JP2022141559A - radial array antenna - Google Patents

Abstract

To provide a radial array antenna device that is a high-gain antenna, easy to manufacture and handle, and beautiful in shape, in which the radiating elements are arranged in a linear array, the strength of the excitation is set to a predetermined value to make it a one-dimensional array, and seven or more of these one-dimensional arrays are arranged in a radial pattern.SOLUTION: In a 2-dimensional array antenna, the substrates 4 of a one-dimensional array antenna are arranged radially to form an aperture plane. Seven or more of these one-dimensional array antennas are arranged to stabilize the radiation characteristics of the antenna. The excitation strength of the one-dimensional array is determined by multiplying the excitation strength distribution function of the aperture plane antenna, which gives the desired radiation characteristics, by a function that is smaller at the center of the aperture as a weight function.SELECTED DRAWING: Figure 6

Description

Article 30, Paragraph 2 of the Patent Act has been applied for. IEEE AP-S/URSI International Symposium on Antennas and Propagation and North American Radio Science Meeting 2020 Archive Papers

The present invention relates to an antenna device which is a high-gain antenna, is easy to manufacture, is easy to handle, and has a beautiful shape.

JP 2015-76703 Antenna device and antenna excitation method

Patent application 2017-103804 array antenna device

S. Silver (Ed.), "Microwave antenna theory and design", Dover Publ. Inc. , New York, 1965.

T. Mizusawa, "Radiation of a mirror-modified Cassegrain antenna. Effect of sub-reflector radiation pattern on characteristics," IEICE Theory (B), vol. J52-B, no. 2, pp. 78-85, Feb. 1969.

Susumu Kato, Hiroyuki Hashiguchi, Toshitaka Tsuda, Mamoru Yamamoto, “MU Radar”, The Institute of Electronics, Information and Communication Engineers, Communication Society Magazine, vol. 9, no. 4, pp. 236-242, 2016.

A high-gain antenna has a two-dimensional aperture, and its representative is the parabolic antenna shown in FIG. The radiation characteristics are determined by the distribution of excitation intensity (electric field intensity) on the aperture plane, as shown in Non-Patent Document 1.

Since the Cassegrain and Gregorian antennas have two reflectors such as the main reflector 1 and the sub-reflector 2, the excitation distribution on the aperture plane can be designed by correcting both reflectors. This is described in Non-Patent Document 2 as a specular correction technique. For example, if a uniform distribution is used, the gain is high, but the sidelobes are high, resulting in susceptibility to interference. Also, if the distribution is such that the excitation is weakened at the aperture end, the side lobe can be reduced although the gain is reduced.

However, the main reflector and the sub-reflector must be designed in a special shape, which is difficult to manufacture. Another drawback is that it is difficult to change once it is made. Since the sub-reflector blocks radio waves from the main reflector (blocking effect), the correction effect deteriorates. In addition, since the main reflector is rounded and the whole including the sub-reflector support column 3 is thick, a special support structure is required for installation, which is difficult to handle.

Another way to achieve a two-dimensional aperture is to line up a linear array of small radiating elements in one dimension. Conventionally, as shown in FIG. 2, there is an example in which they are arranged in a grid pattern or a modified rhombus. In this case, it is practically impossible to obtain the desired radiation characteristics by varying the excitation strength [3].

However, for the one-dimensional array antenna shown in FIG. 3, as shown in Japanese Patent Laid-Open No. 2002-100000, the excitation intensity is made to have a desired distribution. Radiating elements 5 are arranged on a substrate 4 of the array antenna with appropriate distances therebetween.

FIG. 4 shows a method of designing the excitation distribution in a one-dimensional array antenna. The horizontal axis 6 of the graph represents coordinates on the array antenna. A vertical axis 8 of the graph represents the excitation intensity of the element 5 . The elements are arranged between the ends 9 of the one-dimensional array antenna and each element has an excitation strength 8 specific to it. For example, a distribution 10 that is uniform between both ends 9 is called a high-gain excitation distribution, which has high gain but high sidelobes. On the other hand, distribution 11 with shoulders dropped at both ends 9 is a low side lobe type excitation distribution.

A radiation pattern of this one-dimensional array antenna is calculated. A half-wave dipole or the like is actually used as the radiation element. In this calculation, however, we assume isotropy for the sake of simplicity and perspective. That is, an arrangement pattern is obtained. Even if the radiation pattern of the radiating elements alone is not isotropic, the array pattern may be multiplied by the element pattern. Also, the same analysis method can be applied even if the array antenna has a two-dimensional or curved shape.

An example of calculation is the case where the element spacing is a constant value λ/2 (λ: wavelength), 17 elements are arranged, and the edge level is -2 dB. The resulting radiation pattern is shown in FIG. The horizontal axis 12 of the graph represents the angle from the front of the antenna, and the vertical axis 13 of the graph represents the relative value (decibel) of the radiation level. The main lobe 15 is directed in the antenna front direction 14, and the side lobe 16 is as low as about -15 dB. However, since it is a one-dimensional array antenna, it has uniform radiation characteristics around the axis (x direction).

It is also possible to make the excitation intensity or excitation density of a one-dimensional array equivalent by adjusting the spacing between groups of elements with the same input level instead of the element input level (Patent Document 2). In FIG. 5, the radiation patterns are overlaid in the case where the element input level and the element spacing are respectively adjusted as the excitation density, but no difference is recognized.

I would like to construct a two-dimensional array antenna by arranging this one-dimensional array on a plane or a curved surface. However, until now there has been no design theory for changing the excitation strength.
In addition, the number of radial arrays required to make it two-dimensional was also unknown.

In order to eliminate the above-described problems of the prior art, the one-dimensional array antennas are arranged radially to form a two-dimensional array antenna. As shown in FIG. 6, the radiating elements 5 are arranged on the substrate 4 to form a one-dimensional array, and in this case, six elements are arranged radially. A radial array antenna aperture 29 is formed as a whole, and its radiation direction is the z-axis direction of the front face 17 . As described above, the radial array antenna has a beautiful circular outer shape and a flat plate structure, which makes it easy to install the antenna.

Here, if a large number of radial one-dimensional arrays are used, it is likely that characteristics close to those of a continuous parabolic antenna can be obtained. In practice, however, it is desirable to reduce the number of one-dimensional arrays as much as possible, so the problem is how much the number of arrays can be reduced to ensure stable use as an antenna.

In addition, in the radial array antenna, it was not known how the excitation distribution should be set at the stage of the one-dimensional array antenna in order to obtain the same effect as the reflecting mirror surface modification technique used in the Cassegrain antenna of FIG.

In order to eliminate the problems of the prior art described above, the radiation characteristics of a two-dimensional radial array antenna were calculated. As a one-dimensional array, it is half of the example in FIG. 5, that is, the element spacing is a constant value λ/2 (λ: wavelength), 9 elements are arranged, and the edge level is −2 dB. As an example of the results, FIG. 7 shows a radiation pattern when the angle ΔΨ between the one-dimensional arrays is 60 degrees, that is, when there are six one-dimensional arrays. From this figure, the main lobe 15 can be confirmed in the front direction, and the side lobe 16, which is connected to the main lobe, can be read as about -15 dB.

A sidelobe 16' is the first sidelobe when the excitation intensity of the one-dimensional array antenna is replaced by the element spacing (Patent Document 2), and is almost the same as the level 16 of a normal amplitude control array.

Next, the number of one-dimensional arrays constituting the radial array antenna was increased, and changes in antenna characteristics were observed. The results are shown in FIG. The graph horizontal axis 18 represents the angle between the one-dimensional arrays, and the graph horizontal axis 19 represents the number of one-dimensional arrays. A vertical axis 20 of the graph represents the first sidelobe level in relative values (decibels). A change 21 in the first side lobe level in a normal amplitude control array becomes a stable level 22 regardless of the number of lines if the number is 23 or more.

21' shows the change in the first sidelobe level when the excitation intensity of the one-dimensional array antenna is replaced by the element spacing, which is almost the same as 21. FIG. As a result, it can be seen that the radiation pattern is stabilized by arranging seven or more one-dimensional arrays.

In FIG. 7, it was found that the reason why the main lobe and the first side lobe are connected is that the excitation is concentrated in the central part of the radial array antenna. Therefore, in order to convert the excitation distribution on the aperture plane corresponding to the desired radiation characteristics to the excitation distribution of the one-dimensional array, the following theoretical formula is derived.

The radiation pattern F(θ, φ) of the radio waves radiated in the (θ, φ) direction from each point (ρ, ψ) of the aperture antenna is given by the following equation, as shown in Non-Patent Document 1, etc. expressed.
F(θ,φ)=∫∫f(ρ,ψ)exp{(jkρsinθcos(φ−ψ)}ρdρdψ
where ρ and ψ are the radius and angle of the point on the aperture, ie the excitation point. k is the wavenumber and j is the imaginary unit.
In order to achieve desired radiation characteristics F(θ, φ), a distribution function f(ρ, ψ) is obtained in Non-Patent Document 1 and the like.

In the case of radial array antennas, the excitation points exist as radiating elements only on the one-dimensional array. Therefore, the element density increases in inverse proportion to the distance from the center of the aperture. avoid this. To obtain the desired excitation distribution function f(.rho., .psi.) on the aperture, the distribution on the one-dimensional array must be multiplied by the radius .rho.

A distribution determination method on a one-dimensional array is shown in FIG. In an aperture array antenna, 24 is the excitation strength distribution that gives the desired radiation characteristics. The excitation distribution 25 to be applied to each one-dimensional array is the result of multiplying by the radius as a weighting function. The effect of this theory is confirmed by simulation calculation. Here, the distribution function 24 is assumed to be f(ρ, ψ) of a low sidelobe type (low edge level) with a remarkable effect.

Calculation results of the above theory are shown in FIG. Excessive excitation concentration near the center is removed here, and the null 26 of the radiation pattern corresponding to the aperture antenna clearly appears. The main lobe is also clear.

As the above weighting function, the radius ρ is the optimum one according to theory. However, in practice, other functions can be used that are smaller in the center (area where ρ is small). For example, ρ ² or ρ ^0.5 may be used.

The above theory also fits the equivalent excitation density of a radial array antenna to the distribution function 24 on the aperture. Therefore, it can also be applied to a spacing control array (the excitation density is adjusted by the element spacing).

In fact, the case of the spacing control array is also calculated and shown in FIG. The null in this case is 26', much the same as the null 26 for the amplitude control array.

The radial array antenna described above can be designed to have desired radiation characteristics. Moreover, compared with parabolic antennas such as the Cassegrain type, there is no sub-reflector blocking, so there is an advantage that the correction effect can be remarkable. The weight can also be reduced. Furthermore, if the beam is oscillated by adding a phase change function to the radiating element, the installation adjustment of the antenna can be easily performed, and a highly functional wireless communication system can be realized.

Compared to grid-type array antennas, they are circular and beautiful, and their radiation characteristics are excellent in symmetry. When the excitation distribution of the aperture plane is designed in a desired shape, the radiation element in the central part is excited weakly, so there is an advantage that the coupling between the elements, which is a problem in the array antenna, can be reduced.

The principle of the present invention is to match the equivalent excitation density of a radial array antenna to the distribution function 24 over the aperture. Therefore, the number of one-dimensional arrays may vary with radius. For example, in the case of the double radial array antenna shown in FIG. 11, the one-dimensional array has 8 lines inside the boundary 29' and 16 lines outside it. In this case, if the excitation of the outer one-dimensional array is half that of the inner one, the equivalent excitation at the aperture plane will be equal. However, the radiating element is omitted in this figure to avoid complication.

When the array substrates 4 and 4' are exposed in FIGS. 6 and 11, the external appearance of the present invention becomes a shape in which thin plates intersect, giving an impression completely different from that of a parabola. Also, if the whole is covered, it looks like a round disk, so it can be made inconspicuous.

Application example 1

FIG. 12 shows an example of application to a base station in a 5G or local 5G system as an example of application implementation of the present invention. In a base station building or structure 27, a radial array antenna 29 is installed on a surface 28 on which antennas are mounted. Since the antenna 29 has a planar structure, it is easy to install and has a novel appearance.

The radio-radiated service area is inside the boundary 30 of the antenna radiation beam. However, within the cross-sectional area 31 of the radiation beam, the irradiation level is not constant and gradually falls off, so the boundary 30 is determined by the electric field strength required by the communication system. Radial array antennas are easy to install and test because the direction of the radiation beam can be changed by adjusting the phase of the elements. In addition, dynamic phase changes have the advantage of being able to adjust the service area to match communication demands.

Application example 2

FIG. 13 shows a second example of application of the present invention to an antenna mounted on a satellite. In a satellite structure 32, a radial array antenna 29 is installed on a surface 33 on which the satellite antenna is mounted. Since the antenna 29 has a planar structure, it fits well on the plane 33 and is light, so it is most suitable as an antenna mounted on a satellite. The solar array paddle 34 is out of the irradiation range of the antenna beam due to the rotary joint 35 .

As an example of a conventional aperture antenna, the configuration of a Cassegrain parabolic antenna is shown. The configuration of a grid array antenna is shown as an example of a conventional aperture antenna. A one-dimensional array antenna is arranged vertically and horizontally. The configuration of a one-dimensional array antenna is shown as an example of a conventional antenna. An example of excitation intensity distribution in a conventional one-dimensional array antenna is shown. A high gain type and a low side lobe type are shown. 1 shows a radiation pattern realized in a conventional one-dimensional array antenna; An embodiment of this patent shows the configuration of a two-dimensional array antenna in which one-dimensional arrays are arranged radially. 1 is a description of one problem to be solved by the invention, showing a radiation pattern of a radial two-dimensional array antenna; The level change of the first side lobe of the radiation pattern is shown when the number of one-dimensional arrays in the radial array antenna is changed. A second problem to be solved by the invention, that is, a method for obtaining a desired effective excitation distribution by preventing deterioration of the radiation pattern in a radial array antenna, will be described. The effect of the present invention is shown by the radiation pattern. 1 shows the configuration of a double radial array antenna as one embodiment of the present invention. As a first example of application implementation of the present invention, an example of application to a base station in a 5G or local 5G system is shown. As a second example of application implementation of the present invention, an example of application to an antenna mounted on a satellite will be shown.

1 Main reflector 2 Sub-reflector 3 Sub-reflector support column 4 Array antenna substrate 5 Radiating element 6 The horizontal axis of the graph represents the coordinates on the array antenna 7 The vertical axis of the graph represents the excitation strength of the element 8 Each Element excitation strength 9 End of one-dimensional array antenna 10 High-gain type excitation distribution 11 Low sidelobe type excitation distribution 12 The horizontal axis of the graph represents the angle from the front of the antenna 13 The vertical axis of the graph represents the relative radiation level 14 Front direction of antenna 15 Main lobe 16 First side lobe 17 Front direction of radial array antenna 16' First side lobe 18 when excitation intensity of one-dimensional array is replaced by element spacing Graph horizontal axis , where the horizontal axis of the graph represents the angle between the one-dimensional arrays forming the radial array antenna, the vertical axis of the graph represents the number of the one-dimensional arrays forming the radial array antenna, and the first side lobe level is the relative value. 21 Change in first sidelobe level 21' Change in first sidelobe level when the excitation intensity of the one-dimensional array is replaced by element spacing 22 Stable level regardless of the number of one-dimensional arrays 23 The minimum number of lines that provides a stable level regardless of the number 24 Distribution of excitation intensity that gives the desired radiation characteristics in an aperture array antenna 25 Distribution of excitation that should be given to a one-dimensional array 26 Null of radiation pattern 27 Base station buildings and structures 28 Antenna outer edge of the radial array antenna 29' inner section 4' of the double radial array antenna substrate 30 of the outer portion of the double radial array antenna boundary 31 of the antenna radiation beam cross-sectional area 32 of the radiation beam satellite structure 33 Satellite antenna mounting surface 34 Solar paddle 35 Rotary joint

Claims (3)

1. A radial array antenna apparatus characterized by arranging radiating elements linearly, setting excitation strength thereof to a predetermined value to form a one-dimensional array, and arranging the one-dimensional arrays radially. 2. A radial array antenna apparatus according to claim 1, wherein seven or more of said one-dimensional arrays are used. In the device according to claim 1, the excitation distribution on the aperture plane of the aperture antenna that achieves the desired radiation characteristics is multiplied by a weighting function whose value is very small at the center of the aperture to obtain the excitation distribution of the one-dimensional array. A radial array antenna device characterized by:

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