JP2010008319A - Radar antenna and radar system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To electrically measure an azimuth angle and an elevation angle. <P>SOLUTION: A radar antenna includes at least three array antennas 30, 31 and 32 having radiating elements provided linearly, in a z-axis direction which is one direction and being separated in a y-axis direction vertical to the z-axis. The z-axis arrangement positions of the respective array antennas are made different. For a plurality of sets consisting of at least any two selected from among the plurality of array antennas, the azimuth angle ϕ and the elevation angle θ are obtained from each of measured phase differences of the respective sets, by using the relation for the phase difference δ among the array antennas, the azimuth angle ϕ and the elevation angle θ. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radar antenna and a radar apparatus that can measure the arrival direction (elevation angle, azimuth angle) of radio waves.

  Conventionally, as shown in Patent Document 1 below, an array antenna in which radiation pieces are arranged along a feeder line and a two-dimensional array antenna in which a large number of antennas are arranged in parallel are known. In this antenna, in the case of a radiating antenna, the direction in which the radiated power density is maximum, that is, the center direction of the radiated radio wave is set to a predetermined angular direction with respect to the normal of the antenna substrate surface. In the case of a receiving antenna, the arrival direction of a radio wave that provides maximum sensitivity, that is, the center direction of the received radio wave is set to a predetermined angular direction with respect to the normal of the antenna substrate surface. Patent Document 2 below discloses an antenna that changes the elevation angle of a radiated radio wave or an incoming radio wave by changing the frequency using a leaky wave antenna.

Japanese Patent No. 3306592 JP 2007-81825 A

  The array antenna described in Patent Document 1 described above is mounted on a vehicle and used to detect a forward vehicle and an obstacle. And after providing in the mounting base adjusted so that the center direction of the incoming radio wave of this antenna may become a predetermined direction (predetermined elevation angle), this mounting base is provided in the predetermined position of a vehicle. However, this array antenna cannot scan the direction of radio wave emission or detect the direction of arrival.

  On the other hand, in the method described in Patent Document 2, when the linear leaky wave antenna is provided perpendicular to the ground, the arrival direction of the radio wave in the elevation direction can be scanned according to the frequency. Cannot scan. In addition, when considering application to automobile radar, it is practically unsuitable because it is difficult to secure a frequency band necessary for obtaining a sufficient scanning angle.

  Therefore, the present invention has been made to solve the above-described problems, and an object thereof is to make it possible to measure the arrival direction of two degrees of freedom of radio waves.

  The present invention relates to a radar antenna having at least three radiating elements arranged linearly in a z-axis direction that is one direction and spaced apart in a y-axis direction that is a direction perpendicular to the z-axis. The radar antenna is characterized in that each array antenna has a different arrangement position in the z-axis direction.

  As the array antenna, a one-dimensional array or a two-dimensional array can be used. As each array antenna, a microstrip antenna element in which rectangular radio wave radiation elements are arranged on one side or both sides of a feeder line can be used. In addition to the microstrip antenna, a slot array antenna or a coplanar antenna may be used. The radar antenna can be used for monopulse radar.

  Further, in a plurality of sets formed by selecting any two of the plurality of array antennas, it is desirable that the distance in the y-axis direction between the array antennas of each set is different. By adopting this structure, it is possible to change the phase return period in the relationship between the phase difference between the array antennas and the arrival angle of the radio wave. As a result, the measurement range of the arrival direction of radio waves and the resolution thereof can be arbitrarily set according to the required performance.

  Further, in a plurality of sets configured by selecting at least two arbitrary antennas from a plurality of array antennas, a line segment connecting the phase centers of one set of array antennas and a phase center of another set of array antennas The connecting line segments may be configured not to be parallel. By adopting this configuration, it is possible to improve the measurement accuracy of the arrival direction of radio waves.

  According to another aspect of the present invention, there is provided a radar device using the radar antenna according to any one of claims 1 to 3, wherein a plurality of arrays are provided when a direction perpendicular to the z axis and the y axis is an x axis. In a plurality of groups configured by selecting at least two arbitrary antennas, the phase difference between the array antennas and the radio wave arrival directions φ and θ, where φ is the projection of the radio wave arrival direction on the xz plane The angle formed with the x axis, θ is the relationship between the projection of the radio wave arrival direction on the xy plane and the angle formed with the x axis, and the radio wave arrival direction φ, θ is calculated from each measured phase difference of each set. The radar device is characterized in that it is obtained. That is, if at least two phase differences are known, φ and θ which are two degrees of freedom in the direction of arrival of radio waves can be determined.

  In the present invention, in the radar antenna in which at least three radiating elements are arranged in the z-axis direction, which is one direction, and arranged in a straight line, apart from each other in the y-axis direction perpendicular to the z-axis. Since the arrangement positions of the array antennas in the z-axis direction are different positions, the phase-independent correspondence between the phase difference between the array antennas and the two radio wave arrival directions φ and θ having at least two degrees of freedom is obtained. Pairs can be set. As a result, in the radio wave arrival direction, the two-degree-of-freedom directions φ and θ can be determined using at least two phase differences and at least two correspondence relationships. This is different from that controlled by mechanical driving or power feeding, and the direction of two degrees of freedom can be determined simply by measuring the phase difference.

  Hereinafter, the present invention will be described based on specific examples. The present invention is not limited to the following examples.

  As shown in FIG. 1, the radar antenna 100 of this embodiment is composed of four array antennas 20, 30, 31, and 32. Of course, the array antenna may be a two-dimensional direction, that is, a planar array antenna in which many illustrated array antennas are arranged in parallel in addition to the array antenna illustrated in the illustrated one-dimensional direction. In this embodiment, a monopulse radar is assumed. The array antenna 20 is a transmission antenna, and the three array antennas 30, 31, and 32 are reception antennas. These three array antennas 30, 31, and 32 correspond to the antenna of the present invention.

  The coordinate system is the z axis perpendicular to the horizontal plane, the y axis on the plane of the radar antenna 100, the x axis in the normal direction of the plane of the radar antenna 100 on the horizontal plane, and the origin is the center of the radar antenna 100. Take a point. In this embodiment, the array antenna 20 is a one-dimensional microstrip array antenna. As shown in the cross-sectional view of FIG. 2, the feeding strip line 200 and the entire second main surface 101 b (back surface) of the dielectric substrate 101 are formed on the first main surface 101 a of the dielectric substrate 101. A ground conductor 102 is formed.

As shown in FIG. 1, in this array antenna, an angle of 45 degrees is formed on one side of the feeding strip line 200 with respect to the line for the purpose of generating oblique 45-degree polarized waves used in automobile radar. Thus, eight rectangular radiating elements 201 are formed. The arrangement interval w of each radiating element 201 is the in-tube wavelength λ _g of the feeding strip line 200 at the operating frequency, and the length of each radiating element 201 (the distance from the connection point center p to the open end q) is the in-tube wavelength λ _g. It is set to about half of. One side of the open end of each of the projecting radiating antenna elements 201 is parallel to each other and is substantially −45 degrees (angle from the y axis) with respect to the feeding strip line 200.

  The radiating element 201 is connected to the side of the feed stripline 200 at one apex angle with a width of about ½ or less of the length L of the short side of the rectangular radiating element. The dielectric plate 101 is made of a plate-like material whose base material is a tetrafluoroethylene resin (: relative dielectric constant 2.2).

  The configurations of the other array antennas 30, 31 and 32 are the same as the configuration of the array antenna 20. On the feeding strip line of the array antenna 31 located at the center in the y-axis direction, the middle point of the feeding strip line in the z-axis direction (fourth and fifth radiating antenna elements from the smallest z-axis value) The origin o is set at the midpoint of Then, the midpoint of the feeding strip line of each array antenna is set as the reference point of each array antenna. The z coordinates of the reference points of the array antennas 20, 30, 31, and 32 are 0, −a, 0, and a (a> 0), respectively. Also, let d be the distance between adjacent array antennas in the y-axis direction. As described above, in this embodiment, the positions of the reference points of the three array antennas 30, 31, and 32 in the z-axis direction are different.

（１）式から、（２）式により到来波の方位角θが求められる。

Next, the operation of the array antenna according to the present embodiment will be described. Before that, an operation related to two array antennas having different reference point z-axis positions will be described.
First, as shown in FIG. 3A, consider the case of two array antennas in which the positions of the reference points in the z-axis direction are not different. The reverse vector of the traveling direction vector of the arrival wave is defined as the arrival direction vector, and the angle formed by the orthogonal projection of the arrival direction vector onto the xy plane is the azimuth angle θ (the y axis positive direction on the xy plane) The angle formed by the x-axis of the orthogonal projection of the arrival direction vector on the xz plane is the elevation angle φ (the rotation direction in the z-axis positive direction on the xz plane is positive) And The interval in the y-axis direction is D. The phase difference δ of the waves arriving at the two array antennas is expressed by equation (1).

From the equation (1), the azimuth angle θ of the incoming wave is obtained by the equation (2).

Next, as shown in FIG. 3B, in the present invention, the z coordinates of the reference points P1, P2 of the two array antennas 31, 32 are set to different values 0, a. That is, the line segment P1P2 connecting the reference points P1 and P2 of the two array antennas intersects the y axis at an angle Ψ. Therefore, a = dtan Ψ, and the position in the z-axis direction differs by this value a. Where d is the distance between the array antennas in the y-axis direction. Further, when the distance between the reference points P1 and P2 is D, the equation (3) is established.

Next, a coordinate system obtained by rotating the y-axis around the x-axis by an angle Ψ is defined as o-xYZ. Then, the expression (2) is established for the angle β formed by the x-axis of the projection of the arrival direction vector onto the xY plane. That is, the expression (2) is established with respect to the azimuth angle β in the coordinate system o-xYZ.
Therefore, when equation (3) is substituted into equation (2) and θ = β, equation (4) is obtained.

となる。したがって、ｏ−ｘｙｚ座標系で定義される方位角θと仰角φについて次式が成立する。

この式から、

となり、

が得られる。ただし、Ａ＝λδ/(２πｄ）、 Next, let the arrival direction vector in the o-xYZ system be (a, b, c). When this direction-of-arrival vector is expressed in the o-xyz coordinate system,

It becomes. Therefore, the following equation is established for the azimuth angle θ and the elevation angle φ defined in the o-xyz coordinate system.

From this formula:

And

Is obtained. However, A = λδ / (2πd),

  The relational expression (9) is established between the phase difference δ and the azimuth angle θ using Ψ and d as parameters. The characteristics of the phase difference δ of the incoming waves received by the two array antennas when the distance d and the angle ψ are changed were simulated. The results are shown in FIGS.

  FIG. 4 shows characteristics indicating the relationship between the azimuth angle θ and the phase difference δ when Ψ = 60 degrees and d = 2 mm, and FIG. 5 shows the azimuth angle θ and the phase difference when Ψ = 30 degrees and d = 8 mm. This is a characteristic indicating the relationship with δ. Comparing FIG. 4 with FIG. 5, when the interval d is large, the phase return period of the characteristic of the phase difference δ with respect to the azimuth angle θ becomes short. Moreover, the resolution with respect to the elevation angle φ is improved as the angle ψ is increased. By using the characteristics shown in FIGS. 4 and 5, an azimuth angle range of −60 degrees to +60 degrees can be measured. 5 has a larger absolute value of the derivative with respect to the azimuth angle θ of the phase difference δ. Therefore, the resolution of the antenna set that realizes the characteristics of FIG. 5 is larger. However, due to the periodicity, in the characteristics of FIG. 5, the range of the main value of the azimuth angle θ is as narrow as −15 degrees to +15 degrees. Therefore, the azimuth angle θ is determined over a wide range from −60 degrees to +60 degrees with the resolution determined by the characteristics of FIG. 5 by using the characteristics of FIG. 4 to determine the range of 30 degrees width. can do.

第２組のアンテナに関する（９）式を、

とおく。関数ｆ、ｇは、パラメータｄ、Ψが異なるだけである。 Consider two sets of antennas, each of which is composed of two antennas, by selecting two of the three array antennas. The first set of antennas are array antennas 31 and 32, and the second set of antennas are array antennas 30 and 32. Equation (9) for the first set of antennas is

Equation (9) for the second set of antennas is

far. The functions f and g differ only in the parameters d and Ψ.

  In this way, if two sets of antennas having different parameters d and Ψ are formed, and their phase difference δ is measured, the azimuth angle θ and the elevation angle φ are calculated from the equations (10) and (11). Can be sought. In this way, the azimuth angle θ and elevation angle φ of the incoming wave can be measured.

  In the arrangement of FIG. 1, the two angles are the same for the angle ψ, and the distance is d and 2d. Since the interval values are different, two sets of relational expressions (10) and (11) can be determined. If the first set is the array antennas 30 and 31, and the second set is the array antennas 31 and 32, the angles and the intervals are equal to Ψ and d, so the above two formulas are the same. However, such a choice is not possible. In addition, an array antenna can be arranged as shown in FIG. The first set antenna is a set of array antennas H1 and H3, and the second set antenna is a set of array antennas H1 and H2. The angle formed by the line P4P6 connecting the reference point P4 of the array antenna H1 and the reference point P6 of the array antenna H3 and the y axis is γ, the reference point P4 of the array antenna H1 and the reference point P5 of the array antenna H2 An angle formed by the connecting line segment P4P5 and the y-axis is assumed to be ζ. Then, γ + ζ = π / 2. In this case, when the origin of the coordinate system is taken as the reference point P5 of the array antenna H2, the z coordinate of the reference point P4 of the array antenna H1 is dtanζ, and the z coordinate of the reference point P6 of the array antenna H3 is 2dtanγ + dtanζ. is there. You may arrange in this way.

  The configuration of the radar apparatus is as shown in FIG. The measurement of the azimuth angle θ and the elevation angle φ can be realized by a phase monopulse method. The output of the oscillator 11 that generates a carrier wave in the GHz band is pulse-modulated by the mixer 40 with the signal of the pulse generator 10. Next, the pulse signal passes through the band pass filter 60 and is sent to the array antenna 20 for transmission. Then, the radio waves reflected from the front object are received by the array antennas 30, 31 and 32. The received signals of these antennas are input to the demodulators 50, 51, 52 and demodulated into baseband pulse signals by the carrier wave output from the oscillator 11. Then, the signal processing unit 70 obtains the phase difference δ1 of the pulse signals received by the array antennas 31 and 32 and the phase difference δ2 of the pulse signals received by the array antennas 30 and 32. The azimuth angle θ and the elevation angle φ can be obtained from the two phase differences δ1 and δ2 and the above equations (10) and (11). In addition, as for the expressions (10) and (11), the azimuth angle θ and the elevation angle φ may be obtained by solving simultaneous equations of two functions as functions represented by the expression (9). Further, the characteristics indicating the relationship between θ, φ, and δ as shown in FIGS. 4 and 5 are stored in a table, and θ and φ corresponding to the measured values δ1 and δ2 are obtained by interpolation calculation. good.

  Further, the FM-CW method can be used for measuring the distance. In addition to the microstrip antenna, the array antenna used in the above embodiment may be a slot array antenna or a coplanar attenuator. In addition, these array antennas can be used for antennas of all configurations described in Japanese Patent No. 3306592 by the present applicant.

  The present invention can be used for a radar that can electrically measure an azimuth angle and an elevation angle.

The block diagram which showed the structure of the radar antenna and radar apparatus which concern on the Example of this invention. Sectional drawing of the radar antenna which concerns on the Example. Explanatory drawing for demonstrating the effect | action of the radar antenna which concerns on the Example. The characteristic figure of a radar antenna. The characteristic figure of a radar antenna. The block diagram of the radar antenna which concerns on another Example.

Explanation of symbols

20, 30, 31, 32 ... array antennas P1, P2, P4, P5, P6 ... reference points H1, H2, H3 ... array antennas

Claims (4)

In a radar antenna in which at least three radiating elements are arranged in a z-axis direction that is one direction and arranged in a straight line, and spaced apart in the y-axis direction that is perpendicular to the z-axis,
2. A radar antenna according to claim 1, wherein the array antennas are arranged at different positions in the z-axis direction. 2. The distance in the y-axis direction between the array antennas of each set differs in a plurality of sets configured by selecting at least two arbitrary antennas from the plurality of array antennas. Radar antenna. In a plurality of sets configured by selecting at least two arbitrary antennas from the plurality of array antennas, a line segment connecting the phase centers of one set of array antennas and a phase center of another array antenna are connected. The radar antenna according to claim 1 or 2, wherein the line segment is not parallel to the line segment. In the radar apparatus using the radar antenna according to any one of claims 1 to 3,
When the direction perpendicular to the z-axis and the y-axis is the x-axis, the phase difference between the array antennas in a plurality of sets configured by selecting at least any two of the plurality of array antennas , Radio wave arrival direction φ, θ, where φ is the angle formed by the projection of the radio wave arrival direction on the xz plane and the x axis, θ is the angle formed by the projection of the radio wave arrival direction on the xy plane and the x axis, The radar apparatus is characterized in that the radio wave arrival directions φ and θ are obtained from the measured phase differences of each set using the relationship of

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