JPH09246854A - Radar antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the antenna itself small with a simple structure by suppressing a side lobe sufficiently over a broad frequency band to obtain a high FB ratio. SOLUTION: A radiation plane 2a of a reflecting plate 2 emitting a radio wave toward an object is formed by a strip parabolic plane with a width H2 around an apex P of a paraboloid of rotation. Shield planes 2b, 2c are extended in parallel at upper and lower ridges of the radiation plane 2a in the lengthwise direction along the rotation center line L1-L1 of the paraboloid of rotation. An aperture width H1 of an aperture 3a of a primary radiator 3 is formed smaller than a width H2 of the radiation plane 2a and a width H3 between the upper and lower shield planes 2b, 2c and feeding is made to a reflecting plate 2 via a guide path. A phase center of a radio wave at an aperture 3a of the primary radiator 3 is placed on the center line L1-L1 of the paraboloid of rotation. The reflecting plate 2 and the primary radiator 3 are contained in a radome 4 and fixed integrally and driven together by the drive of a motor 12 and emit a radio wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small radar antenna mounted on a ship or the like and rotatably housed in a circular radome.

[0002]

2. Description of the Related Art Generally, a radar irradiates a target with a radio wave and receives a reflected wave from the target or a radio wave re-emitted from the target. Is judging.

By the way, a marine radar used for general navigation is designed to cope with the fluctuation of a ship, so that a beam pattern in a vertical plane is set to a wide angle and a pattern in a horizontal plane is narrowed as much as possible to obtain a fan-shaped beam, that is, a fan. Emitting a beam.

FIGS. 5 to 7 show an example of the structure of a radar antenna used as this type of marine radar.

FIGS. 5A and 5B show a parabolic cylinder type antenna. The parabolic cylinder type antenna includes a reflecting plate 31 formed in a band shape having a cylindrical parabolic surface forming a radiation surface 31a, and a primary radiator 32 arranged in a predetermined positional relationship with respect to the reflecting plate 31. Is roughly configured. To further explain, the reflector 3
1 is a predetermined angle θ1 from the vertical as shown in FIG.
It is arranged so as to be inclined (for example, 15 °). Primary radiator 32
Depending on the position where the reflection plate 31 is arranged,
Is disposed below the reflection plate 31 with a predetermined angle θ2 (for example, 32 °) inclined from the vertical. As a result, the radio wave from the primary radiator 32 is radiated toward the target without being reflected by the reflector 31 and hitting the primary radiator 32 again.

6 and 7 show a cheese-shaped antenna. The cheese antenna is roughly configured by including a reflecting plate 35 having a cylindrical paraboloid forming a radiation surface 35a and a primary radiator 36 arranged in a predetermined positional relationship with respect to the reflecting plate 35. . To further explain, the reflector 3
5 has a cheese shape in which upper and lower edges of the radiation surface are covered with shielding surfaces 37 parallel to each other, and only one surface is open. The primary radiator 36 is provided with the reflector 35 in a state where the tip portions of the openings 36 a are in contact with the upper and lower shield surfaces 37 of the reflector 35, respectively.
Is arranged in the center of the opening surface of the.

When the cheese antenna having such a structure is used as a marine radar, as shown in FIG. 7, a radome 4 having a waterproof structure to withstand wind and rain is used.
0. Then, the reflector 35 is a radome 40.
The primary radiator 3 is driven by the power of the motor 41 fixed in the inside.
Rotate with 6. When a radio wave is radiated from the primary radiator 36 to the reflecting plate 35 in accordance with this rotating operation, this radio wave is reflected by the radiation surface 35a of the reflecting plate 35 and radiated toward the target.

[0008]

By the way, when the antenna having the above structure is used as a marine radar, side lobes SL as shown in FIG. 8 occur on both sides of the main beam ML, and the level of this side lobe SL is the main beam. If it is larger than ML (for example, −20 dB or more), as shown in FIG. 9, false images DL are displayed on both sides of the real image DT on the radar screen.
This makes it difficult to judge the figure. Therefore, the main beam M
The level of the side lobe SL with respect to L is -25d, for example.
It is necessary to keep it lower than B.

However, any of the above-mentioned antennas has the following problems. That is,
In the parabolic cylinder type antenna shown in FIG. 5, side lobes SL with respect to the main beam ML are spread over a wide frequency band.
However, since the upper and lower sides of the reflector 31 are open, when the radio wave from the primary radiator 32 enters the reflector 31, a part of the radio wave leaks out from the reflector 31. Sometimes. Therefore, the radio wave ratio in the front-rear direction of the reflector 31, that is, the so-called FB ratio, is reduced.

In the FB ratio, the incident direction of the radio wave from the primary radiator 32 to the reflector 31 is the backward direction, and the opposite direction is the forward direction, the backward radio wave level is B, and the forward radio wave level is When the level is F, it is expressed by 10 × log B / F.

Further, in order to increase the FB ratio to solve the above problem, it is necessary to design the primary radiator 32 in the height direction orthogonal to the rotation direction so that the leakage of the radio wave to the reflection plate 31 becomes small. there were. Furthermore, when the radome 40 is configured to be housed as shown in FIG. 7, since the housing area is taken in the height direction of the reflection plate 31, there is a problem that the antenna itself becomes large.

On the other hand, in the cheese antenna of FIG. 6, the opening of the primary radiator 36 is in contact with the upper and lower shield surfaces 37 of the reflector 35, and the radiation surface 35a of the reflector 35 is the primary radiator 36. Is parallel to the opening surface of the opening 36a. Therefore, when the opening surface of the reflecting plate 35 is viewed, the central portion of the opening surface is divided by the primary radiator 36, and when the radio wave from the primary radiator 36 is radiated by the reflecting plate 35, the primary radiator 36 is radiated. Was in the way. Therefore, the distribution of the electric field on the aperture plane becomes non-uniform, and the main beam M
There has been a problem that the level of the side lobe SL with respect to L is increased and the beam pattern of the antenna is deteriorated.

By the way, in the cheese type antenna of FIG. 6, the reflector 35 is enlarged in the height direction to make the primary radiator 32.
A configuration in which the upper and lower shield surfaces 37 are separated from each other is conceivable. With this configuration, it is possible to suppress the side lobe of the reflecting plate 35, which rotates the antenna, in the horizontal direction to be low. However, the side lobe in the direction of the rotation axis of the antenna (the direction perpendicular to the reflection plate 35) cannot be kept low. Further, when the radome 40 is configured to be housed as shown in FIG. 7, like the parabolic cylinder type antenna, the housing area is taken in the height direction of the reflection plate 35, and the antenna itself becomes large. there were.

Therefore, the present invention has been made in view of the above problems, and it is possible to sufficiently suppress the side lobe over a wide frequency band to obtain a high FB ratio, and to downsize the antenna itself with a simple structure. An object is to provide a radar antenna that can be achieved.

[0015]

To achieve the above object, a radar antenna according to claim 1 of the present invention comprises a primary radiator 3 having an opening 3a for feeding power through a waveguide,
In a radar antenna including a reflection plate 2 provided with a radiation surface 2a for radiating radio waves from the primary radiator toward a target, a radiation surface of the reflection plate is: The parabola is formed by a band-shaped parabolic surface having a predetermined width H2 including the apex P of the rotating parabola, and the radiation surface has longitudinal upper and lower edges along the rotation center line L1-L1 of the rotating parabola. The extending shield surfaces 2b and 2c are formed to face each other, and the primary radiator is
The opening width H1 of the opening is formed to be smaller than the width H2 of the radiation surface and the width H3 between the upper and lower shielding surfaces, and the phase center of the radio wave in the opening is on the rotation center line L1-L1 of the rotating parabola. It is characterized by

In the radar antenna of claim 1, the vertex P of the rotating parabola is the center of the radiation surface 2a, or the lower shield surface 2c of the reflector 2 is the lower edge 3ab of the opening 3a of the primary radiator 3. It is preferable to continue with.

According to a fourth aspect of the radar antenna of the present invention, the reflecting plate 2 and the primary radiator 3 are integrated with each other, the driving means 12 for rotating the reflecting plate and the primary radiator, the reflecting plate and the primary radiation. And a radome 4 for accommodating the container and the driving means.

In the above radar antenna, the radiation surface 2a of the reflector 2 is formed by a paraboloid in the shape of a strip parabola, and the upper and lower surfaces of the shields 2b, 2c of the reflector 2 are separated from the primary radiator 3. There is. Therefore, the area ratio of the primary radiator 3 occupying the radiation surface 2a is increased, and the side lobe levels of the reflection plate 2 in the horizontal and vertical directions can be suppressed low. As a result, even when used as a marine radar,
The sidelobe level is kept sufficiently low, and the target can be reliably determined without causing false images on both sides of the real image on the radar screen.

The reflecting plate 2 is covered on all the surfaces except the opening, so that the leakage of radio waves from the primary radiator 3 to the reflecting plate 2 is small and a high FB ratio can be obtained.

Like the primary radiator of a parabolic antenna,
Sufficient radiation to the target can be performed without paying close attention to the radiation amount of the paraboloid deviating from the radiation surface 2a. Moreover,
The distance (focal length) between the radiation surface 2a of the reflector 2 and the primary radiator 3 can be set to the shortest, and even when the antenna 1 is housed in the radome 4, the radial dimension of the antenna 1 can be reduced, The overall size of the antenna can be reduced.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan sectional view of a radar antenna according to the present invention, FIG. 2 is a sectional view taken along the line AA with a cover of the antenna, and FIG. FIG. 6 is a sectional view taken along line BB of FIG.

The radar antenna according to this embodiment is
For example, it is used as a marine radar, and a reflector 2 and a primary radiator 3 which constitute an antenna 1 are rotatably housed in a radome 4.

The radome 4 has a substantially cylindrical shape with a hollow inside, and has a cover 4a and a bottom base 4 which are vertically divided into two parts.
b. The cover 4a and the bottom base 4b are detachably fixed via fixing means such as screws and bolts. Although not shown, the radome 4 is provided with waterproof packing along the entire circumference of the edge of the base 4b so that the joint portion with the cover 4a is waterproof.

The bottom base 4b is provided with a base 5 made of, for example, an alloy that rotatably supports the antenna 1. In the central portion of the bottom base 5, a cylindrical support cylinder 5a is integrally formed so as to extend in a direction orthogonal to the horizontal plane 4ba of the bottom base 4b.

A rotary shaft 6 is inserted into the support cylinder 5a of the base 5 with one end rotatably supported by the horizontal plane 4ba of the bottom base 4b. The rotating shaft 6 has a cylindrical shape, and a rectangular through hole 6a forming a waveguide is formed therein. A large-diameter portion 6b is formed in the central portion of the outer periphery of the rotating shaft 6, and small-diameter portions 6c having the same diameter and slightly smaller than the large-diameter portion 6b are formed above and below the large-diameter portion 6b. Bearings 7 are provided on the outer periphery of the rotary shaft 6 in the upper and lower small diameter portions 6 respectively.
It is fitted and fixed in a state of being in contact with the stepped portion 8 between the c and the large diameter portion 6b.

The reflector 2 converts a radio wave fed from a wave source (not shown) through the primary radiator 3 into a plane wave and radiates it to a target. The reflection plate 2 has a radiation surface 2a which is a part of a paraboloid 9 including a vertex P of a rotating parabola formed by rotating a parabola.

In the examples of FIGS. 1 to 3, the vertices P of the rotating parabola are cut at equal vertical positions from the rotation center line L1-L1, and the vertices P of the rotating parabola are centered. The radiation surface 2a having a parabolic shape is formed.

At the upper and lower edges of the radiation surface 2a in the longitudinal direction, arcuate shield plates 2b and 2c extend in parallel along the rotation center line L1-L1 of the rotating parabola. An attachment portion 15 for attaching to the primary radiator 3 is extended and integrally formed on the back surface of the lower shield plate 2c. A through hole 15a is formed in the central portion of the mounting portion 15 so that the primary radiator 3 can be inserted therethrough.

The center of rotation L1-L1 where the apex P is located in the reflector 2 coincides with the phase center of the radio wave in the opening 3a of the primary radiator 3 which will be described later. And the reflector 2
Is fixed to the primary radiator 3 via a mounting portion 15 by fixing means 16 such as a screw so that the focal point of the radiation surface 2a and the phase center of the primary radiator 3 coincide with each other.

The reflector 2 having such a structure is, for example, AB
A synthetic resin such as S resin and PC (polycarbonate), which is resistant to vibrations and impacts, is used, and is formed by die casting or resin molding to reduce the weight. Further, the inner surface 2A of the reflection plate 2 is subjected to electroless plating (conduction) in which nickel is plated on copper.

The reflection plate 2 is not limited to the synthetic resin, and may be formed by sheet metal working of a metal plate such as aluminum.

The primary radiator 3 feeds radio waves (spherical waves) emitted from a wave source (not shown) to the reflector 2. The primary radiator 3 has an opening 3 a formed in a horn shape by gradually expanding the waveguide, and the tip portion of the opening 3 a is provided so as to face the opening of the reflection plate 2.

In the primary radiator 3, the phase center of the radio wave in the opening 3a is set on the rotation center line L1-L1 of the rotating parabola. The opening width H1 of the opening 3a in the primary radiator 3 is formed to be smaller than the width H2 of the radiation surface 2a of the reflection plate 2 and the width H3 between the shield plates 2b and 2c. That is, the upper edge 3aa and the lower edge 3ab of the opening 3a are located at a predetermined distance from the shield plates 2b and 2c of the reflector 2.

The primary radiator 3 has a fixing means 17 such as a screw.
Is fixed to the rotary shaft 6. A flat plate-shaped flange 10 is integrally formed on the lower outer peripheral surface of the primary radiator 3. The outer peripheral surface of the flange 10 has teeth 11 over the entire circumference.
a is formed and constitutes the transmission gear 11. The transmission gear 11 meshes with a motor gear 13 of a motor 12 fixed to the base 5. When the power of the motor 12 is transmitted to the transmission gear 11 via the motor gear 13, the primary radiator 3 rotates around the rotation shaft 6 together with the reflection plate 2.

As the primary radiator 3, an E-plane fan-shaped horn fan-shaped in the direction of the electric field E, an H-plane fan-shaped horn fan-shaped in the direction of the magnetic field H, and both the E-plane and the H-plane were opened. Various horns such as a composite horn can be adopted.

In the radar antenna having the above structure, when the motor 12 rotates, its power is transmitted to the transmission gear 11 of the primary radiator 3 via the motor gear 13 and the antenna 1
The whole, that is, the primary radiator 3 and the reflector 2 rotate together about the rotation axis 6. When radio waves are fed from the primary radiator 3 to the reflection plate 2 as the antenna 1 rotates, the radio waves are reflected by the reflection plate 2 and radiated toward the target. Then, when the reflected wave from the target or the electric wave re-emitted from the target is received by the irradiation of the radio wave to the target, a predetermined detection operation for determining the position of the target from the relationship between the round-trip time and the directional characteristics of the antenna. Is executed.

The radar antenna constructed as described above has the following effects. Since the radiation surface 2a of the reflector 2 is formed by a parabolic surface in the shape of a strip parabola and the upper and lower surfaces (shielding plates 2b, 2c) of the reflector 2 are separated from the primary radiator 3, When looking at the aperture surface, the central portion of the aperture surface is not divided by the primary radiator 3 as in the conventional cheese antenna,
The area ratio of the primary radiator 3 to the radiation surface 2a becomes large. As a result, in any of the rotation direction of the antenna 1 (horizontal direction of the reflection plate 2 (X direction in FIG. 2)) and the rotation axis direction of the antenna 1 (vertical direction of the reflection plate 2 (Y direction in FIG. 2)). The side lobe level can be suppressed to a low level. As a result, the side lobe level required when used as a marine radar is suppressed to, for example, -25 dB or lower, and false images DL are generated on both sides of the real image DT on the radar screen as shown in FIG. Without it, it is possible to reliably judge the target.

Since the reflector 2 has a structure in which all the surfaces other than the opening surface are covered, like the cheese antenna, the leakage of radio waves from the primary radiator 3 to the reflector 2 is small,
A high FB ratio is obtained.

Like the primary radiator of a parabolic antenna,
Sufficient radiation can be performed to the target without paying close attention to the radiation amount of the paraboloid deviating from the radiation surface 2a. Moreover, like the cheese antenna, the distance (focal length) between the radiation surface 2a of the reflector 2 and the primary radiator 3 can be set to the shortest. Therefore, even if the antenna 1 is housed in the radome 4, The size in the radial direction of 1 can be reduced, and the overall size of the antenna can be reduced.

Next, FIG. 4 is a plan sectional view of a radar antenna according to another embodiment of the present invention. The antenna of FIG. 4 differs from the antennas of FIGS. 1 to 3 in the shape of the radiation surface 2a of the reflector 2 and the positional relationship between the reflector 2 and the primary radiator 3.

In FIG. 4, the reflector 2 is cut at a predetermined distance upward from the rotation center line L1-L1 so as to include the apex of the rotating parabola, and forms a radiation surface 2a in the shape of a strip parabola. ing. Arcuate shield surfaces 2b and 2c are provided on the upper and lower edges of the radiation surface 2a in the longitudinal direction so as to extend substantially parallel to each other along the rotation center line L1-L1 of the rotating parabola.

In the primary radiator 3, the phase center of the radio wave in the opening 3a is set on the rotation center line L1-L1 of the rotating parabola, and the lower edge 3ab of the opening 3a is the shielding plate 2c below the reflecting plate 2. It is provided in contact with the.

The antenna configured as described above can also achieve the same effect as the antenna shown in FIGS.

By the way, in the antenna according to each of the above-mentioned embodiments, the primary radiator 3 is separated from at least one of the shield plates 2b (or 2c) of the reflection plate 2, and if it is the focal point of the rotating parabola, the radiation surface 2a. It may be arranged at any position with respect to.

[0045]

As described above, according to the radar antenna of the present invention, the radiation surface of the reflector is formed by a parabolic surface in the shape of a strip parabola, and the upper and lower edges of the radiation surface of the reflector in the longitudinal direction. Since at least one of the shielding surfaces formed on the radiation surface is separated from the primary radiator, the area ratio of the primary radiator to the radiation surface becomes large, and the horizontal direction (rotation direction) and vertical direction (rotation axis direction) of the antenna are increased. It is possible to suppress the side lobe level to be low in any of the above directions. As a result, the side lobe level required when used as a marine radar can be suppressed to a sufficiently low level, and the target can be reliably determined without causing false images on the radar screen as in the conventional case.

Since the reflector is constructed so as to cover all the surfaces other than the opening, the leakage of radio waves from the primary radiator to the reflector is small and the F-value is high, as in the cheese antenna.
A B ratio is obtained.

Like the primary radiator of a parabolic antenna,
Sufficient radiation to the target can be performed without paying close attention to the amount of radiation deviating from the radiation surface due to the paraboloid. Moreover, like the cheese antenna, the distance between the radiation surface of the reflector and the primary radiator (focal length) can be set to the shortest, so even when the antenna is housed in a radome, the radial dimension of the antenna Can be made smaller, and the antenna as a whole can be made smaller.

[Brief description of drawings]

FIG. 1 is a plan sectional view of a radar antenna according to the present invention.

FIG. 2 is a cross-sectional view taken along the line AA with the cover shown in FIG.

FIG. 3 is a cross-sectional view taken along the line BB with the cover shown in FIG.

FIG. 4 is a plan sectional view of a radar antenna according to another embodiment of the present invention.

5A is a perspective view of a parabolic cylinder type antenna, and FIG. 5B is a side view of the antenna.

FIG. 6 is a perspective view of a cheese antenna.

FIG. 7 is a plan sectional view of a cheese-shaped antenna housed in a radome.

FIG. 8 is a diagram showing an example of an antenna pattern when a side lobe occurs.

FIG. 9 is a diagram showing a display example of a radar screen when a false image occurs.

[Explanation of symbols]

1 ... Antenna, 2 ... Reflector, 2a ... Radiating surface, 2b, 2c
... Shielding plate, 3 ... Primary radiator, 3a ... Opening part, 4 ... Radome, 4a ... Cover, 4b ... Bottom base, 6 ... Rotation axis,
9 ... Paraboloid, 11 ... Transmission gear, 12 ... Motor, 13 ... Motor gear, P ... Apex.

Claims (4)

[Claims] 1. An opening (3a) for feeding power through a waveguide.
A primary radiator (3) and a reflector (2) having a radiation surface (2a) for radiating radio waves from the primary radiator toward a target, the reflector (2) being provided toward the opening of the primary radiator. In the provided radar antenna, the radiation surface of the reflector is formed by a band-shaped parabolic surface having a predetermined width (H2) including the apex (P) of a rotating parabola formed by rotating a parabola, and the radiation surface in the longitudinal direction. Shielding surfaces (2b, 2c) extending along the rotation center line (L1-L1) of the rotating parabola are formed on the upper and lower edges so as to substantially face each other, and the primary radiator has the opening. Has an opening width (H1) of the radiation surface (H2) and a width between the upper and lower shielding surfaces (H3).
A radar antenna, wherein the radar antenna is formed smaller, and the phase center of the radio wave in the opening is on the rotation center line (L1-L1) of the rotating parabola. 2. The radar antenna according to claim 1, wherein the vertex (P) of the rotating parabola is the center of the radiation surface (2a). 3. The lower shielding surface (2c) of the reflector (2) has a lower edge (3a) of the opening (3a) of the primary radiator (3).
The radar antenna according to claim 1, which is continuous with b). 4. The drive means (12) for rotating the reflector and the primary radiator by integrating the reflector (2) and the primary radiator (3).
The radar antenna according to any one of claims 1 to 3, further comprising: a radome (4) accommodating the reflector, the primary radiator, and a driving unit.