Rectenna array device

Abstract

To provide a rectenna array device that reduces the number of elements while maintaining collection efficiency.SOLUTION: A rectenna array device includes a plurality of antenna elements 20 arranged in an array, and a rectifier circuit 15 connected to the antenna elements 20. The antenna elements 20 each has a first conductor plate 23 connected to the rectifier circuit 15, a grounding conductor plate 25 arranged on one side of the first conductor plate 23 and opposing the first conductor plate 23, and a second conductor plate 24 arranged on the other side of the first conductor plate 23 and opposing the first conductor plate 23. The distance between the first conductor plate 23 and the second conductor plate 24 is longer than the distance between the first conductor plate 23 and the grounding conductor plate 25.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a rectenna array device used for wireless power transmission. [Background technology]

[0002] Conventionally, rectenna array devices have been proposed that convert received radio waves into direct current to generate DC power. Patent Document 1 discloses a rectenna array device having multiple rectenna elements. The multiple rectenna elements are arranged in a two-dimensional lattice pattern. Each rectenna element has a patch antenna element and a rectifier arranged on a grounded substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2009-513098 Summary of the Invention [Problem to be solved by the invention]

[0004] A rectenna array device such as that disclosed in Patent Document 1 needs to have a size that corresponds to the spread of the radio wave beam and a high collection efficiency in order to receive most of the power carried by the radio waves. However, when fabricating a rectenna array device of a given size, if one tries to reduce the number of elements in order to reduce fabrication costs, the collection efficiency tends to decrease.

[0005] An object of the present invention is to provide a rectenna array device that reduces the number of elements while maintaining collection efficiency. [Means for solving the problem]

[0006] The rectenna array device of the present invention comprises a plurality of arranged antenna elements and a rectifier circuit connected to the antenna elements, wherein each of the antenna elements has a first conductor plate connected to the rectifier circuit, a ground conductor plate arranged on one side of the first conductor plate and facing the first conductor plate, and a second conductor plate arranged on the other side of the first conductor plate and facing the first conductor plate, and the distance between the first conductor plate and the second conductor plate is longer than the distance between the first conductor plate and the ground conductor plate. [Effects of the Invention]

[0007] According to the present invention, it is possible to realize a rectenna array device with a reduced number of elements while maintaining collection efficiency. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view of a power receiving panel 10 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the power receiving module 11. As shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the power receiving module 11. As shown in FIG. [Figure 4] FIG. 4 is a block diagram of the subarray 12. [Figure 5] FIG. 5 is a perspective view of the antenna element 20. As shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view of a power receiving module 41 according to a modified example of the embodiment of the present invention. [Figure 7] FIG. 7 is a plan view of a typical array antenna. [Figure 8] FIG. 8 is a graph showing the relationship between the gain of an array antenna and the element spacing Ld. [Figure 9] 9A is a plan view of the array antenna 50. FIG. 9B is a cross-sectional view of the array antenna 50. [Figure 10] 10(A) is a plan view of the array antenna 60. FIG. 10(B) is a cross-sectional view of the array antenna 60. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, several embodiments for carrying out the present invention will be described. Each embodiment is an example, and partial substitution or combination of the configurations shown in different embodiments is possible. In each embodiment, differences from the previous embodiments will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0010] FIG. 1 is a plan view of a power receiving panel 10 according to an embodiment of the present invention. The power receiving panel 10 is an example of a "rectenna array device" of the present invention. The power receiving panel 10 has power receiving modules 11 arranged vertically and horizontally. FIG. 1 illustrates a power receiving panel 10 in which 11 x 11 power receiving modules 11 are arranged, i.e., 11 vertically and 11 horizontally.

[0011] In this specification, the terms "vertical" and "horizontal" are used for convenience to distinguish between an arbitrarily selected direction and a direction perpendicular to that direction.

[0012] The power receiving modules 11 are preferably arranged at equal intervals, but are not limited to this.

[0013] The power receiving panel 10 is used in the microwave band of, for example, 3 GHz to 30 GHz, and more specifically, in the 5.8 GHz band, for example.

[0014] Fig. 2 is a plan view of the power receiving module 11. Fig. 3 is a cross-sectional view of the power receiving module 11. Fig. 4 is a block diagram of the subarray 12. Fig. 5 is a perspective view of the antenna element 20. Fig. 5 shows a portion of the first dielectric plate 21, the second dielectric plate 22, and the ground conductor plate 25, and therefore also shows cross sections of the first dielectric plate 21, the second dielectric plate 22, and the ground conductor plate 25.

[0015] As shown in Fig. 2, the power receiving module 11 has subarrays 12 arranged in the vertical and horizontal directions. Fig. 2 illustrates a power receiving module 11 in which 6 x 6 subarrays 12, i.e., six subarrays 12 are arranged vertically and six subarrays 12 are arranged horizontally. The subarrays 12 have antenna elements 20 arranged vertically and horizontally. Fig. 2 illustrates a subarray 12 in which 2 x 2 subarrays 12, i.e., two antenna elements 20 are arranged vertically and two antenna elements 20 are arranged horizontally. The arranged antenna elements 20 constitute the array antenna 13 of the power receiving panel 10.

[0016] The subarrays 12 and antenna elements 20 are preferably, but not limited to, equally spaced apart.

[0017] As shown in FIG. 4, the subarray 12 has, in addition to the antenna elements 20, a rectifier circuit 15, a matching circuit 16, and an output terminal 17. The antenna elements 20 are connected to an input terminal of the rectifier circuit 15. The output terminal of the rectifier circuit 15 is connected to a first terminal of the matching circuit 16. The second terminal of the matching circuit 16 is connected to the output terminal 17. FIG. 4 illustrates a subarray 12 in which one rectifier circuit 15 is connected to two antenna elements 20, and one matching circuit 16 is connected to the two rectifier circuits 15. The rectifier circuit 15 rectifies and converts radio waves input to the antenna elements 20 to generate DC power. The matching circuit 16 matches impedance between the circuit connected to its first terminal and the circuit connected to its second terminal. The output terminal 17 is connected to a load circuit (not shown) via a current collecting wiring (not shown).

[0018] The configuration of the subarray 12 is not limited to the example shown in Fig. 4. For example, one rectifier circuit 15 may be connected to four antenna elements 20, or one rectifier circuit 15 may be connected to one antenna element 20.

[0019] As shown in Figures 2, 3, and 5, the antenna element 20 corresponds to a microstrip antenna provided with a parasitic element and includes a first dielectric plate 21, a second dielectric plate 22, a first conductor plate 23, a second conductor plate 24, and a ground conductor plate 25. The second dielectric plate 22 is disposed above the first dielectric plate 21. The first dielectric plate 21 and the second dielectric plate 22 face each other with an air layer 26 between them. The first conductor plate 23 corresponds to the feeding element of the microstrip antenna and is formed on the upper surface of the first dielectric plate 21. The ground conductor plate 25 is formed on the lower surface of the first dielectric plate 21, i.e., is disposed below the first conductor plate 23 and faces the first conductor plate 23. The second conductor plate 24 corresponds to the parasitic element of the microstrip antenna and is formed on the second dielectric plate 22, i.e., is disposed above the first conductor plate 23 and faces the first conductor plate 23. The first conductive plate 23 and the second conductive plate 24 are disposed with an air layer 26 sandwiched between them. The distance between the first conductive plate 23 and the second conductive plate 24 is longer than the distance between the first conductive plate 23 and the ground conductive plate 25.

[0020] In this specification, the terms "upper surface" and "lower surface" are used for convenience to distinguish between a main surface on one side and a main surface on the other side. Similarly, the terms "upper side" and "lower side" are used for convenience to distinguish between a main surface on one side and a main surface on the other side.

[0021] Instead of the air layer 26, a dielectric layer having a low dielectric constant, made of, for example, expanded polystyrene, may be provided between the first dielectric plate 21 and the second dielectric plate 22.

[0022] The second conductor plate 24 is formed on the upper surface of the second dielectric plate 22, but may be formed on the lower surface of the second dielectric plate 22.

[0023] The first conductor plate 23 and the second conductor plate 24 have a square shape, but may have other shapes such as a circle. Furthermore, it is preferable that the area where the first conductor plate 23 is formed and the area where the second conductor plate 24 is formed completely coincide with each other in a plan view, but they do not necessarily have to completely coincide with each other.

[0024] The distance h between the first dielectric plate 21 and the second dielectric plate 22 is set to 0.5λ in order to increase the gain of the antenna element 20. d Preferably, where λ d is the wavelength of the radio wave received by the antenna element 20 when the radio wave propagates through the material occupying between the first dielectric plate 21 and the second dielectric plate 22.

[0025] The first conductor plate 23 is connected to the rectifier circuit 15 by a wiring 32. The wiring 32 is connected to an appropriate location on the first conductor plate 23 so that the impedance on the antenna element 20 side and the characteristic impedance of the wiring 32 match.

[0026] The wiring 32 is formed of a conductive wire, but may also be formed of a through-hole.

[0027] The rectifier circuit 15 and the matching circuit 16 are modularized and disposed below the ground conductor plate 25 .

[0028] The second dielectric plate 22 is fixed to the first dielectric plate 21 at a distance by a plurality of columnar spacers 31. One end of the spacer 31 is fixed to the first dielectric plate 21. The other end of the spacer 31 is fixed to the second dielectric plate 22. The spacer 31 is made of a dielectric material such as plastic.

[0029] The spacer 31 may be formed of a dielectric member of another shape, for example, a lattice-shaped dielectric member, instead of a plurality of columnar dielectric members. Also, when a dielectric layer made of a dielectric member is provided instead of the air layer 26, the dielectric layer also serves as a spacer.

[0030] Element spacing L of array antenna 13 d It is preferable that the element spacing L is 0.75λ or less. dis the spacing between the antenna elements of the array antenna in question, which in this embodiment corresponds to the distance between the centers (i.e., geometric centers) of the first conductor plates 23 of adjacent antenna elements 20. λ is the wavelength of the radio waves received by the antenna element in question. In other words, λ is the speed of radio waves in a vacuum divided by the resonant frequency of the antenna element.

[0031] The first dielectric plate 21, the second dielectric plate 22, and the ground conductor plate 25 are shared by a plurality of antenna elements 20. Therefore, the antenna elements 20 are arranged without any gaps, and the element spacing L of the array antenna 13 is d It can be considered that the image has vertical and horizontal dimensions equal to

[0032] 6 is a cross-sectional view of a power receiving module 41 according to a modified example of the embodiment of the present invention. The power receiving module 41 differs from the power receiving module 11 in the following points: The ground conductor plate 25 is formed within the first dielectric plate 21. The rectifier circuit 15 is formed on the lower surface of the first dielectric plate 21. The matching circuit 16 is modularized and placed below the rectifier circuit 15. The ground conductor plate 25 is shared by the antenna element 20 and the rectifier circuit 15.

[0033] The dielectric constant of the dielectric layer between the first conductor plate 23 and the ground conductor plate 25 is preferably lower than the dielectric constant of the dielectric layer between the ground conductor plate 25 and the rectifier circuit 15. This reduces the power loss occurring in the antenna element 20.

[0034] Figure 7 shows a plan view of a typical array antenna, which has antenna elements arranged in a two-dimensional grid pattern with equal spacing and no gaps between them.

[0035] Here, the filter is configured as shown in FIG. 7 and has a predetermined collection efficiency η p and physical area A p In the case of fabricating an array antenna having the above structure, if the gain G of the antenna element is increased, the number of elements N of the array antenna can be reduced. First, the collection efficiency η and gain G of the antenna element are expressed as follows: η=A e / A (1) G=4πA e / λ 2 (2) where A e is the effective aperture area of ​​the antenna element, A is the physical area of ​​the antenna element, and A=L d 2 From equations (1) and (2), the gain G and element spacing L that must be satisfied to obtain collection efficiency η are d The relationship between G=f η (L d )=4πηL d 2 / λ 2 (3) The relationship between the gain G and size of the antenna element, i.e., the gain G and the element spacing L d The relationship between G=f σ (L d ), the element spacing L required to obtain collection efficiency η is d is f σ (L d )=f η (L d Therefore, if the gain G of the antenna element is increased, the element spacing L can be increased while maintaining the collection efficiency η. d In addition, the physical area A of the array antenna can be increased. p teeth, A p =NA=NL d 2 (4) Furthermore, the collection efficiency of the array antenna η p The value of is close to the value of the collection efficiency η of the antenna element. However, if the collection efficiency η of the antenna element is higher than 100%, the collection efficiency η of the array antenna p is close to 100%.

[0036] From the above, if the gain G of the antenna element is increased, the element spacing L of the array antenna can be reduced. d As a result, the number of elements N of the array antenna can be reduced.

[0037] Figure 8 shows the relationship between the gain of the array antenna and the element spacing L dThe horizontal axis of the graph in FIG. d is normalized by wavelength λ. a1 is the gain of the array antenna 50 and the element spacing L d a2 shows the relationship between the gain of the array antenna 60 and the element spacing L d b1, b2, b3, b4, and b5 are the relationship between the gain of the array antenna and the element spacing L that must be satisfied to obtain 50%, 70%, 80%, 90%, and 100% collection efficiency of the array antenna, respectively. d Shows the relationship between

[0038] Fig. 9(A) is a plan view of array antenna 50. Fig. 9(B) is a cross-sectional view of array antenna 50. Fig. 10(A) is a plan view of array antenna 60. Fig. 10(B) is a cross-sectional view of array antenna 60. Array antenna 50 has 2 x 2 antenna elements 20. Array antenna 60 has 2 x 2 antenna elements, but the antenna elements are microstrip antennas that are not provided with parasitic elements.

[0039] 8, the array antenna 50 has a higher gain than the array antenna 60. Therefore, when fabricating an array antenna having a predetermined collection efficiency and size, the element spacing L can be reduced by using the antenna elements 20. d As a result, the number of elements can be reduced.

[0040] For example, consider the case of fabricating an array antenna for use at a frequency of 5.8 GHz, with 100% collection efficiency and a size of 3 m x 3 m. As can be seen from Figure 8, for the array antenna 50, the maximum possible element spacing L at 100% collection efficiency is d In the case of the array antenna 60, the maximum possible element spacing L for 100% collection efficiency is dis approximately 0.5λ. Therefore, when fabricating the array antenna 13, approximately 6,000 antenna elements 20 are required. On the other hand, when fabricating an array antenna by closely arranging microstrip antennas without parasitic elements, approximately 13,500 antenna elements are required.

[0041] According to this embodiment, the power receiving panel 10 includes the antenna element 20 with a high gain. Therefore, when manufacturing a power receiving panel having a predetermined size, it is possible to reduce the element spacing L while maintaining the collection efficiency. d In particular, according to this embodiment, the element spacing L can be set to 0.75λ or less. d By setting the value of the number of elements, it is possible to reduce the number of elements while maintaining 100% collection efficiency. The effect of this embodiment is particularly noticeable in the case of a large-sized power receiving panel.

[0042] Although the antenna elements 20 of the power receiving panel 10 according to this embodiment are arranged in a two-dimensional lattice pattern, the antenna elements of a power receiving panel according to another embodiment may be arranged in a different pattern.

[0043] Finally, the above description of the embodiments is illustrative in all respects and is not restrictive. Variations and modifications are possible for those skilled in the art. The scope of the present invention is defined not by the above embodiments but by the claims. Furthermore, the scope of the present invention includes modifications from the embodiments within the scope of the claims and their equivalents. [Explanation of symbols]

[0044] 10...Power receiving panel 11, 41... Power receiving module 12...Subarray 13...Array antenna 15... Rectifier circuit 16...Matching circuit 17...Output terminal 20...Antenna element 21...First dielectric plate 22...Second dielectric plate 23...First conductor plate 24...Second conductor plate 25...Ground conductor plate 26...Air layer 31...Spacer 32...Wiring 50, 60... Array antenna

Claims

1. A plurality of arrayed antenna elements; a rectifier circuit connected to the antenna element, The antenna elements each have: a first conductor plate connected to the rectifier circuit; a ground conductor plate disposed on one side of the first conductor plate and facing the first conductor plate; a second conductor plate disposed on the other side of the first conductor plate and facing the first conductor plate, a distance between the first conductive plate and the second conductive plate is longer than a distance between the first conductive plate and the ground conductive plate; A rectenna array device, wherein the distance between the centers of the first conductor plates of adjacent antenna elements is 0.75λ, where λ is the wavelength of the radio waves received by the antenna elements.

2. Further comprising a first dielectric plate and a second dielectric plate, the first conductor plate and the ground conductor plate are formed on the first dielectric plate; The rectenna array device of claim 1 , wherein the second conductor plate is formed on the second dielectric plate.

3. the first conductor plate is formed on one main surface of the first dielectric plate, the rectifier circuit is formed on the other main surface of the first dielectric plate, The rectenna array device of claim 2 , wherein the ground conductor plate is formed within the first dielectric plate.

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