Method and apparatus for self-calibration and phasing of array antenna
First Claim
1. In a phased array antenna incorporating a separate reciprocal phase shifter in the broadcast path from a central feed to each antenna element, each phase shifter being individually controllable, a method for self-calibration and phasing said array elements to compensate for any deviation from a precomputed pattern from an assumed array structure comprising the steps ofbroadcasting a continuous coherent reference wave from said feed to said elements, while stopping normal operation and with said phase shifters set to perform a lens operation for said precomputed pattern using said assumed array structure, and receiving at said feed electromagnetic wave energy returned from each phase shifter,advancing the phase angle of said phase shifters at different rates, thereby providing distinct frequency modulation of returned energy from said phase shifters,coherently demodulating the composite of return energy received by said feed,deriving a response function for each antenna element as the Fourier transform of the demodulated return energy,deriving an error signal for each antenna element as the reciprocal of the square root of its response function, andusing said error signal for each antenna element for phase compensation of its phase shifter.
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Abstract
A technique for self-calibration and phasing of a lens-feed array antenna, while normal operation is stopped, utilizes reflected energy of a continuous and coherent wave broadcast by a transmitter (11) through a central feed (10) while a phase controller (21) advances the phase angles of reciprocal phase shifters (14) in radiation electronics (RE1-REN) of the array elements (1-N) at different rates to provide a distinct frequency modulation of electromagnetic wave energy returned by reflection in one mode (switch 19 closed) and leakage in another mode (switch 19 open) from the radiation electronics of each array element. The composite return signal received by a synchronous receiver (12) goes through a Fourier transform processing system (20) and produces a response function for each antenna element. Compensation of the phase angles for the antenna elements required to conform the antenna response to a precomputed array pattern is derived from the reciprocal square root of the response functions for the antenna elements which, for a rectangular array of N×M elements, is a response function T(n,m). A third mode of calibration uses an external pilot tone from a separate antenna element (44). Respective responses T1 (n,m), T2 (n,m) and T3 (n,m) are thus obtained from the three modes of calibration. From those, the separate responses T.sub.φ, Tt and Tr of the reciprocal phase shifter, radiation electronics, and synchronous receiver can be obtained by solving the following three simultaneous equations:
T.sub.φ (n,m)=T.sub.1 (n,m)
T.sub.φ (n,m)×T.sub.t (n,m)×T.sub.r (n,m)=T.sub.2 (n,m)
T.sub.φ.sup.1/2 (n,m)×T.sub.r (n,m)=T.sub.3 (n,m).
80 Citations
14 Claims
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1. In a phased array antenna incorporating a separate reciprocal phase shifter in the broadcast path from a central feed to each antenna element, each phase shifter being individually controllable, a method for self-calibration and phasing said array elements to compensate for any deviation from a precomputed pattern from an assumed array structure comprising the steps of
broadcasting a continuous coherent reference wave from said feed to said elements, while stopping normal operation and with said phase shifters set to perform a lens operation for said precomputed pattern using said assumed array structure, and receiving at said feed electromagnetic wave energy returned from each phase shifter, advancing the phase angle of said phase shifters at different rates, thereby providing distinct frequency modulation of returned energy from said phase shifters, coherently demodulating the composite of return energy received by said feed, deriving a response function for each antenna element as the Fourier transform of the demodulated return energy, deriving an error signal for each antenna element as the reciprocal of the square root of its response function, and using said error signal for each antenna element for phase compensation of its phase shifter.
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3. A method for on-board self-calibration and phasing of an array antenna having a plurality of antenna elements distributed in an array, each element being equipped with separate radiator electronics including a reciprocal phase shifter, and having a central feed for broadcasting a coherent wave to said array elements through their respective radiator electronics, the calibration steps carried out while normal operation is stopped, comprising
broadcasting a continuous and coherent carrier wave from said feed to said array elements through their respective phase shifters set to perform a perfect lens operation for a precomputed array pattern which assumes a predetermined array structure, advancing the phase angles of said phase shifters at different rates relative to one another, thereby to effect a distinct frequency modulation of the reflected signal from each phase shifter, receiving through said feed returned electromagnetic wave energy from the phase shifters of said array elements, coherently demodulating the composite return signal received at said feed from said phase shifters, deriving the Fourier transform of the demodulated composite signal to determine the response for each element of the array antenna, deriving an error signal for each antenna element that is the reciprocal of the square root of said antenna response for each antenna element, and deriving from said error signal the phase compensation required to be combined with predetermined array pattern control to compensate for any deviation from said predetermined array structure, whereby the array antenna thus compensated will be correctly phased to achieve said precomputed array pattern during normal operation.
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9. Apparatus for on-board self-calibration and phasing of an array antenna having a plurality of antenna elements distributed in an array, each element being equipped with separate radiator electronics including a reciprocal phase shifter, and having a central feed for broadcasting a coherent wave to said array elements through their respective radiator electronics, comprising
means for broadcasting a continuous and coherent carrier reference wave from said feed to said array elements through their respective phase shifters set to perform a perfect lens operation for a precomputed array pattern which assumes a predetermined array structure, means for advancing the phase angles of said phase shifters at different rates relative to one another, thereby to effect a distinct frequency modulation of the reflected signal from each phase shifter, means for receiving through said feed reflected electromagnetic wave energy from the phase shifters of said array elements, means for coherently demodulating the composite return signal received at said feed from said phase shifters, means for deriving the Fourier transform of the demodulated composite signal to determine the response for each element of the array antenna, means for deriving an error signal for each antenna element that is the reciprocal of the square root of said antenna response for each antenna element, and means for deriving from said error signal the phase compensation required to be combined with predetermined array pattern control to compensate for any deviation from said predetermined array structure, whereby the array antenna thus compensated will be correctly phased to achieve said precomputed array pattern during normal operation.
Specification