Communications: directive radio wave systems and devices (e.g. – Directive – Including antenna orientation
Reexamination Certificate
2002-05-17
2003-11-11
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including antenna orientation
Reexamination Certificate
active
06646598
ABSTRACT:
TECHNICAL FIELD
The field of this invention is radar and RF communications, in particular specifying the orientation of a highly directional airborne antenna.
BACKGROUND OF THE INVENTION
In the field of radar and highly directional RF communications antennas, it is necessary to calibrate the angular orientation and position of an antenna in order to use the output of the antenna to specify the azimuth and elevation of the object that the antenna points to. The angular orientation of the antenna (usually the centerline of a parabolic dish reflector) is called the Line-of-Sight (LOS) or RF axis of the antenna. The antenna LOS is the direction of maximum transmitted and received RF energy. Ideally, as shown in
FIG. 1
, a local antenna (
110
) LOS is pointed at a remote antenna (
200
) along a straight line connecting the two antennas. The straight line connecting two antennas is also called the LOS. High frequency RF, radar, and light essentially travel in a straight line.
For example, an antenna mounted on a local airborne (A/B) platform
110
or aircraft (A/C) points to a remote target aircraft
200
. In order to point the local antenna LOS at the remote target A/C antenna, the local antenna control computer must have the following information: a) local A/C position (latitude, longitude, and altitude) from the local navigator computer and remote A/C position from the remote navigator; and b) the orientation (roll, pitch, and heading shown in
FIG. 2
) of the local A/C from the local navigator. This navigational information is used to calculate (specify) and command azimuth and elevation antenna gimbal angles, with respect to the local A/C, to point at the remote target as shown in FIG.
6
.
FIG. 6
illustrates a portion of a computer system
100
, in which antenna control computer
50
sends signals to the antenna gimbal servos
70
, receiving input from keyboard
55
and from INS
60
. Box
80
represents other portions of a system, such as disk drives, memory for storing software according to the invention, CRTs, other computers processing other input data (e.g. data indicating the general location of a potential target, etc.). In the example of target acquisition, information on the general location of a potential target may come from a coarse antenna on board the A/C or from a remote source, such as an AWACs plane. The antenna computer takes the INS data from system
60
and commands the antenna system
70
to sweep over the approximate location until acquisition occurs. After acquisition of the remote A/C, it will send location data over the data link. The signals sent to the antenna (and received from the antenna and transmitted to other parts of the system) will be corrected by bias values determined in the inventive procedure.
The antenna azimuth and elevation gimbals with resolvers (for sending measurements of the actual pointing direction of the antenna), in an xyz frame, determine the antenna coordinate system. This system must be aligned with the A/C navigator X
1
roll, Y
1
pitch, and Z
1
heading coordinates as shown in
FIG. 3
illustrating the relationship of the coordinate systems. Alignment of xyz to X
1
Y
1
Z
1
is called “LOS boresighting”. Alignment can be achieved either mechanically or with computer software. This invention presents a software method.
In the past, the coordinates were mechanically measured in a lengthy process involving surveyor's methods using theodolites, tape measures, and aligned with mechanical shims to adjust the azimuth and elevation orientations of the antenna to match the A/C navigator roll, pitch, and heading coordinates. Most methods involving survey theodolites, tapes, and shims have been very time consuming.
Highly directional airborne antennas can be pointed with an accuracy of about +/−0.1 degree when referenced to the vehicle's Inertial Navigation System (INS). The art has felt a need for a quick, economical method of boresighting consistent with this accuracy.
SUMMARY OF THE INVENTION
The invention relates to a method of boresighting an antenna mounted to an aircraft in which the Global Positioning System (GPS) is used to provide input to the boresighting process.
A feature of the invention is a set of measurements of a cooperative target RF source that points the A/B antenna LOS at a known location in space.
Another feature of the invention is the software calculation of adjustment parameters that adjusts radar and RF LOS output data without physically changing the orientation of the antenna.
REFERENCES:
patent: 4823134 (1989-04-01), James et al.
patent: 5347286 (1994-09-01), Babitch
patent: 6400315 (2002-06-01), Adler et al.
Keller Merle L.
Lunsford Roy F.
Timothy LaMar K.
Harrington & Smith ,LLP
L-3 Communications Corporation
Phan Dao
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