Abstract
A synthetic aperture radar sensor having five degrees of freedom (DoF) is disclosed. The five DoF enable multiple imaging operations, including multiple simultaneous imaging operations. The sensor includes multiple transceivers mounted to track segments, with variable spacing between the transceivers being the first DoF. The second DoF is about a vertical axis allowing side-to-side motion of the transceivers. The third DoF is about a horizontal axis parallel to a direction of travel with the segments perpendicular to the direction of travel, thereby allowing the transceivers to form a horizontal line, a vertical line, or some intervening angle. The transceivers can be at different angles, corresponding to the fourth DoF, which permits simultaneous vertical and side-looking operation. The fifth degree of freedom is about a horizontal axis parallel to the direction of travel with the segments parallel to the direction of travel, allowing pointing of the transceivers at a desired scene.
Claims
1. A synthetic aperture radar sensor system comprising: a gimbal; a plurality of segments defining a longitudinal axis, the plurality of segments mechanically coupled to the gimbal so the plurality of segments may be rotated about a central vertical axis perpendicular to the longitudinal axis and may be rotated about the longitudinal axis; a plurality of antennas, each antenna coupled to a separate one of the plurality of segments and adapted to move along the longitudinal axis formed by the plurality of segments so the plurality of antennas may move relative to each other along the longitudinal axis, each antenna adapted to at least one of transmit or receive a corresponding radio frequency signal; and wherein the synthetic aperture radar sensor is adapted for one or more of high-gain synthetic aperture radar operation, altimetry operation, moving target indication operation, monopulse operation, pulse repetition frequency operation, side-looking operation, vertical-looking operation, interferometric synthetic aperture radar operation, or terrain point cloud operation.
2. The synthetic aperture radar sensor system of claim 1, wherein the plurality of segments includes two segments; and wherein the plurality of antennas includes two antennas, each coupled to one of the two segments.
3. The synthetic aperture radar sensor system of claim 1, wherein the plurality of segments consists of two segments.
4. The synthetic aperture radar sensor system of claim 3, wherein the plurality of antennas consists of two antennas, each coupled to one of the two segments.
5. The synthetic aperture radar sensor system of claim 4, wherein a pivot is located between the two segments that enables independent rotation of the two segments in the plane formed by the longitudinal axis between the two segments.
6. The synthetic aperture radar sensor system of claim 1, wherein each antenna includes one or more phase centers.
7. The synthetic aperture radar sensor system of claim 1 further comprising a plurality of optical imaging arrays, each antenna having a corresponding one of the plurality of optical imaging arrays, each optical imaging array adapted to sense a corresponding optical image.
8. The synthetic aperture radar sensor system of claim 4, wherein a pivot is located substantially equally between the two segments that enables independent rotation of the two segments in the plane formed by the longitudinal axis between the two segments.
9. The synthetic aperture sensor system of claim 4, wherein a pivot is located between the two segments that enables dependent rotation of the two segments in the plane formed by the longitudinal axis between the two segments.
10. The synthetic aperture sensor system of claim 4 wherein a pivot is located substantially equally between the two segments that enables dependent rotation of the two segments in the plane formed by the longitudinal axis between the two segments.
11. The synthetic aperture sensor system of claim 8, wherein each transceiver includes one or more phase centers.
12. The synthetic aperture sensor system of claim 10 further comprising a plurality of optical imaging arrays, each transceiver having a corresponding one of the plurality of optical imaging arrays, each optical imaging array adapted to sense a corresponding optical image.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The drawings illustrate several embodiments of the invention, wherein identical reference numerals refer to identical or similar elements or features in different views or embodiments shown in the drawings. The drawings are not to scale and are intended only to illustrate the elements of various embodiments of the present invention.
(2) FIG. 1 illustrates a SAR sensor in accordance with one or more embodiments of the present invention.
(3) FIG. 2 illustrates a SAR sensor in accordance with one or more embodiments of the present invention operating in a first physical configuration.
(4) FIG. 3 illustrates a SAR sensor in accordance with one or more embodiments of the present invention operating in a second physical configuration.
(5) FIG. 4 illustrates a SAR sensor in accordance with one or more embodiments of the present invention operating in a third physical configuration.
(6) FIG. 5 illustrates a SAR sensor in accordance with one or more embodiments of the present invention operating in a fourth physical configuration.
DETAILED DESCRIPTION
(7) At least one embodiment of the present invention employs a modular antenna array on a gimbaled track with pivoting capability, as illustrated in FIG. 1. In the embodiment illustrated in FIG. 1, the SAR sensor 100 includes a track with two segments 110.sub.A, 110.sub.B, to which two antennas 120.sub.A, 120.sub.B are attached. As will be appreciated by one of ordinary skill in the art, each antenna 120.sub.A, 120.sub.B may include one or more phase centers as part of an overall transceiver. A gimbal 130 mechanically coupled to the segments 110.sub.A, 110.sub.B allows the segments 110.sub.A, 110.sub.B to be rotated about a central vertical axis perpendicular to a longitudinal axis defined by the segments 110.sub.A, 110.sub.B. This vertical rotational axis defines a first axis for the gimbal 130. The gimbal 130 thus allows one to place the two antennas 120.sub.A, 120.sub.B in either side-looking operation (the segments 110.sub.A, 110.sub.B are parallel to the flight path, which, for example, is left to right in FIG. 1) or vertical operation (the segments 110.sub.A, 110.sub.B are perpendicular to the flight path, which, for example, is into FIG. 1).
(8) As illustrated in FIG. 2, the gimbal 130 includes a second axis that allows the track segments 110.sub.A, 110.sub.B to be rotated about the longitudinal axis defined by the segments 110.sub.A, 110.sub.B. This longitudinal rotational axis defines a second degree of freedom for the gimbal 130. As illustrated in FIG. 2, the segments 110.sub.A, 110.sub.B are parallel to the flight path, which, for example, is left to right in FIG. 2. The gimbal 130 thus allows one to orient the antennas 120.sub.A, 120.sub.B for side-looking operation, i.e., left, or right, or vertical operation. The specific angle of rotation will depend upon the altitude of the flight path and the desired scene. At low altitudes, the angle of rotation will likely be closer to 90, i.e., horizontal. At higher altitudes or for scenes more directly under the SAR sensor 100, the angle of rotation may, for example, be between 10 and 45. The rotation angle will be 0 during vertical operation. When the two antennas 120.sub.A, 120.sub.B are joined together, the resultant extended length antenna permits high-gain SAR imaging or altimetry operation of the SAR sensor 100 with a single transmit/receive beam 200.
(9) As illustrated in FIG. 3, the two antennas 120.sub.A, 120.sub.B can be separated from each other along the segments 110.sub.A, 110.sub.B. The two antennas 120.sub.A, 120.sub.B may, for example, be separated using corresponding screw drives (not illustrated) embedded in the segments 110.sub.A, 110.sub.B, thereby allowing independent positioning of the antennas 120.sub.A, 120.sub.B along their corresponding segments 110.sub.A, 110.sub.B. This separation of the antennas 120.sub.A, 120.sub.B may alternatively be implemented using cogged segments 110.sub.A, 110.sub.B, with a motor-driven gear on the antennas 120.sub.A, 120.sub.B engaging the cogged segments 110.sub.A, 110.sub.B. With the two antennas 120.sub.A, 120.sub.B separated, and thus two separate transmit and/or receive beams 300A, 300B, multiple operations can be performed by the SAR sensor 100. A first operation provides moving target indication (MTI) functionality. A second operation employs a monopulse configuration in which a radar pulse is encoded to provide both range and direction information. A third operation employs a high PRF, with one of the antennas, for example, 120.sub.A, operating as a transmitter, with the other one of the antennas, for example, 120.sub.B, operating as a receiver. As will be appreciated by one of ordinary skill in the art, depending upon the operation, the segments 110.sub.A, 110.sub.B will be either parallel or perpendicular to the flight path.
(10) As illustrated in FIG. 4, the two antennas 120.sub.A, 120.sub.B can be separated, while an angle between the segments 110.sub.A, 110.sub.B can be changed due to a pivot 400, i.e., the pivot 400 flexibly mechanically couples the segments 110.sub.A, 110.sub.B. The gimbal 130 drives the pivot 400 such that the angle between the two segments 110.sub.A, 110.sub.B can be changed. This pivot axis defines a third degree of freedom for the gimbal 130. With the two antennas 120.sub.A, 120.sub.B separated and the segments 110.sub.A, 110.sub.B pivoted, the SAR sensor 100 can simultaneously perform both vertical and side-looking operations due to two separate transmit and/or receive beams 410A, 410B. During operation, the segments 110.sub.A, 110.sub.B will be perpendicular to the flight path, with, for example, right-side-looking operation requiring a flight path into FIG. 4. Further, with the gimbal 130 having pivoted both segments 110.sub.A, 110.sub.B, for example, to equal angles, the SAR sensor 100 can simultaneously perform both right-side-looking and left-side-looking operations as the segments 110.sub.A, 110.sub.B form a V.
(11) As illustrated in FIG. 5, the two antennas 120.sub.A, 120.sub.B can be separated, while the segments 110.sub.A, 110.sub.B are pivoted into a vertical side-looking position, as opposed to the horizontal orientation illustrated in FIG. 3. FIG. 5 corresponds to the case illustrated in FIG. 4, but with the gimbal 130 having pivoted the segments 110.sub.A, 110.sub.B to equal and opposite 90 angles, i.e., 90 and 90, respectively. With the two antennas 120.sub.A, 120.sub.B in this orientation, and thus two separate transmit and/or receive beams 500A, 500B, multiple operations can be performed by the SAR sensor 100. A first operation, with cross-track separation of the two antennas 120.sub.A, 120.sub.B, provides interferometric SAR functionality. A second operation, with the segments 110.sub.A, 110.sub.B rotated by the gimbal 130, provides terrain point cloud functionality. While FIG. 5 illustrates the longitudinal axis defined by the segments 110.sub.A, 110.sub.B being vertical, angles near this extreme would typically be employed for interferometric SAR only at low flight path altitudes. At higher flight path altitudes, the longitudinal axis defined by the segments 110.sub.A, 110.sub.B would be changed such that the SAR sensor 100 would view the desired terrain. In this case, the angle of rotation of the longitudinal axis may, for example, result in an angular rotation of between 10 and 45 for segment 110.sub.A, and between 10 and 45 for segment 110.sub.B.
(12) As described above with reference to FIGS. 2-5, various embodiments of the present invention overcome limitations of traditional SAR antenna configurations. Placing multiple antennas on multiple segments that are multi-axis gimbaled gives these embodiments additional degrees of freedom that have not previously been achieved.
(13) The geometric relationship of the two antennas 120.sub.A, 120.sub.B, with respect to the vehicle heading, is an important factor in the resulting SAR information content. With proper geometric relationships, and suitable reference information, SAR information can be used to estimate navigational information regarding the vehicle.
(14) As will be appreciated by one of ordinary skill in the art, various embodiments of the present invention may provide the benefits of both a multi-angle SAR sensor and a multiple phase center SAR sensor. These benefits may be provided individually, as illustrated in FIGS. 2, 3, and 5, or simultaneously, as illustrated in FIG. 4.
(15) The SAR sensor illustrated in FIG. 1 includes two segments, though other embodiments of the present invention may employ three or more segments, with each pair of segments separated by a pivot. The SAR sensor illustrated in FIG. 1 includes two antennas, though other embodiments of the present invention may employ three or more antennas. The SAR sensor illustrated in FIG. 1 includes a multi-axis gimbal attached between two segments, though other embodiments of the present invention may locate a multi-axis gimbal between a segment and an antenna. In this embodiment, each antenna would have its own corresponding multi-axis gimbal, thereby allowing each antenna to be rotated independently. Further, with each antenna having its own corresponding multi-axis gimbal, the antennas may be independently pointed, thereby enabling spotlight operation and, if desired, dual spotlight operation as each antenna can be pointed at a different scene.
(16) The SAR sensor illustrated in FIG. 1 includes two segments, though other embodiments of the present invention may employ only a single segment having a corresponding longitudinal segment axis. These embodiments include a gimbal allowing the single segment to be rotated about a vertical axis, similar to that illustrated and described above with reference to FIG. 1. The gimbal also allows the segment to be rotated about a longitudinal axis parallel to the longitudinal segment axis, for example, from side-looking operation to vertical operation, similar to that illustrated and described above with reference to FIG. 2. The gimbal further allows the segment to be rotated, for example, from a horizontal configuration (as illustrated and described above with reference to FIG. 3) to a vertical configuration (as illustrated and described above with reference to FIG. 5), i.e., about a horizontal rotation axis parallel to the flight path. As with the multiple segment embodiments, these single segment embodiments would employ two (or more) antennas, thereby enabling multiple imaging operations.
(17) While the above described embodiments employed a single multi-axis gimbal to implement the desired rotations, other embodiments may employ multiple single-axis gimbals to implement the desired rotations.
(18) One or more embodiments of the present invention may be employed in commercial applications, such as a redundant navigational aid on commercial airliners and helicopters. Further, due to the gimbal and pivoting capabilities of the multiple segments, the SAR sensor can be positioned for ranging to help with collision avoidance. The articulation provided by the gimbal and pivoting segments may be employed in boats equipped with sonar transceivers for synthetic aperture sonar and ranging. Given baseline sonar maps, these sonar systems may also be used for navigation purposes, much like the corresponding radar embodiments. In addition, one or more embodiments may find application in autonomous vehicles.
(19) One or more embodiments may also include one or more optical imaging arrays, for example, each antenna would have a corresponding optical imaging array. By combining these different imaging modalities, i.e., radar and optical, one can further improve the overall imaging capability. As will be appreciated by one of ordinary skill in the art, performance of the one or more optical imaging arrays may suffer under various scenarios, including: poor lighting conditions, such as nighttime, if the optical imaging array operates at visible wavelengths, or blocking/scattering of the light when clouds or rain is present.
(20) The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
