JP5032910B2 - Antenna device for pulse radar - Google Patents

Description

  The present invention relates to a pulse radar antenna that can reduce deterioration of radar performance due to reflected waves even when reflected waves from the ground and direct interference waves between transmitting and receiving antennas are strong.

  In general, distance measurement by pulse radar outputs a pulsed signal from the transmitting antenna, reflects the signal that hits the target, and measures the time until it is received by the receiving antenna, thereby determining the distance to the target. Calculated. This distance measurement technique using pulse radar is also adopted as a safety support technique in vehicles such as automobiles, and the surroundings of automobiles are sensed by pulse radar to recognize obstacles.

  In such a pulse radar, when measuring the close range where the reflected pulse from the target returns before the transmission of the pulse signal is completed, the diffracted wave that diffracts from the transmitting antenna and directly enters the receiving antenna is a disturbing signal. Thus, the measurement distance and position accuracy are greatly affected. For this reason, various techniques for reducing interference due to interference signals have been proposed.

For example, Patent Document 1 discloses a technique of providing a shielding plate for shielding radio waves between a transmission antenna and a reception antenna. Patent Document 2 discloses a technique in which antennas are arranged in a straight line to form an array antenna, thereby narrowing the beam pattern of the antenna to increase isolation between the transmission antenna and the reception antenna.
JP 2003-279649 A JP 2003-344535 A

  However, pulse radars are often attached to parts that are relatively close to the ground, such as when antennas are attached to vehicle bumpers, etc. In addition, detection of pedestrians and obstacles on the road in in-vehicle pulse radars, etc. As described above, there is a case where the accuracy of distance measurement at a close distance is required.

  An example applied to an in-vehicle pulse radar is shown in FIG. In FIG. 14, a transmitting antenna 102 and a receiving antenna 103 are arranged inside the bumper 101 of the vehicle body 100. In this arrangement example, in the region where the radiation of the pulse signal from the transmitting antenna 102 is completed and the reflected pulse from the target returns, the response signal S reflected or scattered from the target is reflected by the reflected wave 105 from the ground 104 or the like. This is the sum of clutter signals that are diffusely reflected in the surrounding environment. In this case, the clutter signal becomes the interference signal I. Furthermore, in the close-range distance measurement in which the reflected pulse from the target returns while the transmission of the pulse signal is not completed, a diffracted wave 106 that is diffracted from the transmitting antenna 102 and directly enters the receiving antenna 103 is added to the interference signal I. Is done.

  Therefore, when the antenna is installed in a relatively close area and distance measurement is performed at a close distance, in addition to the first interference wave that the signal output from the transmitting antenna directly goes around to the receiving antenna, The reflected second interference wave is directly received by the receiving antenna. For this reason, the weak reflected signal from the target is received by the receiving antenna so as to overlap with the much stronger first and second interference waves, and as a result, the reception sensitivity of the radar is greatly increased. There is a problem of making it worse.

To achieve the above object, pulse radar antenna device according to the invention is mounted on a vehicle to transmit a pulsed radar waves, distance between the target from the time until receiving the reflected wave from the target a pulse radar antenna apparatus for detecting a transmitting antenna consisting of a single element, and a receiving antenna consists of separate single elements and the transmitting antenna, the transmitting antenna and the A reception antenna is installed near the left and right ends of the bumper of the vehicle, and at least one of the transmission antenna and the reception antenna is installed so that the ground plane is positioned in the null direction of the beam, and the transmission antenna is It is characterized in that it is installed so that the incident angle with the ground plane is near the Brewster angle.

  That is, in the conventional technique, when an antenna is installed in a relatively close portion such as an in-vehicle pulse radar to measure a close range, a reflected wave from the ground cannot be suppressed, and S / There arises a problem that the I ratio cannot be improved sufficiently. Furthermore, in the region where the transmission of the pulse signal is completed and the reflected pulse from the target returns, the interference wave is almost composed of the reflected wave from the ground, so the conventional technology improves the S / I ratio completely. Can not do it.

  In this regard, according to the technique of providing a shielding plate between the transmission antenna and the reception antenna as disclosed in Patent Document 1, when the frequency of the high-frequency signal is high as in a millimeter wave band radar, However, it is possible to suppress the interference wave sufficiently with respect to the diffracted wave. However, if the frequency of the high frequency signal is relatively low, such as a pulse radar in the VHF band, the diffractive effect is not obtained. Since it is very large, a sufficiently large shielding plate that cannot be mounted in the bumper is necessary to sufficiently suppress the diffracted wave. When the shielding plate is sized to fit within the bumper, it is difficult to sufficiently suppress the interference wave.

  Further, the technique of narrowing the beam pattern of the antenna as disclosed in Patent Document 2 requires a large number of antenna elements, which increases the size of the entire antenna. Since the size of the antenna element is inversely proportional to the frequency, there is no problem when the frequency of the high frequency signal is high. However, when the frequency of the high frequency signal is relatively low, such as a VHF band pulse radar, the array antenna cannot be mounted on the vehicle. If the size of the array antenna is increased so that it can be mounted on a vehicle, similarly, it is difficult to sufficiently suppress the interference wave.

  Further, when an antenna is arrayed, a control unit for individually optimizing the voltage amplitude and phase supplied to each antenna element is required for the number of antenna elements. Furthermore, when antennas are arrayed, the directivity of the antennas is narrowed down and the radar detection range is narrowed.

  To solve this problem, the voltage amplitude and phase supplied to each antenna element are controlled temporally, and the antenna directivity is scanned by electronic control, or the antenna itself is physically moved by a motor. It is conceivable to employ a technique for mechanically scanning the antenna beam. However, these techniques not only require time for sweeping the entire detection range, but also increase the cost of the control device.

  The present invention has been made in view of the above circumstances, and a pulse capable of efficiently suppressing an interference wave at low cost even when there is strong reflection from the ground or interference due to direct coupling from a transmitting antenna to a receiving antenna. A first object is to provide a radar antenna apparatus, and a second object is to provide a low-cost pulse radar antenna apparatus having a wide detection range by configuring the antenna with a single element.

  In order to achieve the above object, a pulse radar antenna device according to the present invention transmits a pulsed radar wave, and detects a distance and direction from the target until receiving a reflected wave from the target. A radar antenna device, comprising: a transmission antenna composed of a single element; and a reception antenna composed of a single element different from the transmission antenna, wherein the transmission antenna and the reception antenna At least one of the antennas is installed so that the ground is positioned in the beam null direction, and the transmitting antenna is installed so that an incident angle with the ground plane is near the Brewster angle.

  According to the present invention, even when there is strong reflection from the ground or interference due to direct coupling from a transmitting antenna to a receiving antenna, an interference wave can be efficiently suppressed at a low cost, and an antenna using a single element As a result, the cost can be reduced and the detection range can be expanded.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 10 relate to the first embodiment of the present invention, FIG. 1 is an explanatory diagram showing the arrangement of the transmitting / receiving antenna with respect to the target, FIG. 2 is an explanatory diagram showing the arrangement of the transmitting / receiving antenna with respect to the ground surface, 4 is an explanatory diagram showing an example in which a transmission / reception antenna is arranged on the side of the vehicle body, FIG. 4 is an explanatory diagram showing a state where the transmission / reception antenna is installed inside the bumper, FIG. 5 is an explanatory diagram showing a coordinate system of the antenna, and FIG. FIG. 7 is an explanatory diagram showing the antenna beam pattern on the ZX plane, FIG. 8 is an explanatory diagram showing reflection on the dry ground surface, and FIG. 9 is an explanatory diagram showing the relationship between the incident angle and the reflection coefficient. FIG. 10 is an explanatory diagram showing the arrangement of transmission antennas.

  The present embodiment is applied to an on-vehicle pulse radar device, and uses a radar signal in a weak radio band. That is, as shown in FIGS. 1 and 2, the pulse radar antenna apparatus according to the present embodiment includes a transmission antenna 1 that transmits a pulsed radar wave and a reception antenna that receives a reflected wave reflected from a target 3. 2 are arranged in the vicinity of the left and right ends inside the bumper 5 of the vehicle body 4.

  Specifically, the vicinity of the VHF band (30 MHz to 300 MHz) can be used as the radar frequency band. Preferably, a frequency band from about 200 MHz to about 300 MHz is used, and the antenna size decreases as the frequency increases. Therefore, considering the miniaturization of the apparatus, more specifically, near 300 MHz, more specifically, around 322 MHz, and as much as possible to 322 MHz. It is preferable to use a close frequency band.

  At least one of the transmission antenna 1 and the reception antenna 2 is composed of a single element such as a bow tie antenna, a dipole antenna, or a loop antenna. Therefore, the antenna can be reduced in size by shortening the elements of the antenna with lumped constant elements.

  The transmission antenna 1 and the reception antenna 2 can be appropriately installed on the front and rear parts of the vehicle body and the side parts of the vehicle body according to the direction in which the obstacle is to be recognized. In the present embodiment, the transmitting antenna 1 and the receiving antenna 2 are arranged on the bumper 5, and as this bumper 5, the transmitting antenna 1 and the receiving antenna 2 are arranged on the rear bumper 5r as shown in FIG. However, as shown in FIG. 2B, the transmission antenna 1 and the reception antenna 2 may be arranged on the front bumper 5f. Furthermore, as shown in FIG. 3, it is also possible to arrange the transmitting antenna 1 and the receiving antenna 2 inside the panel-like member 10 such as a side protector or a side molding on the side surface of the vehicle body.

  In this case, the bumper 5 on which the transmitting antenna 1 and the receiving antenna 2 are installed and the panel-like member 10 on the side of the vehicle body are generally formed of a resin member, and the antenna is integrated inside the resin member. It is also possible to mold.

  FIG. 4 shows a state in which the transmitting antenna 1 and the receiving antenna 2 are installed inside the bumper 5, and the transmitting antenna 1 and the receiving antenna 2 are directly attached to the bumper face back surface 5b, or the bumper face back surface 5b and the bumper beam. The transmitting antenna 1 and the receiving antenna 2 can be arranged inside the bumper 5 by providing a concave portion in the foam between and the bumper 5.

  The transmission antenna 1 is driven by a radar transmission device (not shown), and a radar wave (pulsed radar signal; hereinafter simply referred to as “pulse signal”) is radiated from the transmission antenna 1 into space. The pulse signal propagates through the air and is reflected by the surface of the target 3. The reflected signal 9 from the target 3 propagates in the air, reaches the receiving antenna 2, and is input to a radar receiver (not shown).

  At this time, as shown in FIG. 2, a part of the pulse signal radiated from the transmitting antenna 1 wraps around the receiving antenna 2 as a direct wave 6, and the other part is reflected by the ground surface 7. A ground reflected wave 8 is input to the receiving antenna 2.

  Therefore, at least one of the transmission antenna 1 and the reception antenna 2 is installed so that the ground plane is positioned in the direction of the beam pattern null (directivity pattern drop point), and the transmission antenna 1 is used as the ground plane. It is installed so that the incident angle i is near the Brewster angle described later.

  Specifically, the coordinate system of the antenna will be described using the XYZ orthogonal coordinate system shown in FIG. 5. First, the coordinate origin and the center of the antenna are matched, and then the ZX plane and the antenna plane are positioned in parallel. Determine. At this time, the antenna beam pattern is the beam pattern shown in FIG. 6 on the XY plane, which is a substantially omnidirectional pattern. Further, on the ZX plane, the beam pattern shown in FIG. 7 is obtained, and the power radiated in the Z-axis direction is a weak pattern.

  Therefore, if the transmitting / receiving antenna is installed so that the ground is located in the Z-axis direction, the power radiated from the transmitting antenna in the ground direction becomes weak, and at the same time, the power propagated from the ground direction and input to the receiving antenna is weakened. Can do.

Here, the reflection coefficient when a plane wave propagates from the medium a (dielectric constant ε1, permeability μ1, conductivity σ1) to the medium b (dielectric constant ε2, permeability μ2, conductivity σ2) is considered. The reflection coefficient R1 at the surface of the medium b when a plane wave parallel to the incident surface propagates, and the reflection coefficient R2 when the electric field is orthogonal to the incident surface are expressed by the following (1), ( 2) It is given by the formula.
R1 = (μ1 · n ² · cos (i) −μ2 · (n ² −sin ² (i)) ^1/2 ) / (μ1 · n ² · cos (i) + μ2 · (n ² −sin ² (i )) ^1/2 )… (1)
R2 = (μ2 · cos (i ) -μ1 · (n 2 -sin 2 (i)) 1/2) / (μ2 · cos (i) + μ1 · (n 2 -sin 2 (i)) 1/2) ... (2)

In the above equations (1) and (2), i is an incident angle, and n is a relative refractive index. The relative refractive index n is given by the following equation (3).
n = (μ2 / μ1) ^1/2 · ((ε2−j · σ2 / ω) / (ε1−j · σ1 / ω)) ^1/2 (3)

  As shown in FIG. 8, when the above-described relationship is examined for the reflection coefficient on the dry ground surface between the incident wave and the reflected wave incident at the incident angle i, the relationship shown in FIG. 9 is obtained. That is, when the electric field is orthogonal to the incident surface, the characteristic is as indicated by a broken line with respect to the incident angle i. When the electric field is parallel to the incident surface, the characteristic is as indicated by a solid line with respect to the incident angle i. There is an incident angle at which the reflection coefficient is minimal. The incident angle at which the reflection coefficient is minimized when this electric field is parallel to the incident surface is called the Brewster Angle.

In the arrangement shown in the antenna shown in FIG. 2, for example, the transmitting antenna 1 and the receiving antenna 2 are mounted inside the bumper 5 of the vehicle body 4 so that the ground height is 0.5 m and the transmitting and receiving antenna spacing is 1.5 m. The incident angle i from the transmitting antenna 1 to the ground is given by the following equation (4).
i = tan ⁻¹ ((1.5 / 2) /0.5) (4)

  The value of the incident angle i given by the above equation (4) is approximately 56.3 °. From FIG. 9, when the incident angle is 56.3 °, the reflection coefficient when the electric field is parallel to the incident surface is about Whereas it is 0.1, the reflection coefficient when the electric field is orthogonal to the incident surface is about 0.5.

  Accordingly, at least one of the transmission antenna 1 and the reception antenna 2 is installed so that the ground is located in the Z-axis direction in the antenna coordinate system shown in FIGS. 5 to 7, and as shown in FIG. If it is installed so that the incident angle formed by the ground is near the Brewster angle iB, not only the power propagating from the transmitting antenna 1 toward the ground can be reduced, but also the reflection coefficient on the ground can be minimized, Interference due to ground reflected waves can be minimized.

  As described above, the pulse radar antenna apparatus according to the present embodiment uses a single element antenna without arraying antennas, directs at least one null of the transmission / reception antenna in the ground direction, and transmits from the transmission antenna to the ground. The incident angle of the radio wave is set to be close to the Brewster angle.

  Accordingly, interference due to ground reflected waves in the pulse radar can be effectively suppressed without expensive array antennas or complicated signal processing, and measurement distance and position accuracy can be improved. Moreover, since the single element antenna has a wide beam angle, it is possible to realize a pulse radar antenna having a wide detection range at low cost.

  Next, a second embodiment of the present invention will be described. 11 to 13 relate to a second embodiment of the present invention, FIG. 11 is an explanatory view showing the arrangement of the transmitting and receiving antennas, FIG. 12 is an explanatory view showing a first modification of the arrangement of the transmitting and receiving antennas, and FIG. It is explanatory drawing which shows the 2nd modification of arrangement | positioning of a transmission / reception antenna.

  The second embodiment is different from the first embodiment only in the installation of the transmission / reception antenna on the vehicle body. In the first embodiment described above, the direction of the receiving antenna 2 viewed from the transmitting antenna 1 in the coordinate system shown in FIG. 5 coincides with the X-axis direction, and as shown in FIGS. There is a possibility that interference from the direct wave 6 to the receiving antenna 2 will increase. For this reason, in the second embodiment, not only the ground reflected wave is suppressed, but also the direct interference wave between the transmitting and receiving antennas is suppressed.

  In general, in a pulse radar, in order to suppress a direct sneak wave from a transmission antenna to a reception antenna, a null of the beam pattern of the transmission antenna is positioned from the transmission antenna to the reception antenna, and the direction from the reception antenna to the transmission antenna It is sufficient to install the antenna so that the null of the beam pattern of the receiving antenna is located in the position.

  However, when an antenna composed of a single element is used, it is difficult to suppress the ground reflection and the direct sneak wave simultaneously by the above method because the antenna has a wide beam angle. Therefore, at first, the transmitting / receiving antenna is installed so as to sufficiently suppress the ground reflected wave with the same arrangement as in the first embodiment, and then the transmitting / receiving antenna until the direct sneak wave between the transmitting / receiving antennas becomes sufficiently small. By tilting at least one of them, it is possible to simultaneously suppress the ground reflected wave and the direct sneak wave between the transmitting and receiving antennas.

  In this case, the antenna has polarization characteristics, and it is important to align the polarization of the radio wave with that of the receiving antenna in order to efficiently receive the radio wave. In this embodiment, when the target surface is rough with respect to the wavelength, or when the target size is smaller than the wavelength, the radio wave is scattered on the target surface, and the energy is reflected and spreads in all directions. However, when the wavelength is relatively long, scattering occurs on the target surface, and good operation can be ensured even if the polarizations of the transmission antenna 1 and the reception antenna 2 are slightly shifted.

  Specifically, as shown in FIG. 11, the transmission antenna 1 and the ground are arranged so that the incident angle is in the vicinity of the Brewster angle iB, and the transmission antenna 1 and the reception antenna 2 are kept parallel to each other. Install it at an angle θ. At this time, the direction of the receiving antenna 2 viewed from the transmitting antenna 1 is a direction inclined by an angle θ from the X-axis direction to the Z-axis direction in the beam pattern on the ZX plane (see FIG. 7). As the tilt angle θ is increased in the range of 90 °, interference from the direct wave from the transmitting antenna 1 to the receiving antenna 2 can be reduced.

  FIG. 11 is an example in which both the transmitting and receiving antennas are arranged in parallel and inclined at the same angle. However, the transmitting antenna 1 and the receiving antenna 2 have a C-shape with an inclination angle θ as shown in FIG. It may be arranged so as to be inclined, or as shown in FIG. Furthermore, only one of the transmission / reception antennas may be disposed to be inclined, and the transmission / reception antennas may be disposed to be inclined at different angles.

  In the second mode, it is possible to suppress both interference waves due to ground reflection and direct interference waves between the transmitting and receiving antennas. Further, by using a single element antenna with a wide beam angle without using a high-cost array antenna, a pulse radar antenna with a wide detection range can be realized at a low cost.

Explanatory drawing which shows arrangement | positioning with respect to the target object of a transmission / reception antenna concerning 1st Embodiment of this invention. As above, an explanatory diagram showing the arrangement of the transmitting and receiving antennas with respect to the ground surface Explanatory drawing which shows the example which has arrange | positioned the transmission / reception antenna on the vehicle body side surface same as the above Same as above, explanatory diagram showing a state where a transmission / reception antenna is installed inside the bumper Same as above, explanatory diagram showing the coordinate system of the antenna As above, an explanatory diagram showing an antenna beam pattern on the XY plane As above, an explanatory diagram showing an antenna beam pattern on the ZX plane Same as above, explanatory diagram showing reflection on dry ground surface As above, an explanatory diagram showing the relationship between the incident angle and the reflection coefficient Same as above, explanatory diagram showing arrangement of transmitting antenna Explanatory drawing which shows arrangement | positioning of a transmission / reception antenna concerning 2nd Embodiment of this invention. Explanatory drawing which shows the 1st modification of arrangement | positioning of a transmission / reception antenna same as the above. Explanatory drawing which shows the 2nd modification of arrangement | positioning of a transmission / reception antenna same as the above. Explanatory drawing which shows arrangement of the conventional transmitting and receiving antenna

Explanation of symbols

1 Transmitting Antenna 2 Receiving Antenna 3 Target 4 Car Body 5 Bumper 7 Ground Surface iB Brewster Angle

Claims (8)

Is mounted on a vehicle to transmit a pulsed radar wave, a pulse radar antenna apparatus for detecting the distance between the target from the time until receiving the reflected wave from the target,
A transmission antenna composed of a single element, and a reception antenna composed of a single element different from the transmission antenna;
The transmission antenna and the reception antenna are installed near the left and right ends of the bumper of the vehicle, and at least one of the transmission antenna and the reception antenna is installed so that the ground plane is positioned in the beam null direction, A pulse radar antenna apparatus, wherein the transmitting antenna is installed such that an incident angle with a ground plane is near a Brewster angle.   2. The pulse radar antenna device according to claim 1, wherein at least one of the transmitting antenna and the receiving antenna is inclined.   3. The pulse radar antenna device according to claim 1, wherein at least one of the transmission antenna and the reception antenna is a dipole antenna.   3. The pulse radar antenna device according to claim 1, wherein at least one of the transmission antenna and the reception antenna is a loop antenna.   3. The pulse radar antenna device according to claim 1, wherein at least one of the transmission antenna and the reception antenna is a bow tie antenna.   6. The pulse radar antenna device according to claim 3, wherein at least one of the transmitting antenna and the receiving antenna is shortened by a lumped constant element.   7. The pulse radar antenna device according to claim 1, wherein a radar signal in a weak radio band is used.   8. The pulse radar antenna device according to claim 1, wherein the bumper is made of resin, and the transmitting antenna and the receiving antenna are integrally formed inside the resin bumper.

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