JP2005303801A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device capable of reducing a side lobe. <P>SOLUTION: An antenna device is configured by disposing two sub antennas 10A, 10B having the same aperture shape so as not to physically overlap with each other. The two sub antennas 10A, 10B are then disposed while deviating positions of their phase centers parallel to a plane (xy-plane) including a side lobe that is generated by the two sub antennas 10A, 10B and desired to suppress, and orthogonally to a direction (y-direction) of arraying the two sub antennas 10A, 10B. Namely, the sub antennas 10A, 10B are disposed while deviating the positions of their phase centers in an x-axis direction just for a length of a deviation amount δx. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an antenna device capable of suppressing side lobes of a directivity pattern of the antenna device.

  In an automotive radar for the purpose of forward monitoring, etc., it is necessary to supplement an object in a relatively wide angle range of 10 degrees or more in a horizontal plane. As a method of an antenna device that achieves this, a monopulse method that detects a difference in phase and amplitude of a plurality of antennas, a scanning method that electronically or mechanically scans the antenna directivity, and the like have been proposed and used. . Of these, except for the method of changing the direction of the directional beam by shaking the antenna itself as in mechanical scanning, using multiple (array) antennas instead of a single (array) antenna, In particular, there are methods for detecting phase and amplitude information (monopulse method) and scanning directivity (electronic scan method). In these cases, a plurality of (array) antennas (referred to as sub (array) antennas) used have a wide-angle directional characteristic in the plane in order to enhance detection capability in a wide range in the horizontal plane. Therefore, the aperture length of the antenna is generally set to approximately two wavelengths or less.

  Here, a method using an array antenna using a microstrip antenna element is shown as a conventional example. The configuration of the array antenna is shown in FIGS. 7 (a) and 7 (b). 7A and 7B, the square elements indicate microstrip antenna elements, and in this example, they are arranged in a direction inclined at an angle of 45 ° on the paper surface. This is for the purpose of generating polarization polarized in an oblique 45 ° direction, assuming use with a millimeter wave radar or the like. A solid line connected to each microstrip antenna element represents a microstrip line that is a feed line. The difference between the configuration of FIG. 7 (a) and the configuration of FIG. 7 (b) is classified according to the direction of the branching / combining section of the feed line and the excitation phase of each antenna element. It is classified by the second classification characters 1 and 2. However, in either case of FIG. 7 (a) or FIG. 7 (b), each group is finally synthesized in phase. That is, in FIG. 7 (a), A1 and B1 are connected in the same phase, and in FIG. 7 (b), A1 and A2 are connected in the opposite phase. Further, among the element arrangements, the arrangement in the vertical direction toward the paper surface is a straight line in which the centers of all the antenna elements are indicated by a one-dot chain line in the figure in both cases of FIG. 7 (a) and FIG. 7 (b). Is arranged.

  In the element arrangement of 2 columns × 12 rows as shown in FIG. 7, assuming that the wavelength of the frequency to be used is λ, for example, the dielectric constant of the dielectric substrate used for the microstrip antenna is 2.2, the substrate thickness is 0.025λ, and the horizontal direction When the element spacing of dx is 0.73λ, the FWHM of directivity is calculated to be approximately 37 degrees and the first sidelobe level is approximately -13 dB in the horizontal plane of the infinite ground plate (including the horizontal direction of the paper). The When a microstrip antenna element is used as the antenna element and the above parameters are used, the opening length Dx in the left-right direction is equivalent to approximately 1.5λ (= dx × 2).

As related techniques, there are the following documents (see Patent Document 1).
JP-A-6-61737

  However, in the conventional antenna device, since the number of elements in the horizontal plane is small, side lobes by excitation amplitude control are difficult, and all the vertical arrangements of the antenna elements are linearly arranged. The first side lobe level in the horizontal plane is a relatively large value of about -13 dB, which is likely to cause a false detection in applications such as automobile radar.

  The present invention has been made in view of the above facts, and an object thereof is to provide an antenna device capable of reducing side lobes.

  In order to achieve the above object, an invention according to claim 1 is an antenna device configured by a divided sub-antenna obtained by dividing an antenna having an arbitrary aperture shape into an arbitrary plurality of antennas, wherein The sub-antennas of the first classification group and the second classification group are classified into groups, the axis connecting the phase center to the main lobe direction of each of the sub-antennas, the phase center and the side lobe direction to be suppressed In the plane including the axis connecting the main lobe direction, the divided sub-antennas are combined in phase with each other in a direction perpendicular to the axis connecting the main lobe direction.

  That is, the antenna device of the present invention is configured by a divided sub-antenna obtained by dividing an antenna having an arbitrary aperture shape into an arbitrary plurality. For example, the antenna has a divided sub-antenna obtained by dividing an antenna having a predetermined aperture shape into a plurality of pieces.

  Here, when the antenna device is configured by arranging two sub-antennas, side lobes that adversely affect signals to be transmitted and received are generated.

  Therefore, in the present invention, the sub antennas of the first classification group and the second classification group are divided into axes connecting the phase center and the main lobe direction of each of the sub antennas, and the side lobe direction to be suppressed with the phase center. Are shifted in a direction perpendicular to the axis connecting the main lobe direction in a plane including the axis connecting the main lobe direction.

  As described above, the sub-antennas of the first classification group and the second classification group are divided into the axis connecting the phase center and the main lobe direction of each sub-antenna, and the phase center and the side lobe direction to be suppressed. In the plane including the connecting axis, if the arrangement is shifted in a direction orthogonal to the axis connecting the main lobe direction, an array factor for reducing the side lobe is generated. Therefore, side lobes can be reduced.

  Here, the antenna may be a planar array antenna composed of element antennas, and the planar array antenna may be a microstrip array antenna.

  Further, the opening length in the direction of deviation of the phase center of the sub-antennas of the two classification groups may be approximately twice or less the wavelength of the radio wave transmitted and received by the sub-antenna. Thereby, the array factor which reduces a side lobe can be generated reliably.

  Furthermore, the amount of shift between the phase centers of the sub-antennas of the two classification groups may be set to about three times or less the wavelength of the radio wave transmitted and received by the sub-anna. Thereby, the array factor which reduces a side lobe can be generated reliably.

  As described above, according to the present invention, the sub-antennas of the first classification group and the second classification group are divided into axes connecting the phase center of each of the sub-antennas to the main lobe direction, and the phase center. In the plane including the axis connecting the side lobe direction to be suppressed, and shifted in a direction perpendicular to the axis connecting the main lobe direction, an array factor for reducing the side lobe is generated. The effect that side lobes can be reduced is obtained.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the antenna device according to the present embodiment is an antenna device including divided sub-antennas obtained by dividing an antenna having an arbitrary aperture shape into an arbitrary plurality (two in the present embodiment). The divided sub-antennas are classified into two groups, and a first classification group sub-antenna 10A and a second classification group sub-antenna 10B are arranged.

  In the present embodiment, the two sub-antennas 10A and 10B are arranged so as not to physically overlap each other.

  In each of the two sub antennas 10A and 10B, the microstrip antenna elements 12 are arranged in two columns and six rows. It is not limited to 2 columns and 6 rows. Each of the two sub-antennas 10A and 10B can configure the microstrip antenna element 12 in n columns and m rows. Note that n and m are natural numbers.

  The microstrip antenna element 12 is disposed in a direction inclined by 45 ° from the x axis (y axis) in the xy plane. This is for the purpose of generating polarized waves inclined in an oblique 45 ° direction, assuming use in millimeter wave radars and the like.

The aperture length L in the x direction of each of the two array antennas 10A and 10B is approximately twice or less than the radio wave transmitted and received by the sub antennas 10A and 10B. In this embodiment, 1.46 wavelengths (1.46λ), that is, 2d _x . Here, d _x is the interval between the two rows of microstrip antenna elements 12 constituting each of the sub-antennas 10A and 10B. Specifically, d _x is 0.73λ.

  A solid line 14 connected to each microstrip antenna element 12 represents a microstrip line that is a feed line. Usually, the branching / combining section indicated by D section uses a technique of changing the line width to perform impedance matching, but since it is not the essence of the present invention, it is simplified and shown with the same line width in FIG.

  In addition, the line lengths from the input / output to the microstrip antenna element 12 branched from the top and bottom of the paper to the first input / output (line lengths up to A1 and B1) are set to be equal, and the first input / output The line length of the output antenna element and the second input / output antenna element (line length between A1 and A2) is set to an integral multiple of the propagation wavelength of the line (usually 1 time), that is, in phase. Has been.

  In the antenna device according to the present embodiment, signals are branched / combined in the same phase in the corresponding microstrip antenna elements 12 of the two sub-antennas 10A and 10B.

  That is, when receiving signals, the two signals received by the corresponding microstrip antenna elements 12 of the two sub-antennas are combined in the same phase. When transmitting, the signal branched in the same phase is transmitted from the corresponding microstrip antenna element 12 of each of the two sub-antennas.

  Thereby, the antenna apparatus of this Embodiment operate | moves as an antenna which has the maximum directivity in a bore sight (z surface direction).

  In the present embodiment, the two sub-antennas 10A and 10B are each connected to an axis connecting the phase center of each sub-antenna to the main lobe direction, and an axis connecting the phase center and the side lobe direction to be suppressed. Are shifted in a direction orthogonal to the axis connecting the main lobe direction. That is, a direction (x direction) that is parallel to a plane (xy plane) that is generated by the two sub antennas 10A and 10B and includes a side lobe to be suppressed and that is orthogonal to the arrangement direction (y direction) of the two sub antennas 10A and 10B. ). The positions of the phase centers of the sub-antennas 10A and 10B are shifted in the x-axis direction by a length corresponding to the shift amount δx. Here, the position of the phase center of each of the sub-antennas 10A and 10B is the physical center position of each antenna opening. In the present embodiment, the center position of each column of antenna elements constituting each of sub antennas 10A and 10B is the phase center.

  In this way, the phase center positions of the two sub-antennas 10A and 10B are parallel to the xy plane generated by the two sub-antennas 10A and 10B and including the side lobes to be suppressed, and the two sub-antennas 10A and 10B. The shift amount is shifted by δx in the x direction perpendicular to the arrangement direction (y direction). Therefore, an array factor for reducing the side lobe is generated. Therefore, side lobes can be reduced. That is, for example, by shifting a sub-antenna whose aperture length L is 2.0 wavelengths or less by approximately 0.75 wavelengths or less, an array factor smaller than 1 is generated in the wide angle direction (approximately 45 degrees or more), and the side lobes in the wide angle direction are suppressed. can do.

  Hereinafter, this will be described in more detail. The sidelobe suppression effect is closely related to the directivity (amplitude / phase distribution of the aperture) of the sub-antennas 10A and 10B and the array factor. For example, as shown in FIGS. 7 (a) and 7 (b), an antenna device having an aperture length of about two wavelengths or less and excited with an equal phase and an equal amplitude is indicated by a dotted line in FIG. Thus, the largest side lobe exists in a wider angle range than 45 °.

  On the other hand, in an antenna device configured by arranging two sub-antennas, the combined directivity of the two sub-antennas is a product of the directivity of each sub-array of the two sub-antennas and the array factor.

  Therefore, the side lobe can be suppressed if the array factor becomes a value smaller than 1 in a wide angle range of 45 °, and the smaller the value, the greater the suppression effect.

  FIG. 3 shows the calculated values of the array factor when the deviation δx is variously changed. In any case, the relative amplitude is smaller than 0, that is, the array factor is smaller than 1 when the deviation amount δx is within the range of 0.75 wavelength or less.

Therefore, it can be seen that a large suppression effect can be obtained by setting within a predetermined range, for example, 0.35λ to 0.75λ. In particular, in FIG. 2, as a value within the predetermined range, a solid line indicates a result in which the shift amount δx is d _x / 2, that is, (0.73 / 2) · λ. As shown in FIG. 2, it can be seen that the side lobe level is suppressed by about 2 to 8 dB. In detail, as shown in Table 1 below, there is an improvement.

Next, a second embodiment of the present invention will be described in detail.
In the present embodiment, as shown in FIG. 4, the connection method of the feeder line 14 is the same as that of the first embodiment described above except that the connection method is point-symmetric between the two sub-antennas 10A and 10A ′. It is the same.
As in the present embodiment, for example, by shifting the sub-antenna 10A (A group) to the left side without increasing the size of the entire antenna including the feed line 14, the first embodiment described above Similar effects can be obtained.

  In each of the above embodiments, an example in which the deviation amount δx is (0.73 / 2) · λ is shown. However, the present invention is not limited to this, and as shown in FIG. When δx is a value within the range of 0.75 wavelength or less, the relative amplitude can be smaller than 0, that is, the array factor can be smaller than 1, and the side lobe can be reduced.

  Next, a third embodiment of the present invention will be described in detail.

  In the present embodiment, as shown in FIG. 5, the number of divisions of the divided sub-array antenna is 4 and the above-described part is added except that a part for further combining / branching the A group, the B group, and the combined output branch input is added. This is the same as in the first embodiment. According to the present embodiment, since the number of series-fed elements is reduced, the amount of gain deterioration due to frequency shift is reduced, that is, the gain characteristic is flat over a wider band, and the same as in the first embodiment described above. The effect of can be obtained.

  Next, a fourth embodiment of the present invention will be described in detail.

  As shown in FIG. 6, the present embodiment is the same as the first embodiment described above except that the direction in which the divided sub-array antenna is shifted is the y-axis direction. According to the present embodiment, the same effects as those of the first embodiment described above can be obtained in the y-axis plane.

It is a figure which shows the structure of the antenna apparatus in 1st Embodiment. It is the figure which showed the directivity pattern in the antenna apparatus of the structure similar to the structure of FIG. It is the figure which showed the calculated value of the array factor when changing deviation | shift amount variously. It is a figure which shows the structure of the antenna apparatus in 2nd Embodiment. It is a figure which shows the structure of the antenna apparatus in 3rd Embodiment. It is a figure which shows the structure of the antenna apparatus in 4th Embodiment. It is a figure which shows the structure of the antenna apparatus in a prior art.

Explanation of symbols

10A, 10B Subantenna 12 Microstrip antenna element 14 Feed line

Claims (5)

An antenna device composed of divided sub-antennas obtained by dividing an antenna having an arbitrary aperture shape into an arbitrary plurality,
Classifying the divided sub-antennas into two groups;
An axis connecting the sub-antennas of the first classification group and the second classification group from the phase center of each of the sub-antennas to the main lobe direction, and an axis connecting the phase center and the side lobe direction to be suppressed; In a plane that includes the main lobe direction and shifted in a direction perpendicular to the axis connecting the main lobe direction,
The divided sub-antennas are combined in phase,
An antenna device characterized by that.   2. The antenna device according to claim 1, wherein the antenna is a planar array antenna composed of element antennas.   3. The antenna device according to claim 1, wherein the planar array antenna is a microstrip array antenna.   The aperture length in the direction of deviation of the phase center of the sub-antennas of the two classification groups is approximately twice or less the wavelength of the radio wave transmitted and received by the sub-antenna. The antenna device according to claim 1.   5. The shift amount of the phase center of the sub antennas of the two classification groups is approximately three times or less of a wavelength of a radio wave transmitted / received by the sub-anna. 5. The antenna device according to item 1.

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