JP2002232228A - Fan beam antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a fan beam antenna without using an accessory such as a suppression element. SOLUTION: A circular opening 4 is formed on a base 2, and a conductive plate 8 is arranged so as to cover the opening to form a cavity. The diameter of the cavity is made λg/2 (λg is wavelength in waveguide). Slots 10a to 10d are respectively provided on the orthogonally crossing diameters of the cavity. The slots located on the same diameter are separated with a space of 3λg/2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fan beam antenna having different directivities between a horizontal plane and a vertical plane.

[0002]

2. Description of the Related Art Conventionally, when a fan beam antenna is constructed, a plurality of microstrip antenna elements are arranged on the other surface of a main body having a ground conductor formed on one surface, and the output of each microstrip antenna element is It has been practiced to combine a microstrip line provided on the other surface of the main body with a combiner and to provide a suppression element above each microstrip antenna element.

[0003]

However, since such a fan beam antenna requires a combiner, a loss is caused in the antenna output, and an accessory element such as a suppression element is added to each microstrip antenna element. It had to be provided on top and the production was troublesome.

[0004] It is an object of the present invention to provide a fan beam antenna which has no loss in output and requires no additional elements.

[0005]

SUMMARY OF THE INVENTION A fan beam antenna according to the present invention has a cavity. This cavity has a short-circuit surface at a position n · λg / 4 (n is a positive integer, λg is a guide wavelength) away from the center point. In this cavity, m · λg / 4 from the center point
(M is a positive integer, m <n), and a plurality of slots are formed so as to be at equal angles to each other.
These slots are paired with slots that are point-symmetric with respect to the center point.

[0006] A probe may be arranged at the center point on one surface of the cavity. In this case, each of the slots is formed on a surface facing the one surface.

The cavity may have a shape in which two rectangular waveguides, both ends of which are short-circuited, are combined in a cross shape. In this case, the pairs of slots are respectively arranged in two rectangular waveguides.

The cavity has a diameter of n · λg /
2 can be formed in a columnar shape. In this case, the pair of slots is respectively formed on at least two diameters of the column that intersect and are at equal angles to each other.

The cavity may be formed as a regular polygonal column circumscribing a circle having a diameter of n · λg / 2.
In this case, the pair of slits is formed between opposing short-circuit surfaces of the regular polygonal column.

[0010] The cavity may be formed as a regular polygonal column having a plurality of diagonal lines at equal angles to each other. In this case, the pair of slots is formed on each of the diagonal lines.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fan beam antenna according to a first embodiment of the present invention has a flat rectangular parallelepiped conductive body 2 as shown in FIGS. .
The main body 2 has a substantially square planar shape, and has a column-shaped concave portion 4 formed on the upper surface thereof. As shown in FIG. 2, this recess 4 has n / 2λg,
For example, it has a diameter of about 3 / 2λg. n is a positive integer and is preferably an odd number. λg is a guide wavelength of a radio wave to be transmitted / received by the fan beam antenna.

As shown in FIG. 3, a probe 6 for transmitting and receiving radio waves by the fan beam antenna is provided at the center of the bottom surface of the concave portion 4, that is, at the center point.

A conductive plate 8 having substantially the same shape as the upper surface of the main body 2 is disposed in contact with the upper surface so as to cover the opening of the upper surface of the recess 4. The conductive plate 8 and the recess 4 form a columnar cavity having the conductive plate 8 and the bottom surface of the recess 4 as parallel flat plates. This cavity is about 3/2
The entire surrounding area is short-circuited by a circumferential wall having a diameter of λg. Therefore, the distance from the probe 6 to the circumferential wall which is the short-circuit surface is nλg / 4. The conductive plate 8 has a plurality of, for example, four slots 10a, 10b, 10c, 1
0d is formed. The slots 10a and 10b form a pair, and the slots 10c and 10d form a pair.

The slots 10a and 10b are located in the propagation direction of the radio wave in the cavity, that is, on the diameter of one cavity. As shown in FIG. 2, these slots 10a and 10b have a length in the diameter direction of about λ / 6 (where λ is a free space wavelength of a radio wave to be transmitted and received by the fan beam antenna), and are orthogonal to the diameter direction. Is formed in a rectangular opening of, for example, about λ / 2. These slots 10a and 10b are defined as mλg / 2 (m is a positive integer and m
<N and m are preferably odd numbers. ), For example about λ
g / 2. These slots 1
0a and 10b are located at equidistant positions with the probe 6 interposed therebetween, in other words, at point-symmetric positions. The slots 10a and 10b are located at a position of about λg / 2 (an even multiple of about λg / 4) from the peripheral surface of the cavity, which is a short-circuit surface.

Slots 10c and 10d are slot 10
It is configured similarly to the slots 10a, 10b, except that it is located on a diameter orthogonal to the diameter at which the a, 10b is formed. Therefore, the slots 10a, 10b, 10c, 1
0d is a slot 1 which is arranged at a position of about mλg / 4 from the probe 6 and at a point-symmetric position with respect to the probe 6.
0a and 10b form a pair, and similarly slots 10c and 10b
d is a pair. There are even pairs. An even number of the slots 10a to 10d are arranged on the circumference of the probe 6 having a radius of about mλg / 4 so as to be equiangular with each other.

The cavity has a circular recess 4 as described above.
Is formed by short-circuiting a parallel flat plate composed of the bottom surface of the base plate and the conductive plate 8 with a column having a diameter of about 3 / 2λg, and a resonance width of about 3 / 2λ.
g. Therefore, as shown in FIG. 4, the node of the electric field (the maximum point of the current) on one diameter, including the short-circuit surface,
If there is a point and one diameter includes the slots 10a and 10b, the slots 10a and 10b are located at the maximum point of the current. In FIG. 4, the solid line shows the state of the current and the broken line shows the state of the voltage at the time of resonance.

The Z-axis direction in FIG. 5 (the direction perpendicular to the conductive plate 8;
That is, the angle θ with respect to the Z axis = 0, and the direction X of one side of the conductive plate 8
Consider an incident wave from an angle φ (see FIG. 7) = 0 with respect to. The slots 10a, 10b, 10c, and 10d are all in a plane orthogonal to the incoming wave (the XY plane in FIG. 7), and the incident waves in each of the slots 10a, 10b, 10c, and 10d have the same phase. 10a, 10
Resonates with b, 10c and 10d to excite the inside of the cavity. The traveling waves traveling in the cavity are respectively reflected by the short-circuit surface and received by the probe 6. Since the cavity resonates and its current and voltage are as shown in FIG. 4, two opposing slots, for example, 10a and 1
0b, or 10c and 10d, the currents are in opposite phases, and the distance from each slot to the probe 6 via the short-circuit plane is equal to the distance between the slots 10a and 10b or
The arriving waves received in the two opposing slots are equal in c and 10d, and are canceled by the probe 6 and eventually not received.

When one or both of θ and φ are not 0 as shown in FIG. 5, the direction of the arriving wave is located between two opposing slots 10a and 10b or 10c and 10d.
For example, since a phase difference corresponding to the distance difference δ (when θ ≠ 0, φ = 0) occurs, the traveling wave in the cavity following the same path as described above generates some current and voltage in the probe 6, The incoming wave is received by 6.

Each of a pair of slots, for example, slots 10a and 10b or 10c and 10d is a two-element linear array of slot antennas, and has a θ plane directivity having no side lobe due to an array factor. Since the wave incident on the front is not received as described above, its directivity is a pair of the slots 10a and 1a.
As shown in FIG. 6 in the plane extending between 0b or 10c and 10d.

The two pairs of slots 10a and 10b, 10c and 10d are antennas for linear polarization, respectively. Since the slots 10a and 10b are orthogonal to the slots 10c and 10d, for example, θ in FIG. With θ fixed at about 35 degrees, the directivity in the φ direction with the Z axis of FIG. 5 as the rotation axis is considered.

For linear (horizontal or vertical) polarization, φ = 0
At degrees, 90 degrees, 180 degrees, and 270 degrees, the directivity gain is a pair of slot arrays. This is because, for example, a pair of slots 10a and 10b have the same polarization, and the other pair of slots 10c and 10d have a cross polarization.

Φ = 45 degrees, 135 degrees, 225 degrees, 315
This is the directivity gain of a pair of slot arrays. This is because two pairs of slots 10a, 10b and 10c, 10c
In both c and 10d, the polarization is shifted by 45 degrees in the positive or negative direction, and each has a polarization loss of 3 dB. However, combining two pairs results in a directivity gain of one pair of the same polarization. is there.

Even when φ is an arbitrary angle other than the above angle, the directivity gain of a pair of slot arrays is obtained. This is because the polarization difference between the pair of slots 10a and 10b and the other pair of slots 10c and 10d is always 90 degrees,
As in the case of 45 degrees positive or negative deviation described above,
This is because the vector sum becomes a directivity gain of a pair of the same polarization.

Further, even in the case of receiving a circular (right-handed or left-handed) polarized wave by using a configuration like the fifth and sixth embodiments described later, regardless of the value of φ, two pairs are always used. Therefore, the directivity in the φ direction in the relative value of both the linearly polarized wave and the circularly polarized wave is the same as that of FIG.
As shown in (2), even if φ is changed, a circular pattern with little change in the electric field is obtained.

As described above, the θ plane directivity of an arbitrary φ value cross section has no side lobe as shown in FIG.
The directivity in the φ direction becomes a circle as shown in FIG. 8, and a fan beam antenna having different directivities in the θ plane and in the φ direction can be obtained.

FIG. 9 shows a frequency vs. VSWR characteristic of the fan beam antenna. VSWR is at worst 1.2
Smaller and more practical. The θ plane directivity shows a high relative gain in a direction of 40 degrees or more and 60 degrees or less. This angle range corresponds to an elevation angle of 30 to 50 degrees required for receiving satellite broadcasts, so that the antenna is suitable for receiving satellite broadcasts.

Since this fan beam antenna is formed by providing a plurality of slots in the cavity, it is not necessary to combine the outputs of the microstrip antenna elements with the microstrip line, and no output loss occurs. . Further, since it is not necessary to provide a suppressing element to obtain the fan beam characteristic, the manufacturing is easy.

FIGS. 10 to 13 show a fan beam antenna according to a second embodiment. This fan beam antenna also has a flat rectangular parallelepiped conductive main body 2, similarly to the fan beam antenna of the first embodiment of the present invention. The main body 2 has a substantially square planar shape, and has a cross-shaped recess 4a formed on the upper surface thereof. As shown in FIG. 11, the recess 4a has a shape in which two rectangular recesses having a width of about 0.8λg and a length of about 5 / 2λg are orthogonal to each other.

At the center of the bottom surface of the recess 4a, as shown in FIG. 3, a probe 6 for transmitting and receiving radio waves by the fan beam antenna is provided.

A conductive plate 8 having substantially the same shape as the upper surface of the main body 2 is arranged in contact with the upper surface so as to cover the opening of the upper surface of the recess 4a. The conductive plate 8 and the recess 4a form a waveguide-type cross cavity. In each linear waveguide section of this cavity, about 5 / 2λg
The short-circuit plane is located only at a distance. The conductive plate 8 has a plurality of slots 10a, 10b, 10c, and 10d. The slots 10a and 10b form a pair, and the slots 10c and 10d form a pair.

The slots 10a and 10b are located in the propagation direction of the radio wave in the cavity, that is, on the straight line connecting the short-circuit surfaces of one linear portion of the cavity. As shown in FIG. 2, these slots 10a and 10b are formed in a rectangular shape having a length of about λ / 6 in the linear direction and a length of about λ / 2 in a direction orthogonal to the linear direction. I have. These slots 10a and 10b are located at an interval of mλg / 2 (m is a positive integer, m <n, and m is preferably an odd number), for example, about 3 / 2λg. These slots 10a and 10b are located at equidistant point-symmetric positions with the probe 6 interposed therebetween. Slot 10a,
10b is located at about λg / 2 (an even multiple of about λg / 4) from the short-circuit plane.

The slots 10c and 10d are
a, 10b make an angle with the linear portion on which it is formed,
For example, except that the slot 10
a, 10b. Therefore, these slots 10a to 10d are
Those that are formed so as to be at an equal angle to each other at a distance of λg / 4 and that are at point-symmetric positions with the probe 6 therebetween form a pair. In addition, these slots 10a to 10d
Are arranged at equal angles to each other on a circumference having a radius of mλg / 4 around the probe 6.

The fan beam antenna of the second embodiment operates similarly to the fan beam antenna of the first embodiment. FIG. 13 shows the θ plane directivity of an arbitrary φ value cross section of the fan beam antenna according to the second embodiment. Further, the directivity in the φ direction of the fan beam antenna according to the second embodiment is the same as that shown in FIG. Also, in FIG.
FIG. 5 shows a frequency vs. VSWR characteristic diagram of the fan beam antenna. As is clear from this characteristic diagram, the worst case VSWR
The maximum value is 1.3, which is sufficiently practical.

FIGS. 15 and 16 show a fan beam antenna according to the third embodiment. This fan beam antenna also has a flat rectangular parallelepiped conductive main body 2. The main body 2 is formed in a substantially square shape in plan view, and is a regular polygonal column, for example, a concave portion 4b of an octagonal column opened on the upper surface side.
Are formed. The recess 4b is formed so as to circumscribe a circle having a diameter of n / 2λg, for example, about 3 / 2λg, as shown in FIG. n is a positive integer and is preferably an odd number. λg is a guide wavelength of a radio wave to be transmitted / received by the fan beam antenna.

At the center of the bottom surface of the recess 4b, a probe 6 for transmitting and receiving radio waves by the fan beam antenna is provided.

A conductive plate 8 having substantially the same shape as the upper surface of the main body 2 is arranged in contact with the upper surface so as to cover the opening on the upper surface of the recess 4b. The conductive plate 8 and the recess 4b form a cavity in which the conductive plate 8 and the bottom surface of the recess 4b are parallel flat plates. The entire cavity is short-circuited by a short-circuit wall having a distance of about 3 / 2λg, which is opposed to the cavity. The conductive plate 8 has a plurality of slots 10a, 10b, 10c, and 10d.
Slots 10a, 10b form a pair, slot 10c,
10d are paired.

The slots 10a and 10b are located in the propagation direction of the radio wave in the cavity, that is, on one straight line connecting the opposing short-circuit walls of the cavity. As shown in FIG. 16, each of the slots 10a and 10b is formed in a rectangular shape having a length of about λ / 6 in the linear direction and a length of about λ / 2 in a direction orthogonal to the linear direction. . These slots 10a and 10b are located at an interval of mλg / 2 (m is a positive integer, m <n, and m is preferably an odd number), for example, about λg / 2. These slots 10a and 10b are located point-symmetrically at positions equidistant with respect to the probe 6. Slots 10a, 10b
Is located at a position of about λg / 2 (about an even multiple of about λg / 4) from the peripheral surface of the cavity which is the short-circuit surface.

The slots 10c and 10d are
a, 10b make an angle equal to the diameter formed,
For example, except that they are located on orthogonal diameters,
a, 10b. Accordingly, the slots 10a to 10d are respectively separated from the probe 6 by mλg /
It is formed at a position four distances away, and is arranged at a point-symmetrical position with the probe 6 interposed therebetween. Further, an even number of these slots 10a to 10d are arranged on a circumference of a radius mλg / 4 centered on the probe 6 so as to form an equal angle with each other.

The fan beam antenna of the third embodiment operates similarly to the fan beam antenna of the first embodiment. FIG. 17 shows the θ plane directivity of an arbitrary φ value cross section of the fan beam antenna according to the third embodiment. Further, the directivity in the φ direction of the fan beam antenna according to the third embodiment is the same as that shown in FIG. Also, in FIG.
FIG. 5 shows a frequency vs. VSWR characteristic diagram of the fan beam antenna. As is clear from this characteristic diagram, the worst case VSWR
The maximum value is 1.17, which is sufficiently practical.

FIGS. 19 and 20 show a fan beam antenna according to the fourth embodiment. The fan beam antenna according to the fourth embodiment also has a conductive main body 2 formed in a flat rectangular parallelepiped shape. A regular polygonal concave portion 4d opened on the upper surface side of the main body 2 is formed. This recess 4d
On the upper surface of the main body 2, recesses having a substantially rectangular planar shape are formed in two columns and two rows at predetermined intervals, and some of the recesses are cut off at the center side of the conductive plate 2. It has a communicating shape. Also, from the midpoint of each side of the approximate square toward the center, the length of each side is about 1 / 2λg,
It can also be called a cut shape. Note that each corner of the square has an R shape.

The probe 6 is arranged at the center of a square with each corner having an R shape. As shown in FIG. 20, the lengths of the two diagonal lines of this square are n / 2λg,
For example, it is selected to be about 3 / 2λg. n is a positive integer and is preferably an odd number. λg is a guide wavelength of a radio wave to be transmitted / received by the fan beam antenna.

In order to cover the main body 2 by contacting it,
The conductive plate 8 is arranged. The conductive plate 8 has two pairs of slots 10a, 10b, 10c, and 10d. The slots 10a and 10b are rectangular openings that are on one diagonal, have a length along the diagonal of about λ / 10, and have a length in a direction perpendicular to the diagonal of about λ / 2, for example. These slots 10a, 10b are
/ 2 (m is a positive integer, m <n, and m is preferably an odd number), for example, at an interval of about λg / 2. These slots 10a and 10b
Are arranged point-symmetrically at positions equidistant from each other. The slots 10a and 10b are located at a position of about λg / 2 (an even multiple of about λg / 4) from the peripheral surface of the cavity, which is a short-circuit surface.

The slots 10c and 10d are also
It has the same configuration except that it is orthogonal to a and 10b. Therefore, the slots 10a, 10b, 10c, and 10d are arranged at a position of about mλg / 4 from the probe 6, and the slots 10a and 10b are located at point-symmetric positions with respect to the probe 6.
Form a pair, and similarly, the slots 10c and 10d form a pair. There are even pairs. An even number of the slots 10a to 10d are arranged on the circumference of the probe 6 having a radius of about mλg / 4 so as to be equiangular with each other.

This fan beam antenna operates similarly to the fan beam antenna of the first embodiment. FIG.
1 shows the θ of an arbitrary φ value cross section of this fan beam antenna.
Shows surface directivity. Further, the directivity in the φ direction of the fan beam antenna according to the fourth embodiment is the same as that shown in FIG. FIG. 22 shows a frequency vs. VSWR characteristic diagram of the fan beam antenna. As is apparent from this characteristic diagram, the VSWR value is about 1.2 at worst, which is sufficiently practical.

FIG. 23 shows a fan beam antenna according to the fifth embodiment. This fan beam antenna is for transmitting and receiving circularly polarized waves, and has a parasitic dipole antenna 22 disposed above a conductor plate 8 of the first embodiment via a spacer 20 made of a dielectric material. . The passive dipole 22 is formed by forming four slots 26 in a conductive plate 24. The slots 26 are provided corresponding to the slots 10a to 10d, respectively, and are configured to form a predetermined angle, for example, about 45 degrees with the corresponding slots 10a to 10d. By arranging the slots 26 in this manner, transmission and reception of circularly polarized waves can be performed.

FIG. 24 shows a fan beam antenna according to the sixth embodiment. This fan beam antenna is also for transmitting and receiving circularly polarized waves, and is different from the fan beam antenna of the fourth embodiment in that the spacer 20 and the parasitic dipole antenna used in the fan beam antenna of the fifth embodiment are used. 22 are arranged. Each slot 26 formed in the conductor plate 24 of the parasitic dipole antenna 22
Are arranged at a predetermined angle to the corresponding slots 10a to 10d, for example, 45 degrees.

FIG. 25 shows a fan beam array antenna according to the seventh embodiment. This fan beam array antenna 28 is an array of the fan beam antennas described in the second embodiment. In this fan beam array antenna 28, a recess 40a corresponding to the recess 4a of the second embodiment is formed in the main body 2 over four rows and four columns. The size of the recess 40a is the same as that of the recess 4a of the second embodiment. Each of the recesses 4 is provided in the conductor plate 8a.
A large number of slots 10 are formed such that slots corresponding to the slots 10a to 10d of the second embodiment are arranged on 0a.

Such a fan beam array antenna 2
For example, as shown in FIG. 26, the conductive plate 8 is attached to the ceiling so that the conductive plate 8 is parallel to the floor surface, and can be used as a wireless LAN antenna. Since it is mounted as described above, the directivity in the φ direction is directed to the floor surface, and it is possible to receive radio waves from various directions.

Alternatively, as shown in FIG. 27, a frequency converter, for example, a low noise block converter 30 is connected to each of the fan beam array antennas 28a of the fan beam array antenna 28 of FIG. 25, and their output signals are phase-shifted. 32 to the synthesizer 34, and
4 is divided by the divider 36 into an output.
8 and detects each phase shifter 3 based on the detection output.
By adjusting the phase of the second by the CPU 36, a phased array antenna can also be configured. In this case, arranging the fan beam antenna 28 such that the conductive plate 8 is parallel to the ground facilitates beam combining in the required elevation angle direction. The fan beam antenna 28a
A phase shifter may be provided on each output side to adjust the phase.

In each of the above embodiments, two slots, for example, 10a and 10b, are provided along the propagation direction of radio waves. However, if the interval between adjacent slots satisfies the condition of m / 2λg, more slots are provided. Slots can also be provided. Further, in each of the above embodiments, the cavity is formed by the rectangular parallelepiped main body having the concave portion and the conductive plate, but the main body is formed by pressing a thin conductive metal, for example, aluminum, to form the concave portion. May be.

[0051]

As described above, according to the present invention, a fan beam antenna can be realized without using an accessory such as a suppression element, and a combining circuit is not required. Does not occur.

[Brief description of the drawings]

FIG. 1 is an assembly diagram of a fan beam antenna according to a first embodiment of the present invention.

FIG. 2 is a plan view of the fan beam antenna of FIG.

FIG. 3 is a vertical sectional view of the fan beam antenna of FIG. 1;

FIG. 4 is a diagram illustrating a resonance state in a cavity of the fan beam antenna of FIG. 4;

FIG. 5 is a diagram showing the incidence of radio waves from the θ direction on the fan beam antenna of FIG. 1;

FIG. 6 is a directional characteristic diagram in the θ direction of the fan beam antenna of FIG. 1;

FIG. 7 is a diagram showing incidence of radio waves from the φ direction in the fan beam antenna of FIG. 1;

FIG. 8 is a directional characteristic diagram in the φ direction of the fan beam antenna of FIG. 1;

FIG. 9 is a diagram showing frequency versus VSWR characteristics in the fan beam antenna of FIG. 1;

FIG. 10 is an assembly view of a fan beam antenna according to a second embodiment of the present invention.

FIG. 11 is a plan view of the fan beam antenna of FIG. 10;

FIG. 12 is a longitudinal sectional view of the fan beam antenna of FIG. 10;

13 is a directional pattern of the fan beam antenna of FIG. 10 in the θ direction.

14 is a diagram showing a frequency vs. VSWR characteristic in the fan beam antenna of FIG.

FIG. 15 is an assembly view of a fan beam antenna according to a third embodiment of the present invention.

FIG. 16 is a plan view of the fan beam antenna of FIG.

17 is a directional characteristic diagram of the fan beam antenna of FIG. 15 in the θ direction.

18 is a diagram showing a frequency vs. VSWR characteristic in the fan beam antenna of FIG.

FIG. 19 is an assembly view of the fan beam antenna according to the fourth embodiment of the present invention.

FIG. 20 is a plan view of the fan beam antenna of FIG. 19;

21 is a directional characteristic diagram of the fan beam antenna of FIG. 19 in the θ direction.

FIG. 22 is a frequency vs. VSWR characteristic diagram in the fan beam antenna of FIG. 19;

FIG. 23 is an assembly view of the fan beam antenna according to the fifth embodiment of the present invention.

FIG. 24 is an assembly view of the fan beam array antenna according to the sixth embodiment of the present invention.

FIG. 25 is an assembly view of the fan array beam antenna according to the seventh embodiment of the present invention.

26 is a perspective view showing a state where the fan beam array antenna of FIG. 25 is arranged.

FIG. 27 is a block diagram of a phased array antenna configured using the fan beam array antenna of FIG.

[Explanation of symbols]

 2 body 4 recess (cavity) 8 conductive plate (cavity) 10a to 10d slot

Claims (6)

[Claims] 1. A cavity having a short-circuit surface at a position n · λg / 4 (n is a positive integer, λg is a guide wavelength) from a center point, and m · m from the center point in the cavity.
λg / 4 (m is a positive integer, m <n) and a plurality of slots formed at equal angles to each other, and these slots are located at points A fan beam antenna paired with a symmetrically located slot. 2. The fan beam antenna according to claim 1, wherein a probe is arranged at the center point on one surface of the cavity, and the slots are formed on a surface facing the one surface. antenna. 3. The fan beam antenna according to claim 1, wherein said cavity is formed by combining two rectangular waveguides, both ends of which are short-circuited, in a cross shape, and said pair of slots is formed in said two rectangular waveguides. The fan beam antenna where each is arranged. 4. A fan beam antenna according to claim 1, wherein said cavity is formed in a cylindrical shape having a diameter of said n · λg / 2, and at least two of said cylindrical shapes intersecting and forming an equal angle to each other. A fan beam antenna, wherein the pair of slots is formed on a diameter of the fan beam antenna. 5. The fan beam antenna according to claim 1, wherein the cavity is formed in a regular polygonal column circumscribing a circle having a diameter of n · λg / 2, and opposing short-circuit surfaces of the regular polygonal column. A fan beam antenna having the pair of slits formed therebetween. 6. The fan beam antenna according to claim 1, wherein the cavity is formed as a regular polygonal column having a plurality of diagonal lines at equal angles to each other, and the pair of slots is formed on each of the diagonal lines. The fan beam antenna being formed.