Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-11-04
2001-12-25
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S368000, C342S081000
Reexamination Certificate
active
06333712
ABSTRACT:
TECHNICAL FIELD
This invention relates to large phased-array antennas, and more particularly to a structural deformation compensation system for compensating for surface deformations in a large, space-based, phased-array antenna.
BACKGROUND OF THE INVENTION
Current spacecraft often employ large, phased-array antennas to perform reconnaissance missions, collect radar images, track ground-based and air-based targets and provide high bandwidth communications. These large, phased-array antennas are made up of a large plurality of independent antenna elements. The surfaces forming the phased-array antenna must be maintained very flat or the distortion in the antenna surface must be known to within a very small fraction of the wavelength corresponding to the operational frequency of the antenna (e.g., one-thirtieth of the wavelength for space-based radar at 10 GHz=1 mm flatness tolerance) in order for the antenna to perform correctly. In particular, for space-based radar (SBR) applications, a very high degree of surface planarity must be maintained to enable the effective use of ground clutter suppression algorithms. A high degree of surface planarity is also critical for space-based optics applications and ground moving target tracking applications.
Present day large, phased-array antennas achieve this required flatness by using high stiffness structural designs (i.e., trusses) that add significant weight and volume to the antenna when it is stowed in a launch vehicle. As will be appreciated, as the antenna area increases, the stowed volume of the array limits the antenna size due to the restrictions imposed by the launch vehicle fairing within which the stowed antenna must fit.
Other systems for measuring the flatness of planar structures have relied on metrology devices that measure the distance from a common source to pre-determined points on the structure, typically through laser reflection from a surface mounted target. For large, deployable, space-based phased-array antenna systems, there is a need for a measurement system that does not interfere with the operation of the antenna, and which provides feedback, in real time, and which further does not add significantly to the complexity of the antenna system or to the spacecraft with which it is associated.
Accordingly, it is a principal object of the present invention to provide a system for compensating for deformation occurring in a large, phased-array antenna which eliminates the need for large and heavy structural members, such as trusses, to maintain the planarity of the antenna when the antenna is subjected to external factors which would otherwise cause a deformation of its surface.
It is another object of the present invention to provide an apparatus and method for electronically compensating, in real time, for the deformation experienced by a large, phased-array antenna through non-intrusive means which permit the deformation to be monitored and suitable corrections generated to provide needed phase shifting or time delay of the signals transmitted by or received by the phased-array antenna.
It is still another object of the present invention to provide a system for detecting and compensating for the deformation occurring in a large, phased-array antenna, in real time, without significantly complicating the construction of the antenna and without impeding the ability of the antenna to be deployed in space-based applications.
SUMMARY OF THE INVENTION
The above and other objects are provided by a structural deformation compensation system and method for use with a large, phased-array antenna. The system and method of the present invention are particularly well adapted for use with large, spaced-based, phased-array antennas, but could just as readily be implemented with ground-based or aircraft based phased-array antennas.
The present invention employs a number of deformation sensing devices which are either placed on or formed within structure supporting the antenna elements of the phased-array antenna at predetermined locations on the antenna where significant stresses or strains are expected to occur. In one preferred embodiment the deformation sensing devices are comprised of strain gauges. At least one such strain gauge is disposed on, or formed within, the composite structure supporting the phased-array antenna at each of those locations where strains are expected to occur as a result of the external forces experienced by the antenna which can cause deformation of the antenna. In some applications, a pair of strain gauges are preferably located at each such location. If a pair of strain gauges is used, then one of each pair may be orientated in the X direction and the other may be orientated in the Y direction. Each strain gauge provides output signals indicative of the stresses experienced by the phased-array antenna at that approximate location where it is located.
The output signal from each strain gauge is then input to a data acquisition system which makes use of a transformation algorithm for transforming the detected surface strains into signals representing the displacements of the antenna at various locations thereof. Electronic signals corresponding to these displacements are then output to a beam steering controller which generates phase or time delay commands needed to provide the necessary degree of phase shifting or time delay of the signals transmitted or received by the antenna elements making up the phased-array antenna to correct for the estimated overall deformation of the phased-array antenna. In this manner, the antenna can be electronically “steered” to compensate, in real time, for the deformations occurring over the entire area of the phased-array antenna as a result of various factors, such as changes in temperature, experienced by the antenna. Advantageously, the compensation of surface deformation is accomplished “non-intrusively” and without interfering with normal antenna operation.
In one preferred embodiment, the deformation sensing devices are comprised of fiber-optic strain gauges which output signals to a fiber-optic strain demodulator. The fiber-optic strain demodulator, in turn, provides corresponding signals to the data acquisition system. In this embodiment true-time-delay (TTD) units are used for receiving the output signals from the beam steering controller to electronically compensate for the surface deformations of the antenna. The beam steering controller may also receive attitude information concerning the antenna if the antenna is a space-based antenna system. A beam pointing command generated is also used to supply beam pointing commands to the beam steering controller.
The method of the present invention makes use of suitable surface modeling equations developed during laboratory testing and on-orbit measurements made for space-based, large, phased-array antennas in order to collect a sufficient number of modes to represent displacements likely to occur as a result of predicted load conditions which the antenna will likely experience. From this testing a suitable “strain-to-displacement” algorithm is developed. The information obtained from ground-based testing and on-orbit measurements is also used to optimize the number and location of the strain gauges used on the antenna. This information is then used to place deformation sensing devices at those locations on the antenna where significant degrees of strain are likely (i.e., predicted) to occur. The strain-to-displacement algorithm is used by the data acquisition system to generate displacement signals corresponding to the strains occurring at those approximate areas of the antenna where the deformation sensing devices are located.
The apparatus and method of the present invention thus provides a means for compensating for surface deformations occurring over the entire area of a large, phased-array antenna system, in real time, and further in a manner which allows smaller, lighter and less costly antenna support structures to be used.
REFERENCES:
patent: 3706989 (1972-12-01), Taylor, Jr.
patent: 4550589 (1
Haugse Eric David
Hightower Charles Howard
Ridgway Robert Irving
Warren Ryon Christopher
Harness & Dickey & Pierce P.L.C.
Phan Dao
The Boeing Company
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