Note: Descriptions are shown in the official language in which they were submitted.
CA 02325355 2000-11-08
1 METHOD FOR HOMING !N ON A SELECTED SATELLITE, AND A
2 CONTROLLER FOR ORIENTING A ROTATABLE ANTENNA
3
4 CROSS~REFERENCES TO RELATED APPLICATIONS
6 This application claims the priority of German Patent Application Serial
7 No. 199 54 .531 _6, filed November 12, 1999, the subject matter of which is
8 incorporated herein by reference.
9
",0 BACKGROUND OF THE INVENTION
11
12 The present invention relates to a method for homing in on a selected
13 satellite from a predetermined geographic location whose geographic
14 coordinates are known, with an antenna that is rotatabiy supported for
rotation in
a respective horizontal and vertical plane. The invention also relates to a
16 controller for orienting a rotatable antenna with respect to an
electromagnetic
17 radiation source of a sateffite_
18
19 Antennas for receiving electromagnetic radiation from a transmitter that is
part of a satellite positioned at a specified location in an orbit has become
21 increasingly important. An antenna capable of receiving a signals that are
22 transmitted by the transmitter of the satellite can be used to monitor
events that
23 occur over a wide area on the Earth surface, for example traffic
patternsSuch
1
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1 an antenna can alsa be used to receive television programs transmitted by
the
2 transmitter. A rotatable antennas can be oriented with respect to the
transmitter
3 so as to receive an optimal power level radiated by the transmitter. For
this
purpose, a controller has to be provided that can generate control signals and
transmit these control signals to drives that rotate the antenna in an
horizontal
6 and a vertical plane.
8 The control signals are difficult tQ produce because not only has the
9 antenna to be positioned to receive the signals radiated by a specified
transmitter, but the antenna also has to be adjusted so as to guarantee
reception
11 of the radiated transmitter power.
~2
13 SUMMARY OF THE INVENTION
14
It is thus an object of the present invention to provide an improved method
16 for receiving signals transmitted by a satellite transmitter, obviating the
afore-
17 stated drawbacks.
18
19 In particular, it is an object of the present invention to improve the
method
for receiving signals transmitted by a satellite transmitter so that the
antenna
21 orientation with respect to the transmitter is automatically adjusted.
22
23 According to one aspect of the invention, the antenna is aligned with a
2
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1 theoretical receive direction corresponding to a known location of the
satellite.
2 The electromagnetic power received in the receive direction is compared with
an
3 optimally possible satellite power known for the selected satellite. if the
received
4 electromagnetic power is different from the optimally possible satellite
power of
the selected satellite, then the antenna is rotated in a direction where the
G received power is greater.
7
8 With this method, it is possible to use the transmitter pf a specified
satellite
9 to adjust the antenna to an optimal receive position. For this purpose, the
known
position of the satellite is first entered into a computer. The computation is
based
11 n the respective terrestrial coordinates of the antenna location. The
computer
12 uses these two data sets to calculate a direction in which theoretically an
optimal
13 power reception from the satellite's transmitter can be expected. The
antenna is
~? 4 then rotated in the horizontal and vertical direction according to this
calculated
direction Thereafter, the power reaching the antenna is compared with the
16 optimal power expected from the transmitter to determine if the antenna is
17 optimally oriented with respect to the transmitter. If the orientation is
not yet
18 optimized, then the measure of the deviation from the optimal power is also
a
19 measure in which direction and by how much the antenna has to be rotated
until
it is in a position where the expected received power is optimal.
21
22 According to a preferred embodiment of the invention, the theoretical
23 receive direction of the antenna is calculated from a known orbital
position of the
3
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1 selected satellite and the geographic coordinates of the terrestrial
location. In
2 view of the substantially linear path of the electromagnetic beam radiated
from
3 the transmitter, the antenna can be oriented so as to substantially meet the
4 optimal receiving conditions The antenna is aligned by checking if the
received
satellite power increases or decreases in an adjacent rotation position.
6
7 According to another preferred embodiment of the invention, an antenna
8 window is defined and a search for the satellite is performed in the window
9 opening. If the satellite is not found within the window opening, then a
second
window with an enlarged window opening is superimposed on the first window,
11 and the search is continued. It can then be determined by decreasing or
12 increasing the respective window size how a further search for the
specified
13 transmitter is to be conducted.
14
According to another preferred embodiment of the invention, the identity of
16 a detected satellite is checked and the coordinates of the detected
satellite are
17 compared with the coordinates of the selected satellite. Difference data
are
18 determined from this comparison and the antenna is adjusted in response to
19 these difference data to paint in the direction of the selECted satellite.
In this way,
also satellites that are not selected are included in the search pattern_ A
further
21 search for the desired satellite can then be based on the satellites that
are not
22 selected and their position relative to the desired selected satellite.
23
4
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1 According to another preferred embodiment of the invention, the
2 difference data are determined as a deviation between the direction and an
angle
3 of a detected satellite from the direction and angle of a selected satellite-
These
4 two data sets, the direction and the angle between these directions,
respectively,
provide a measurement by which the antenna has to be aligned with respect to
6 the direction of the selected satellite-
8 According to another preferred embodiment of the invention, a satellite
9 that has already been detected once, is not located a second time during a
search for the selected satellite- Excluding an already tracked satellite
during a
11 search a the desired satellite prevents the search for the desired
satellite from
12 being restricted to the region where a certain satellite with a
particularly high
13 radiated transmitter power has been found before. Without the exclusion of
this
14 particular satellite, the selected satellite which may have a smaller
radiated
transmitter powEr may never be found in a furkher search or may be found only
16 with great difficulty.
17
18 According to another preferred embodiment of the invention, the direction
19 of an antenna is calibrated with reference to an already detected satellite
whose
direction has been recognized This measurement for the antenna can then be
21 used to adjust the antenna with respect to the selected satellite.
22
23 According to another preferred embodiment of the invention, the antenna
5
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1 can include a polarotor, wherein the polarization rotation can optimized via
a
2 control line. The signal can be optimized by a suitable alignment of the
polarotor
3 and adjustment of its rotation speed, with the signal being optimized based
on
4 the received and radiated power of the antenna.
6 The antenna is preferably aligned with the help of a controller capable of
7 orienting the rotatable antenna towards an electromagnetic radiation source
of a
8 satellite. Such controllers should be compact and easy to operate.
9
According to another aspect of the invention, the controller includes a first
11 input for inputting signals corresponding to a terrestrial location and a
second
12 input for inputting signals corresponding to an actual orbital location of
the
13 radiation source. The two inputs are connected with a comparator that
compares
14 the respective signals with each other. The outputs of the controller are
connected with drives for rotating the antenna. Such a controller can be
16 connected easily with input devices capable of providing, on one hand,
17 information about the respective terrestrial location and, on the other
hand,
1 ~3 indicating the known orbital location of the selected satEllite. These
two data
19 sets are then correlated in the controller by a computer, causing the
output of the
controller to transmit signals to the antenna drives. The signals controllably
21 move the antenna to a position where the power radiated by t>~e transmitter
can
22 be received.
23
6
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1 According to another preferred embodiment of the invention, a housing
2 with those inputs can have an outside dimension corresponding tQ the outside
3 dimension of a housing in which customarily devices of radio navigation
system
4 that control a ship's course are housed. The dimension of the housing
enables
the controller to conform to the housing dimensions customarily used onboard
6 ships, so that these two housing types can be easily intermingled. Since the
7 controller is preferably intended for used onboard ships, the controller
will find
8 increased use because of its advantageous housing dimensions.
9
1o BRIEF DESCRIPTION GF THE DRAWING
11
1'o The above and other objects, features and advantages of the present
13 invention will be more readily apparent upon reading the following
description of
14 a preferred exemplified embodiment of the invention with reference to the
accompanying drawing, in which
16
17 FIG. 1 shows schematically a ship traveling within the range of two
18 satellites;
19
FIG. 2 shows schematically a rotatable antenna connected with a
21 controller; and
22
23 FIGS- 3 is a section through a controller along the line 111-III of FIG. 2.
7
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1 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
2
3 Throughout all the Figures, same or corresponding elements are generally
4 indicated by same reference numerals.
6 Turning now to the drawing, and in particular to FIG. 1, there is shown a
7 Referring first to FIG_ 1, a ship 1 is at sea 2 at a location 3 with assumed
8 coordinates X, Y. At this location 3, the ship travels within the range of
twd
9 satellites 4, 5 which are equipped with transmitters 6, 7_ The transmitters
6, 7
radiate electromagnetic beams 8, 9 in the direction of the location 3. The
11 direction of the electromagnetic beams 8, 9 is determined, on one hand, by
the
12 coordinates X, Y of the location 3 and, on the other hand, by the orbital
'! 3 positions 10, 11 of the two satellites 4, 5. The electromagnetic beams 8,
9
14 radiated by the transmitters 6, 7 enclose an angle 12 according to the
orbital
positions 10, 11.
16
17 The electromagnetic beams 8, 9 are received by a rotatable antenna 13
18 installed on board the ship 1. The received beams 8, 9 provide exact data
about
19 the ship's location 3. The transmitters 6, 7 can also transmit programs of
interest
onboard the ship 1, for example television programs, if the transmitters 6, 7
have
21 access to such television programs.
12
23 The connection between the ship 1 and the satellites 4, 5 as established
8
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1 by the electromagnetic beams 8, 9 can be lost, for example when changing
2 course or in heavy seas. There are other situations in which a connection
3 between the rotatable antenna 13 and the transmitters 6, 7 of the satellites
4, 5
4 has to be established- For this purpose, as seen more clearly in FIG 2, a
controller 14 is provided onboard the ship 1 to establish a relationship
between
6 the rotatable antenna 13 and the transmitter 6 of satellite 4_ For this
purpose, a
tiltable dish 15 is provided inside the rotatable antenna 13, with the dish
being
8 rotatably supported for rotation about a horizontal axis 16 in a vertical
plane and
9 about a vertical axis 17 in a horizontal plane 1$. An electric drive 19 is
provided
far rotating the dish 15 in the vertical plane and another electric drive 24
far
11 rotating the dish 15 in a horizontal plane.
12
13 ThE dish is connected by a connecting line 21 with an upper jack 22, the
14 drive 19 by a fine 23 with a center jack 24, and the drive 20 by a line 25
with a
lower jack 26 of the controller 14. The jacks 22, 24, 26 are connected on top
of
15 one another in a side wall 27 of the controller 14.
17
18 A computer 28 is located inside the controller 14_ The computer 28 is
19 connected to a satellite memory device 30 via a connecting line 29 and to a
coordinate memory device 32 via a connecting line 31. Moreover, the two
21 memory devices 30, 32, the computer 28 and the jacks 22, 24, 26 are
connected
22 to a current source 39, for example a rectifier The current source 39 also
23 supplies electric power to operating switches 40, 41, 42, 43 implemented,
for
9
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1 example, as momentary contact switches_ The operating switches 40, 41, 42,
43
2 are arranged on a front panel 44 of the controller 14 The front panel 44 may
also
3 incorporate a display 45 to indicate the respective operating state of the
4 controller 14_
6 Two additional jacks 47, 48 which connect the controller 14 to a
7 compass 49 and a power source 15 for supplying power to the rectifier 39 are
8 arranged in a side wall located opposite the side wall 27. Also located on
the
9 front panel 44 of the controller 14 are three LED's 51, 52, 53 which can
emit light
in different colors, such as red, yellow and green, to indicate the switching
state
1 1 of the controller 14.
12
13 The rotatable antenna 13 can be aligned with a selected satellite 4 by
first
14 inputting the orbital coordinates of satellite 4 from the satellite memory
device 30
into the computer 28 via the connecting line 29. The terrestrial coordinates
of the
16 location 3 are then determined by the compass 49 and inputted into the
computer
17 28 via the jack 47. For these two values, the computer 28 then calculates
the
18 ideal path of the electromagnetic beams 8 from the satellite's transmitter
6 to the
19 rotatable antenna 13. The computer 28 controls the electric drives 19, 20
according to the ideal path so as to align the rotatable dish 15 in the
direction of
21 the transmitters 0 of the selected satellite 4. The memory device 30 not
only
22 stores the orbital position of the satellite, but also the optimal power of
the
23 beam 8 radiated by the transmitter 6. These values are also inputted in the
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1 computer 28. After the dish 15 is oriented, the received electric power is
also
2 inputted in the computer 28 for a comparison with this optimal power, The
3 computer 28 compares the optimal power of the transmitter 6 with the power
4 received by the dish 15. When the computer 28 detects the difference between
the optimal power of the transmitter 6 and the received power of the dish 15,
then
6 the computer 28 converts this difference into a switching signal which is
used to
7 move the electric drive 19 or the electric drive 20 or both drives 19, 20.
These
8 drives rotate the dish 15 in accordance with the received control signal in
a
9 direction for which of the computer 28 has computed an increase of the power
received by the dish 15. If the program and the computer 28 operate correctly,
11 then the dish 15 rotates in a direction in which the power recEived by the
dish 15
12 from the transmitters 6 increases. This rotation continues until the
received
13 power corresponds to the programmed reduction of the transmitted power of
14 transmitter 6.
16 However, if after a rotation of the dish 15 the received power is less than
17 the theoretical power computed by the computer 28 for the position of the
8 dish 15, then the value of the power that was mast recently received by the
19 dish 15 is entered into the computer 28 and compared with the previously
computed power received by the dish 15. If a difference is observed which
would
21 necessitate a further rotation of the dish 15, then the computer 28
computes
22 which of the two drives 19, 20 has to be energized to rotate the dish 15 in
a
23 direction where the dish 15 receives more electromagnetic power from the
11
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1 transmitter 6 than before. By properly comparing the power received by the
dish
2 15 with the power transmitted by the transmitter 6, the antenna 13 is
finally
3 placed in a position where an optimal portion of a power transmitted by the
4 transmitter 6 is received.
6 The operating switches 4~ can be used to select one of several
7 satellites 4, 5. The selected satellite 4 is then indicated on the display
45.
8
9 When the ship 1 changes course, the new course determined by the
compass 49 is entered into the computer via the switch 41. The computer 28
11 then controls the dish 15 in accordance to the new course via the two
drives 19,
~ 0 20. If the orientation of the dish has to be corrected manually
independent of the
13 control exercised by the computer 28, then the dish 15 can be rotated
vertically
14 by energizing the drive 19 via the operating switch 42. The dish 15 can be
rotated horizontally relative to the satellite 4 by energizing the drive 2D
via the
16 operating switch 43.
17
18 The antenna 13 can also be aligned by tilting the antenna by an angle 12
19 from the direct line of sight with the satellite 5. In this case, the
direction of the
beam 9 can be entered into the computer 28 if this direction has not yet been
21 stored based on a previous tilting motion of the dish 15, The direction of
the
22 beam 8 can tie inputted into the computer 28 by entering the angle 12,
thereby
23 controlling the drives 19, 20 with respect to the desired position of the
satellite 4.
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1 In a similar manner, when searching for a selected satellite 4, the antenna
13 can
2 be initially aimed at the satellite 5. In this case, it turns out to be
faster to base a
3 change in the antenna direction on the location of the satellite 5 and to
then aim
4 the antenna at the satellite 4 with a corrective motion, rather than
starting a new
search by using the known orbital cQOrdinates of the satellite 4.
6
7 In the event that the orbital position of the satellite 4, 5 has not yet
been
8 established, the measured direction of the electromagnetic beams 9 and the
9 orbital position of the satellite 5 can also be used to calibrate the entire
system.
1 Q Based on this calibration and the deviation of the orbital position of the
selected
11 satellite 4 from the orbital position of the satellite 5, the antenna 13
can be
12 quickly adjusted with respect to the selected satellite 4.
73
14 The computer 28 is programmed so that the satellite 5 which is not
selected, is targeted only once when searching for the selected satellite 4.
This
16 prevents multiple targeting of this satellite 5 which may still serve as a
reference
17 satellite. This multiple targeting could pose a problem if the power of the
18 transmitter 7 is significantly greater than the power of transmitter 6
located in the
19 selected satellite 4. The search for the satellite 4 would become much more
difficult in that the satellite 5 could be detected several times in a row,
whereby
21 the orbital position of the selected satellite 4 would be computed based on
the
22 position of satellite 5, without actually closing in on the satellite 4.
23
13
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1 As seen in FIG 1, a search region can be initially defined in which a
2 search for the satellite 4 is performed. This produces a window 54 with
3 boundaries within which the selected satellite 4 should be found. However,
if the
4 satellite 4 cannot be fiound inside this window 54, then the size of the
window 54
is systematically increased by adding extensions 55 until the selected
satellite 4
6 falls inside the window 54, 55
7
8 Moreover, the efficiency of the antenna 13 may be further enhanced by
9 controlling a polarotor 56 located in front of the dish 15 in the direction
of the
beams 8. The polarotor 56 is driven by a drive 57 and rotates in front of the
11 dish 15. The poiarotor 56 can be tilted relative to the beams 8 depending
on the
12 characteristic properties of the incoming electromagnetic beams 8.
13
14 The effect from the polarotor 5f can be enhanced by adjusting its rotation
speed and tilt relative to the beams 8. For example, when the computer 28
16 detects a difference between the power radiated by the transmitter 6 and
the
17 power received by the dish 15, the rotation speed andJor tilt of the
polarotor 56
18 can be adjusted to make the antenna 13 more efFective
19
While the invention has been illustrated and described as embodied in a
21 method for homing in on a selected satellite and a controller for orienting
a
22 rotatable antenna, it is not intended to be limited to the details shown
since
23 various modifications and structural changes may be made without departing
in
14
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1 any way from the spirit of the present invention.
3 What is claimed as new and desired to be protected by Letters Patent is
4 set forth in the appendEd claims;
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