System and method for pointing and control of an antenna

• US 7,333,064 B1
• Filed: 02/23/2006
• Issued: 02/19/2008
• Est. Priority Date: 11/30/2004
• Status: Active Grant

• Current Assignee: L3 Technologies, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Buchanan, Alan M., Timothy, LaMar K., Batzer, Patricia F., Sato, Jeffrey S.
• Primary Examiner(s): Wimer; Michael C.
• Application Number:
  US11/361,494
• Time in Patent Office: 726 Days
• Field of Search: 343/705, 343/708, 343/765, 343/766, 343/882, 342/359
• US Class Current: 343/705
• CPC Class Codes: H01Q 1/125 Means for positioning
• CPC Class Codes: H01Q 1/28 Adaptation for use in or on aircraft, missiles, satellites, or balloons
• CPC Class Codes: H01Q 3/08 for varying two co-ordinates of the orientation

Abstract

A method is disclosed for directing an antenna mounted in a restricted radome on an aircraft. The method can include the operation of determining whether the antenna is directed in a keyhole. A further operation can involve controlling the antenna using an elevation gimbal and an azimuth gimbal when it is determined the antenna is directed outside the keyhole. Another operation can include directing the antenna using an elevation, azimuth, and cross elevation gimbal when it is determined the antenna is pointing in the keyhole.

Claims

1. A method for directing an antenna mounted in a radome on an aircraft, comprising the steps of:

determining whether the antenna is directed in a keyhole, wherein the keyhole is an area in which excessive gimbal rates are required to accurately point an antenna mounted on a two-gimbal pedestal;

controlling the antenna using an elevation gimbal and an azimuth gimbal when it is determined the antenna is directed outside the keyhole; and

directing the antenna using an elevation, azimuth, and cross elevation gimbal when it is determined the antenna is pointing in the keyhole.

2. A method as in claim 1, further comprising directing the antenna in a radome mounted on the aircraft, the radome having a flattened shape configured to substantially minimize aerodynamic drag.

3. A method as in claim 1, further comprising directing the antenna in a radome mounted on the aircraft, wherein the antenna has a width dimension that is at least 2.5 times a height dimension in order to have sufficient surface area to achieve a predetermined amount of antenna gain.

4. A method as in claim 1, further comprising directing each gimbal to a predetermined angle with respect to a tangential plane of the aircraft, wherein the tangential plane is orthogonal to a gravity vector.

5. A method as in claim 1, further comprising directing the antenna in a restricted radome, wherein the size of the radome is such that the antenna will come in contact with the radome if the antenna is moved at certain angles.

6. A method as in claim 1, further comprising restricting movement of the elevation and cross elevation gimbals to enable the antenna to substantially avoid contact with the radome.

7. A method as in claim 6, further comprising limiting the movement of the elevation gimbal to movement between 0 degrees and 120 degrees.

8. A method as in claim 6, further comprising limiting the movement of the cross elevation gimbal to movement between −

10 degrees and +10 degrees.

9. A method as in claim 1, wherein the step of determining whether the antenna is directed in the keyhole further comprises determining whether the elevation gimbal is positioned at less than a predetermined elevation angle.

10. A method as in claim 4, further comprising determining that the antenna is not directed in the keyhole if the elevation gimbal is directed at an elevation angle of less than 80°

.

11. A method as in claim 1, wherein the step of controlling the antenna when the antenna is directed outside the keyhole further comprises calculating line of sight coordinates from the aircraft to a satellite for X₁, Y₁, and Z₁ axes.

12. A method as in claim 11, further comprising measuring the aircraft'"'"'s movement when the aircraft is in flight with an inertial navigation system, wherein the inertial navigation system is used to measure changes in roll, pitch, and yaw of the aircraft.

13. A method as in claim 12, further comprising calculating the line of sight coordinates for the X₁, Y₁, and Z₁, axes with measured changes in roll, pitch, and yaw of the aircraft, using:

$\underset{\begin{array}{c}\mathrm{LOS}<br><br><br><br>\mathrm{IN}\\ A/C<br><br><br><br>\mathrm{COOR}\end{array}}{\left[\begin{array}{c}{X}_1\\ Y_1\\ Z_1\end{array}\right]}=\underset{\mathrm{AIRCRAFT}<br><br><br><br>\mathrm{ROTATIONS}}{\left[\begin{array}{ccc}\mathrm{CPSH}& -\mathrm{CPSH}& \mathrm{SP}\\ \mathrm{CRSH}-\mathrm{SRSPCH}& \mathrm{CRCH}+\mathrm{SRSPSH}& \mathrm{SRCP}\\ -\mathrm{SRSH}-\mathrm{CRSPCH}& -\mathrm{SRCH}+\mathrm{CRSPSH}& \mathrm{CRCP}\end{array}\right]}$ $\underset{\mathrm{EARTH}<br><br><br><br>\mathrm{ROTATIONS}}{\left[\begin{array}{c}C<br><br><br><br>{\mathrm{\phi <br><br>}}_1<br><br>S<br><br><br><br>{\mathrm{\phi <br><br>}}_0-S<br><br><br><br>{\mathrm{\phi <br><br>}}_1<br><br>C<br><br><br><br>{\mathrm{\phi <br><br>}}_0<br><br>C<br><br><br><br>\mathrm{\Delta <br><br>}\\ -C<br><br><br><br>{\mathrm{\phi <br><br>}}_0<br><br>S<br><br><br><br>\mathrm{\Delta <br><br>}\\ C<br><br><br><br>{\mathrm{\phi <br><br>}}_1<br><br>C<br><br><br><br>{\mathrm{\phi <br><br>}}_0<br><br>C<br><br><br><br>\mathrm{\Delta <br><br>}+S<br><br><br><br>{\mathrm{\phi <br><br>}}_1<br><br>S<br><br><br><br>{\mathrm{\phi <br><br>}}_0-<br><br>r_1/r_0<br><br>\end{array}\right]}<br><br><br><br>r_0<br><br>.$

14. A method as in claim 13, further comprising calculating an azimuth angle for the azimuth gimbal using

$\mathrm{Tan}$

⁢

Az = - Y 1 X 1

and using

$\mathrm{Tan}<br><br><br><br>\mathrm{El}=\frac{Z_1}{\sqrt{X_1^2+Y_1^2}}$

to calculate an elevation angle for the elevation gimbal, the azimuth and elevation angles being used to point the antenna to a substantially correct line of sight from the aircraft to the satellite.

15. A method as in claim 4, further comprising determining that the antenna is directed in the keyhole if the elevation gimbal is directed at an elevation angle of greater than 80°

.

16. A method as in claim 15, wherein the step of controlling the antenna when the antenna is directed outside the keyhole further comprises calculating line of sight coordinates from the aircraft to a satellite for X₂, Y₂, and Z₂ axes.

17. A method as in claim 16, further comprising calculating the line of sight coordinates for the X₂, Y₂, and Z₂ axes with measured changes in roll, pitch, and yaw of the aircraft, using:

$\left[\begin{array}{c}{X}_2\\ Y_2\\ Z_2\end{array}\right]=\left[\begin{array}{ccc}\mathrm{CAz}& -\mathrm{SAz}& 0\\ \mathrm{SAz}& \mathrm{CAz}& 1\\ 0& 0& 1\end{array}\right]<br><br>\left[\begin{array}{c}{X}_1\\ Y_1\\ Z_1\end{array}\right]$

where CAz, SAz, and −

SAz are measured using a gimbal resolver.

18. A method as in claim 17, further comprising calculating a cross elevation angle for the cross elevation gimbal using

$\mathrm{Tan}$

⁢

CEl = - Y 2 X 2 2 + Z 2 2

to calculate the cross elevation angle for the cross elevation gimbal.

19. A method as in claim 18, further comprising determining if a calculated azimuth gimbal angle is different from an azimuth gimbal resolver measurement.

20. A method as in claim 19, further comprising using the azimuth gimbal resolver measurement to determine values of X₂, Y₂, and Z₂ when a difference between the calculated azimuth gimbal angle and the azimuth gimbal resolver measurement is greater than a predetermined number.

21. A method as in claim 19, further comprising determining using the azimuth gimbal resolver measurement to determine the values of X₂, Y₂, and Z₂ when the difference between the calculated azimuth gimbal angle and the azimuth gimbal resolver measurement is greater than ±

0.1 degrees.

22. A method as in claim 19, further comprising setting the cross elevation gimbal to a cross elevation angle of approximately zero degrees if the elevation gimbal is directed at an elevation angle of less than 80 degrees and the difference between the calculated azimuth gimbal angle and the azimuth gimbal resolver measurement is less than a predetermined number.

23. A method as in claim 1, further comprising selecting an azimuth gimbal position when the antenna is directed in the keyhole such that a rate of change of the azimuth gimbal'"'"'s position is less than a predetermined rate of change.

24. A method as in claim 23, further comprising selecting the azimuth gimbal position such that the rate of change of the azimuth gimbal'"'"'s position is less than ±

60 degrees per second.