JP4083848B2 - parabolic antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microwave parabolic antenna, and more particularly to an offset parabolic antenna for satellite broadcast reception.
[0002]
[Prior art]
The parabolic reflector of the conventional satellite broadcasting receiving antenna is circular when the portion not including the Z axis of the surface of the object expressed by x ² + y ² = 4 fz is seen from a direction parallel to the Z axis (radiation direction). Many are cut out in various shapes. In FIG. 1, reference numeral 1 denotes a bowl surface focusing on a point F expressed by z = f on the Z axis, 2 is a conventional parabolic reflector cut out from the surface, and A and B are Z axes on the periphery thereof. Indicates the end closest to and the end farthest. In order to capture the reflected wave from the parabolic reflector 2, a primary radiator is placed at the focal point F.
[0003]
[Problems to be solved by the invention]
As shown in FIG. 7, when the direction of arrival of the radio wave is changed around the X axis as shown in FIG. 7, the antenna as described above has a reception gain as shown in FIG. 8 near the incident angle θ of the radio wave with respect to the Z axis is ± 145 °. Will increase. This is because a part 5 of the radio wave 4 from the back direction of the parabolic reflector 2 directly enters the primary radiator 3 without being blocked by the parabolic reflector 2, as shown in FIG. This contributes to reception noise. The spillover gain needs to be 10 to 15 dB lower than the reception gain of the radio wave 6 from the normal direction. However, in the example shown in FIG. As a result, the spillover reception gain 82 partially exceeds the −45 dB level 83 which is 10 dB lower than this, and greatly exceeds the −84 dB level 84 which is 15 dB lower than this. This spillover tends to increase as the aperture diameter of the parabolic reflector is reduced for miniaturization.
[0004]
In addition, the shape of the parabolic reflector for receiving satellite broadcasts was limited to an oval whose length of the major axis was slightly larger than the length of the minor axis so that it was circular when viewed from the direction of arrival of radio waves. . Such a shape requires a packaging box whose inner dimensions are substantially equal to the major axis dimension and the minor axis dimension when packaging, and the utilization efficiency of the packaging space is very poor. If the opening diameter of the parabolic reflector is increased in order to reduce spillover, the volume of the packaging box increases in proportion to the square of the opening diameter, which is extremely bulky and inconvenient in the merchandise distribution process.
[0005]
Accordingly, the main object of the present invention is to greatly reduce spillover without increasing the major axis and minor axis dimensions of the parabolic reflector. Another object is to improve the reception gain without increasing the minor axis dimension of the reflecting mirror, and to reduce the bulk of the assembled parabolic antenna.
[0006]
[Means for Solving the Problems]
The antenna of the present invention is expressed by x ² + y ² = 4 fz on the Cartesian coordinate system X, Y, Z, and forms a part of a saddle surface having a focal point at a position of z = f on the Z axis, and enters the XY plane. of the parabolic reflector projected image is circular, the focal position of the boric compound surface placed facing the parabolic reflector, and a primary radiator central axis of the directivity is inclined with respect to Z axis in the XZ plane It has. Four regions in which the projected image is partitioned by two axes passing through a projection point on the XY plane where the central axis of the primary radiator collides with the parabolic reflector, and parallel to the X axis and the Y axis, respectively. In each case, the parabolic reflector is deformed so that the direction with the longest length dimension is in the middle of the two parallel axes. In other words , the antenna of the present invention is characterized in that the projected image tends to be a quadrilateral.
[0007]
Furthermore, the parabolic reflector makes the length dimension in the X direction larger than the length dimension in the Y direction in the projected image on the XY plane. By expanding this dimension, the distance from the Z axis to the end farthest from the position where the central axis of the directing range of the primary radiator collides with the parabolic reflector to the end closest to the Z axis is increased. Alternatively, the angles formed by the lines connecting the focal point of the parabolic reflector and the end portion farthest from the Z-axis of the parabolic reflector and the closest end portion are made to substantially coincide with the directing range of the primary radiator.
[0008]
In the present invention, as described above, in the projection image of the parabolic reflector on the XY plane, the dimension in the intermediate direction is made larger than the length dimension in the X direction and the Y direction, thereby effectively reducing the spillover. Can be reduced. Then, by increasing the length dimension in the X direction in the projected image, it is possible to effectively improve the reception gain without increasing the length dimension in the Y direction.
[0009]
The rate of increase in the X-direction length dimension with respect to the Y-direction length dimension of the parabolic reflector in the projected image on the XY plane is determined by the relationship between the pointing range of the primary radiator and the length dimension of the parabolic reflector. . The primary radiator usually has the highest sensitivity to radio waves from the center direction of the directivity range, and the reflected wave from the parabolic reflector is strongest from the center direction of its aperture, so it is usually the primary radiation. The instrument is installed with the central axis of the pointing range facing the center of the aperture of the parabolic reflector. In order to make maximum use of the reflected wave in the parabolic reflector and to reduce spillover as much as possible, the limit closest to the Z-axis of the primary radiator pointing range is the end closest to the Z-axis of the parabolic reflector. It is made to almost coincide with the part.
[0010]
As a result, in the case of a normal parabolic antenna, the directivity range on the side farther from the Z-axis of the primary radiator extends outward than the edge of the parabolic reflector. By extending the dimension away from the Z-axis, the amount of reflected wave in the parabolic reflector captured by the primary radiator can be increased. For this purpose, the amount of increase in the length dimension in the X direction relative to the length dimension in the Y direction in the projected image on the XY plane is around several percent, and it is meaningless to exceed 10%.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the relationship between a normal parabolic reflector 2 and a parabolic reflector 12 of a reference example of the present invention, where (a) is a cross section along the XZ plane in the orthogonal coordinate system, and (b) is a projected view on the XY plane. (Shape viewed from the direction of radio wave arrival). Reference numeral 1 denotes a bowl surface having the Z axis as a central axis and a focal point at a point F thereon. The parabolic reflector 2 of the normal offset antenna is shaped so that the projected image on the XY plane viewed from the direction of arrival of the radio wave at a position off the Z axis on the surface 1 is a circle with a radius r centered on the O point. A is the end closest to the Z axis, and B is the end farthest from the Z axis. In the reference example of the present invention, the parabolic reflector 12 has the same length in the X direction and the Y direction in the projected image on the XY plane as the normal parabolic reflector 2, but with respect to the X direction and the Y direction. In the direction of about 45 °, Δ protrudes outward from the normal parabolic reflector 2, and the length dimension l in this direction is larger by 2Δ than the diameter 2r of the normal parabolic reflector 2.
[0012]
2A and 2B show a parabolic antenna using the parabolic reflector 12, wherein FIG. 2A is a side view and FIG. 2B is a front view. From the antenna mounting bracket 13 fixed to the back surface of the parabolic reflector 12, the support arm 15 extends forward through the notch 14 formed in the lowermost portion of the parabolic reflector 12, and the parabolic reflector 12 is extended to the front end. A primary radiator 16 oriented in the direction of is attached.
[0013]
3A and 3B show an embodiment of the present invention, in which FIG. 3A is a cross-sectional view along the XZ plane, and FIG. 3B is a projection view (shape viewed from the direction of arrival of radio waves) onto the XY plane. Also in this embodiment, the parabolic reflector 32 has a length dimension L in a direction oblique to the X direction and the Y direction on the projection view on the XY plane. In addition to this, the edge of the parabolic reflector 32 on the side farther from the Z axis extends beyond the end B of the normal parabolic reflector 2 on the surface 1 to the point C.
[0014]
As a result, the parabolic reflector 32 is projected onto the XY plane so that the length dimension in the Y direction is larger than the length dimension in the X direction, and the line FO and the line FC, which are the central axes of the primary radiator, are formed. The size of the angle CFO to be created can be close to or equal to the divergence angle α of the directivity range on both sides of the central axis of the primary radiator, effectively supplying the reflected wave in the parabolic reflector to the directivity range of the primary radiator Will be able to. In parallel with this, the parabolic reflector 32 may be extended in the Z-axis direction beyond the end A of the normal parabolic reflector 2, thereby further reducing spillover.
[0015]
【Example】
FIG. 4 shows the shape of the parabolic reflector 32 shown in FIG. 3 as viewed from the direction perpendicular to the straight line connecting the points A and C. The length H of the straight line AC is 510 mm, and the length in the direction perpendicular thereto. The dimension W is 432 mm, the longest diameter L is 524 mm, and its directivity is shown in FIG. Incidentally, FIG. 8 shows the directivity characteristics of a normal parabolic reflector 2 having an aperture diameter r of 430 mm. The length dimension between the point A and the point B of the parabolic reflector 2 is 479 mm, and the length in the direction orthogonal thereto. The dimension is 430 mm.
[0016]
In the directivity shown in FIG. 5, when the gain 50 of the regular received radio wave concentrated in the vicinity of θ = 0 ° is set to −35 dB or more as shown by the level 51, and the level 53 and the level 54 which are 10 dB and 15 dB lower than this are viewed. The gain 52 due to spillover existing in the vicinity of θ = ± 145 ° does not reach the level 53 but only exceeds the level 54 in some parts. Therefore, comparing this with FIG. 8, it can be seen that the gain due to spillover is significantly reduced. Note that even if the notch 14 for positioning the primary radiator support arm 15 (see FIG. 2) is formed below the parabolic reflector 32 as shown by the dotted line in FIG. There wasn't.
[0017]
FIG. 6 shows a comparison between the frequency characteristic line 61 of the normal parabolic reflector 2 having an aperture diameter r of 430 mm and the frequency characteristic line 62 of the parabolic reflector 32 shown in FIG. 4, from 11.0 GHz to 13.0 GHz. It can be seen that the parabolic reflector 32 shown in FIG.
[0018]
【The invention's effect】
As described above, in the present invention, the spillover is remarkably suppressed by increasing the length dimension of the parabolic reflector in the direction oblique to the X direction and the Y direction, and the packaging volume. This can be realized without increasing. Furthermore, the reception gain of the antenna can be increased by increasing the length dimension of the parabolic reflector in the X direction.
[Brief description of the drawings]
FIG. 1 is a contrast diagram of a normal parabolic reflector and a parabolic reflector according to a reference example of the present invention, in which (a) is a cross-sectional view in the XZ plane, and (b) is a projected view on the XY plane.
2A and 2B are diagrams showing a parabolic antenna, where FIG. 2A is a side view and FIG. 2B is a front view.
[3] In contrast view of the parabolic reflector of an embodiment of a conventional parabolic reflector and the present invention is a cross-sectional view, a projection drawing to (b) is an XY plane in (a) is an XZ plane.
4 is a front view of the parabolic reflector of the embodiment of the present invention shown in FIG.
FIG. 5 is a characteristic diagram of a radio wave incident angle of a parabolic antenna using the parabolic reflector shown in FIG. 4;
6 is a frequency characteristic diagram of a parabolic antenna using a normal parabolic reflector and a parabolic antenna using the parabolic reflector shown in FIG. 3 of the present invention. FIG.
FIG. 7 is an explanatory diagram of spillover in a parabolic antenna.
FIG. 8 is a characteristic diagram of radio wave incident angle characteristics of an antenna using a normal parabolic reflector.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Parasitic surface 2 Conventional parabolic reflector 3 Primary radiator 12 Parabolic reflector of the present invention 14 Notch 15 Support arm 16 Primary radiator 32 Parabolic reflector of the present invention 50 Received radio wave gain 52 Spillover gain 61 Characteristics of conventional parabolic antenna 62 Characteristics of the parabolic antenna of the present invention 80 Received radio wave gain 82 Spillover gain r Radius of the conventional parabolic reflector l Longest dimension of the parabolic reflector of the present invention α Directional spread angle of the primary radiator H Long diameter of the parabolic reflector of the present invention W The short diameter of the parabolic reflector of the present invention L The longest dimension of the parabolic reflector of the present invention

Claims (5)

Expressed as x ² + y ² = 4 fz on the Cartesian coordinate system X, Y, Z, forming a part of the surface of the object having a focus at the position of z = f on the Z axis, and the projected image on the XY plane is circular A parabolic reflector,
A primary radiator which is placed at the focal position of the surface of the object and faces the parabolic reflector, and whose central axis is inclined with respect to the Z axis in the XZ plane;
The projected image is equally divided by two axes parallel to the X axis and the Y axis, respectively, through the projection point on the XY plane where the central axis of the primary radiator collides with the parabolic reflector. In each of the four regions, the parabolic reflector is deformed so that the direction in which the longest dimension is the longest exists at about 45 degrees between the two parallel axes, and the focal point of the parabolic reflector, Projection image of the parabolic reflector on the XY plane so that the angles formed by the lines connecting the end closest to the Z axis and the end farthest from the parabolic reflector substantially coincide with the directivity range of the primary radiator. A parabolic antenna in which the length dimension in the X direction is larger than the length in the Y direction of the projected image . The parabola according to claim 1 , wherein the difference between the length dimension in the X direction and the length dimension in the Y direction on the XY plane of the parabolic reflector is within 10% of the length dimension in the Y direction. antenna. The point at which the central axis of the primary radiator collides with the parabolic reflector is that the projected image on the XY plane of the parabolic reflector is closer to the Z axis than the center of the parabolic reflector in the X direction. The parabolic antenna according to claim 1 or 2, wherein The angle formed by the line connecting the end farthest to the Z-axis of the parabolic reflector and the focal point of the parabolic reflector with respect to the central axis of the primary radiator directing is as described above with respect to the central axis of the primary radiator directing. 4. The parabolic antenna according to claim 2, wherein the parabolic antenna is substantially equal to an angle formed by a line connecting an end portion closest to the Z-axis of the parabolic reflector and the focal plane focus. The parabolic antenna according to any one of claims 1 to 4 , wherein a support arm of the primary radiator is provided in a notch formed in a peripheral edge closest to the Z-axis of the parabolic reflector.

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