JPH0758855B2 - Sub-reflector driving device for multi-beam antenna - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sub-reflecting mirror displacement driving device for changing the antenna beam direction by displacing the sub-reflecting mirror in a two-reflection mirror antenna for wireless communication. In particular, the present invention relates to a sub-reflector driving device for a multi-beam antenna.

(2) Conventional technology When the beam width of the antenna mounted on the satellite becomes less than 0.5 °, the beam direction changes remarkably due to the attitude stability error of the satellite. Therefore, in order to stabilize the beam direction, a device that redirects the beam in a direction that compensates for posture variation is required. FIG. 1 shows a general antenna mechanism that changes the beam direction of the antenna by displacing the sub-reflecting mirror. In the figure, 1 is a main reflecting mirror, 2 is a sub-reflecting mirror, 3 is a radiator, 4 is a radiation beam, point C is the center of rotation of the sub-reflecting mirror, point O is the focal position of the main reflecting mirror 1 and coordinate system (X ,
Y, Z) indicates the origin. The sub-reflecting mirror 2 is supported with a point C as a fulcrum, and is configured to be able to rotate vertically and horizontally. The various quantities that have been considered so far regarding the beam deflection are the amount of beam deviation with respect to the rotation angle, the decrease in gain, and the increase in sidelobe level. The main characteristics are shown in FIG. The antenna used for the calculation is an offset Cassegrain antenna with an aperture diameter of 2.5 mφ, the frequency is 30 GHz, and the 3 dB beam width is about 0.3 °. In this antenna, the distance between the point O and the sub-reflecting mirror 2 is about 500 mm. The figure shows changes in gain and side lobe levels due to the difference in the position of the rotation center when the sub-reflecting mirror 2 is rotated so that the beam is deflected by 0.5 °. It has been said that it is preferable to set the rotation center near the origin O because the gain decrease and the sidelobe level increase increase as the rotation center gets closer to the sub-reflecting mirror 2. Recently, in order to increase communication capacity and effectively use frequencies, a multi-beam antenna in which one antenna shares many beams is being introduced. In such a multi-beam antenna, when the beam is deflected by rotating the sub-reflecting mirror, it is necessary to consider a change in the relative positional relationship between the beams, which has not been considered in the past. In this case, there is a drawback in that the rotation of the beam near the origin O causes a large shift in the relative position between the beams.

(3) Object of the Invention An object of the present invention is to reduce the change in the relative positional relationship between the beams and to reduce the gain and the increase in the side lobe when the beam is deflected by driving the sub-reflecting mirror in the multi-beam antenna. Thus, it is an object of the present invention to provide a sub-reflector driving device for a multi-beam antenna in which the rotation center of the sub-reflector is set.

(4) Configuration of the Invention (4-1) Differences between Features of the Invention and Conventional Techniques In the present invention, in an antenna having many beams, when beam deflection is realized by displacing a sub-reflecting mirror, Focusing on the change in the relative positional relationship of the beams, the most important feature is to determine the optimum position of the rotation center of the sub-reflecting mirror and use it for the driving device. In the conventional technique, the center of rotation of the sub-reflecting mirror is selected mainly by paying attention to changes in antenna gain and side lobe level during beam deflection, and the viewpoint is completely different and the optimum position is also greatly different.

(4-2) Example FIG. 3 shows the definition of the beam deflection amount in a plurality of beams when the sub-reflecting mirror is driven. In the figure, (Az, El) is a spherical coordinate system that defines the beam direction, and Az and El are angles in the Y-axis direction and the X-axis direction, respectively. # 1 represents a beam in the direction of the principal axis (Z axis in FIG. 1) of the antenna, and # 2 represents an arbitrary beam among the multi-beams. The beam positions when the sub-reflector is rotated around the Y axis are # 1 'and # 2'.
, And the beam deflection amounts are represented by (ΔAz ₁ ′, ΔEl ₁ ′) and (ΔAz ₂ ′, ΔEl ₂ ′), respectively. Similarly, the beam positions during rotation around the X axis are indicated by # 1 ″ and # 2 ″, and the beam deflection amounts are (ΔAz ₁ ″, ΔEl ₁ ″) and (ΔAz ₂ ″, ΔE
l ₂ ″). Using these notations, the relative deviation in the beam direction when the subreflector is rotated can be defined by the following equations.

Rotation of sub-reflector about Y-axis ΔEl = ΔEl ₁ ′ -ΔEl ₂ ′ (1) ΔElt = ΔAz ₁ ′ -ΔAz ₂ ′ (2) Rotation of sub-reflector about X-axis ΔAz = ΔAz ₁ ″ − ΔAz ₂ ″ (3) ΔAzt = ΔEl ₁ ″ −ΔEl ₂ ″ (4) FIG. 4 is a diagram for explaining the deviation amount according to the present invention, which is a relative deviation difference in the beam direction between two beams. is there. The calculated values are for the beams whose beam directions are 3 beams and 5 beams away from the main axis beam. Figure 4 (a)
Shows the characteristics when the sub-reflector is rotated around the X axis, and (b) shows the characteristics when rotated around the Y axis. In both cases, the relative deviation in the direction parallel to the rotation direction of the sub-reflecting mirror is large. Judging from this amount, the rotation center of the sub-reflecting mirror should be set as close to the sub-reflecting mirror as possible.

On the other hand, from the antenna gain and side lobe characteristics in FIG. 2, it is understood that the rotation center of the sub-reflecting mirror should be selected near the focus of the main reflecting mirror.

Considering the above contradictory characteristics, in order to reduce the relative deviation in the beam direction and the deterioration of the antenna gain and side lobe characteristics in the multi-beam antenna,
It is appropriate to select a value of 200 to 300 mm as the rotation axis (L) of the sub-reflecting mirror. This value is the center point of the sub-reflecting mirror 2 (denoted by S in FIG. 1) and the focus of the main reflecting mirror 1 (denoted by O in FIG. 1).
It corresponds to approximately 1/2 of the line segment connecting and, and when applied to the apparatus of FIG. 1, it will be corrected to L ▲ ▼ / 2.

(5) Effects of the Invention As described above, according to the present invention, if the center of rotation of the sub-reflecting mirror is installed near the midpoint between the focal points of the sub-reflecting mirror and the main reflecting mirror, the positional relationship between the beams, which is a problem in the multi-beam antenna, is caused. There is an advantage that the error and the antenna gain and the deterioration of the side lobe characteristics can be designed to be balanced values.

[Brief description of drawings]

FIG. 1 is a block diagram of an antenna equipped with a sub-reflector driving device,
FIG. 2 is a characteristic diagram showing a conventional drive center design example, FIG. 3 is a pattern explanatory diagram for explaining a radiation beam of an antenna controlled by the present invention, and FIGS. 4 (a) and (b) are the present invention. FIG. 4 is an operation characteristic diagram of the embodiment that best represents the characteristics of FIG. 1 ... Main reflecting mirror, 2 ... Sub-reflecting mirror, 3 ... Radiator, 4 ...
… Radiation beam, point C …… Center of rotation of subreflector, point O ……
The focal point of the main reflector and the origin of the Cartesian coordinate system.

Claims (1)

[Claims] 1. A sub-reflector of a multi-beam antenna having two reflectors consisting of a main reflector and a sub-reflector, and having a plurality of radiators corresponding to a plurality of radiation beams. In the device, the rotation center position for changing the directions of all the beams by rotating the sub-reflecting mirror is approximately the center of a line segment connecting the center point of the sub-reflecting mirror and the focal point of the main reflecting mirror. A sub-reflector driving device for a multi-beam antenna, characterized in that the sub-reflector driving device is set at a position in the vicinity.