The present invention relates to a conical scanning antenna system using a nutation method; and more particularly to a conical scanning antenna system using a nutation method for effectively tracking a satellite by using a nutation method of a sub-reflector in an offset dual reflector antenna structure.
Generally, tracking algorithms for the satellite communication is classified into a closed loop method and an open loop method. The closed loop method is further classified into a lobing method and a mono-pulse method.
The closed loop method is designed to control the antenna in a predicted orbit direction by processing satellite orbit forecasting data, standard time data, and antenna digital angle data using a computer. Therefore, the tracking performance of the antenna depends on the accuracy of the data. The lobbing method is designed to control the orientation of the antenna by detecting a coming direction of a bicorn wave by moving a beam of the antenna using a predetermined method. The mono-pulse method is designed to detect an azimuth error on occasion in accordance with a radio wave with a single pulse in a state where the beam of the antenna is fixed.
The lobbing methods are further classified into a conical scanning method, a beam switching method, and a step tracking method. The conical scanning method is designed to rotate the beam of an antenna in a conical-shape having a minute angle to perform a closed tracking. The beam switching method is designed to determine a relative receiving signal level while discretely moving the beam to more than four pre-determined locations disposed around the axis of the antenna. The step tracking method is designed to move the beam in a direction where the receiving level is increased by checking the variation of the receiving level while moving the antenna by a minute angle in a step manner at a predetermined time interval.
As shown in
However, offset dual reflector antenna systems generally employ a sub-reflector having a predetermined asymmetric shape to have an axial asymmetric characteristic in order to optimize the performance thereof. Therefore, the tracking method using the rotation of the sub-reflector may cause a tracking beam to have an asymmetry characteristic for an asymmetric axis.
It is, therefore, an object of the present invention to provide a conical scanning antenna using a nutation method for tracking a satellite by nutating a sub-reflector in an offset dual reflector antenna structure.
In accordance with one aspect of the present invention, there is provided a conical scanning antenna system using a nutation method of a sub-reflector in an offset dual reflector structure, the conical scanning antenna system including: a main reflecting unit; a sub-reflecting unit which is disposed apart from the main reflecting unit by a predetermined distance and performing a conical scanning tracking by using the nutation method; and a feeding horn which doubly reflects electromagnetic wave inputted and radiated by the main reflecting unit and the sub-reflecting unit and inputting and outputting the electromagnetic wave by electrically steering beams.
A conical scanning antenna system according to the present invention performs a satellite tracking function using a nutation method of a sub-reflector in an offset dual reflector antenna structure.
The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:
Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.
Referring to
As shown in
The sub-reflector 501 has an oval contour line. The motor 505 is connected to the bracket 506 and the rotator 503 is connected to the one end of the motor 505. The rotator 503 is mounted at the first supporting frame 502 to enable the sub-reflector 501 to nutate. The second supporting frame 504 is formed in a ring shape. The ring shaped second supporting frame 504 is connected to the one end of the first supporting frame 502 to support the first supporting frame 501. It is preferable that the rotator 503 may be formed of bearings.
Also, the motor 505 and the rotator 503 are disposed to align the extension lines of the central shaft C of the motor 505 and the central shaft C of the rotator 503 to be met at the central shaft of the second supporting frame. Furthermore, the central shaft of the motor 505, which is the central axis of the sub-reflector 501, is separated from the central shaft of the rotator 503 by about 15 mm and tilted at an angle of 0.76.
The second supporting frame 504 connected to the first supporting frame 502 functions as a fixing unit by rotation motions made by the rotator 503, and the sub-reflector makes a nutation motion as a motion eccentric to the central point of the motor.
Furthermore, the conical scanning antenna system according to the present embodiment further includes an orthogonal polarization mode separator 605, a receiving band filter 606, a low-noise downlink frequency converter 607, and a high-power uplink frequency converter 608.
The orthogonal polarization mode separator 605 is for transmitting and receiving a signal. The receiving band filter 606 suppresses a transmit signal not to inflow into a receiving band. The low-noise downlink frequency converter 607 performs low-noise amplification and down-conversion to transform a signal into an intermediate frequency signal, and the high-power uplink frequency converter 608 up-converts the transmit band intermediate frequency signal and performs the high-power amplification on the up-converted signal.
Comparing with the conventional on-set antenna or the signal reflector, electric wave blockage caused by a sub-reflector and supporting frames is minimized so as to increase the efficiency thereof. The feeding horn is disposed at a focus point 202 for electric feeding.
More concretely, the feeding horn 604 is disposed at a focus point, and the nutation motion of the sub-reflector 501 is decided by a distance 304 between a center point 303 and the sub-reflector 501 and an offset angle 305 from the central point for the nutation motion.
The sub-reflector also has a predetermined offset angle to the left and to the right when a conical scanning is performed from the left to the right. That is, the sub-reflector has a predetermined sub-reflector angle tilted at a predetermined axis direction, and the sub-reflector makes the nutation motion while moving in the axis direction for a predetermined time.
If the oval sub-reflector rotates at 90 from the top/bottom tracking to the left/right tracking according to the conventional rotating motion, the oval sub-reflector becomes unable to form identical beam patterns for tracking a satellite because the longitudinal axis and the short axis of the oval circle of the sub-reflector are reversed.
The sub-reflector according to the present embodiment makes the nutation motion at about 15 mm of a gap 304 from the center point 303 of the sub-reflector with 0.76 of a tilting angle 305.
The present application contains subject matter related to Korean patent application No. 2005-119510, filed with the Korean Intellectual Property Office on Dec. 8, 2005, the entire contents of which is incorporated herein by reference.
While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
Number | Date | Country | Kind |
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10-2005-0119510 | Dec 2005 | KR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/KR2006/003359 | 8/25/2006 | WO | 00 | 6/6/2008 |
Publishing Document | Publishing Date | Country | Kind |
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WO2007/066874 | 6/14/2007 | WO | A |
Number | Name | Date | Kind |
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4041500 | Lapp | Aug 1977 | A |
4305075 | Salvat et al. | Dec 1981 | A |
6307523 | Green et al. | Oct 2001 | B1 |
6833819 | Lynch | Dec 2004 | B2 |
Number | Date | Country |
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10-2004-0057306 | Jul 2004 | KR |
9960656 | Nov 1999 | WO |
Number | Date | Country | |
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20080291102 A1 | Nov 2008 | US |