US 5,347,286 A · Automatic antenna pointing system based on global positioning system (GPS) attitude information

Abstract

An embodiment of the present invention is a system for automatically pointing a directional antenna. The system comprises two GPS antennas mounted at horizontally opposed extremities of the directional antenna, the placement is such that the GPS antennas lie on a line having a normal vector approximately parallel to a boresight of the directional antenna. The outputs from the GPS antennas are downconverted to a measurement frequency and differentially phase compared for each of a plurality of radio visible GPS satellites. A measurement controller that receives the phase comparisons. A navigation computer receives measurements from the measurement controller and uses a microprocessor to calculate the GPS latitude and longitude and the attitude angles of the pair of GPS antennas. A servo points the directional antenna at a particular target communications satellite, based on the computed azimuth, elevation, latitude, and longitude, as provided by the navigation computer. One of these servos is used to move the GPS antennas in roughly a circle to average out multipath effects to improve accuracy and to reduce integer ambiguities.

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Claims10

Dependent claims

A communications system, comprising:

a directional antenna supported by a mobile platform subject to continuous irregular motion;
a plurality of GPS patch antennas mounted non-collinearly apart from one another and attached to said mobile platform at points where said platform shadows the GPS antennas from GPS satellite visibility to a minimum extent;
attitude determination means including maximum likelihood estimations (MLE) optimization means for resolving integer ambiguities and multiplexing means for coupling all of the GPS patch antennas into a single GPS receiver downconverter for calculating a platform attitude based on the phases of a plurality of GPS signals received by the GPS patch antennas from at least three GPS satellites;
and
servo means mechanically connected to the directional antenna and for automatically positioning the directional antenna according to a pointing direction obtained by the attitude determination means wherein a radio communication may be established.

2 more elements

A portable satellite communications system including automatic antenna pointing for rapid field setup by relatively unskilled operators, the system comprising:

a portable carrying case;
a parabolic dish antenna supported by the portable carrying case for satellite communications with a communications satellite;
a pair of GPS patch antennas mounted apart from one another on the parabolic dish antenna;
attitude determination means for calculating a pointing direction for the parabolic dish antenna to said communications satellite with a known orbital position based on GPS carrier signals received by the GPS patch antennas from a GPS satellite that is apart from said communications satellite and that is based on an earth position derived for the GPS patch antennas from information included in said GPS signals, and comprises maximum likelihood estimation (MLE) integer resolution means for:
collecting a plurality of carrier phase measurements from the GPS patch antennas based on a reception of a plurality of GPS satellites such that each of said carrier phase measurements can add a range of possible integer values according to the whole-cycle ambiguity of a GPS carrier signal;
forming a decision tree expressing each of said possible combinations of said integer values;
computing a weighted-fit error at one or more stages of said decision tree, such that a determination may be made that none of said integer combinations connected to a current branch of the tree can be optimum and said current branch may accordingly be cut thereby speeding up a search through said decision tree;
and
selecting a final integer combination on the basis of a best fit with said measured phase data, as indicated by its weighted-fit error;
and
servo means for automatically positioning the parabolic dish antenna according to a result obtained by the attitude determination means such that a radio communication may be established between said communications satellite and the parabolic dish antenna.

8 more elements

A satellite communications system, comprising:

a platform subject to continuous motion while the system is in operation;
a directional dish antenna supported by the platform for satellite communications with a communications satellite;
a set of three of GPS patch antennas non-colinearly mounted apart from one another on the directional dish antenna and having a known geometric relationship to the directional dish antenna;
continuous attitude determination means for calculating a series of pointing directions for the directional antenna from a GPS satellite that is apart from said communications satellite and that is based on an earth position derived for the GPS patch antennas from information included in said GPS signals;
servo means mounted on the platform for automatically positioning the parabolic dish antenna with respect to the platform according to a result obtained by the attitude determination means to establish a radio communication between a communications satellite and the parabolic dish antenna;
multipath interference reduction means for improving an attitude solution result and including sampling means for moving the parabolic dish antenna to collect several sets of relative GPS signal phase data by the pair of GPS patch antennas and for use by the attitude determination means to calculate an ultimate pointing direction;
and
maximum likelihood estimation (MLE) integer resolution means for:
collecting a plurality of carrier phase measurements from the GPS patch antennas based on a reception of a plurality of GPS satellites such that each of said carrier phase measurements adds a range of possible integer values according to the whole-cycle ambiguity of a GPS carrier signal;
forming a decision tree expressing each of said possible combinations of said integer values;
computing a weighted-fit error at one or more stages of said decision tree, and determining that none of said integer combinations connected to a current branch of the tree are optimum and said current branch may accordingly be cut thereby speeding up a search through said decision tree;
and
selecting a final integer combination on the basis of a best fit with said measured phase data, as indicated by its weighted-fit error.

10 more elements

Dependencies are inferred from the claim text.

Description9,744 words

Summary4,316 words

#1. Field of the Invention

#The invention relates generally to antenna pointing systems and more specifically to using elements of the global positioning system (GPS) to provide azimuth and elevation information so that a directional antenna can be quickly and accurately pointed at its intended target location.

#2. Description of the Prior Art

Brief description of the drawings8 figures

#FIG. 1 is a graph showing the error sources which limit performance when compiled into a single set of curves that collectively define the performance of GPS-based attitude determination;

#FIG. 2A is a front view of a portable system according to an embodiment of the present invention;

#FIG. 2B is a side view of the system of FIG. 2A and showing the suitcase enclosure is open and laid out flat, such as on the ground;

Detailed description5,248 words

#First Embodiment

#A first embodiment of the present invention, in FIGS. 2A-2C, is a satellite communications system 10, according to an embodiment of the present invention, comprises a satellite parabolic dish antenna reflector 12 and feed 14, a pair of side mounted omni-directional GPS patch antennas 16 and 17, an elevation motor and gear assembly 18, a vertical support shaft 20, and a top case 22 and a bottom case 24 joined by a hinge 26. An azimuth motor and gear assembly 28 fits at the end of shaft 20 within bottom case 24. System 10 is transportable and dish assembly 12, 14, 16, and 18 can be taken off of shaft 20 and stowed away. The whole system can be closed inside cases 22 and 24 and carried like a suitcase with a handle. In an alternative embodiment, four corners of dish reflector 12 can notched to make it fit easier into cases 22 and 24. Dish assembly 12, 14, and 16 can be raised and lowered in elevation (FIG. 2B), and turned in azimuth (FIG. 2C). In an alternative embodiment, it can be spun along the longitudinal axis of feed 14 by setting the elevation to point upward and turning the azimuth such that patch antennas 16 and 17 will move in an orbit (FIG. 2A). In some instances, having only two GPS sensor antennas is a preferred configuration. It is possible, although mathematically more complex, to use only one GPS sensor antenna. Where cost is less of an object, and solution frequency is more important, three or more GPS sensor antennas will make the computational solution of pointing attitude less complex. This, of course, can reduce the demands on a computer used for this purpose, and help moderate the cost increase by allowing a less expensive computer to be used. If a deliberate motion of the GPS sensors can be introduced, then only one or two sensors are needed for good pointing. If no motion can be elicited, it is preferable to incorporate three or more sensors, although the inherent motion of the GPS satellites will eventually make up the deficiency if a 15-20 minute wait to collect more data from the new satellite positions is possible. For a spin motion, elevation can be set to 90.degree. and the azimuth is adjusted to generate the spin. Additional drives to do this are avoided, because they can add to the cost significantly.

#A parabolic dish antenna is in no way unique. It is the preferred type in those situations where frequency and gain considerations necessitate the choice. The use of a parabolic dish antenna herein is therefore merely an example of what can be used, and the present invention should not be construed as being limited to pointing any particular type of directional antenna.

Facts

Application

08/033,953Filed 19 Mar 1993 · continuation

Priority

13 Feb 1992

Granted

13 Sep 1994

Term ended

13 Feb 2012

Estimated · how

Pre-1995 term; greater of 17 years from grant or 20 years from filing when eligible. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification7 codes

H04B 7/0814
With single receiver and antenna switching: based on current reception conditions, e.g. switching to different antenna when signal level is below…
G01S 19/54
Determining attitude: using carrier phase measurements; using long or short baseline interferometry
H01Q 1/3275
Characterised by the location of the antenna on the vehicle: mounted on a horizontal surface of the vehicle, e.g. on roof, hood, trunk
H01Q 3/10
For varying two co-ordinates of the orientation: to produce a conical or spiral scan

Automatic antenna pointing system based on global positioning system (GPS) attitude information

Life of this patent

Automatic antenna pointing system based on global positioning system (GPS) attitude information

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims10

Description9,744 words

Drawings

Classification7 codes

Life of this patent

Description9,744 words