JP2024029307A - radar antenna - Google Patents

Abstract

An object of the present invention is to provide a radar antenna that can obtain vertical directivity without having a flare and can also obtain desired sidelobe level characteristics. A plurality of waveguides 2 each having a cylindrical shape with a substantially rectangular cross section and having a slot 2a formed in the front surface, and a plurality of waveguides 2 extending substantially horizontally and arranged vertically, A strip-shaped horizontal plate portion 4 protrudes approximately horizontally toward the front side from at least the upper edge side of the uppermost waveguide 2 and the lower edge side of the lowest waveguide 2, and extends along the longitudinal direction of the waveguide 2. The length of the lowest horizontal plate portion 4 in the substantially horizontal direction is set longer than the length of the other horizontal plate portions 4 in the substantially horizontal direction. [Selection diagram] Figure 1

Description

The present invention relates to a radar antenna used on land, on ships, etc.

As a radar antenna used on land or on ships, it is known to combine a slot waveguide for shaping horizontal plane directivity with a flare for shaping vertical plane directivity (for example, a patent (See Reference 1 etc.). This radar antenna has multiple slots (elongated holes) formed in the front of the waveguide, and by adjusting the inclination angle, width, depth of cut, placement, etc. of each slot, a predetermined directional characteristic or frequency characteristic can be achieved. is now available. In addition, a horn-shaped flare consisting of an upper flare and a lower flare is arranged to sandwich the waveguide in which multiple slots are formed, and the waveguide and flare are held together by multiple waveguide holding fittings. It is assembled.

Since such a radar antenna includes a flare, there is a problem in that the depth dimension of the radar antenna becomes large. For this reason, a radar antenna/slot array antenna is known in which the vertical plane directivity is formed without a flare and the depth dimension can be reduced (see, for example, Patent Document 2). In this radar antenna, a plurality of slots are provided in the front surface of the waveguide in the horizontal and vertical directions, so that the waveguide can shape the horizontal directionality and the vertical directionality.

JP2017-79424A Japanese Patent Application Publication No. 2012-19258

By the way, in a radar antenna mounted on a ship, if multiple slots are provided in the front surface of the waveguide in the horizontal and vertical directions, a high level of sidelobes will occur on the sea side of the vertical plane directivity, resulting in a virtual image. In addition, the inventor of the present application has confirmed that there is a possibility that a gain null/zero occurs within a predetermined angle of elevation angle (EL), and that a target object that falls within that angle may not be recognized.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a radar antenna that can provide vertical directivity without flare and can also provide desired sidelobe level characteristics.

To achieve the above object, the invention according to claim 1 includes a plurality of waveguides each having a cylindrical shape with a substantially square cross section and having a slot formed in the front part, and a plurality of waveguides extending substantially horizontally. protruding approximately horizontally to the front side from at least the upper edge side of the uppermost waveguide and the lower edge side of the lowermost waveguide, and extending along the longitudinal direction of the waveguide. a strip-like horizontal plate portion extending from the uppermost horizontal plate portion or the lowermost horizontal plate portion, the length in the approximately horizontal direction of the uppermost horizontal plate portion or the lowermost horizontal plate portion is the approximately horizontal length of the other horizontal plate portions. This radar antenna is characterized by being set longer than the actual length.

According to the invention described in claim 1, since the plurality of waveguides in which slots are formed extend substantially horizontally and are arranged above and below, vertical directivity can be obtained without flare, It is possible to keep the depth dimension of the radar antenna small.

In addition, since the length of the highest or lowest horizontal plate is set longer than the other horizontal plates, unnecessary radiation to the side where the horizontal plate is longer (for example, the sea side) is suppressed. . As a result, it is possible to suppress the occurrence of side lobes and gain nulls/zeros in the vertical plane directivity on the side where the horizontal plate portion is longer, and to obtain desired side lobe level characteristics.

1 is a perspective view showing a schematic configuration of a radar antenna according to an embodiment of the present invention. FIG. 2 is a side view of the radar antenna of FIG. 1; FIG. 6 is a diagram showing vertical directivity in a radar antenna in which all horizontal plate portions have the same length. FIG. 2 is a diagram showing the vertical directionality (electromagnetic field analysis result) of the radar antenna of FIG. 1. FIG. FIG. 3 is a diagram showing an electric field distribution in the XZ plane in a conventional radar antenna without a mode filter structure. FIG. 2 is a diagram showing an electric field distribution in the XZ plane in the radar antenna of FIG. 1. FIG. FIG. 3 is a diagram showing three-dimensional directivity in a conventional radar antenna without a mode filter structure. FIG. 2 is a diagram showing three-dimensional directivity in the radar antenna of FIG. 1. FIG. FIG. 2 is a diagram showing vertical directivity in a conventional radar antenna without a mode filter structure. FIG. 3 is a diagram showing vertical directivity in a radar antenna having a mode filter structure. FIG. 1A is a diagram that defines the length L1 of the horizontal plate portion in the radar antenna of FIG. 1, and FIGS. is 0, Figure (c) is when the length L1 is 0.22λ, Figure (d) is when the length L1 is 0.30λ, Figure (e) is when the length L1 is 0.38λ, Figure (f) shows the case where the length L1 is 0.53λ, and Figure (g) shows the case where the length L1 is 0.69λ. FIG. 2 is a side view showing a radar antenna to which the present invention is applied.

The present invention will be described below based on the illustrated embodiments.

FIG. 1 is a perspective view showing a schematic configuration of a radar antenna 1 according to this embodiment, and FIG. 2 is a side view of the radar antenna 1 of FIG. 1. This radar antenna 1 is an array antenna including a plurality of waveguides 2 in which slots 2a are formed, and no flare is required. Here, in this embodiment, the case where three waveguides 2 are provided will be mainly described below, but two or four or more waveguides may be provided. Further, in this embodiment, it is assumed that the radar antenna 1 is mounted on a ship, and the upper side of the radar antenna 1 in FIGS. 1 and 2 is the sky, and the lower side is the sea.

Each waveguide 2 is a cylindrical body with a substantially square cross section, and a plurality of slots 2a are formed in the front face portion 21 along the longitudinal direction. Three such waveguides 2 extend substantially horizontally and are arranged one above the other at a predetermined interval. At this time, each waveguide 2 is arranged so that its front surface 21a is located on the same plane.

In such an arrangement state, a strip-like (vertical plate-like) vertical plate portion 3 is provided that projects approximately perpendicularly from the slot 2a side of the upper surface portion 22 and lower surface portion 23 of each waveguide 2. . This vertical plate portion 3 extends along the longitudinal direction of the waveguide 2 and is provided at a position retreating from the front surface 21a of the waveguide 2 (on the back surface portion 24 side of the waveguide 2).

By providing the vertical plate portion 3 in this manner, vertically adjacent waveguides 2 are connected to each other by the vertical plate portion 3. That is, the vertical plate part 3 from the lower surface part 23 of the upper waveguide 2 and the vertical plate part 3 from the upper surface part 22 of the adjacent lower waveguide 2 become one body, and the upper waveguide 2 and a lower waveguide 2 are connected by a vertical plate portion 3. The vertical plate portions 3 extend from the upper surface portion 22 of the uppermost waveguide 2 and the lower surface portion 23 of the lowermost waveguide 2, respectively.

Additionally, horizontal plate portions (fins) 4 are provided that protrude substantially horizontally from each vertical plate portion 3 toward the front surface portion 21 side of the waveguide 2 . The horizontal plate portion 4 is shaped like a strip (flat plate), is spaced apart from the waveguide 2, and extends along the longitudinal direction of the waveguide 2. Further, the horizontal plate part 4 provided on the vertical plate part 3 between the waveguides 2 and 2 is located at the center of the vertical plate part 3, and the horizontal plate part 4 provided in the vertical plate part 3 at the top and bottom The plate portion 4 is located at the free end of the vertical plate portion 3 (the end on the side opposite to the waveguide 2). Furthermore, the vertical plate part 3 and the horizontal plate part 4 are provided so that the distances from the horizontal plate part 4 to the waveguide 2 are all the same dimension.

As described above, in this embodiment, the horizontal plate portions 4 are provided not only on the upper edge side of the uppermost waveguide 2 and the lower edge side of the lowest waveguide 2, but also on the upper and lower edge sides of all the waveguides 2. It is being

The corner portion 34 formed by the vertical plate portion 3 and the horizontal plate portion 4 is provided at a position retreating from the front surface 21a of the waveguide 2 (on the back surface portion 24 side of the waveguide 2), and the corner portion 34 is formed by the vertical plate portion 3 and the horizontal plate portion 4. A structure for filtering modes (mode filter structure) using the section 3 and the horizontal plate section 4 is formed in each waveguide 2. The position of the vertical plate part 3 and the gap between the horizontal plate part 4 and the waveguide 2 are such that the cross-polarized wave component and the vertically polarized wave component radiated from the slot 2a are controlled by the mode filter structure of the waveguide 2. It is set to prevent it from turning around in the vertical direction.

Further, the substantially horizontal length of each horizontal plate portion 4 is set such that its free end extends beyond the front surface 21a of the waveguide 2, and unnecessary radiation can be suppressed to a predetermined value. That is, as will be described later, the horizontal plate portion 4 extends beyond the front surface 21a of the waveguide 2, and the longer it is, the more the cross-polarized components can be suppressed from going around in the vertical direction, and the beam width in the vertical direction can be narrowed. - It becomes possible to narrow the area and increase the gain.

On the other hand, if the horizontal plate part 4 is long, the radar antenna 1 becomes large, so the horizontal plate part 4 is set long enough to suppress the unnecessary radiation level to desired characteristics. Specifically, in this embodiment, when the antenna height H shown in FIG. 2 is approximately 2.6λ (λ: wavelength), the length (protrusion amount) L1 of the waveguide 2 from the front surface 21a is approximately It is set to 0.5λ.

Furthermore, the length of the lowest horizontal plate portion 4 in the substantially horizontal direction is set longer than the length of the other horizontal plate portions 4 in the substantially horizontal direction. That is, in order to suppress the occurrence of side lobes and gain nulls/zeros in the vertical plane directivity on the sea side, the lowest horizontal plate part 4 protrudes further to the front side than the other horizontal plate parts 4. .

For example, in the other horizontal plate portions 4, the length L1 from the front surface 21a of the waveguide 2 is 0.5λ, while the length of the lowest horizontal plate portion 4 is as follows. It is set longer than the other horizontal plate parts 4 by an extension dimension L2. The extension dimension L2 is a length that can effectively suppress side lobes and gain nulls on the sea side, and is set to, for example, about 0.5λ (λ: wavelength). Here, when the waveguide 2 is stacked in three stages, side lobes and gain nulls can be suppressed when L2>0.3λ.

The radar antenna 1 including such a plurality of waveguides 2, vertical plate portions 3, and horizontal plate portions 4 is integrally formed by extrusion molding.

According to the radar antenna 1 having such a configuration, the plurality of waveguides 2 in which the slots 2a are formed extend substantially horizontally and are arranged above and below, so that vertical directivity is achieved without flare. As a result, the depth dimension of the radar antenna 1 can be kept small.

Moreover, since the length of the lowest horizontal plate part 4 is set longer than the other horizontal plate parts 4, unnecessary radiation toward the side where the horizontal plate part 4 is longer, that is, toward the sea side, is suppressed. As a result, it is possible to suppress the occurrence of side lobes and gain nulls/zeros in the vertical plane directivity on the sea side, and to obtain desired side lobe level characteristics. In other words, if all the horizontal plate parts 4 have the same length, as shown in FIG. (EL) A gain null occurs within -30 degrees, and there is a possibility that a target within that angle cannot be recognized.

On the other hand, in this radar antenna 1, as shown in Fig. 4, on the sea side of the vertical plane directivity, the sidelobe level is reduced at elevation angles of -30 degrees and beyond, and the gain null is also reduced within elevation angles of -30 degrees. The desired sidelobe level characteristics are obtained. Here, in FIG. 4, high side lobes occur on the side away from the sea surface (sky side), but in a ship radar, side lobes on the side away from the sea surface are generally allowed, so there is no operational problem. Moreover, the amplitude ratio in FIGS. 3 and 4 means the amplitude ratio of each waveguide 2.

Furthermore, as described above, since a mode filter structure is formed for each waveguide 2 by the vertical plate part 3 and the horizontal plate part 4, the cross-polarized wave component radiated from the slot 2a is canceled, and the It is possible to suppress side lobes caused by wraparound in the vertical direction of the wave tube 2. In other words, when the mode filter structure is not provided, as shown in FIG. 5, the cross-polarized wave component (arrow in the figure) radiated from the slot 2a wraps around in the vertical direction of the radar antenna. , when a mode filter structure is provided, as shown in FIG. 6, the wraparound of cross-polarized components in the vertical direction is suppressed. As a result, when the mode filter structure is not provided, high level side lobes and unnecessary radiation are generated as shown in FIG. 7, whereas when the mode filter structure is provided, as shown in FIG. As such, sidelobes are suppressed.

Furthermore, since a horizontal plate part 4 is provided to protrude from each vertical plate part 3 toward the front part 21 side of the waveguide 2, and a mode filter structure is formed, the beam is narrowed in the vertical direction. It becomes possible to increase the area and increase the gain. That is, when the mode filter structure is not provided, the beam width in the vertical direction is wide (for example, 22.99 deg.) as shown in FIG. 10, the beam width in the vertical direction is narrow (for example, 16.91 deg.) and the gain is increased (for example, increased by 1.3 dB).

Moreover, the free end of each horizontal plate part 4 extends beyond the front surface 21a of the waveguide 2, and the length of each horizontal plate part 4 is set so that unnecessary radiation can be suppressed to a predetermined value. By simply adjusting the length of 4, it is possible to set the unnecessary radiation level to a desired characteristic. That is, as shown in FIG. 11(a), the amount of protrusion of the horizontal plate portion 4 from the front surface 21a of the waveguide 2 is the length L1, and the length L1 is 0 (FIG. 11(b)) and 0.22λ. (Fig. 11(c)), 0.30λ (Fig. 11(d)), 0.38λ (Fig. 11(e)), 0.53λ (Fig. 11(f)), 0.69λ (Fig. 11(g) ), the longer the length L1 is, the more the cross-polarized components can be suppressed from going around in the vertical direction, and the beam width in the vertical direction can be narrowed and narrowed. Then, by simply adjusting the length of the horizontal plate portion 4 to a length L1 that can suppress unnecessary radiation to a predetermined value, it is possible to make the unnecessary radiation level a desired characteristic.

Although the embodiments of this invention have been described above, the specific configuration is not limited to the above embodiments, and even if there are changes in the design within the scope of the gist of this invention, Included in invention. For example, in the above embodiment, the length of the lowest horizontal plate part 4 is set longer than the other horizontal plate parts 4, but the side lobe of the highest or lowest horizontal plate part 4 is The horizontal plate portion 4 on the side where it is desired to suppress gain null may be made longer than the other portions.

Further, in the above embodiment, a case has been described in which horizontal plate portions 4 are provided on the upper and lower edges of all waveguides 2, but the present invention is also applicable to other cases. For example, as shown in FIG. 12, a plurality of waveguides 2 are stacked vertically without any gaps, and horizontal plate portions 4 are formed only on the upper edge side of the uppermost waveguide 2 and the lower edge side of the lowest waveguide 2. It is also applicable to cases where Even in such a case, the horizontal plate portion 4 on one side (for example, the sea side) on which side lobes and gain nulls are to be suppressed may be made longer than on the other side.

1, 10 Radar antenna 2 Waveguide 2a Slot 21 Front part 21a Front part 22 Top part 23 Bottom part 24 Back part 3 Vertical plate part 4 Horizontal plate part

Claims (1)

A plurality of waveguides each having a cylindrical shape with a substantially rectangular cross section and having a slot formed in the front part;
In a state in which the plurality of waveguides extend substantially horizontally and are arranged vertically, the waveguides extend substantially horizontally from the upper edge side of the uppermost waveguide and the lower edge side of the lowermost waveguide to the front side. a strip-shaped horizontal plate portion that protrudes and extends along the longitudinal direction of the waveguide;
Equipped with
The length in the substantially horizontal direction of the uppermost horizontal plate portion or the lowermost horizontal plate portion is set to be longer than the length in the substantially horizontal direction of the other horizontal plate portions.
A radar antenna characterized by: