Circular array antenna

Abstract

To provide a circular array antenna that improves ripple in an omnidirectional radiation pattern without causing characteristic deterioration.SOLUTION: In a circular array antenna 1, a plurality of planar antennas 4, 5, 6, 7 having a rectangular substrate 41, 51, 61, 71 and a radiating element 42, 52, 62, 72 are placed in a rectangular tube shape, and the circular array antenna includes an antenna main body 2 in which each of the radiating elements is arranged on the outer circumferential side of the rectangular tube shape, and an annular ripple improvement ring 3 arranged on the outer periphery of the antenna main body 2 and provided along the circumferential direction of the central axis C of the antenna main body 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a circular array antenna in which a plurality of planar antennas are combined in a square tube shape.

Background Art

[0002] There is known a circular array antenna in which a plurality of planar antennas each including a rectangular substrate and a radiation element provided on one surface of the substrate are combined such that each radiation element faces outward in a square tube shape (see, for example, paragraphs

[0057] to

[0065] and FIGS. 19 to 23 of Patent Document 1). According to this circular array antenna, an omnidirectional radiation pattern can be obtained by feeding each radiation element with the same phase.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above circular array antenna, a ripple occurs in the radiation pattern, and the radiated power decreases in a specific direction. This is because the electric field distribution of each radiation element spreads outward from the antenna body, so that the distance between the phase centers becomes larger than the actual distance between the radiation elements (hereinafter referred to as the element interval). In order to improve the ripple of such a circular array antenna, the actual element interval may be reduced. However, if the radiation element is miniaturized to reduce the element interval, characteristic degradation (such as gain reduction and VSWR degradation) occurs.

[0005] Therefore, an object of the present invention is to provide a circular array antenna capable of improving the ripple of an omnidirectional radiation pattern without causing characteristic degradation.

Means for Solving the Problems

[0006] To solve the above problems, the invention described in claim 1 provides a plurality of planar antennas comprising a rectangular substrate and radiating elements provided on one side of the substrate, arranged such that a rectangular tube is formed by the substrates, with each radiating element positioned on the outer circumferential surface side of the rectangular tube, and an annular ripple-improving ring made of a conductive material positioned on the outer circumferential surface of the antenna body and provided along the circumferential direction of the central axis of the antenna body, wherein in-phase power is supplied to each radiating element to make it an omnidirectional antenna death , The ripple-improving ring is attached to the inner surface of a radome made of a dielectric material with high radio wave transmittance. This is a circular array antenna characterized by the following features.

[0007] The invention described in claim 2 is characterized in that, in the circular array antenna described in claim 1, the ripple-improving ring is arranged on the outer circumference of the central part of each radiating element.

[0008] The invention described in claim 3 is characterized in that, in the circular array antenna described in claim 1 or 2, the width of the ripple-improving ring in the axial direction of the central axis is smaller than the width of the radiating element in the axial direction. [Effects of the Invention]

[0009] According to the invention described in claim 1, the ripple-improving ring made of a conductive material changes the electric field distribution around each radiating element so that it spreads out inside the ripple-improving ring, and the distance between phase centers becomes smaller than the actual element spacing. This makes it possible to improve ripple without miniaturizing the radiating elements and reducing the element spacing. In other words, it is possible to improve the ripple of an omnidirectional radiation pattern without causing performance degradation.

[0010] Furthermore, according to the invention described in claim 2, by arranging the ripple improvement ring on the outer circumference of the central part of each radiating element, the electric field distribution can be more effectively changed so that the distance between phase centers becomes smaller than the actual element spacing. Therefore, it is possible to improve the ripple of the omnidirectional radiation pattern without causing characteristic degradation.

[0011] Furthermore, according to the invention described in claim 3, since the width of the ripple improvement ring in the axial direction is made smaller than the width of the radiating element in the axial direction, it is possible to improve the ripple of the omnidirectional radiation pattern while suppressing return loss. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view showing the external shape of a circular array antenna according to an embodiment of the present invention. [Figure 2] Figure 1 shows a top view and a side view of the circular array antenna. [Figure 3] This figure shows the horizontal polarization radiation characteristics of a circular array antenna as shown in Figure 1 and a conventional circular array antenna without a ripple correction ring. [Figure 4] This figure shows the results of electromagnetic field simulations for a conventional circular array antenna without a ripple correction ring. [Figure 5] Figure 1 shows the results of a circular array antenna electromagnetic field simulation. [Figure 6] This figure shows the radiation characteristics of samples of circular array antennas with modified diameters and widths of the ripple-improving rings. [Figure 7] Figure 6 shows a table illustrating the dimensions and ripple of each part of the sample. [Figure 8] This is a perspective view showing the external shape of a circular array antenna, which is obtained by scaling down the substrates of each planar antenna. [Figure 9] This figure shows the horizontal polarization radiation characteristics of the circular array antenna shown in Figure 8 and a conventional circular array antenna without a ripple correction ring.

Best Mode for Carrying Out the Invention

[0013] Hereinafter, this invention will be described based on the illustrated embodiments.

[0014] FIG. 1 shows an external perspective view of a circular array antenna 1 according to an embodiment of this invention, FIG. 2(A) shows a top view of the circular array antenna 1, and FIG. 2(B) shows a side view of the circular array antenna 1. The circular array antenna 1 is, for example, an omnidirectional antenna for receiving radio waves in the 800 MHz band, and includes an antenna body 2 and a ripple improvement ring 3.

[0015] The antenna body 2 is, for example, composed of four planar antennas 4, 5, 6, and 7. The planar antenna 4 includes a square substrate 41 and a square radiation element 42 provided on one surface of the substrate 41. The substrate 41 includes a ground plate 41a disposed on the back side and a dielectric plate 41b disposed on the front side. The radiation element 42 is made of a conductive material and is disposed at the center of the front side of the dielectric plate 41b. This planar antenna 41 is a so-called square microstrip antenna, which receives radio waves and outputs a received signal.

[0016] The planar antennas 5, 6, and 7 are the same as the planar antenna 4, that is, they have the same configuration and size as the planar antenna 4. Therefore, detailed descriptions of the planar antennas 5, 6, and 7 are omitted, but they each include substrates 51, 61, and 71 and radiation elements 52, 62, and 72, respectively. Also, the substrates 51, 61, and 71 each include a ground plate 51a, 61a, and 71a and a dielectric plate 51b, 61b, and 71b, respectively.

[0017] The four planar antennas 4, 5, 6, and 7 are arranged by the respective substrates 41, 51, 61, and 71 such that a square tube facing the vertical direction is formed. More specifically, the four planar antennas 4, 5, 6, and 7 are arranged such that the vertical sides of the respective substrates 41, 51, 61, and 71 are adjacent to each other. Further, the planar antennas 4, 5, 6, and 7 are arranged such that the radiating elements 42, 52, 62, and 72 face the outer peripheral surface side of the square tube, that is, the outside of the antenna body 2. The reference symbol C in the figure indicates the central axis of the antenna body 2 configured in a square tube shape by the four planar antennas 4, 5, 6, and 7.

[0018] The length of one side of the substrates 41, 51, 61, and 71 is L1. That is, the array diameter D1, which is the interval between the respective radiating elements 42, 52, 62, and 72 centered on the central axis C of the antenna body 2, is D1 = L1. Also, as is well known, in a square microstrip antenna, the length L2 of one side of the radiating elements 42, 52, 62, and 72 is 1 / 2 of the wavelength λ of the received radio wave.

[0019] In the antenna body 2 configured as described above, the radiation beams of the respective planar antennas 4, 5, 6, and 7 are radiated without intersecting each other. However, by feeding the horizontal polarization in phase to the respective radiating elements 42, 52, 62, and 72, an omnidirectional radiation pattern can be obtained.

[0020] The ripple improvement ring 3 improves the ripple generated in the radiation pattern of the antenna body 2. The ripple improvement ring 3 is an annular ring arranged on the outer periphery of the antenna body 2 and provided along the circumferential direction of the central axis C of the antenna body 2. The ripple improvement ring 3 is, for example, formed by bending a strip-shaped conductive plate having a thickness of 1 mm or less into an annular shape. The ripple improvement ring 3 is arranged on the outer periphery of the central portion of each of the radiating elements 42, 52, 62, and 72. Also, the diameter D2 of the ripple improvement ring 3 is larger than the array diameter D1. Further, the width W of the ripple improvement ring 3 in the axial direction of the central axis C is smaller than the width L2 of the radiating elements 42, 52, 62, and 72 in the axial direction.

[0021] The ripple correction ring 3 is attached, for example, to the inner surface of a substantially cylindrical radome 8 that protects the outside of the circular array antenna 1. The radome 8 is made of a dielectric material with high radio wave transmittance. When this radome 8 is mounted on the outside of the circular array antenna 1, the ripple correction ring 3 is positioned on the outer circumference of the antenna body 2.

[0022] Figure 3 shows the horizontal polarization radiation pattern (radiation characteristics) of the circular array antenna 1 described above, and the horizontal polarization radiation pattern of the antenna body 2 alone. Specifically, Figure 3 shows a comparison of the radiation pattern of the antenna body 2 equipped with the ripple correction ring 3 (shown by a solid line in the figure) and the radiation pattern of the antenna body 2 without the ripple correction ring 3 (shown by a dashed line in the figure). Specifically, the frequency of the received radio waves is 800 MHz, the side length L1 and array diameter D1 of the substrates 41, 51, 61, and 71 are 500 mm, the side length L2 of the radiating elements 42, 52, 62, and 72 is 187 mm, the diameter D2 of the ripple correction ring 3 is 800 mm, and the width W of the ripple correction ring 3 is 30 mm.

[0023] As can be seen from this radiation pattern, the radiation pattern of antenna body 2 without the ripple-improving ring 3 (dashed line) shows a ripple of approximately 8.0 dB, resulting in a decrease in radiated power in certain directions. In contrast, the radiation pattern of antenna body 2 (circular array antenna 1) equipped with the ripple-improving ring 3 (solid line) shows improved ripple (approximately 4.8 dB), suppressing the decrease in radiated power in certain directions.

[0024] In a circular array antenna using multiple planar antennas, ripple occurs in the horizontal polarization radiation pattern because the electric field distribution of each radiating element spreads outward from the antenna body, causing the distance between phase centers to become larger than the actual element spacing. Figure 4 shows an electromagnetic field simulation of the antenna body 2 without the ripple correction ring 3. As can be seen from this figure, while the length of one side L1 of the substrates 41, 51, 61, and 71, i.e., the array diameter D1, is 500 mm, the electric field distribution of each radiating element 42, 52, 62, and 72 spreads outward from the antenna body 2, resulting in a distance L3 between the phase centers of adjacent electric field distributions of 495 mm (1.3λ) and a diameter D3 between each phase center of 700 mm.

[0025] In contrast, Figure 5 shows an electromagnetic field simulation of a circular array antenna 1 equipped with a ripple-improving ring 3. As can be seen from this figure, the electric field distribution of each radiating element 42, 52, 62, and 72 changes to spread out inside the ripple-improving ring 3, resulting in a distance L4 between adjacent phase centers of 375 mm (1λ) and a diameter D4 between each phase center of 530 mm, which is smaller than the actual element spacing L1 and array diameter of 500 mm. This makes it possible to improve ripple without miniaturizing each radiating element 42, 52, 62, and 72 and reducing the element spacing. In other words, it is possible to improve the ripple of an omnidirectional radiation pattern without causing performance degradation.

[0026] Next, the optimal position of the ripple correction ring 3 relative to the antenna body 2, and the optimal values ​​for each dimension of the ripple correction ring 3, will be explained based on the radiation characteristics results of several samples. Measurements of the radiation characteristics at various positions where the ripple correction ring 3 is moved along the central axis C relative to the antenna body 2 revealed that it is most preferable to position the ripple correction ring 3 on the outer circumference of the central part O of each radiating element 42, 52, 62, and 72. Therefore, in the following samples, the ripple correction ring 3 will be positioned on the outer circumference of the central part O of each radiating element 42, 52, 62, and 72.

[0027] Figure 6 shows the simulation results of the radiation patterns of samples A to F, where the diameter D2 and width W of the ripple correction ring 3 of the circular array antenna 1 are changed. The dimensions of each part of the antenna body 2 are as follows: the side length L1 of the substrates 41, 51, 61, and 71 and the array diameter D1 are 500 mm, the side length L2 of the radiating elements 42, 52, 62, and 72 is 187 mm, and the frequency of the received radio waves is 800 MHz.

[0028] Figure 6(A) shows the radiation pattern of sample A, which does not have the ripple improvement ring 3. In contrast, Figure 6(B) shows the radiation pattern of sample B, where the diameter D2 of the ripple improvement ring 3 is 1.5 times the array diameter D1 (500 mm) (750 mm), and the width W of the ripple improvement ring 3 is 0.08λ (30 mm).

[0029] Furthermore, Figure 6(C) shows the radiation pattern of sample C, where the diameter D2 of the ripple improvement ring 3 is 1.6 times the array diameter D1 (500 mm) (800 mm), and the width W of the ripple improvement ring 3 is 0.08λ (30 mm). In addition, Figure 6(D) shows the radiation pattern of sample C, where the diameter D2 of the ripple improvement ring 3 is 1.7 times the array diameter D1 (500 mm) (850 mm), and the width W of the ripple improvement ring 3 is 0.08λ (30 mm).

[0030] Furthermore, Figure 6(E) shows the radiation pattern of sample E, where the diameter D2 of the ripple improvement ring 3 is 1.6 times the array diameter D1 (500 mm) (800 mm), and the width W of the ripple improvement ring 3 is 0.026λ (10 mm). In addition, Figure 6(F) shows the radiation pattern of sample F, where the diameter D2 of the ripple improvement ring 3 is 1.6 times the array diameter D1 (500 mm) (800 mm), and the width W of the ripple improvement ring 3 is 0.13λ (50 mm).

[0031] As shown in the table in Figure 7, the ripple of sample A is 8.0 dB, the ripple of sample B is 5.3 dB, the ripple of sample C is 4.8 dB, and the ripple of sample D is 5.2 dB. From these results, it was found that the smaller the diameter D2 of the ripple correction ring 3, the better the ripple correction effect, but the highest ripple correction effect is achieved when the diameter is about 1.6 times the array diameter D1. In other words, it is preferable that the diameter D2 of the ripple correction ring 3 is greater than or equal to the outer diameter of the antenna body 2 and about 1.5 times the array diameter D1.

[0032] Furthermore, as shown in the table in Figure 7, the ripple of sample C is 4.8 dB, the ripple of sample E is 5.6 dB, and the ripple of sample F is 4.3 dB. From these results, it can be seen that the wider the width W of the ripple correction ring 3, the better the ripple is reduced. Although not shown in the table in Figure 7, it was found that the return loss increases as the width W of the ripple correction ring 3 increases. Therefore, a practical width W of the ripple correction ring 3 is preferably around 0.1λ.

[0033] Furthermore, although not shown in the table in Figure 7, it was found that in all samples B to F equipped with the ripple-improving ring 3, no significant change occurred in the vertical polarization, and in sample C, the return loss was slightly improved. In other words, the circular array antenna 1 of this embodiment can improve only the ripple of the horizontal polarization radiation characteristics without affecting the vertical polarization radiation characteristics.

[0034] As described above, with the circular array antenna 1 according to this embodiment, the electric field distribution around each radiating element 42, 52, 62, and 72 changes to spread inside the ripple-improving ring 3 made of a conductive material, and the distance between phase centers becomes smaller than the actual element spacing. This makes it possible to improve ripple without miniaturizing the radiating elements 42, 52, 62, and 72 to reduce the element spacing. In other words, it is possible to improve the ripple of the omnidirectional radiation pattern without causing performance degradation.

[0035] Furthermore, according to the circular array antenna 1 of this embodiment, by arranging the ripple-improving ring 3 on the outer circumference of the central part O of each radiating element 42, 52, 62, and 72, the electric field distribution can be more effectively changed so that the distance between phase centers becomes smaller than the actual element spacing. Therefore, it is possible to improve the ripple of the omnidirectional radiation pattern without causing characteristic degradation.

[0036] Furthermore, according to the circular array antenna 1 of this embodiment, the axial width W of the ripple improvement ring 3 is made smaller than the axial width L2 of the radiating elements 42, 52, 62, and 72, making it possible to improve the ripple of the omnidirectional radiation pattern while suppressing return loss.

[0037] Although embodiments of this invention have been described above, the specific configuration is not limited to the embodiments described above, and any design changes, etc., that do not depart from the gist of this invention are also included. For example, as in the antenna body 2A of the circular array antenna 1A shown in Figure 8, even if the size of the substrates 41, 51, 61, and 71 for the radiating elements 42, 52, 62, and 72 is reduced from 500 mm as shown in Figures 1 and 2 to 220 mm, and the diameter D2 of the ripple improvement ring 3 is reduced from 800 mm to 350 mm in accordance with this reduction ratio, it is still possible to reduce ripple as shown in the radiation characteristics in Figure 9.

[0038] Furthermore, although the cross-sectional shape of the rectangular tube of the antenna body 2 was explained using a square, other polygonal shapes such as triangles, pentagons, hexagons, and octagons may also be used. When the cross-sectional shape of the rectangular tube is triangular, the number of radiating elements decreases, resulting in larger ripple compared to a square. However, by using the ripple reduction ring 3, it is possible to appropriately suppress the ripple. Also, when the number of sides of the cross-sectional shape of the rectangular tube is greater than that of a square, the number of radiating elements increases, resulting in smaller ripple compared to a square. In this case as well, it is possible to appropriately suppress the ripple by using the ripple reduction ring 3.

[0039] Furthermore, the shape of the ripple improvement ring 3 is not limited to an annular shape; for example, it may be an annular shape with polygonal shapes such as triangles, squares, pentagons, and octagons, or an annular shape with numerous protrusions and indentations in a gear-like manner. In addition, a large number of vertical polarization elements may be provided on the outer circumference of the annular ripple improvement ring 3. This makes it possible to improve vertical polarization ripple, null characteristics, cross-polarization characteristics, reflection characteristics, etc. [Explanation of symbols]

[0040] 1. 1A circular array antenna 2. 2A Antenna Body 3 Ripple Improvement Ring 4, 5, 6, 7 Planar antennas 41, 51, 61, 71 circuit boards 42, 52, 62, 72 radiating elements

Claims

1. A plurality of planar antennas, each comprising a rectangular substrate and a radiating element provided on one side of the substrate, are arranged such that a rectangular tube is formed by the substrates, and the radiating elements are arranged on the outer circumferential surface side of the rectangular tube, forming an antenna body. An annular ripple-improving ring made of a conductive material is arranged on the outer circumference of the antenna body and provided so as to be aligned with the circumferential direction of the central axis of the antenna body, Equipped with, In order to create an omnidirectional antenna, the aforementioned radiating elements are fed in phase, The ripple-improving ring is attached to the inner surface of a radome made of a dielectric material with high radio wave transmittance. A circular array antenna characterized by its features.

2. The ripple improvement ring is positioned on the outer circumference of the central part of each radiating element. The circular array antenna according to feature 1.

3. The ripple-improving ring has a width in the axial direction of the central axis that is smaller than the width of the radiating element in the axial direction. A circular array antenna as described in claim 1 or 2.

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