JP4874917B2 - Array antenna, antenna element arrangement method and beam forming method - Google Patents

Description

  The present invention relates to an array antenna used in radar and communication, and more particularly to an antenna element arrangement method and a beam forming method for reducing a side lobe level.

  As is well known, as a means for reducing the side lobe level of the antenna, there is a method of distributing the excitation distribution in the antenna aperture so as to correspond to a cosine distribution, a Taylor distribution, or the like. However, it is physically very difficult to realize such a distribution with an aperture antenna. In the case of an array antenna, there is a method of providing a non-uniform amplitude distribution on the aperture for the purpose of reducing side lobes, but the realization thereof is often mechanically limited.

  Furthermore, if the distance between the antenna elements is more than a certain value, a grating lobe is generated in the visible region. For this reason, the antenna element interval is generally shorter than a specified value. However, since the prescribed element spacing is determined by the wavelength, selection of an appropriate element spacing often limits the frequency. At this time, it is possible to reduce the level of the generated grating lobe by increasing the opening length of the antenna, but the side lobe level tends to be larger than the side lobe level of the antenna alone.

For the purpose of reducing side lobes, Patent Document 1 discloses an antenna having a configuration in which two sub-antennas having the same opening shape are arranged so as not to physically overlap each other.
JP-A-2005-303801

  As described above, with the conventional array antenna, it is difficult to reduce the side lobe level due to physical and mechanical restrictions.

  The present invention has been made in view of the above circumstances, and provides an array antenna that can reduce the side lobe level without being subjected to physical and mechanical restrictions, an antenna element arrangement method thereof, and a beam forming method thereof. The purpose is to provide.

  In order to solve the above problems, the array antennas according to the present invention have uniform amplitude distributions having the same phase with each other, the aperture shape and the distribution amplitude are equal, and are arranged shifted in the X-axis direction on the XY plane. A plurality of antenna elements are provided, and the amount of shift is smaller than the opening length of each antenna element.

  Also, the antenna element arrangement method of the array antenna according to the present invention has a uniform amplitude distribution with the same phase, the same aperture shape and distributed amplitude, and a plurality of antenna elements are shifted in the X-axis direction on the XY plane. The side lobe level is adjusted by adjusting the amount of deviation within a range smaller than the aperture length of each antenna element.

  Also, the beam forming method of the array antenna according to the present invention has uniform amplitude distributions in the same phase, the same aperture shape and distribution amplitude, and a plurality of antenna elements are shifted in the X-axis direction on the XY plane. It is characterized in that the beam is formed after adjusting the side lobe level by adjusting the amount of deviation within a range smaller than the aperture length of each antenna element.

  That is, in the present invention, an appropriate antenna element interval that can reduce the side lobe level is obtained from only the antenna aperture length and the amplitude distribution in the antenna aperture. The aperture length at this time is the straight line (hereinafter referred to as the adjustment target axis) where the plane including the main beam and the side lobe to be reduced (hereinafter referred to as the evaluation symmetry plane) and the plane where the antenna elements are distributed intersect. This is the length of the excitation distribution in the antenna element in the direction component, and the excitation distribution is the excitation distribution in the direction component of the adjustment target axis (the direction of the adjustment target axis obtained by integrating the excitation distribution orthogonal to the adjustment target axis. Distribution). This element arrangement method can be used in a wide band because it is hardly affected by frequency characteristics. Therefore, in the antenna directivity pattern in the use of radar and communication, it is possible to reduce the side lobe level and apply it in a wide band.

  Note that, as in the present invention, Patent Document 1 discloses a configuration in which two sub-antennas having the same aperture shape are arranged so as not to physically overlap each other. However, the antenna described in this document 1 is different from the configuration of the present invention in which the sub-antenna is displaced in a direction different from the opening surface and shifted in the same direction as the opening surface. Due to this difference in configuration, the antenna of Literature 1 is limited to only the first side lobe, which is different from the present invention in which the entire side lobe is suppressed.

  As described above, according to the present invention, it is possible to provide an array antenna, an antenna element arrangement method, and a beam forming method capable of reducing the side lobe level without being subjected to physical and mechanical restrictions. it can.

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

(First embodiment)
FIG. 1 is a block diagram showing a first embodiment of an array antenna according to the present invention. In FIG. 1, antenna elements 11 and 12 each have a uniform amplitude distribution of the same phase, the aperture shape and the distribution amplitude are equal, the aperture length in the X-axis direction is a _X , and the width is a _Y on the XY plane. It is. It is assumed that the reference phases of these two antenna elements 11 and 12 are the same phase, and both are shifted by a shift amount d _{Y in the} Y-axis direction.

At this time, the side lobe level in the directivity of the XZ cut surface can be adjusted by appropriately setting the displacement amount d _X of the arrangement of the two antennas 11 and 12 in the X-axis direction. In particular, the side lobe level can be reduced by making the shift amount d _X smaller than the opening length a _X. Furthermore, the arrangement as shown in FIG. 1 can reduce the side lobe level on the X-Z cut surface compared to the antenna alone, and the beam width is narrow, and the directivity level other than the main lobe is in any direction. It becomes possible to suppress the directivity level below the antenna alone, and the gain can be increased.

In the case of the antenna arrangement shown in FIG. 1, when the amount of deviation d _X in the X-axis direction of the two antennas 11 and 12 is set so that the expression (1) is satisfied, the side lobe level in the directivity of the XZ cut plane Can be reduced to -21 dB, which is 8 dB lower than the side lobe level of the antenna alone, which is -13 dB.
d _X = 0.27a _X (1)
FIG. 2 shows the maximum lobe level characteristics other than the main beam due to the change of the deviation amount dX. The horizontal axis indicates the amount of deviation d _X , and the unit is d _X = 16λ (λ is the wavelength), which is the same as a _X. The vertical axis represents the maximum lobe level other than the main beam with reference to the side lobe level (−13.3 dB) at the antenna element by normal uniform excitation. From this figure, it can be seen that the side lobe level can be reduced in the range of d _X <a _X.

As is apparent from the characteristics shown in FIG. 2, for example, when a _X = 16λ, the side lobe level can be adjusted from an arbitrary shift amount d _X. In FIG. 2, when the horizontal axis is expressed as the ratio of the element spacing to the aperture length (d _X / a _X ), the aperture length and the beam scanning direction are excluded except when the peak side lobe is out of the visible region. Regardless, it shows the same characteristics. From this, it can be seen that the side lobe level is minimized even on the curve of FIG. 2 when the value of the deviation d _x is set to 4.32λ by the equation (1).

  FIG. 3 shows the directivity pattern on the X-Z cut plane when the single antenna and two antennas are arranged at this time. FIG. 3 is a directivity pattern of the XZ cut surface under a certain condition. The horizontal axis indicates the orientation with the Z-axis set to 0 deg, and indicates 0 to 90 deg. Since the beam scanning direction is 0 deg, −90 to 0 deg is symmetric to 0 to 90 deg. The vertical axis indicates the directivity intensity, and the maximum value on the cut surface is 0 deg. As can be seen from FIG. 3, the arrangement as shown in FIG. 1 makes the beam width narrower than that of the antenna alone, the side lobe level is reduced, and the directivity level other than the beam lobe is independent of the antenna in any direction. The directivity level is kept below.

  The formula (1) is characterized in that there is no frequency characteristic in the formula. Therefore, by adopting such an antenna element arrangement method for an array antenna, the beam width becomes narrower and the side lobe level decreases at a wideband frequency than the antenna alone. In addition, any directivity level other than the main lobe can be suppressed to be equal to or less than the directivity level of the antenna alone, and the gain can be increased. This also enables the combined use with the pulse compression technique.

(Second Embodiment)
Next, a second embodiment of the array antenna according to the present invention will be described. Here, as in the first embodiment shown in FIG. 1, the two antenna elements 11 and 12 having the same aperture shape and distribution amplitude, the aperture length in the X-axis direction a _X , and the width a _Y are used. However, in this embodiment, it is assumed that the antenna elements 11 and 12 have a uniform amplitude distribution capable of aligning the wavefront with respect to the beam scanning direction.

The phase difference between the reference phases of the two antenna elements 11 and 12 is such that when beam scanning is performed on the XZ cut surface, the wavefront with respect to the beam scanning direction is calculated using the difference in antenna reference coordinates in the X-axis direction. Decide to align. At this time, the side lobe level in the directivity of the XZ cut surface can be adjusted by appropriately setting the displacement amount d _X of the arrangement of the two antenna elements 11 and 12 in the X-axis direction. In particular, the side lobe level can be reduced by making the shift amount d _X smaller than the opening length a _X. Also in this embodiment, the arrangement as shown in FIG. 1 can reduce the side lobe level on the X-Z cut surface compared to the antenna alone, and also the beam width is narrow, and the directivity other than the main lobe. The level can be suppressed to any antenna unidirectional level or less in any direction, and the gain can be increased.

In the case of the antenna arrangement with the above configuration, if the amount of deviation d _X in the X-axis direction of the two antenna elements 11 and 12 is set so that the expression (2) is established as in the first embodiment, the XZ cut surface It is possible to reduce the side lobe level in the directivity of -21 dB, which is 8 dB lower than the side lobe level −13 dB of the single antenna, regardless of the beam scanning direction.
d _X = 0.27a _X (2)
For example, when a _X = 16λ, the side lobe level can be adjusted from an arbitrary shift amount d _X as shown in the characteristic diagram of FIG. In this figure, when the horizontal axis is expressed as the ratio of the element interval to the aperture length (d _X / a _X ), it depends on the aperture length and the beam scanning direction except when the peak side lobe is out of the visible region. It shows the same characteristics. It can be seen that when the value of d _X is set to 4.32λ according to equation (2), the side lobe level is minimized even on the curve of FIG.

  The directivity pattern of the XZ cut surface at this time is as shown in FIG. As can be seen from FIG. 3, the beam forming method arranged as shown in FIG. 1 has a narrower beam width, a lower sidelobe level, and a directivity level other than the beam lobe in which direction. Is also suppressed below the antenna directivity level.

  As described in the first embodiment, the characteristic of the expression (2) that is the same as the expression (1) is that there is no frequency characteristic in the expression. Therefore, by forming the beams arranged in this way, the beam width becomes narrower than that of the antenna alone at a wide band frequency, the side lobe level is reduced, and the directivity levels other than the main lobe are directed to the antenna alone in any direction. Therefore, the gain can be increased. This also enables the combined use with the pulse compression technique.

(Third embodiment)
FIG. 4 is a block diagram showing a third embodiment of the array antenna according to the present invention. In FIG. 4, 21, 22, and 23 each have a uniform amplitude distribution capable of aligning the wavefront with respect to the beam scanning direction, the aperture shape and the distribution amplitude are equal, and in the X-axis direction on the XY plane. aperture length is three antenna elements of a _X. The phase difference between the reference phases of the antenna elements 21 to 23 aligns the wavefront with respect to the beam scanning direction by using the difference of the antenna reference coordinates in the X-axis direction when beam scanning is performed on the XZ cut surface. To be determined.

At this time, the side lobe level in the directivity of the XZ cut surface can be adjusted by appropriately setting the displacement amounts d _X1 and d _X2 of the arrangement of the three antenna elements 21 to 23 in the X-axis direction. In particular, the side lobe level can be reduced by making both or one of the shift amounts d _X1 and d _X2 smaller than a _X. Furthermore, the arrangement as shown in FIG. 4 can reduce the side lobe level on the X-Z cut surface compared to the antenna alone, the beam width is narrow, and the directivity level other than the main lobe is in any direction. It becomes possible to suppress the directivity level below the antenna alone, and the gain can be increased.

In the case of the antenna arrangement with the above configuration, if the deviation amounts d _X1 and d _X2 in the X-axis direction of the three antenna elements 21 to 23 are set so that the expression (3) is established, the side in the directivity of the XZ cut surface Regardless of the beam scanning direction, the lobe level can be reduced to −25 dB, which is 12 dB lower than the side lobe level of the antenna alone, −13 dB. Note that the values of the shift amounts d _X1 and d _X2 at this time may be reversed.
d _X1 = 0.19a _X , d _X2 = 0.29a _X2 (3)
Here, FIG. 5 shows the maximum lobe level characteristics other than the main beam due to the change of the shift amounts d _X1 and d _X2 . In FIG. 5, the horizontal axis represents d _X1 and the vertical axis represents d _X2 . The gray scale distribution is a distribution indicating a maximum lobe level other than the main beam with reference to a side lobe level (−13.3 dB) in a normal uniformly excited antenna element. Also from this figure, it can be seen that there are places where the side lobe level can be reduced in the range of d _X1 <a _X or d _X2 <a _X.

For example, when a _X = 16λ, the side lobe level can be adjusted from arbitrary d _X1 and d _X2 as shown in the characteristic diagram of FIG. In this figure, when the horizontal axis and the vertical axis are expressed as the ratio of the element spacing to the aperture length (d _X1 / a _X , d _X2 / a _X ), except when the peak side lobe deviates from the visible region, The same characteristics are exhibited regardless of the aperture length and the beam scanning direction. It can be seen that when the values of the deviations d _X1 and d _X2 are set as d _X1 = 3.04λ and d _X2 = 4.64λ by the equation (3), the side lobe level is minimized even in the characteristic diagram of FIG.

The directivity pattern of the XZ cut surface at this time is shown in FIG. FIG. 6 shows the directivity pattern on the X-Z cut surface when a _X = 16λ, d _X1 = 3.04λ, and d _X2 = 4.64λ in the array antenna shown in FIG. The horizontal axis indicates the orientation with the Z-axis set to 0 deg, and indicates 0 to 90 deg. Since the beam scanning direction is 0 deg, −90 to 0 deg is symmetric to 0 to 90 deg. The vertical axis indicates the directivity intensity, and the maximum value on the cut surface is 0 deg.

  As can be seen from FIG. 6, the beam forming method arranged as shown in FIG. 4 has a narrower beam width than the antenna alone, the side lobe level is reduced, and the directivity level other than the beam lobe is in any direction. Is also kept below the directivity level of the antenna alone.

  The formula (3) is also characterized in that there is no frequency characteristic in the formula. Therefore, beam formation with this array arrangement reduces the beam width compared to the antenna alone at a wideband frequency, reduces the side lobe level, and directivity levels other than the main lobe are below the antenna single directivity level in any direction. The gain can be increased. This also enables the combined use with the pulse compression technique.

(Fourth embodiment)
FIG. 7 is a block diagram showing a fourth embodiment of the array antenna according to the present invention. In FIG. 4, 31 and 32 have a uniform amplitude distribution capable of aligning the wavefront with respect to the beam scanning direction, are equal in aperture shape and distribution amplitude, are arranged on the XY plane, and are square diagonal lines. Is an antenna element whose length (opening length in the X-axis direction) is a _X. The phase difference between the reference phases of the two antenna elements 31 and 32 is that when performing beam scanning on the X-Z cut surface, the wavefront with respect to the beam scanning direction is calculated using the difference in antenna reference coordinates in the X-axis direction. Decide to align. At this time, the side lobe level in the directivity of the XZ cut surface can be adjusted by appropriately setting the displacement d _X of the arrangement of the two antenna elements 31 and 32 in the X-axis direction. In particular, the side lobe level can be reduced by making the shift amount d _X smaller than 0.44a. Further, the arrangement as shown in FIG. 7 can reduce the side lobe level on the X-Z cut surface compared to the antenna alone, the beam width is narrow, and the directivity level other than the main lobe is in any direction. It becomes possible to suppress the directivity level below the antenna alone.

In the case of the antenna arrangement with the above configuration, the excitation distribution of the adjustment target axis component (X-axis component) is a triangular distribution. In the case of an antenna element in which the opening length of the two antenna elements is a _X and the excitation distribution is a triangular distribution, if the deviation in the direction of the adjustment target axis of the two antennas is set so that Equation (4) holds, The side lobe level in the directivity can be reduced to -38 dB, which is 11 dB lower than the side lobe level of the antenna alone -27 dB. Therefore, in the antenna arrangement shown in FIG. 7, when the shift amount d _X is similarly set so that the expression (4) is established, the side lobe level in the directivity of the XZ cut surface is not dependent on the beam scanning direction. Thus, the side lobe level of the antenna alone can be reduced to -38 dB, which is 11 dB lower than -27 dB.
d _X = 0.115a _X (4)
Here, FIG. 8 shows the maximum lobe level characteristics other than the main beam due to the change of the shift amount d _X. In FIG. 8, the horizontal axis is d _X , and the vertical axis is the maximum lobe level other than the main beam with reference to the side lobe level (−26.6 dB) in a normal triangular distributed excitation antenna element. Also from this figure, it can be seen that the side lobe level can be reduced in the range of d _X <0.44a _X.

For example, when a _X = 16 · 2 ^1/2 λ = 22.6λ, as is apparent from the characteristic diagram shown in FIG. 8, the side lobe level can be adjusted from an arbitrary shift amount d _X. In this figure, when the horizontal axis is expressed as the ratio of the element interval to the aperture length (d _X / a _X ), it depends on the aperture length and the beam scanning direction except when the peak side lobe is out of the visible region. It shows the same characteristics. It can be seen that when the value of d _X is set to 2.6λ according to equation (4), the side lobe level is minimized even on the curve of FIG.

The directivity pattern of the XZ cut surface at this time is shown in FIG. FIG. 9 is a directivity pattern on the XZ cut surface when a _X = 16λ and d _X = 2.60λ in FIG. The horizontal axis indicates the orientation with the Z-axis set to 0 deg, and indicates 0 to 90 deg. Since the beam scanning direction is 0 deg, −90 to 0 deg is symmetric to 0 to 90 deg. The vertical axis indicates the directivity intensity, and the maximum value on the cut surface is 0 deg.

  As can be seen from FIG. 9, the beam forming method arranged as shown in FIG. 7 has a narrower beam width, a lower sidelobe level, and a directivity level other than the beam lobe in which direction. Is also suppressed below the antenna directivity level.

  The formula (4) is also characterized in that there is no frequency characteristic in the formula. Therefore, beam formation with this array arrangement reduces the beam width compared to the antenna alone at a wideband frequency, reduces the side lobe level, and directivity levels other than the main lobe are below the antenna single directivity level in any direction. It becomes possible to suppress to. This also enables the combined use with the pulse compression technique.

  Note that the present invention is not limited to the above-described embodiment as it is. For example, the present invention may be applied to other excitation distributions or the number of antenna elements. In the implementation stage, the constituent elements may be modified and embodied without departing from the scope of the invention. it can. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows 1st, 2nd embodiment of the array antenna which concerns on this invention. Characteristic diagram showing the maximum lobe level characteristics other than the main beam due to a change in the shift amount d _X of the array antenna shown in FIG. FIG. 3 is a pattern waveform diagram showing the directivity pattern on the XZ cut surface in comparison with the case of a single antenna for the two antenna elements shown in FIG. 1. The block diagram which shows 3rd Embodiment of the array antenna which concerns on this invention. FIG. 5 is a characteristic diagram showing a maximum lobe level characteristic other than the main beam due to changes in the shift amounts d _X1 and d _X2 of the array antenna shown in FIG. FIG. 5 is a pattern waveform diagram showing the directivity pattern on the XZ cut surface in comparison with the case of the single antenna for the three antenna elements shown in FIG. 4. The block diagram which shows 4th Embodiment of the array antenna which concerns on this invention. FIG. 8 is a characteristic diagram showing a maximum lobe level characteristic other than the main beam due to a change in the shift amount d _X of the array antenna shown in FIG. FIG. 8 is a pattern waveform diagram showing the directivity pattern in the XZ cut plane in comparison with the case of a single antenna for the two antenna elements shown in FIG. 7.

Explanation of symbols

11, 12, 21, 22, 23, 31, 32 ... antenna element, a _X ... opening length, a _Y ... width, d _X , d _X1 , d _X2 ... X-axis direction deviation, d _Y ... Y-axis direction deviation amount.

Claims (8)

They have a uniform amplitude distribution in which the wavefronts of the entire aperture plane are in phase with each other and have uniform amplitude intensity , the aperture shape and the amplitude of the distribution are equal, and are shifted in the X-axis direction on the XY plane. comprising a plurality of antenna elements, the array characterized by having a uniform amplitude distribution the deviation amount is rather smaller than the aperture length of each antenna element, said plurality of antenna elements aligned wavefront for each beam scanning direction antenna. The phase difference between the reference phases of the plurality of antenna elements is such that when beam scanning is performed on the X-Z cut plane, the wavefront is aligned with respect to the beam scanning direction by using the difference in antenna reference coordinates in the X-axis direction. The array antenna according to claim 1, wherein the array antenna is determined as follows.   2. The array antenna according to claim 1, wherein the plurality of antenna elements have a square shape on an XY plane, and a length of a diagonal line is set as the opening length. The wave front of the entire aperture plane has the same amplitude distribution with the same amplitude, the aperture shape and the amplitude of the distribution are equal, and a plurality of antenna elements are arranged in the X-axis direction on the XY plane. Uniform amplitude distribution in which the wavefronts are aligned with respect to the beam scanning direction in the plurality of antenna elements by adjusting the side lobe level by adjusting the amount of deviation within a range smaller than the aperture length of each antenna element. antenna element arrangement method of the array antenna, characterized in that to have. The phase difference between the reference phases of the plurality of antenna elements is such that when beam scanning is performed on the X-Z cut surface, the wavefront is aligned with respect to the beam scanning direction by using the difference in antenna reference coordinates in the X-axis direction. The antenna element arrangement method for an array antenna according to claim 4, wherein the antenna element is determined as follows. 5. The array element arrangement method for an array antenna according to claim 4, wherein the plurality of antenna elements have a square shape on an XY plane, and a length of a diagonal line is set as the opening length. The wave front of the entire aperture plane has the same amplitude distribution with the same amplitude, the aperture shape and the amplitude of the distribution are equal, and a plurality of antenna elements are arranged in the X-axis direction on the XY plane. A beam is formed after adjusting the side lobe level by adjusting the amount of shift within a range smaller than the aperture length of each antenna element, and each of the antenna elements is respectively scanned with respect to the beam scanning direction. A beam forming method for an array antenna, characterized by having a uniform amplitude distribution for aligning wave fronts . The phase difference between the reference phases of the plurality of antenna elements is such that when beam scanning is performed on the X-Z cut surface, the wavefront is aligned with respect to the beam scanning direction by using the difference in antenna reference coordinates in the X-axis direction. 8. The array antenna beam forming method according to claim 7, wherein:

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