JP2010136258A - Tracking antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tracking antenna capable of avoiding gimbal lock without using three high-torque motors. <P>SOLUTION: In an azimuth angle axis, an elevation angle axis and an orthogonal elevation angle axis, an orientation direction around the orthogonal elevation angle axis is controlled within a relatively limited range in accordance with a physical technique for moving a physical position of a feeding section or an electrical technique with which a plurality of element antennas constituting the feeding section are provided and excited with appropriate amplitude and phase distributions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pointing direction tracking antenna technique in an earth station device for mobile satellite communication.

  Since the pointing direction tracking antenna adjusts the pointing direction in the elevation and azimuth directions, a mechanism that rotates around each of the elevation and azimuth axes is required. FIG. 1 shows a configuration of a tracking antenna (hereinafter, a conventional two-axis control antenna) in which a tracking range is limited to a low elevation angle in a conventional tracking antenna based on this mechanism. When directing a low elevation angle as shown in FIG. 1, the orientation direction can be controlled two-dimensionally by rotating around the elevation axis and the azimuth axis. However, when pointing to the zenith (elevation angle 90 degrees), it cannot be driven in a direction perpendicular to the elevation axis. In order to control the directivity direction orthogonal to the elevation angle axis in this state, the azimuth angle axis must be instantaneously rotated by 90 degrees, but this is impossible in practice. This state is generally called gimbal lock. In order to avoid the gimbal lock, as described in Non-Patent Document 1, as shown in FIG. 2, a three-axis rotation mechanism to which an axis orthogonal to the elevation angle axis (orthogonal elevation angle axis) is added is taken. This configuration is called a conventional three-axis control antenna.

  In the case of a communication antenna, it is necessary to align the polarization axis, and as shown in FIG. 3, the polarization axis is aligned by rotating the power feeding unit around the axis with respect to the directivity direction. In general, this is done by physically rotating the feeding portion of the antenna.

“Tracking 3-axis swivel device”, Narumi et al., Toshiba Review Vol. 59, no. 10, 2004

  In a conventional three-axis control antenna, the azimuth axis and two orthogonal elevation axes need to rotate the entire antenna. The antenna used for the mobile satellite earth station is a large structure having an aperture diameter exceeding φ1 m, and three high-torque motors are required to realize the tracking antenna.

  At this time, since a high torque motor is not small in weight, the necessity of providing a plurality of high torque motors causes a further increase in the weight of the entire antenna and requires a torque request in consideration of the weight of the motor. Further, when the tracking speed and tracking accuracy are increased, higher torque performance is required, which leads to further increase in antenna weight.

  Therefore, an object of the present invention is to provide a tracking antenna that can avoid gimbal lock without using three high torque motors.

  In order to achieve the above object, the tracking antenna according to the present invention comprises means for controlling a directivity direction with respect to two axes of an elevation angle axis and an azimuth angle axis, and the two axes with respect to an orthogonal elevation angle axis orthogonal to the elevation angle axis. And sub-adjusting means for controlling the directivity direction in a narrower range.

  The tracking antenna is preferably composed of a plurality of element antennas, and the sub-adjusting means is means for changing an excitation distribution of each element antenna.

  In order to achieve the above object, the tracking antenna according to the present invention is a tracking antenna composed of a reflecting mirror and a power feeding unit for feeding the reflecting mirror. Means for controlling the directivity direction of the mirror, and sub-adjustment means for controlling the directivity direction of the reflecting mirror within a range narrower than the two axes with respect to the orthogonal elevation angle axis orthogonal to the elevation angle axis.

  Moreover, it is preferable that the said sub adjustment means is a means to move the position of the said electric power feeding part.

  The reflecting mirror is a rotationally symmetric reflecting mirror, the power feeding unit is arranged at a position shifted from the focal position of the reflecting mirror, and the sub-adjusting means is means for rotating the power feeding unit around the focal point. It is also preferable that there is.

  It is also preferable to further include means for controlling the electromagnetic field distribution of the power feeding unit.

  In addition, it is preferable that the power feeding unit includes a plurality of element antennas, and the sub-adjusting unit is a unit that changes an excitation distribution of each element antenna.

  The tracking antenna according to the present invention is a conventional three-axis control antenna that avoids gimbal lock, and is configured by three high torque motors (azimuth axis, elevation axis, orthogonal elevation axis) for rotating the entire antenna. A tracking antenna can be configured with two high-torque motors (azimuth angle axis and elevation angle axis) and sub-adjustment means for the antenna, which can contribute to reduction of antenna weight and cost reduction.

  Furthermore, by performing two-dimensional directivity control with the sub-adjusting means, it contributes to the realization of higher speed and higher accuracy tracking.

  In the conventional three-axis control antenna that has been configured with three conventional high-torque motors (azimuth axis, elevation axis, orthogonal elevation axis), the required number of high-torque motors is two (azimuth axis and elevation axis). An example of the antenna configuration of a tracking antenna that can avoid locking is shown below.

  The technical point of the present invention is to control the directivity of the portion that was responsible for the directivity control around the orthogonal elevation axis without changing the attitude of the entire antenna by the high torque motor as in the prior art. . Specifically, a physical method of moving the physical position of the power feeding unit, or an electrical method in which a plurality of element antennas constituting the power feeding unit are provided and excited with an appropriate amplitude and phase distribution are used. The directivity is controlled within a relatively limited range. By these methods, the directivity direction control means around the orthogonal elevation axis is referred to as sub-adjustment means.

  When the conventional biaxial control antenna is directed to the zenith (elevation angle 90 degrees) and driven in the orthogonal elevation axis direction, the azimuth axis must be instantaneously rotated 90 degrees. When using the sub-adjusting unit, the azimuth axis may be rotated by 90 degrees while the sub-adjusting unit is tracking around the orthogonal elevation axis. Thereafter, the control amount in the elevation angle direction is transferred to the tracking by the elevation angle axis, thereby avoiding gimbal lock. As shown in FIG. 5C of Non-Patent Document 1, since it can be confirmed that the variable range around the orthogonal elevation axis is at most several degrees and the gimbal lock can be avoided, the control range of the sub-adjusting means may be as narrow as that. Absent.

  In addition, coarse adjustment is performed for the whole antenna shaft rotation, and the variable range is limited, but the sub-adjustment means that can be expected to achieve high-speed and high-accuracy control can apply two-dimensional directivity control so that the antenna as a whole・ High precision tracking can be realized. When the sub-adjusting means is realized by a physical method, the moving part becomes lighter than the case where the entire antenna is rotated, so that the torque requirement for the motor for realizing high-speed tracking is also reduced. Further, when the sub-adjusting means is realized by an electrical method, it can be dealt with only by switching the setting.

  FIG. 4 shows a configuration example of the pointing direction tracking antenna in the first embodiment of the present invention. This configuration example includes a reflecting mirror and a power feeding part (element antenna) for feeding power to the reflecting mirror, and a mechanism for moving the azimuth angle axis, the elevation angle axis, and the power feeding part position. In the reflector antenna, since the directivity direction changes according to the physical position of the element antenna, the directivity direction can be controlled by moving the feeding unit around the orthogonal elevation axis so that the directivity direction changes. At this time, since only the position of the power feeding unit needs to be moved within a minute range, it can be realized by a small motor with low torque. FIG. 5 is a conceptual diagram in a case where the zenith direction is directed. By controlling the position of the power feeding unit, the directing direction can be controlled around the orthogonal elevation axis, and the avoidance of gimbal lock can be confirmed.

  An analysis example is shown for the characteristics when the reflecting mirror is a parabola with an aperture diameter of φ1 m and the feeding portion is shifted ± 5 cm from the focal position. The frequency was in the 14 GHz band. 6 and 7 show the characteristics when the power feeding position is +5 cm and −5 cm, respectively, with respect to the focal position, and FIG. 8 shows the characteristics when the power feeding position is installed at the focus. FIG. 9 shows a cut pattern. In the case of this example, it can be confirmed that continuous directivity control of 5 degrees can be realized on the orthogonal elevation axis.

  FIG. 10 shows an antenna configuration in the second embodiment of the present invention. This configuration example includes a rotationally symmetric reflecting mirror and a power feeding unit for feeding power to the reflecting mirror, and an azimuth axis, an elevation angle axis, and a mechanism for rotating the power feeding unit (hereinafter referred to as a power feeding unit rotation axis). This antenna is characterized in that a power feeding unit is disposed at a position deviated from the focal position of the reflecting mirror, and the position of the power feeding unit is rotated around the focal point by a power feeding unit rotating shaft. By shifting the position of the power feeding unit from the focal position, the directivity direction of the antenna is deviated from the front of the antenna, and by rotating the power feeding unit, the directivity direction of the antenna has a certain angle around the front of the antenna. Rotate. At this time, since the motor used for the power feeding unit rotating shaft only needs to rotate the power feeding unit, it can be realized by a small motor with low torque. FIG. 11 is a conceptual diagram when the zenith direction is directed. By controlling the position of the power feeding unit, the directivity direction can be controlled with respect to the orthogonal elevation axis, and the avoidance of gimbal lock can be confirmed.

  Regarding the analysis example, the characteristics when the rotation angle of the power feeding unit position is 0 and 180 degrees coincide with those in FIGS. 6 and 7. In the case of this example, it can be confirmed that the pointing method is rotating while maintaining a 5 degree separation from the center of the origin.

  However, since the feeding unit rotation axis in the antenna of the present invention is used for polarization adjustment in the conventional biaxial and triaxial control antennas, the polarization tracking function is impaired. Therefore, the antenna of the present invention is limited to a system that does not require polarization tracking such as circular polarization.

  In the case of this example, the larger the angle of separation from the center, the larger the variable range around the orthogonal elevation axis, and it is desirable to increase the amount of deviation from the focal point. However, if the amount of shift of the power feeding unit position is simply increased, the gain decreases as shown in FIG. 12, the side rope level increases, and the antenna characteristics deteriorate. In order to avoid this, the reflection mirror surface correction specialized for the position of the power feeding unit and the electromagnetic field distribution of the power feeding unit may be controlled. The electromagnetic field distribution can be controlled by correcting the shape of the opening surface or by forming an array of the power feeding unit.

  FIG. 13 is an analysis example in the case where the power feeding unit is configured by two elements and the electromagnetic field distribution of the power feeding unit is controlled, and it can be confirmed that the gain and the side rope characteristics are improved. In this example, another element is arranged on the rotation axis of the power supply unit with the element movable with respect to the rotation axis of the power supply unit as a reference, and excitation is performed by reducing the 10 dB gain.

  As a guideline for the control of the electromagnetic field distribution, a low side rope and an improvement in gain can be realized. That is, in an antenna composed of a plurality of element antennas, the excitation amplitude / phase distribution of each element antenna is set so that the antenna pattern has a desired characteristic (for example, a characteristic in which a side rope as a transmission antenna satisfies a regulation). Optimization or optimization is performed so that the antenna pattern has a desired characteristic and the gain of the antenna is maximized.

  FIG. 14 shows an antenna configuration according to the third embodiment of the present invention. In this configuration example, a reflecting mirror antenna is fed by two or more element antennas, and the directivity is controlled by exciting each element antenna with a predetermined amplitude according to the directivity direction. Each element antenna includes a 90-degree hybrid, phase control means, and transmission and reception amplification means. At this time, the positions of the amplifying means in the transmission and reception systems are different, but there is no problem in operation. However, in the receiving system, it is required to connect immediately after the element antenna due to the influence of noise, and in the transmitting system, the connection is made between two 90-degree hybrids in order to equalize the operation level.

  The two element antennas are arranged at a position where the reception level is highest with respect to the incoming wave in the directivity direction from ± θ. At this time, it is necessary to set the half-value angle of the beam when power is supplied from one element antenna to be smaller than 2θ. At this time, by adjusting the excitation amplitude of each element antenna, the directivity direction around the orthogonal elevation axis can be controlled to be −θ to + θ. In this example, by changing the phase control means, the excitation power to the two antenna elements can be controlled continuously, and the directivity direction around the orthogonal elevation axis can be controlled to -θ to + θ. it can.

のように表せる。なお、ここでλは自由空間波長である。
図１５は、２つの平面アンテナの組み合わせで構成される追尾アンテナの構成例を示す。このとき、衛星で一般的に使用される１２／１４ＧＨｚ帯での自由空間波長は２０ｍｍ〜２５ｍｍ、アンテナ開口を１ｍとした場合、素子数を２とする場合、ｄ＝０．５ｍとなるため、±１．２度程度指向方向を可変させることが可能である。さらなる指向方向を得る場合は、素子アンテナ数を増加させ、素子間隔が小さくさせればよい。 The tracking antenna of the present invention is not limited to a reflector antenna. For example, the present invention can be applied to a tracking antenna configured by a combination of planar antennas. In an antenna composed of a plurality of elements, the directivity can be adjusted by exciting the element antenna with an appropriate phase. When the distance between the element antennas is d, the directing direction around the orthogonal elevation axis is

It can be expressed as Here, λ is a free space wavelength.
FIG. 15 shows a configuration example of a tracking antenna configured by a combination of two planar antennas. At this time, when the free space wavelength in the 12/14 GHz band generally used for satellites is 20 to 25 mm, the antenna aperture is 1 m, and the number of elements is 2, d = 0.5 m, It is possible to vary the directivity direction by about ± 1.2 degrees. In order to obtain a further directivity direction, the number of element antennas may be increased and the element spacing may be reduced.

  Moreover, all the embodiment described above shows the present invention exemplarily, and does not limit the present invention, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

Conceptual diagram of pointing method in conventional biaxial control antenna Gimbal lock avoidance method for conventional 3-axis control antenna The concept of polarization tracking in communication antennas. Configuration example of pointing direction tracking antenna in the first embodiment of the present invention The movable range near the zenith in the first embodiment of the present invention Calculation example of antenna pattern in the first embodiment of the present invention (feeding portion position: −5 cm) Calculation example of antenna pattern in the first embodiment of the present invention (feeding portion position: +5 cm) Calculation example of antenna pattern in the first embodiment of the present invention (feeding portion position: focal position) Comparison of antenna patterns by cut patterns in the first embodiment of the present invention Antenna configuration in the second embodiment of the present invention The movable range near the zenith in the second embodiment of the present invention Comparison of antenna pattern by cut pattern with respect to deviation from focus in the second embodiment of the present invention Comparison of antenna patterns by cut patterns in the second embodiment of the present invention Configuration example of pointing direction tracking antenna according to the third embodiment of the present invention Configuration example of a tracking antenna composed of a combination of two planar antennas

Claims (7)

Means for controlling a directivity direction with respect to two axes of an elevation angle axis and an azimuth angle axis;
Sub-adjusting means for controlling the directing direction in a range narrower than the two axes with respect to the orthogonal elevation angle axis orthogonal to the elevation angle axis;
A tracking antenna characterized by comprising: The tracking antenna is composed of a plurality of element antennas,
The tracking antenna according to claim 1, wherein the sub-adjusting means is means for changing an excitation distribution of each element antenna. In a tracking antenna composed of a reflecting mirror and a feeding unit for feeding the reflecting mirror,
Means for controlling the directing direction of the reflecting mirror with respect to two axes of an elevation angle axis and an azimuth angle axis;
Sub-adjusting means for controlling the directing direction of the reflecting mirror in a range narrower than the two axes with respect to the orthogonal elevation angle axis orthogonal to the elevation angle axis;
A tracking antenna characterized by comprising:   The tracking antenna according to claim 3, wherein the sub adjustment unit is a unit that moves the position of the power feeding unit. The reflecting mirror is a rotationally symmetric reflecting mirror, and the power feeding unit is disposed at a position shifted from a focal position of the reflecting mirror,
The tracking antenna according to claim 3, wherein the sub-adjusting unit is a unit that rotates the power feeding unit around the focal point.   The tracking antenna according to claim 5, further comprising means for controlling an electromagnetic field distribution of the power feeding unit. The feeding unit is composed of a plurality of element antennas,
The tracking antenna according to claim 3, wherein the sub-adjusting means is means for changing an excitation distribution of each element antenna.

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