said antenna when said antenna is perfectly functioning and the beam thereof is directed toward said detector.
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Accused Products
Abstract
Method and means for monitoring the performance of a phase array antenna. The antenna comprises an array of individual radiating element seach of which radiates a prescribed proportion of the energy to be transmitted thereby shaping such energy into a beam. Individual phase shifters are associated with each radiating element, the phases of which control the direction of the beam pointing. The method of the invention involves sampling the beam by means including a single receiver located along a fixed radial from the array. The beam scans at a constant rate. The samples are collected at non-uniform intervals of time during a beam scan. The samples are, however, separated by equal increments of arcsine θ, where θ is the pointing angle of the beam. The samples are analyzed by means including a Fourier transform to provide the value of the amplitude and phase of the signal radiated by each of the radiating elements. Comparison of the amplitude and phase values for each radiating element as determined by analysis with design values for each element reveals any element or phase shifter which may be faulty. The method can also be used to calibrate an antenna when it is first put into service.
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Citations
19 Claims
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1. The method of monitoring the performance of a scanning phased array antenna to identify faults in said antenna, said antenna having a plurality of radiating elements and plurality of phase shifters associated with said elements to control the direction of a beam of energy transmitted by said radiating elements, said antenna scanning between the maximum angles of +θ
-
o and -θ
o, θ
being the angle between the axis of said beam and the normal to the axis of the array of said antenna, comprising;
collecting, from a single detector of signals transmitted by said antenna, at equal increments of arcsin θ
, a plurality of signal samples;analyzing said collected samples by means of a Fourier transform to provide a sequence of data indicating the amplitude and phase of the signal radiated by each of said antenna radiating elements when the beam of said antenna was directed toward said detector; and comparing the data of said sequence with known values of the amplitude and phase of the signal radiated by each of the radiating elements of said antenna when said antenna is perfectly functioning and the beam thereof is directed toward said detector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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o and -θ
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10. The method of calibrating a scanning phased array antenna to adjust the performance thereof to conform to design spcifications therefor, said antenna having a plurality of radiating elements and a plurality of phase shifters associated with said elements to control the direction of a beam of energy transmitted by said radiating elements, said beam being a scanning beam which scans between the maximum angles of -θ
-
o and +θ
o, θ
being the angle between the axis of said beam and the normal to the axis of the array of said antenna, comprising;collecting, at equal increments of arcsin θ
, from a single detector of signals transmitted by said antenna, a plurality of signal samples;analyzing said collected samples, by means including a Fourier transform, to provide a sequence of data indicating the amplitude and phase of the signal radiated by each of said antenna radiating elements when said beam of said antenna was directed toward said detector; comparing the amplitude of the signal radiated by each of said radiating elements as given by said sequence of data with design values of amplitude for the signal intended to be radiated by each of the radiating elements when the beam thereof is directed toward said detector; and adjusting the amplitude of the signal radiated by any one of said radiating elements of said antenna to conform to the design value of the amplitude of the signal intended to be radiated by that said one radiating element when the amplitude of the signal radiated by that said one radiating element as given by said sequence of data differs from said design value therefor. - View Dependent Claims (11, 12, 14, 16, 18)
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o and +θ
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13. said antenna radiates energy having a wavelength λ
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said plurality of radiating elements of said antenna comprises a total number N, each of said elements being separated by equal distances d; said beam is a scanning beam which scans at a constant rate equal to θ
s ; andsaid collected samples comprise a sequence of samples taken at times tk, where tk is given by;
##EQU35## where k=0, 1, . . . N-1, andto =time at the start of scan.
- ;
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15. A system for monitoring the performance of a phased array antenna to identify faults in said antenna, said antenna having a plurality of radiating elements and a plurality of phase shifters associated with said elements, a transmitter and feed means for distributing output from said transmitter to said phase shifters and said radiating elements, said phase shifters and said radiating elements cooperating to shape the output received by each from said transmitter into a beam of energy and to control the direction in which said beam is pointed, comprising:
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means for receiving the signal radiated by said antenna to provide a received signal; means for synchronously detecting said received signal to provide a first component thereof which is in phase with said output of said transmitter and a second component thereof which is in quadrature phase with said output of said transmitter; means for amplitude detecting said first component to provide a first analog signal which is proportional to the amplitude of said first component; means for amplitude detecting said second component to provide a second analog signal which is proportional to the amplitude of said second component; a first analog to digital (A/D) converter for converting said first analog signal to a first digital signal; a second analog to digital (A/D) converter for converting said second analog signal to a second digital signal; means for controlling said first and second A/D converters whereby said first and second A/D converters provide discrete digital samples of said first and second analog signals with said digital samples being separated from one another by non-uniform intervals of time, said first and second digital samples forming a sequence of data which is in the form of a complex number; and means for mathematically processing said sequence of data to provide the value of the amplitude and phase of the signal radiated by each of said radiating elements of said antenna when said beam of said antenna is pointed in the direction of said means for receiving. - View Dependent Claims (17, 19)
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Specification