JP5103227B2 - Radar antenna - Google Patents

Description

  The present invention is an antenna suitable for a UWB (Ultra Wide Band) radar that will be used in the future as a vehicle-mounted or portable radar, while suppressing radiation to a radio wave emission prohibited band (23.6 to 24.0 GHz) The present invention relates to a technique for obtaining a wide radar detection angle.

  It has been proposed to use UWB, which is a quasi-millimeter wave band of 22 to 29 GHz, mainly as a vehicle-mounted or portable short-range radar.

  The antenna of the radar device used in this UWB has a small and thin planar structure, considering that it is installed in the gap between the vehicle body and the bumper when mounted on the vehicle, in addition to having a wide radiation characteristic. It is necessary to be.

  Moreover, in order to perform exploration with the weak power specified by UWB and suppress wasteful power consumption so that it can be driven by a battery, low loss and high gain are required, and it is necessary to easily achieve an array for that purpose. It is.

  In order to reduce the cost, it is desirable that the antenna element and the power feeding unit have a structure that can be configured by a pattern printing technique.

  In addition, the International Radio Communication Regulation (RR) defines the range of 23.6 to 24.0 GHz as a radio wave emission prohibition zone for protecting passive sensors of the Earth exploration satellite (EESS). It is desirable that the radio wave radiation of this frequency band is also small for the millimeter wave band UWB antenna.

  As an antenna that responds to these requirements, the applicant of the present application provides a ground plane conductor to overlap one surface of the dielectric substrate, forms a pair of antenna elements on the opposite surface of the dielectric substrate, and further uses a metal post as a wavelength. In comparison, the antenna elements are arranged side by side so as to surround the entire circumference at a sufficiently narrow interval to create a cavity structure that creates a notch in the gain in the radio wave emission prohibited band, and the end side of the metal post is short-circuited along the arrangement direction. The following Patent Document 1 and Patent Document 2 propose a technique for suppressing a surface wave by providing a frame-shaped conductor extending a predetermined distance in the antenna element direction.

International Publication WO 2006/051947 A1 International Publication WO 2007/055028 A1

  Since the antenna having the above structure has a closed cavity structure in which metal posts are arranged so as to go around the antenna element, there is an advantage that a large notch can be taken in the radio wave emission prohibited band.

  However, when a linearly polarized antenna element (for example, a dipole type) is surrounded by a closed cavity as described above, not only the arrangement direction of the antenna elements (E plane) but also the direction orthogonal to it (H plane) The beam width becomes narrower. In general, in the case of an on-vehicle radar or the like, since the H plane is installed so as to be a horizontal plane, a new problem arises that the detection width as a radar is insufficient.

  An object of the present invention is to solve this problem and to provide a radar antenna that can obtain a wide radar detection angle while suppressing radiation to a specific frequency band such as a radio wave emission prohibition band in a wide band.

In order to achieve the above object, a radar antenna according to claim 1 of the present invention comprises:
A rectangular dielectric substrate (21);
A rectangular ground plane conductor (22) overlapping one surface of the dielectric substrate;
The pair of elements pieces formed so as to be aligned on a straight line along the longitudinal direction of the dielectric substrate on the opposite surface of the dielectric substrate and (23a, 23b) dipole antenna element made of (2 3),
One end connected to the ground plane conductor, the dielectric substrate wherein the dielectric substrate penetrates along the thickness direction, the metal posts (30) which has the other end extending to the opposite surface of the dielectric substrate at a predetermined interval A pair of post walls (31a, 31b) formed side by side along both short sides of the antenna element, and the antenna element is sandwiched between the pair of post walls in the direction of the electric field, thereby separating the pair of post walls (Lw). An opposite wall surface type cavity (31) for generating a notch in a specific frequency band determined by :
A pair of rims that short-circuit the other end sides of the plurality of metal posts that respectively form the pair of post walls on the opposite surface side of the dielectric substrate along the arrangement direction and extend a predetermined distance in the antenna element direction Conductors (32a, 32b) ,
Further, the width (Lx) in the short side direction in which the post wall of the dielectric substrate extends is formed to be narrower than the interval (Lw) between the pair of post walls that cause notches in the specific frequency band, The beam width of the magnetic field surface along the short side direction is increased with respect to the beam width of the electric field surface along the long side direction of the dielectric substrate .

The radar antenna according to claim 2 of the present invention is
A plurality of sets of radar antennas according to claim 1 are arrayed on a common dielectric substrate in a direction orthogonal to the direction in which the post wall extends .

A radar antenna according to claim 3 of the present invention is the radar antenna according to claim 2 ,
The width (Lx) in the short side direction in which the post walls extend is set to 2/3 or less of the distance (Lw) between the pair of post walls .

  As described above, the radar antenna according to the present invention has a pair of post walls formed by arranging a plurality of metal posts at a predetermined interval, and has a cavity structure of opposing wall surfaces sandwiching the antenna element, and each of the pair of post walls is formed. In this structure, the other end sides of the plurality of metal posts are short-circuited along the arrangement direction, and include a pair of rim conductors extending a predetermined distance in the antenna element direction.

  For this reason, in the case of a linearly polarized antenna such as a dipole type, a pair of post walls exhibit effective resonance characteristics with respect to the arrangement direction (electric field surface) of element pieces where electric fields concentrate, A large notch is generated in the specific band, and the magnetic field side does not have to be sandwiched between the wall surfaces, so that the width can be narrowed regardless of the notch frequency, and the detection width as a radar can be greatly increased. In addition, the antenna can be reduced in size, which is more suitable for in-vehicle use or portable use.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 4 show the structure of a radar antenna 20 (hereinafter simply referred to as antenna 20) suitable for UWB to which the present invention is applied.

(First embodiment)
The antenna 20 includes a dielectric substrate 21, a ground plane conductor 22 that overlaps one surface of the dielectric substrate 21, and a pair of elements formed on the opposite surface of the dielectric substrate 21 so as to be arranged in a straight line (y direction). A dipole antenna element 23 composed of the pieces 23a and 23b, one end side of which is connected to the ground plane conductor 22, penetrates the dielectric substrate 21 along the thickness direction (z direction), and the other end side of the dielectric substrate 22 The antenna element 23 is arranged in a direction in which the element pieces 23a and 23b are arranged by a pair of post walls 31a and 31b formed by arranging the metal posts 30 extending to the opposite surface in the substrate width direction (x direction) at a sufficiently narrow interval compared to the guide wavelength. And a plurality of metal posts that respectively form a pair of post walls 31 a and 31 b on the opposite surface side of the dielectric substrate 21. 30 the other end of the short-circuited along the arrangement direction, and includes and a pair of rims conductor 32a extending a predetermined distance to the antenna element 23 direction, and 32b.

  More specifically, the antenna 20 includes, for example, a dielectric substrate 21 having a low dielectric constant (around 3.5) and a rectangular substrate having a thickness of 1.2 mm, and one surface side of the dielectric substrate 21 (see FIG. 1, a ground plane conductor 22 provided on the back side in FIG. 2 and a dipole antenna element 23 for excitation patterned on the opposite side of the dielectric substrate 21 (front side in FIGS. 1 and 2) And a pair of power supply pins 25 a and 25 b for supplying power to the antenna element 23.

  The antenna element 23 is a so-called bow tie type that can obtain a wide band characteristic, and is formed by a pair of triangular element pieces 23 a and 23 b arranged along the longitudinal direction (y direction) of the dielectric substrate 21. The feed pin 25a connected to the one element piece 23a passes through the dielectric substrate 21 in the thickness direction (z direction), passes through the hole 22a of the ground plane conductor 22, and is connected to the other element piece 23b. The power supply pin 25 b penetrates the dielectric substrate 21 in the thickness direction and is connected to the ground plane conductor 22.

  Here, although the dipole antenna element 23 is a balanced type, the power feeding is an unbalanced type. Therefore, it is necessary to connect the antenna element 23 and the power feeding pins 25a and 25b via a balun. By appropriately devising the wiring or transmission line of the coaxial cable connected to the feed pin 25a, it is possible to feed substantially the same as the balanced type without using a balun, and the antenna element 23 can be linearly polarized. Can be driven by excitation.

  However, since the thickness of the dielectric substrate 21 is relatively large, such as about 1/4 of the propagation wavelength, in order to increase the bandwidth, surface waves along the surface of the dielectric substrate 21 are excited, and the desired characteristics are affected by the surface waves. Cannot be obtained.

  As a technique for solving this, in Patent Documents 1 and 2 described above, a closed cavity structure in which metal posts are arranged at a sufficiently narrow interval compared to the wavelength so as to make a round around the antenna element is adopted. Due to the resonance phenomenon, the antenna gain frequency characteristic causes a sharp drop (notch) in the radio wave emission prohibited band, and a frame-like conductor that short-circuits the tips of the plurality of metal posts on the surface of the dielectric substrate 21. The influence of the along surface wave was suppressed. However, in the conventional structure, not only the linearly polarized electric field plane (E plane) excited by the antenna element 23, that is, the arrangement direction of the element pieces 23a and 23b of the antenna element 23, but also the magnetic field plane (H The beam width in the direction of (surface) becomes narrow, and a wide detection width cannot be obtained as a radar.

  Therefore, in the antenna 20 of this embodiment, in the case of linear polarization, the electric field in the cavity is concentrated in the E plane direction (that is, the y direction in which the pair of element pieces 23a and 23b that constitute the antenna element 23 is a dipole type). Paying attention to this, the cavity structure formed by the metal post 30 is used as a thin (for example, 0.3 mm) metal post 30 from the closed structure surrounding the entire circumference of the antenna element 23 as described above. The antenna element 23 is arranged in the E-plane direction, that is, the direction in which the pair of elements 23a and 23b are arranged, by a pair of post walls 31a and 31b that are linearly arranged with a sufficiently narrow interval (for example, 0.9 mm) compared to the wavelength of the radio wave. The cavity structure is a facing wall surface type sandwiched from (y direction). The interval Lw between the post walls 31a and 31b is 9 mm.

  By adopting the cavity structure composed of the opposing walls in the E-plane direction in this way, the width of the dielectric substrate 21 can be made narrower than the interval Lw between the post walls in a state where notches are generated in a specific frequency band. Accordingly, the radar detection width on the horizontal plane (xz plane) can be greatly increased.

  In addition, a plurality of metal posts 30 forming one wall are formed on the surface side of the dielectric substrate 21 by forming the opposing wall surface type cavity structure sandwiching the antenna element 23 from the E plane direction by the metal posts 30. The rim conductor 32a that short-circuits one end side of the rim conductor and the rim conductor 32b that short-circuits one end side of the plurality of metal posts 30 that form the other wall are separated.

  The metal post 30 is realized, for example, by plating (through-hole plating) the inner wall of a hole that penetrates the dielectric substrate 21.

  Further, the width of the rim conductors 32a and 32b from the metal post 30 to the antenna element (effective rim width) corresponds to approximately ¼ of the wavelength of the surface wave (for example, around 1.2 mm). That is, this effective rim width portion forms a π / 4 transmission line having an infinite impedance with respect to the surface wave when the post wall side is viewed from the tip side. Therefore, no current flows along the surface, and the surface wave is suppressed by this current blocking action, thereby preventing the radiation characteristics from being disturbed.

  However, in this embodiment, as shown in FIG. 2, the effective rim width L1 at both ends of the rim conductors 32a and 32b is reduced (for example, 0.26 mm), and the central effective rim width L2 is maximized (for example, 1.26 mm). The notch width is increased by changing the shape into a mountain shape, but the width may be constant at about 1.2 mm.

  In the above embodiment, the antenna element 23 is an example of a bow tie antenna in which the isosceles triangular element pieces 23a and 23b are arranged symmetrically with their apexes close to each other. Etc.

(Second Embodiment)
The antenna 20 of the above embodiment has a single antenna element 23. However, as in the antenna 20 'shown in FIG. 5 and FIG. 6, the structural antenna corresponds to a vertically long common dielectric substrate 21' and the same. A plurality of sets (four sets in this example) are arranged in an array on the ground plane conductor 22 'in a direction orthogonal to the direction in which the post wall extends (in this example, the arrangement direction of the element pieces 23a and 23b is aligned). By supplying in-phase power to each antenna element 23, a high gain can be obtained while maintaining a wide radar detection width on a horizontal plane (xz plane).

  FIG. 7 shows a change in directivity of the H plane (horizontal plane) when the width Lx of the dielectric substrate 21 ′ is changed in the antenna 20 ′ of this embodiment, and is a closed type with an inner dimension Lw = 9 mm. The half-width (3 dB width) of the conventional antenna having the cavity structure of 70 degrees is 70 degrees, whereas the antenna 20 ′ of the embodiment has 78 degrees when Lx = 9 mm, 96 degrees when Lx = 6 mm, and Lx = When set to 3 mm, a half-width of 126 degrees is obtained.

  FIG. 8 shows the frequency characteristics of the gain when the width Lx of the dielectric substrate 21 'is changed. From this figure, a slight decrease in gain is recognized as the cavity is changed from the closed type to the opposed wall type, but the notch in the radio wave emission prohibited band has a sufficient depth.

  By adopting a cavity structure composed of opposing walls in the E-plane direction, the width of the dielectric substrate 21 'can be made narrower than the interval Lw between the post walls, and the radar detection width is greatly increased accordingly. be able to.

  In this antenna 20 ', five post walls 31a to 31e are used for four sets of antenna elements 23 arranged vertically, and among these, three post walls 31b, 31c and 31d are shared.

  Further, in this antenna 20 ', as shown in FIG. 6, a microstrip line 40 is formed on the surface of the dielectric substrate 24 provided on the back side of the ground plane conductor 22', and each antenna element is formed from the feeding point 40a. 23 shows an example of in-phase power feeding. As for the power feeding method, a coplanar line or the like can be used in addition to the microstrip line.

(Third embodiment)
In the antenna 20 of the above-described embodiment, the antenna element 23 is an example of a linearly polarized dipole. However, as the antenna element 53 shown in FIG. Even when a circularly polarized wave type is used, a notch in the radio wave emission prohibited band is confirmed in the above-described opposed wall type cavity structure. In addition, the other component of this antenna 50 is equivalent to the said embodiment, and attaches | subjects the same code | symbol.

  That is, the antenna 50 includes a dielectric substrate 21, a ground plane conductor 22 that overlaps one surface of the dielectric substrate 21, an antenna element 53 formed in a spiral shape on the opposite surface of the dielectric substrate 21, and a ground plane conductor on one end side. A pair of metal posts 30 connected to 22 and penetrating through the dielectric substrate 21 along the thickness direction and having the other end extending to the opposite surface of the dielectric substrate 22 are arranged at a sufficiently narrow interval compared to the wavelength in the tube. A plurality of metal posts that respectively form a pair of post walls 31a and 31b on the opposite surface side of the dielectric substrate 21 and an opposite wall surface type cavity 31 constituted by sandwiching the antenna element 43 between the post walls 31a and 31b. 30 is provided with a pair of rim conductors 32a and 32b that are short-circuited in the arrangement direction and extend a predetermined distance in the direction of the antenna element 23. The central end of the antenna element 53 is connected to the power feed pin 25a.

  In the case of this antenna 50 as well, the width (substrate width) Lx in the direction orthogonal to the direction in which the post walls 32a and 32b extend can be made smaller than the interval Lw between the post walls 32a and 32b. The radar detection range on the horizontal plane can be expanded by expanding the notch of the gain in the frequency band determined by the interval Lw between the walls 32a and 32b and the directivity in the substrate width direction (xz plane directivity).

(Fourth embodiment)
Further, like the antenna 50 ′ shown in FIGS. 10 and 11, the antenna 50 having the above structure is connected to the vertically long common dielectric substrate 21 ′ and the corresponding ground plane conductor 22 ′ in the direction in which the post wall extends. A plurality of sets (four sets in this example) are arranged in an orthogonal direction to form an array, and each antenna element 43 is excited in the same phase, thereby obtaining a high gain while maintaining a wide radar detection width.

  FIG. 12 shows a change in directivity of the H plane (horizontal plane) when the width Lx of the dielectric substrate 21 ′ is changed in the antenna 50 ′ of this embodiment, and is a closed type with an inner dimension Lw = 9 mm. The half width (3 dB) of the conventional antenna having the cavity structure is 60 degrees, whereas the antenna 50 'of the embodiment can obtain a half width of 92 degrees when Lx = 6 mm.

  FIG. 13 shows the frequency characteristics of the gain when the width Lx of the dielectric substrate 21 ′ is changed. As can be seen from this figure, the gain is reduced by changing the cavity from the closed type to the opposed wall type, but the depth of the notch in the radio wave emission prohibited band can be obtained. In the radar using this antenna 50 ', a notch in the radio wave emission prohibited band can be obtained with a sufficient depth by a filter or the like connected to the antenna 50'.

  The antenna 50 ′ is a sequential array described in Patent Document 1, and two adjacent elements on the upper and lower sides of the spiral antenna element 53 are set as one set, and the angle of the two antenna elements forming the set is determined. As shown in FIG. 11, the microstrip line 40 is formed on the surface of the dielectric substrate 24 provided on the back surface side of the ground plane conductor 22 ', and two antenna elements forming a set are arranged. A phase difference equivalent to π / 2 is given to 53 (the line length to the lower antenna element is made longer by π / 2 than the line length to the upper antenna element of the two vertically adjacent antenna elements). Thus, in-phase excitation is performed while canceling the cross polarization components of the antenna elements forming the set.

A perspective view of an embodiment of the present invention Front view of an embodiment of the present invention AA line sectional view of FIG. Rear view of an embodiment of the present invention Diagram showing configuration example of arrayed antenna Diagram showing configuration example of arrayed antenna feed line The figure which shows the change of the radar detection width with respect to the board | substrate width of embodiment The figure which shows the frequency characteristic of the gain with respect to the board | substrate width of embodiment The figure which shows the structural example when an antenna element is a circular polarization type Diagram showing a configuration example of circularly polarized antenna array Diagram showing a configuration example of a circularly polarized antenna feed line The figure which shows the change of the radar detection width with respect to the board | substrate width of embodiment The figure which shows the frequency characteristic of the gain with respect to the board | substrate width of embodiment

Explanation of symbols

  20, 20'50, 50 '... radar antenna, 21, 21' ... dielectric substrate, 22, 22 '... ground plane conductor, 23 ... antenna element, 23a, 23b ... element piece, 24 ... Dielectric substrate, 25a, 25b ... feed pin, 30 ... metal post, 31 ... cavity, 31a to 31e ... post wall, 32a, 32b ... rim conductor, 40 ... microstrip line, 53 ... antenna element

Claims (3)

A rectangular dielectric substrate (21);
A rectangular ground plane conductor (22) overlapping one surface of the dielectric substrate;
The pair of elements pieces formed so as to be aligned on a straight line along the longitudinal direction of the dielectric substrate on the opposite surface of the dielectric substrate and (23a, 23b) dipole antenna element made of (2 3),
One end connected to the ground plane conductor, the dielectric substrate wherein the dielectric substrate penetrates along the thickness direction, the metal posts (30) which has the other end extending to the opposite surface of the dielectric substrate at a predetermined interval A pair of post walls (31a, 31b) formed side by side along both short sides of the antenna element, and the antenna element is sandwiched between the pair of post walls in the direction of the electric field, thereby separating the pair of post walls (Lw). An opposite wall surface type cavity (31) for generating a notch in a specific frequency band determined by :
A pair of rims that short-circuit the other end sides of the plurality of metal posts that respectively form the pair of post walls on the opposite surface side of the dielectric substrate along the arrangement direction and extend a predetermined distance in the antenna element direction Conductors (32a, 32b) ,
Further, the width (Lx) in the short side direction in which the post wall of the dielectric substrate extends is formed to be narrower than the interval (Lw) between the pair of post walls that cause notches in the specific frequency band, A radar antenna, wherein the beam width of the magnetic field surface along the short side direction is expanded with respect to the beam width of the electric field surface along the long side direction of the dielectric substrate . Claim 1 radar antenna according a common dielectric the features and, Relais over da antennas that it has an array of side by side a plurality of sets in a direction perpendicular to the direction extending post walls on the substrate. The radar antenna according to claim 2 , wherein a width (Lx) in a short side direction in which the post wall extends is set to 2/3 or less of a distance (Lw) between the pair of post walls .

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