Radar Antenna

Abstract

To provide a radar antenna capable of obtaining better directivity characteristics regardless of assembly accuracy.SOLUTION: In a radar antenna 1 with a horn-shaped flare 3 attached to a waveguide 2 with a plurality of slots, the waveguide 2 includes a body portion 21 having a cylindrical shape with a substantially square cross section and a slot formed in the front surface, a characteristic maintaining portion 221 of a predetermined length provided on both side surfaces of the body portion 21 and extending substantially vertically from the front surface portion of the body portion 21 at a predetermined distance from the side surface portion, and a connecting portion 222 that is connected to the characteristic maintaining portion 221 and contacts the base ends 31a and 32c of the flare 3, and further includes a choke portion 2A that prevents radio waves from being transmitted to the back side of the waveguide 2 through the holes protruding toward the connecting portion 222 of the waveguide 2 and between the connecting portion 222 of the waveguide 2 and the base ends 31a and 32c of the flares 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radar antenna for use on land, on ships, etc. [Background technology]

[0002] As a radar antenna used on land or on a ship, there is known a radar antenna equipped with a radiating waveguide in which a plurality of slots (long holes) are formed in the front surface of the waveguide, and the inclination angle, width, cutting depth, arrangement, etc. of each slot are adjusted to obtain a predetermined directional characteristic or frequency characteristic (see, for example, Patent Document 1, etc.). In this radar antenna, horn-shaped flares consisting of upper and lower flares are arranged to sandwich a waveguide in which a plurality of slots are formed, and the waveguide and flares are assembled by a plurality of waveguide clamps.

[0003] In order to obtain good antenna characteristics in such a radar antenna, it is desirable that the waveguide and the flare are in close contact with each other without any gaps, but it is inevitable that some gaps will occur between the waveguide and the flare during assembly. As a result, some of the characteristics of the many formed slots do not meet the design, and the horizontal directivity of the entire array antenna is inferior to the design value. Furthermore, when the required specifications for the radar antenna are strict, this deterioration in characteristics can cause a problem of poor yield.

[0004] To solve such problems, a radar antenna is known that is capable of obtaining good directional characteristics regardless of assembly accuracy (see, for example, Patent Document 2, etc.). The waveguide of this radar antenna includes a main body having a cylindrical shape with a substantially rectangular cross section and a slot formed in the front part, characteristic maintaining parts provided on both side parts of the main body and extending substantially perpendicularly from the front part of the main body for a predetermined distance, and a connecting part provided on the main body for connecting to the base end of the flare. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-79424 A [Patent Document 2] JP 2019-165390 A Summary of the Invention [Problem to be solved by the invention]

[0006] With the radar antenna described in Patent Document 2, it is possible to obtain good directional characteristics regardless of the assembly accuracy. However, as the required specifications for radar antennas are becoming increasingly strict, there is a demand for a radar antenna that can obtain better directional characteristics even if there is a gap between the waveguide and the flare.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a radar antenna that can obtain better directional characteristics regardless of assembly accuracy. [Means for solving the problem]

[0008] In order to achieve the above object, the invention described in claim 1 is a radar antenna in which a horn-shaped flare is attached to a waveguide in which a plurality of slots are formed, the waveguide comprising: a main body portion having a cylindrical shape with a substantially rectangular cross section and in which the slots are formed in a front portion; characteristic maintenance portions of a predetermined length provided on both side portions of the main body portion and extending substantially perpendicularly from the side portions to a predetermined distance from the front portion of the main body portion; and a connecting portion connected to the characteristic maintenance portions and in contact with a base end of the flare, the choke portion being an air hole protruding toward the connecting portion side of the waveguide or the base end side of the flare, and preventing radio waves from propagating to the back side of the waveguide through between the connecting portion of the waveguide and the base end of the flare.

[0009] The invention described in claim 2 is characterized in that, in the radar antenna described in claim 1, ears having a U-shaped cross section are provided on both side portions of the main body with their openings facing the side portions of the main body, the edges of the ears on the front side of the main body constitute the characteristic maintenance portion, the edges of the ears facing the side portions of the main body constitute the connecting portion, and the choke portion extends through the connecting portion and along the longitudinal direction of the connecting portion.

[0010] The invention described in claim 3 is characterized in that, in the radar antenna described in claim 2, at least one of the size of the ear portion and the size and position of the choke portion is set so as to more effectively prevent the radio waves from propagating to the back side of the waveguide. Effect of the Invention

[0011] According to the invention described in claim 1, characteristic maintaining parts are provided on both side parts of the main body part of the waveguide, and further, a choke part is provided to prevent radio waves from propagating to the back side of the waveguide, so that it is possible to obtain better directional characteristics and antenna characteristics regardless of the assembly accuracy. That is, the directional characteristics of the waveguide depend on the position and length of the members extending vertically from both side parts of the waveguide, that is, the position and length of the characteristic maintaining parts in this invention, but since the characteristic maintaining parts are provided in the waveguide itself, their position and length do not change. Therefore, even if a gap occurs between the connection part of the waveguide and the base end of the flare, it is possible to obtain good antenna characteristics.

[0012] Furthermore, since the choke portion is provided, it is possible to prevent radio waves from propagating to the back side of the waveguide through between the connecting portion of the waveguide and the base end of the flare, making it possible to obtain better directional characteristics. Moreover, since the choke portion is a hole protruding toward the connecting portion side of the waveguide or the base end side of the flare, the structure is simple and it can be manufactured easily and with high accuracy.

[0013] According to the invention described in claim 2, the connecting part is formed by one side of the ear part having a U-shaped cross section, and the choke part simply penetrates the connecting part and extends along the longitudinal direction of the connecting part, so that the structure is simple and it can be manufactured easily and with high precision. In particular, when the main body part and the waveguide including the ear part are manufactured as a single unit, it can be easily manufactured by extrusion or drawing. Moreover, because there is a choke part that penetrates the connecting part, that is, because the connecting part is composed of two short sides, the material flows densely (without interruption) without gaps during extrusion or drawing, so it can be manufactured with high precision.

[0014] According to the invention described in claim 3, the size of the ear portion and the size and position of the choke portion are set so as to more effectively prevent radio waves from propagating to the back side of the waveguide, thereby making it possible to obtain better directional characteristics. [Brief description of the drawings]

[0015] [Figure 1] 1 is a side view showing a schematic configuration of a radar antenna according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an enlarged cross-sectional view of the waveguide of the radar antenna of FIG. 1. [Diagram 3] 2 is a diagram showing a propagation state of radio waves from the radar antenna of FIG. 1. [Figure 4] 2 is an enlarged view showing the gap between the waveguide and the flare and the inside of the ear in the radar antenna of FIG. 1. FIG. [Diagram 5] FIG. 5A shows the electric field distribution when the dimensions and shape of the ears are not optimized in the hatched portion of FIG. 4, and FIG. 5B shows the electric field distribution when the dimensions and shape of the ears are optimized. [Figure 6] FIG. 2A shows the transmission coefficient S21 when only the width dimension of the ear is adjusted in the radar antenna of FIG. 1, FIG. 2B shows the transmission coefficient S21 when only the height dimension of the ear is adjusted, and FIG. 2C shows the transmission coefficient S21 when only the width dimension of the choke portion is adjusted. [Figure 7]FIG. 2A shows the transmission coefficient S21 when only the thickness of the ear is adjusted in the radar antenna of FIG. 1, FIG. 2B shows the transmission coefficient S21 when only the position of the choke portion is adjusted, and FIG. 2C shows the transmission coefficient S21 when the width and height dimensions of the ear are adjusted. [Figure 8] FIG. 2 is a diagram showing the transmission coefficient S21 when the size of the ears and the size and position of the chokes are optimized and when they are not optimized in the radar antenna of FIG. [Figure 9] FIG. 1A shows the excitation amplitude of the positive polarization component when no choke portion is provided on the ear portion, and FIG. 1B shows the excitation amplitude of the cross polarization component. [Figure 10] FIG. 1A shows the excitation amplitude of a positive polarization component when a choke portion is provided on the ear portion, and FIG. 1B shows the excitation amplitude of a cross polarization component. [Figure 11] FIG. 2A shows the average gain when the size and position of the ears and the size and position of the chokes are not optimized in the radar antenna of FIG. 1, and FIG. 2B shows the average gain when they are optimized. [Figure 12] FIG. 1A shows a first modified example of an ear portion in an embodiment of the present invention, FIG. 1B shows a second modified example, and FIG. 1C shows a third modified example. [Figure 13] 11 is a diagram showing a case where a choke portion is provided on the flare side in an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the present invention will be described based on the illustrated embodiment.

[0017] Fig. 1 is a side view showing a schematic configuration of a radar antenna 1 according to an embodiment of the present invention, and Fig. 2 is an enlarged cross-sectional view of a waveguide 2 of this radar antenna 1. This radar antenna 1 is a long array antenna in which a horn-shaped flare 3 is attached to a waveguide 2 in which a plurality of slots 2a are formed, and the shape and structure of the waveguide 2 differ from conventional radar antennas, and this different configuration will be mainly described below.

[0018] 2, the waveguide 2 includes a main body 21 and ears 22 provided on both side surfaces 213, 214 of the main body 21, and the main body 21 and the ears 22 are integrally formed. For the sake of convenience in clarifying the shapes and configurations of the main body 21 and the ears 22, a solid line is drawn at the boundary between the main body 21 and the ears 22, and the main body 21 and the ears 22 are hatched differently.

[0019] The main body 21 is a long cylindrical body with a substantially rectangular cross section, and a plurality of slots 2a are formed in the front part 211. That is, the main body 21 is a long cylindrical body with a substantially rectangular cross section, and when it is extended horizontally, the front part 211 and the rear part 212 extend substantially vertically, and the upper side part 213 and the lower side part 214 extend substantially horizontally. A plurality of slots 2a extending vertically are formed in the longitudinal direction of the front part 211, and the inclination angle, width, cutting depth, arrangement, etc. of each slot 2a are set so as to obtain predetermined directional characteristics and frequency characteristics. Such a main body 21 functions as a waveguide, and its shape and thickness are set so as to obtain predetermined antenna characteristics.

[0020] Ear portion 22 is an elongated body having a U-shaped cross section, and is provided so that its opening side faces side surface portions 213, 214 of main body portion 21. In other words, ear portion 22 and side surface portions 213, 214 of main body portion 21 form a cylinder / cavity having a substantially rectangular cross section. Then, the side portion (vertical side) of ear portion 22 on the front surface portion 211 side of main body portion 21 constitutes characteristic maintaining portion 221 provided on both side surface portions 213, 214 of main body portion 21. Also, the side portion (horizontal side) of ear portion 22 facing side surface portions 213, 214 of main body portion 21 constitutes connecting portion 222 that is connected to characteristic maintaining portion 221 and comes into contact with base ends 31a, 32c of flare 3.

[0021] Here, characteristic maintaining portion 221 is a portion that extends substantially perpendicularly from side portions 213, 214 at a predetermined distance D1 from front portion 211 of main body portion 21, and has a predetermined length D2. That is, it defines the antenna characteristics and directional characteristics of main body portion 21 as a waveguide, and its position and shape, that is, distance D1 and length D2, are set so as to obtain predetermined antenna characteristics. Here, distance D1 and length D2 of both characteristic maintaining portions 221 are set to the same dimensions.

[0022] The connecting portion 222 is a portion for connecting to the base ends 31a, 32c of the flare 3, and extends approximately parallel to the side portions 213, 214 of the main body portion 21. A connecting back portion 223 extending from the end of the connecting portion 222 on the side of the inverse characteristic maintaining portion 221 toward the main body portion 21 is connected to the side portions 213, 214 of the main body portion 21. Here, the ears 22 are provided on the main body portion 21 so that the outer surfaces of the connecting back portion 223 and the back portion 212 of the main body portion 21 are flush with each other.

[0023] In this way, when choke portion 2A, which will be described later, is not provided, the cross-sectional shape of waveguide 2 is a substantially rectangular shape divided into three layers and three chambers above and below, with front portion 211 of the center layer protruding. It is formed so that it can be manufactured by extruding or drawing aluminum material, forged copper material, or the like.

[0024] The flare 3 is composed of a flat upper flare 31 and a lower flare 32. On the side of the waveguide 2, the upper flare 31 is formed with an upper horizontal portion (base end) 31a extending substantially horizontally, as shown in Fig. 1, and an upper slope portion 31b extends obliquely upward from the upper horizontal portion 31a. On the other hand, on the side of the waveguide 2, the lower flare 32 is formed with a first lower horizontal portion 32a extending substantially horizontally, a lower vertical portion 32b extending substantially vertically downward from the first lower horizontal portion 32a, and a second lower horizontal portion (base end) 32c extending substantially horizontally from the lower vertical portion 32b, and a lower slope portion 32d extends obliquely downward from the second lower horizontal portion 32c.

[0025] The waveguide 2 is accommodated in a space surrounded by the upper horizontal portion 31a, the lower vertical portion 32b, and the second lower horizontal portion 32c, and the waveguide 2 and the flare 3 are assembled together. That is, the upper horizontal portion 31a and the upper connecting portion 222 are connected by fasteners such as screws or rivets (not shown), the second lower horizontal portion 32c and the lower connecting portion 222 are connected by fasteners, and the lower vertical portion 32b and the connecting back portion 223 of both ears 22 are connected by fasteners. Furthermore, the upper horizontal portion 31a and the first lower horizontal portion 32a are connected by fasteners.

[0026] Here, a plurality of fasteners are provided at predetermined intervals along the longitudinal direction of the waveguide 2 and the flare 3. Furthermore, reference numeral 4 in Fig. 1 denotes a suppressor.

[0027] Meanwhile, choke portion 2A is provided, which is a hole protruding toward coupling portion 222 of waveguide 2 and prevents radio waves from propagating to the back side of waveguide 2 through between coupling portion 222 of waveguide 2 and base ends 31a, 32c of flare 3. Choke portion 2A in this embodiment penetrates coupling portion 222, extends along the longitudinal direction of coupling portion 222, and is formed from one end to the other of coupling portion 222. In other words, two members having an inverted L-shaped cross section are formed on each of side portions 213, 214 of main body 21 along the longitudinal direction of main body 21 with their horizontal ends facing each other, and choke portion 2A is formed between the horizontal ends.

[0028] The inside of choke portion 2A and ear portion 22 act as a cavity, and as shown in Fig. 3, the propagation of radio waves to the rear side of waveguide 2 is suppressed through gap G between connecting portion 222 of waveguide 2 and base ends 31a, 32c of flare 3, and radio waves are propagated only to the front side of waveguide 2. In other words, the antenna characteristics and directional characteristics of radar antenna 1 are not affected by the structure on the rear side from rear end P of choke portion 2A.

[0029] At least one of the size of ear 22 and the size and position of choke 2A is set so as to more effectively prevent radio waves from propagating to the back side of waveguide 2. In other words, by adjusting the size of ear 22 and the size and position of choke 2A to appropriate values, radio waves can be more effectively prevented from propagating to the back side of waveguide 2, and the directional characteristics of radar antenna 1 can be improved.

[0030] First, by optimizing the size of the ear 22, that is, the size and dimensions inside the ear 22, it is possible to more effectively prevent radio waves from propagating to the back side of the waveguide 2. That is, as shown in FIG. 4, focusing on the gap G between the waveguide 2 and the flare 3 and the inside of the ear 22, the space inside the ear 22 is the ear space C1, and the space inside the choke part 2A is the choke space C2. Then, as shown in FIG. 5(a), if the width dimension D3 and height dimension D4 of the ear space C1 are not optimized, radio waves will propagate to the back side of the waveguide 2 in the gap G between the waveguide 2 and the flare 3. On the other hand, as shown in FIG. 5(b), it was confirmed that radio waves will not propagate to the back side of the waveguide 2 in the gap G between the waveguide 2 and the flare 3 when the width dimension D5 and height dimension D6 of the ear space C1 are optimized without changing the dimensions of the choke space C2. Here, the black dots in FIG. 5 indicate the strength of the electric field. The more black dots there are, the stronger the electric field, i.e., radio waves are propagating. The fewer black dots there are, the weaker the electric field, i.e., radio waves are not propagating.

[0031] Next, as shown in FIG. 6(a), by adjusting only the width dimension of the ear space C1, it is possible to lower the value of the transmission coefficient S21 (to exhibit choke characteristics) at the center frequency. Here, the transmission coefficient S21 is the transmission coefficient between the port P1 and the port P2 in FIG. 5. Secondly, as shown in FIG. 6(b), by adjusting only the height dimension of the ear space C1, it is possible to lower the value of the transmission coefficient S21 near the center frequency of use. Thirdly, as shown in FIG. 6(c), by adjusting only the width dimension of the choke portion 2A, it is possible to lower the value of the transmission coefficient S21 near the center frequency of use. Fourthly, as shown in FIG. 7(a), by adjusting only the thickness dimension of the connecting portion 222 of the ear portion 22, it is possible to lower the value of the transmission coefficient S21 near the center frequency of use. Fifthly, as shown in FIG. 7(b), by adjusting only the position of the choke portion 2A, it is possible to lower the value of the transmission coefficient S21 near the center frequency of use. Sixth, as shown in FIG. 7(c), it is possible to lower the value of the transmission coefficient S21 in the vicinity of the center frequency used by adjusting only the width and height dimensions of the ear space C1.

[0032] By adjusting and optimizing all of these, that is, the size of ear 22 (ear space C1) and the size and position of choke portion 2A, a good transmission coefficient S21 can be obtained near the center frequency used, as shown in Fig. 8. Here, the dashed line in Fig. 8 indicates the case where the size of ear 22 and the size and position of choke portion 2A are not optimized. In this way, the size of ear 22 and the size and position of choke portion 2A are set so as to more effectively prevent radio waves from propagating to the back side of waveguide 2.

[0033] According to the radar antenna 1 having such a configuration, the characteristic maintaining portion 221 is provided on both side portions 213, 214 of the main body portion 21 of the waveguide 2, and further, the choke portion 2A is provided to prevent radio waves from propagating to the back side of the waveguide 2, so that it is possible to obtain better directional characteristics and antenna characteristics regardless of the assembly accuracy. That is, the directional characteristics of the waveguide 2 depend on the position and length of the members extending vertically from both side surfaces of the waveguide 2, that is, the position and length of the characteristic maintaining portion 221 in this invention, but since the characteristic maintaining portion 221 is provided in the waveguide 2 itself, its position and length do not change. Therefore, even if a gap occurs between the connecting portion 222 of the waveguide 2 and the base ends 31a, 32c of the flare 3, it is possible to obtain better antenna characteristics.

[0034] Furthermore, since choke portion 2A is provided, it is possible to prevent radio waves from propagating to the back side of waveguide 2 through between connecting portion 222 of waveguide 2 and base ends 31a, 32c of flare 3, making it possible to obtain better directional characteristics. Moreover, since choke portion 2A is a hole that protrudes toward connecting portion 222 of waveguide 2, it has a simple configuration and can be manufactured easily and with high accuracy.

[0035] Moreover, since the connecting portion 222 is formed by one side of the ear 22 having a U-shaped cross section, and the choke portion 2A simply penetrates the connecting portion 222 and extends along the longitudinal direction of the connecting portion 222, the structure is simple and can be manufactured easily and with high precision. In particular, when the waveguide 2 including the main body 21 and the ear 22 is manufactured as a single unit, it can be easily manufactured by extrusion or drawing. Moreover, since the choke portion 2A is provided penetrating the connecting portion 222, that is, the connecting portion 222 is composed of two short sides, the material flows densely (without interruption) without gaps during extrusion or drawing, and it can be manufactured with high precision.

[0036] Furthermore, it is possible to obtain better directional characteristics because the size of ear 22 and the size and position of choke portion 2A are set so as to more effectively prevent radio waves from propagating to the back side of waveguide 2. The effects of such choke portion 2A and the effects of optimizing the size and position of ear 22 and choke portion 2A will be described below.

[0037] 9 and 10 are diagrams showing the change in radiation pattern with respect to the length of the mating surface between the upper flare 31 and the lower flare 32 of the flare 3. Here, the length of the mating surface is the length indicating the overlapping state between the upper horizontal portion 31a and the first lower horizontal portion 32a in FIG. 1, and a positive value indicates the overlapping length, and a negative value indicates the separation length between the upper horizontal portion 31a and the first lower horizontal portion 32a. When the ear portion 22 is not provided with the choke portion 2A, as shown in FIG. 9, it is recognized that both the excitation amplitude (a) of the normal polarization component and the excitation amplitude (b) of the cross polarization component are influenced by the overlapping state between the upper horizontal portion 31a and the first lower horizontal portion 32a, that is, the structure on the back side of the waveguide 2.

[0038] In contrast, when the choke portion 2A is provided on the ear portion 22, as shown in Fig. 10, it is recognized that both the excitation amplitude (a) of the positive polarization component and the excitation amplitude (b) of the cross polarization component are not affected (do not change due to the structure) by the overlapping state of the upper horizontal portion 31a and the first lower horizontal portion 32a, that is, by the structure on the back side of the waveguide 2. Furthermore, when the choke portion 2A is not provided, as shown in Fig. 9(b), radiation to the back side of the waveguide 2 is recognized at around -135° to -270°, but when the choke portion 2A is provided, radiation to the back side of the waveguide 2 is not recognized, as shown in Fig. 10(b).

[0039] 11 is a diagram comparing the average gain patterns when there is a gap between the coupling portion 222 of the waveguide 2 and the base end portions 31a, 32c of the flare 3 and when there is no gap, in a model in which the waveguide 2 has ten slots 2a. When the size of the ear portion 22 and the size and position of the choke portion 2A are not optimized, as shown in FIG. 11(a), there is a large difference in the pattern between the case where there is a gap and the case where there is no gap, that is, it is recognized that the pattern depends on the assembly accuracy. On the other hand, when the size of the ear portion 22 and the size and position of the choke portion 2A are optimized, there is no large difference in the pattern between the case where there is a gap and the case where there is no gap, that is, it is recognized that the pattern does not depend on the assembly accuracy, as shown in FIG. 11(b).

[0040] Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes within the scope of the present invention, they are included in the present invention. For example, in the above embodiment, the cross section of the space (ear space C1) formed by ear portion 22 and side portions 213, 214 of main body portion 21 is approximately rectangular, and the width of the space (choke space C2) in choke portion 2A is smaller than that of ear space C1 and is provided in the upper center of ear space C1, but the shape of ear space C1, the position of choke portion 2A, etc. are not limited to this. For example, as shown in FIG. 12(a), the width of ear space C1 and the width of choke space C2 may be made the same, and ear space C1 and choke space C2 may be integrally formed in the same shape (in a straight line). Also, as shown in FIG. 12(b), choke space C2 may be provided on the upper back side of ear space C1, or on the upper front side of ear space C1.

[0041] Furthermore, in the above embodiment, choke portion 2A is a hole that protrudes towards connecting portion 222 of waveguide 2, but choke portion 2A may also be a hole that protrudes towards base ends 31a, 32c of flare 3. For example, as shown in Fig. 13, choke portion 2A may be formed by bending upper horizontal portion 31a of upper flare 31 so as to protrude away from waveguide 2, and a space / hole extending along waveguide 2 may be provided between choke portion 2A and connecting portion 222 of ear portion 22. [Explanation of symbols]

[0042] 1. Radar Antenna 2 waveguide 2A Choke section 2a Slot 21 Main body 211 Front part 213, 214 Side part 22 Ears 221 Characteristics Maintenance Department 222 Connecting part 3. Flare 31 Upper Flare 32 Lower Flare 31a Upper horizontal part (base end) 32c Second lower horizontal part (base end) D1 Predetermined distance D2 given length

Claims

1. A radar antenna in which a horn-shaped flare is assembled to a waveguide having a plurality of slots formed therein, the waveguide comprises: a main body portion having a generally rectangular cylindrical cross section and the slot formed in a front portion thereof; characteristic maintaining portions of a predetermined length provided on both side portions of the main body portion and extending generally perpendicularly from the side portions to a predetermined distance from the front portion of the main body portion; and a connecting portion connected to the characteristic maintaining portions and in contact with a base end portion of the flare, a choke portion that is a hole protruding toward the connecting portion side of the waveguide or the base end side of the flare and prevents radio waves from propagating to the back side of the waveguide through between the connecting portion of the waveguide and the base end of the flare; A radar antenna comprising:

2. On both side surfaces of the main body, ears having a U-shape in cross section are provided with their openings facing the side surfaces of the main body, the edges of the ears on the front surface side of the main body constitute the characteristic maintaining portion, and the edges of the ears facing the side surfaces of the main body constitute the connecting portion, The choke portion penetrates the connecting portion and extends along the longitudinal direction of the connecting portion.

2. A radar antenna as claimed in claim 1.

3. At least one of the size of the ear portion and the size and position of the choke portion is set so as to more effectively prevent the radio wave from propagating to the back side of the waveguide.

3. A radar antenna as claimed in claim 2.

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