JPH11214921A - Multiple-beam antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a miniaturized antenna to satisfactorily receive radio waves coming from noticeably different directions by forming a reflecting mirror for reflecting the radio waves from a plurality of static satellites at a part of an oval parabolic face. SOLUTION: A multiple-beam antenna 2 is provided with a reflecting mirror 4 for reflecting and converging radio waves arriving from geostationary satellites and a first reception part 6a and a second reception part 6b for receiving radio waves converged by the reflecting mirror 4. The reflecting mirror 4 is a curved face segmented from an oval parabolic face so that its area of opening is an oval (containing circle), where the length of a short axis and a long axis is 1:1 to 1:1.1. The ratio of its effective opening diameter (the length of the short axis of the effective opening) and the focal distance of a parabola which is the cross section of the short axis direction of the oval parabolic face is set to be 1:0.65-1:0.85. The attitude of the reflecting mirror 4 is controlled by the direction of a center axis 8 and a rotary angle with the center axis 8 as an axis, and arriving radio waves from the two geostationary satellites can be received satisfactorily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-beam antenna capable of receiving radio waves from a plurality of geostationary satellites.

[0002]

2. Description of the Related Art Parabolic antennas for receiving radio waves from geostationary satellites such as broadcast satellites and communication satellites have been known. The parabolic antenna includes a reflecting mirror cut out from a part of the paraboloid of revolution, and a receiving unit provided at the focal point of the reflecting mirror. And the receiver receives the collected radio waves. To receive radio waves from multiple geostationary satellites with such a parabolic antenna,
It is sufficient to install a plurality of satellites in the direction of each geostationary satellite, but since they need to be installed at the same time, the direction of each parabolic antenna must be adjusted individually, which is troublesome.
In some cases, a plurality of receivers are provided near the focal point of a reflector, and these receivers individually receive radio waves from a plurality of geostationary satellites.

However, as the direction of arrival of the radio wave deviates from the direction of the center axis of the paraboloid of revolution, the aberration increases, the antenna gain decreases significantly, and the effective aperture area that opens in the direction of arrival of the radio wave decreases. Therefore, there is a problem that the reception power of the antenna is reduced. For example, in Japan, BS (110 ° E) and JC of Japan Communication Satellite Co., Ltd.
When receiving a radio wave from SAT-3 (128 ° east longitude), the angle difference between the directions of arrival of the radio wave (hereinafter also referred to as “beam separation angle”) is small. The antenna gain does not decrease much, but when trying to receive radio waves from the BS and Superbird C (144 ° east longitude) of Space Communications Co., Ltd., the beam separation angle is about 3
Because it is as large as 8 °, the antenna gain is significantly reduced even if the central axis is directed between them. In this case, the received power may be increased by increasing the size of the reflector and increasing the effective aperture area that opens in the direction of arrival of the radio wave, but there is a problem that the installation location is limited.

For this reason, as described in Japanese Patent Application Laid-Open No. 7-46034, for example, a reflecting mirror formed by approximating a spheroid to a paraboloid and a reflecting mirror (ie, spheroid) are used. Multi-beam antennas have been developed which consist of two receivers each located at one focal point. In this type of multi-beam antenna, the reflecting mirror reflects the radio wave passing near one receiving unit to the other receiving unit, so that even if the beam separation angle is large, each radio wave can be transmitted with a good antenna gain. Can receive.

[0005] As described in Japanese Patent Publication No. 4-72881, a reflector formed by fusing a plurality of adjacent paraboloids by weighted averaging and corresponding to each paraboloid of revolution before fusing. A multi-beam antenna including a plurality of receiving units respectively provided at the focal point of a reflecting area that has been developed has also been developed. In this type of multi-beam antenna, radio waves arriving from a plurality of directions are respectively reflected by corresponding reflection units in the respective reflection areas, so that radio waves from each geostationary satellite can be received even if the beam separation angle is large.

[0006]

However, Japanese Patent Application Laid-Open No. 7-4 / 1994
In the multi-beam antenna described in Japanese Patent No. 6034, one of the receiving units is in the direction of arrival of the radio wave to be received by the other receiving unit, so that there is a problem that the radio wave is blocked. There is a problem. Further, the multi-beam antenna described in Japanese Patent Publication No. 4-72881 is merely a set of independent paraboloids of revolution, and it is necessary to fuse a number of paraboloids of revolution corresponding to the arrival direction of radio waves. Therefore, in order to increase the number of radio waves that can be received, the size of the reflector must be increased. Furthermore, since the beam separation angle of the radio waves that can be received by both of these multi-beam antennas is fixed by the shape of the reflecting mirror,
For example, there is a problem that the reception capability is poor for radio waves from a newly launched geostationary satellite.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a multi-beam antenna capable of satisfactorily receiving radio waves having significantly different directions of arrival, even if it is small.

[0008]

Means for Solving the Problems and Effects of the Invention According to the first aspect of the present invention, there is provided a reflector for reflecting radio waves from a plurality of geostationary satellites, and a reflector for reflecting radio waves from the plurality of geostationary satellites. A multi-beam antenna including a plurality of receiving units for respectively receiving the radio waves from the respective geostationary satellites, wherein the reflecting mirror is formed by a part of an elliptic paraboloid.

[0009] In the multibeam antenna according to the present invention (claim 1) configured as described above, the reflecting mirror is formed as an elliptic paraboloid. Therefore, as can be seen from a simulation described later, the center axis of the elliptic paraboloid is oriented between the arrival directions of the radio waves to be received, and the major axis direction having a large curvature is substantially parallel to the arrangement of the geostationary satellites, and the elliptical paraboloid is set. If each radio wave is received from a direction inclined in the major axis direction of the object surface, it is possible to satisfactorily converge each radio wave even if the arrival direction is significantly different.

Therefore, according to the multi-beam antenna of the first aspect, there is no need to use a spheroidal surface or to fuse a plurality of paraboloids of revolution, so that the size of the reflector becomes large or the appearance is impaired. Can be avoided.
Moreover, since the receivable beam separation angle is not fixed, it is possible to receive radio waves from any number of geostationary satellites within a predetermined beam separation angle. In addition, as the receiving unit, for example, a feed horn, a patch-type antenna, or the like can be used.

As will be described later, as a result of a simulation using 3D-CAD, as the major axis of the elliptic paraboloid is made longer with respect to the minor axis, the radio wave from the direction in which the beam separation angle is larger and the distance between them It has been found that incoming radio waves can be better focused. For example, if the ratio of the length in the short axis direction to the length in the long axis direction is 1: 1.05, each radio wave having an angle difference of up to 20 ° in the arrival direction can be well focused and received. If the ratio of the length in the axial direction to the length in the long axis direction is 1: 1.1, each radio wave with an angle difference of up to 40 ° in the arrival direction can be satisfactorily received. Here, the ratio of the length of the minor axis direction and the major axis direction of the elliptic paraboloid is the minor axis of the ellipse, which is a cross section of the elliptical paraboloid cut by a plane perpendicular to the central axis. It shall be defined by the ratio to the long axis.

As described above, as the ratio of the major axis direction to the minor axis direction is increased, the radio waves can be better focused and received even if the beam separation angle is larger. In other words, there is a problem that the position where the receiving unit is to be disposed is separated from the reflecting mirror, and the entire multi-beam antenna becomes large. On the other hand, considering the actual position of the geostationary satellite, the angle difference in the direction of arrival of the radio wave is approximately 40 ° even at the maximum. In addition, in the conventional parabolic antenna using the paraboloid of revolution, when the angle difference between the arrival directions of the radio waves is 20 ° or more, the focusing becomes poor,
Antenna gain decreases. Then, as described in claim 2, the ratio of the length of the minor axis direction and the major axis direction of the elliptic paraboloid is
1: 1.05 to 1: 1.1, and a multi-beam antenna capable of satisfactorily receiving radio waves (beam separation angles of 20 ° to 40 °) having significantly different directions of arrival despite its small size. Obtainable.

As the reflecting mirror, any portion of the elliptical paraboloid may be used. However, if the center of the reflecting mirror is separated from the central axis of the elliptic paraboloid, it becomes difficult for the radio waves to converge. There is a problem that the focusing position is separated from the reflector and the entire antenna is enlarged. Then, as described in claim 3, the reflecting mirror is made to include the central axis of the elliptic paraboloid (that is,
If the reflector is formed so that the center axis of the elliptical paraboloid intersects), the radio wave can be well focused and the focusing position does not depart from the reflector, so that the multi-beam antenna is small and has a high antenna gain. be able to.

The shape of the reflector should be longer in the direction in which the geostationary satellites are arranged (that is, in the major axis direction of the elliptical paraboloid).
Considering that the directivity of a conical horn antenna generally used as a receiving unit has a conical shape, it is preferable because the interference from an adjacent geostationary satellite can be suppressed. It is preferable to make the shape close to an ellipse. Therefore, the shape of the reflecting mirror (hereinafter referred to as “effective aperture”) as viewed from the central axis direction of the elliptic paraboloid is such that the ratio of the short axis to the long axis is 1: 1 to 1:
1.1 (especially 1: 1.06) and an ellipse (including a circle) whose major axis is substantially parallel to the major axis direction of the elliptic paraboloid
It is good to be.

As described above, even when the effective aperture of the reflecting mirror is elliptical, if the reflecting mirror includes the central axis of the elliptic paraboloid, the radio wave can be well focused and a small multi-beam can be obtained. It is preferable because it can be an antenna,
In a state where the center of the effective aperture and the center axis of the elliptic paraboloid are completely coincident with each other, there is a possibility that the influence of the blocking of the incoming radio wave by the receiving unit becomes large. Therefore, it is better to separate the center of the reflecting mirror and the central axis of the elliptic paraboloid, and to set the distance between them as the length of the short axis of the effective aperture (hereinafter referred to as “effective aperture diameter”).
That. It has been confirmed by simulations described later that the effect of blocking can be suppressed and that radio waves can be well focused when the distance is about 1/4 of the value of (1). In this case, the center of the effective aperture is
If the mirror is in the minor axis direction of the elliptic paraboloid, the reflecting mirror becomes bilaterally symmetric about the minor axis, which is also preferable in terms of design.

It is preferable that the ratio between the effective aperture diameter and the focal length of the parabola which is a cross section in the minor axis direction of the elliptic paraboloid is larger because the antenna gain is improved, but overflow radiation is generated. Since there is a problem that the whole antenna becomes large, a range of 1: 0.65 to 1: 0.85,
Particularly, 0.8 is most preferable.

[0017]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing an overall configuration of a multi-beam antenna as one embodiment of the present invention.

The multi-beam antenna 2 includes a reflector 4 for reflecting and converging radio waves arriving from a geostationary satellite, and a first receiver 6a and a second receiver 6b for receiving the radio waves converged by the reflector 4. (Hereinafter, when both receiving units are collectively referred to as “receiving unit 6”).

The effective aperture of the reflecting mirror 4 is such that the length between the short axis and the long axis is from 1: 1 to 1: 1.1 (1: 1.
06) is a curved surface cut out from the elliptical paraboloid 7 so as to have an elliptical shape (including a circle). The ratio between the effective aperture diameter (that is, the length of the minor axis of the effective aperture) and the focal length of a parabola which is a cross section of the elliptical paraboloid 7 in the minor axis direction 7S is 1: 0.65 to 1 : 0.85 (in the present embodiment,
1: 0.8). The effective aperture diameter is, for example, 5
0 cm.

The direction of the central axis 8 of the parabolic ellipse 7 (ie, azimuth and elevation) can be freely adjusted by a support member (not shown). Is rotatable around the axis. In other words, the attitude of the reflecting mirror 4 is adjusted by the direction of the central axis 8 and the rotation angle about the central axis 8 according to the receiving area, so that the incoming radio waves from the two geostationary satellites can be satisfactorily received.

The first receiving section 6a is for receiving an incoming radio wave from a first geostationary satellite (hereinafter, referred to as a "first satellite"), and the second receiving section 6b is for receiving a second radio signal. This is for receiving an incoming radio wave from a geostationary satellite (hereinafter, referred to as a "second satellite"). The first receiving unit 6a and the second receiving unit 6b are fixed to the reflecting mirror 4 so as to correspond to positions where the reflecting mirror 4 focuses the radio waves arriving from both geostationary satellites, respectively. Is aimed at. When the two receiving units 6 are viewed from the central axis 8 direction, the long axis of the effective aperture and the straight line connecting the two receiving units 6 are parallel.

The reflecting mirror 4 is formed by cutting out a part of the elliptic paraboloid 7, and the shape of the reflecting mirror 4 depends on the shape of the cut elliptic paraboloid 7 and the elliptic paraboloid 7. Is determined by the extraction method. The inventor of FIG.
As shown in (c), in determining the shape of the elliptical paraboloid 7, the ratio of the length of the elliptic paraboloid 7 in the short axis direction 7S and the long axis direction 7L is changed variously, and A simulation was performed to determine how much the arriving radio wave from the geostationary satellite converges after being reflected by the reflector 4. In the simulation, the first
144 ° east longitude in geostationary satellite orbit as satellite and second satellite
Space Bird Co., Ltd. Superbird C and East longitude 11
Assuming a BS at 0 °, radio waves arriving from both geostationary satellites are made to enter the reflector 4.

FIG. 2A is an explanatory view showing a state in which radio waves arriving from both geostationary satellites are reflected by the paraboloid of revolution 9, and FIG. 2B shows a short axis direction 7 S and a long axis. FIG. 2C is an explanatory diagram showing a state in which both radio waves are reflected by the elliptic paraboloid 7 whose length ratio to the direction 7L is 1: 1.05, and FIG. It is explanatory drawing which shows a mode that both radio waves are reflected by the elliptic paraboloid 7 whose length ratio with the major axis direction 7L is 1: 1.2. In general, an elliptic paraboloid is represented by the following equation in a rectangular coordinate system: z = (x / a) ² + (y / b) ² (1) 7S
Corresponds to the x-axis direction of the elliptic paraboloid of equation (1), and the major axis direction 7L of the elliptic paraboloid 7 corresponds to the y-axis direction of the elliptic paraboloid of equation (1). The central axis 8 of the object surface 7 corresponds to the z-axis which is the central axis of the elliptic paraboloid of Expression (1). That is, FIG.
The elliptic paraboloid 7 shown in FIG.
a: 2b = 1: 1.05 (where “2a” and “2
“b” is the length of the “short axis” and “long axis” of the ellipse, which is a cross section of the elliptic paraboloid 7 by the plane of z = 1, respectively. same as below. ) Is an ellipsoidal paraboloid represented as FIG.
The elliptic paraboloid 7 shown in FIG.
= 1: 1.2 is an elliptic paraboloid. Here, “z = 1” means x, y, z in equation (1).
And a design is performed by applying actual dimensions to Equation (1) as necessary.

The central axis 8 of these paraboloids (the revolving paraboloid 9 or the ellipsoidal paraboloid 7) is oriented in the direction of 131 ° east longitude on the geostationary satellite orbit between the geostationary satellites. It shall be assumed. 2 (a) to 2 (c) are all views from the concave side of the paraboloid of revolution 9 or the elliptical paraboloid 7 (that is, the side from which radio waves arrive). FIG. 3 shows a perspective view in the case of 2 (B).

As shown in FIGS. 2A to 2C, an incoming radio wave 10a from the first satellite (hereinafter, referred to as "first radio wave 10a") and an incoming radio wave 10b from the second satellite (hereinafter, referred to as "first radio wave 10a"). ,
This is referred to as “second radio wave 10b”. ) Are reflected by the reflecting mirror 4 and converged at different positions. Here, FIG.
Comparing (a) to (c), as the ratio of the length of the major axis direction 7L to the minor axis direction 7S increases, the first radio wave 10
a and the second radio wave 10b both tend to converge in a narrower range, which is preferable. On the other hand, since the convergence position of both radio waves tends to be away from the reflecting mirror 4, the first receiving unit 6a and the second The receiving unit 6b becomes far from the reflecting mirror 4, and the entire multi-beam antenna becomes large.

The inventor performed a similar simulation with the beam separation angle changed. When the beam separation angle was 20 °, the short axis direction 7S and the long axis direction 7S of the elliptic paraboloid 7 were changed.
Suitably, the ratio of the length to L is 1: 1.05,
When the beam separation angle is 40 °, the elliptic paraboloid 7
The length ratio of the short axis direction 7S to the long axis direction 7L is 1: 1.
It has been clarified that a value of 1 is appropriate. And
In particular, when the incoming radio waves from the first satellite and the second satellite assumed as described above are received (the beam separation angle is about 38 °), the short axis direction 7S and the long axis direction 7L of the elliptic paraboloid 7 are It has been found that a length ratio of 1: 1.075 is most preferred.

From the above, the ratio of the short axis direction 7S of the elliptic paraboloid 7 to the long axis direction 7L is 1: 1.05 to 1: 1.1.
Then, it can be understood that the radio waves arriving from the first satellite, the second satellite currently used, and the geostationary satellite in the geostationary satellite orbit between them can be satisfactorily received.

Next, the inventors set the ratio of the length of the short axis direction 7S to the long axis direction 7L of the elliptic paraboloid 7 to 1: 1.075, It was examined by simulation whether it is appropriate to cut out as a reflecting mirror 4. FIGS. 4A to 4C show various positions at which the reflecting mirror 4 is cut out from the elliptic paraboloid 7 whose length ratio between the short axis direction 7S and the long axis direction 7L is 1: 1.075. FIG. 9 is an explanatory diagram showing a state of simulating how the first radio wave 10a and the second radio wave 10b converge when changed. 4 (a) to 4 (c) are diagrams as viewed from the concave side of the elliptic paraboloid 7 (that is, the side of the plane from which radio waves arrive). Here, the ratio of the length of the minor axis to the major axis of the effective aperture of each reflecting mirror 4 is an ellipse of 1: 1.06, and the minor axis of the ellipse matches the minor axis direction 7S of the elliptic paraboloid 7. It is. In addition, incoming radio waves (first radio waves 10) from both geostationary satellites incident on the reflector 4.
a and the second radio wave 10b) indicate only the radio wave incident on the center M of the reflecting mirror 4, and the radio wave incident on other portions is omitted.

As shown in FIGS. 4A to 4C, the reflecting mirror 4
Is the intersection O between the elliptical paraboloid 7 and its central axis 8
The radio waves arriving from both geosynchronous satellites are preferably converged in a narrower range as it approaches (hereinafter, simply referred to as “intersection O”). However, the convergence position approaches the center of the effective aperture of the reflecting mirror 4 and the radio wave is received. Blocking by the unit 6 may occur. On the other hand, as the center M of the reflecting mirror is farther from the intersection O,
Since the focus position of the radio wave is far from the reflector, the receiving unit 6
Can prevent the incoming radio wave from being blocked, but the radio wave convergence deteriorates, and the receiving unit 6 becomes farther from the reflecting mirror 4, resulting in an increase in the size of the multi-beam antenna.

Therefore, as shown in FIG.
Is set to be approximately 1/4 of the length of the minor axis of the reflecting mirror 4, the focusing position of the radio wave is located at the end of the reflecting mirror 4. Therefore, the effect of blocking by the receiving unit 6 can be suppressed, and radio waves can be focused relatively favorably, which is the most preferable. Such blocking can be suppressed or prevented by, for example, downsizing the receiving unit 6. Therefore, when cutting out the reflecting mirror 4 from the elliptical paraboloid 7, the intersection point between the elliptical paraboloid 7 and the central axis 8 is used. It is preferable to include O in the reflecting mirror 4 because the entire multi-beam antenna does not increase in size.

Based on the above simulation results, in this embodiment, the elliptic paraboloid 7 from which the reflecting mirror 4 is cut out
The ratio of the length of the short axis direction 7S to the length of the long axis direction 7L is set to 1: 1.075 so as to correspond to the beam separation angle of 38 °,
The point of intersection O of the reflecting mirror 4 with the central axis 8 of the elliptic paraboloid 7
Is cut out from the elliptical paraboloid 7 so as to be located on the short axis of the effective opening and at a position １ ／ of the effective opening diameter from the center M.

Returning to FIG. 1, the reflecting mirror 4 thus formed
A method of receiving radio waves from the first satellite and the second satellite using the multi-beam antenna having the following will be described.
The first satellite assumed above is 14 east longitude in geostationary satellite orbit.
At 4 °, the second satellite is 110 ° east longitude in geostationary satellite orbit
It is in. In order to receive radio waves arriving from these two geostationary satellites, for example, the central axis 8 (that is, the effective aperture of the reflecting mirror 4) may be directed to the geostationary satellite orbit at 127 ° east in the middle. Considering that the power densities of the arriving radio waves on the ground are different because the transmission powers of the first satellite and the second satellite are respectively about 90 W and about 106 W, respectively, the multi-beam antenna of the present embodiment uses 127 ° east longitude. The central axis 8 is oriented slightly in the 131 ° east longitude direction closer to the first satellite. The elevation angle of the central axis 8 at this time differs depending on the receiving area. For example, in the Nagoya area, the elevation angle of the central axis 8 is 48.66 °. Also, depending on the receiving area,
Since the difference between the elevation angles of the two geostationary satellites is also different, it is necessary to rotate the reflecting mirror 4 about the central axis 8 in accordance with the difference.
Is turned 8.31 ° to the left. As described above, the posture is adjusted according to the receiving area, so that the multi-beam antenna receives the first radio wave 10a at the first receiving unit 6a and receives the second radio wave 10b at the second receiving unit 6b. can do.

As described above, according to the multi-beam antenna of this embodiment, since the reflecting mirror 4 is constituted by a part of the elliptic paraboloid 7, the radio waves having significantly different directions of arrival can be focused well. be able to. That is, since the directivity can be enhanced by suppressing the side lobe in each direction, it is possible to receive with a high antenna gain, and it is possible to prevent a reception failure and C / N deterioration. And since there is no need to use a spheroid or to combine a plurality of paraboloids of revolution, it is possible to avoid the reflector from becoming large or spoiling the appearance, and the effective aperture diameter is, for example, 50 cm. Even if the size is small, the above effects can be obtained.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment and can take various forms. For example, the multi-beam antenna of the above embodiment has been described as having two receiving units. However, the present invention is not limited to this, and any number may be provided. With a simple receiving unit,
For example, an incoming radio wave from JCSAT-3 of Japan Communication Satellite Co., Ltd. located at 128 ° east longitude on a geosynchronous satellite orbit may be received. In the above embodiment, the ratio of the length of the short axis direction 7S to the long axis direction 7L of the elliptic paraboloid 7 is 1: 1.075.
This is because if the angle difference between the directions of arrival of the radio waves is up to about 38 °, it is possible to converge well, so that the radio waves arriving from between them can be well converged.

The multibeam antenna of the above embodiment has been described assuming a geostationary satellite, a CS mainly for communication and a BS for broadcasting.
The present invention is not limited to a geostationary satellite for broadcasting or communication. For example, an incoming radio wave from a geostationary satellite mainly for distribution (only one-way communication) may be received. That is, it can correspond to any geostationary satellite.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a multi-beam antenna as one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state of simulating how incoming radio waves from two geostationary satellites are converged by a rotating paraboloid and an elliptic paraboloid;

FIG. 3 is an explanatory diagram showing the state of the simulation shown in FIG. 2B from the side.

FIG. 4 shows that the ratio of the length in the minor axis direction to the major axis direction is 1: 1.
FIG. 10 is an explanatory diagram showing a simulation of how incoming radio waves from two geosynchronous satellites are focused when the extraction position is variously changed from an elliptic paraboloid of 075.

[Explanation of symbols]

2 multi-beam antenna, 4 reflector, 6 receiver
6a: first receiving section, 6b: second receiving section, 7: elliptical paraboloid, 7L: long axis direction, 7S: short axis direction, O: intersection of the elliptical paraboloid and its central axis.

Claims (3)

[Claims] 1. A multi-beam antenna comprising: a reflector for reflecting radio waves from a plurality of geostationary satellites; and a plurality of receiving units for receiving radio waves from the respective geostationary satellites reflected by the reflectors. A multi-beam antenna, wherein the reflecting mirror is formed by a part of an elliptic paraboloid. 2. The multi-beam antenna according to claim 1, wherein a ratio of a length of the elliptic paraboloid in a minor axis direction to a major axis direction is:
A multi-beam antenna, wherein the ratio is 1: 1.05 to 1: 1.1. 3. The multi-beam antenna according to claim 1, wherein the reflecting mirror includes a center axis of the elliptic paraboloid.