Patch antenna

Abstract

To provide a patch antenna that is small-sized and can increase its antenna gain.SOLUTION: A patch antenna according to an aspect of the present invention has: a first dielectric layer; a patch conductor formed on the first dielectric layer; and a second dielectric layer formed on the patch conductor. The relative dielectric constant of the second dielectric layer is 3.5 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a patch antenna. [Background technology]

[0002] Fifth-generation (5G) mobile communication systems use electromagnetic waves in higher frequency bands (for example, electromagnetic waves in the 28 GHz band, known as millimeter waves) than those used in previous mobile communication systems. However, millimeter waves have the drawback of short propagation distances due to their high degree of directivity and susceptibility to attenuation during propagation. For this reason, communication antennas using millimeter waves are required to have high antenna gain.

[0003] One type of antenna that improves antenna gain is a phased array antenna, which has multiple antenna elements arranged in an array on a dielectric substrate. For example, patch antennas with rectangular flat patch conductors that are easy to arrange in an array are often used in phased array antennas (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-222545 Summary of the Invention [Problem to be solved by the invention]

[0005] The antenna disclosed in Patent Document 1 has an antenna element including a patch conductor and a lens antenna facing the antenna element. Electromagnetic waves radiated from the antenna element enter the lens antenna and are refracted. This forms a beam-shaped plane wave with a coherent phase, thereby increasing the antenna gain. However, since the lens antenna has a curved surface, its dimensions in the front-to-rear direction are large. Placing the lens antenna in front of the antenna element results in an increase in the size of the antenna.

[0006] An object of the present invention is to provide a small patch antenna with improved antenna gain. [Means for solving the problem]

[0007] A patch antenna according to one embodiment of the present invention comprises a first dielectric layer, a patch conductor formed on the first dielectric layer, and a second dielectric layer formed on the patch conductor, wherein the relative dielectric constant of the second dielectric layer is 3.5 or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a small patch antenna with improved antenna gain. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a perspective plan view of the patch antenna according to the present embodiment. [Figure 2] FIG. 2 is a vertical cross-sectional view of the patch antenna according to the present embodiment. [Figure 3] 10 is a graph showing a comparison of antenna gain between Example 6 and Comparative Example 1. [Figure 4] 10 is a graph showing antenna gain when the thickness of the second dielectric layer is changed in Example 9, Example 10, and Comparative Example 4. [Figure 5] 10 is a graph showing antenna gain when the thickness of the second dielectric layer is changed in Example 11, Example 12, and Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Overall configuration of patch antenna> Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0011] The embodiments described below exemplify patch antennas for embodying the technical ideas of the present disclosure, and the present disclosure is not limited to the embodiments described below. Unless otherwise specified, the dimensions, materials, shapes, relative locations, etc. of the components described below are intended for illustration purposes and are not intended to limit the scope of the present disclosure. Furthermore, the sizes and positional relationships of the components shown in the drawings may be exaggerated for clarity.

[0012] The configuration of a patch antenna 1 according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a perspective view illustrating the patch antenna 1 according to this embodiment. Figure 2 is a vertical cross-sectional view of the patch antenna 1 taken along line AA shown in Figure 1. The X direction shown in the figure corresponds to the width direction of the patch antenna 1, the Y direction corresponds to the depth direction of the patch antenna 1, and the Z direction corresponds to the height direction of the patch antenna 1. The X direction, Y direction, and Z direction are perpendicular to one another. Furthermore, any direction within the XY plane may be referred to as an "in-plane direction." The direction along the Z direction may be referred to as a "perpendicular-to-plane direction."

[0013] The patch antenna 1 is an antenna that performs wireless communication by transmitting and receiving electromagnetic waves having a frequency band of 3 GHz to 300 GHz, such as millimeter waves or microwaves. However, the frequency band of the electromagnetic waves that can be transmitted and received by the patch antenna 1 may be other than these. As shown in Fig. 1 and Fig. 2, the patch antenna 1 has a first dielectric layer 10, a patch conductor 20, a second dielectric layer 30, a ground layer 40, and a power feed via 50.

[0014] <First dielectric layer> The first dielectric layer 10 is, for example, a dielectric layer that functions as a substrate for the patch antenna 1. More specifically, the first dielectric layer 10 has a predetermined thickness and is in the form of a sheet extending in an in-plane direction. The first dielectric layer 10 has a first surface (front surface) 11 located on the upper side in the perpendicular direction to the plane, and a second surface (back surface) 12 located on the lower side in the perpendicular direction to the plane.

[0015] Examples of materials for the first dielectric layer 10 include polymeric materials such as polyethylene resin, polypropylene resin, and polystyrene resin. However, the material for the dielectric layer 10 is not limited to these and may be a ceramic material or the like. The material for the first dielectric layer 10 may also be a composite material containing a fluorine-based resin and a filler.

[0016] Examples of fluorine-based resins include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTEF), tetrafluoroethylene-ethylene copolymer (ETFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), and polyvinylidene fluoride (PVDF), which can be used alone or in combination of two or more. Of these, PTFE is particularly preferred.

[0017] The fluororesin is preferably "fibrillated (fibrous structured)." It is more preferable that the fibrillated fibers are oriented not only in one direction but in multiple directions. It is particularly preferable that the fibrils are linked to the inorganic fine particle aggregates described below to form a "three-dimensional micromesh structure." When the fluororesin is fibrillated, particularly when a three-dimensional micromesh structure is formed, the composite material can be assured of excellent mechanical strength and dimensional stability. The fibrillation of the fluororesin can be promoted by applying a shear force, for example, but more specifically, it is preferably carried out by multi-stage rolling. The three-dimensional micromesh structure is preferably formed by anti-directional multi-stage rolling.

[0018] Examples of fillers include granular fillers and fibrous fillers. Examples of granular fillers include solid carbon such as carbon black; silicon dioxide (silica) such as porous silica, fused silica, and silica gel; transition metal oxides (including composite oxides) such as titanium oxide (titanium dioxide (titania)), iron oxide, and zirconium oxide (zirconium dioxide (zirconia)); and nitrides of typical elements such as boron nitride and silicon nitride. Examples of fibrous fillers include glass fiber and carbon fiber. These fillers can be used alone or in combination.

[0019] It is preferable to contain, as the filler, "porous inorganic fine particle aggregates formed by aggregating inorganic fine particles having an average primary particle diameter of 5 to 200 nm (hereinafter, sometimes abbreviated as "inorganic fine particle aggregates")." By containing the inorganic fine particle aggregates as the filler, it is possible to ensure good properties such as a dielectric constant and a thermal expansion coefficient. The inorganic fine particle aggregates refer to aggregates formed by the fusion of a plurality of inorganic fine particles, which are porous with voids between the inorganic fine particles.

[0020] Examples of materials for the inorganic fine particles in the inorganic fine particle aggregate include oxides of typical elements such as silicon oxide (e.g., silicon monoxide, silicon dioxide (silica)) and aluminum oxide (alumina) (including composite oxides); transition metal oxides such as titanium oxide (e.g., titanium dioxide (titania)), iron oxide, and zirconium oxide (zirconium dioxide (zirconia)) (including composite oxides); and nitrides of typical elements such as boron nitride and silicon nitride. These may be used alone or in combination of two or more. Among these, oxides of typical elements are preferred, with silicon dioxide (silica) being particularly preferred. Oxides of typical elements can significantly reduce the dielectric constant of the composite material and enable the composite material to be produced at lower cost. The crystallinity of the inorganic fine particles is not particularly limited, but silicon dioxide is typically amorphous.

[0021] When the first dielectric layer 10 contains, for example, a fluorine-based resin and a filler, the porosity of the first dielectric layer 10 is preferably 30% or more, more preferably 35% or more, even more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more, and is usually 80% or less, preferably 70% or less. Within this range, the composite material can ensure good properties such as dielectric constant and expansion coefficient. The porosity is a value calculated by measuring the bulk density and true density of the material to be the pore-containing layer and substituting them into the following formula: Porosity [%] = (1 - (bulk density [g / cm3] of material containing fluororesin and filler) 3 ] / True density of material containing fluororesin and filler [g / cm 3 ]))×100

[0022] The relative permittivity of the first dielectric layer 10 is not particularly limited, but is preferably, for example, 1.5 to 5.0. By setting the relative permittivity of the first dielectric layer 10 within this range, it is possible to reduce dielectric loss and improve antenna gain. Note that the "relative permittivity" is the value obtained by dividing the "dielectric constant" by the "dielectric constant of a vacuum," and the "dielectric constant of a vacuum" is 1. Therefore, in this specification, "relative permittivity" and "dielectric constant" are treated as synonymous terms.

[0023] The thickness of the first dielectric layer 10 is not particularly limited, but is preferably 0.1 mm to 1.0 mm. By setting the thickness of the first dielectric layer 10 within this range, it is possible to improve the antenna gain and expand the frequency band.

[0024] <Patch conductor> The patch conductor 20 is a conductor layer that functions as an antenna element. The patch conductor 20 is formed on the first surface 11 of the first dielectric layer 10. More specifically, the patch conductor 20 has a rectangular planar shape, and has a first surface (front surface) 21 located on the upper side in the perpendicular direction and a second surface (back surface) 22 located on the lower side in the perpendicular direction. However, the shape of the patch conductor 20 is not limited to this.

[0025] The patch conductor 20 radiates, for example, electromagnetic waves in a predetermined frequency band from the patch antenna 1 toward an external communication device. In addition, the patch conductor 20 receives, for example, electromagnetic waves in a predetermined frequency band radiated toward the patch antenna 1 from the external communication device.

[0026] 1 and 2, there is one patch conductor 20 in this embodiment, but the number of patch conductors 20 is not limited to this. For example, a plurality of patch conductors 20 may be arranged in an array on the first surface 11 of the first dielectric layer 10.

[0027] The material of the patch conductor 20 is not particularly limited, but examples include metals such as titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, and hafnium; conductive metal oxides such as ITO (oxide of indium and tin), zinc oxide, and tin oxide; and materials containing two or more of these metals or metal oxides, or alloys containing these metals as the main component.

[0028] <Second dielectric layer> The second dielectric layer 30 is a dielectric layer that covers at least the first surface 21 of the patch conductor 20. More specifically, the second dielectric layer 30 has a predetermined thickness and is in the form of a sheet extending in an in-plane direction. The second dielectric layer 30 has a first surface (front surface) 31 located on the upper side in the perpendicular direction and a second surface (back surface) 32 located on the lower side in the perpendicular direction. As shown in FIGS. 1 and 2 , the second dielectric layer 30 of this embodiment covers not only the first surface 21 of the patch conductor 20 but also a region of the first surface 11 of the first dielectric layer 10 where the patch conductor 20 is not formed.

[0029] Here, when a dielectric layer is arranged to face the electromagnetic wave radiation surface (first surface 21) of the patch conductor 20 as in this embodiment, the energy of the electromagnetic wave radiated from the patch conductor 20 may be lost when propagating through the dielectric layer (see, for example, paragraph 0039 of Japanese Patent Laid-Open Publication No. 2006-61047). Therefore, from the viewpoint of improving the antenna gain, a configuration in which a dielectric layer is arranged to face the first surface 21 of the patch conductor 20 is not usually considered.

[0030] In contrast, in the patch antenna 1 of this embodiment, the second dielectric layer 30 faces the first surface 21 of the patch conductor 20, and the antenna gain is improved, for example, by configuring the second dielectric layer 30 as follows. More specifically, the relative dielectric constant of the second dielectric layer 30 is preferably 3.5 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. Moreover, the relative dielectric constant of the second dielectric layer 30 is preferably 1.0 or more.

[0031] Examples of the second dielectric layer 30 having a relative dielectric constant of 3.5 or less (hereinafter, a relative dielectric constant within this range may be referred to as a "low dielectric constant") include fluororesins such as polytetrafluoroethylene. The material of the second dielectric layer 30 may also be a composite material containing a fluororesin and filler similar to those of the first dielectric layer 10. The fluororesin and filler contained in the second dielectric layer 30 may be the same as the above-mentioned fluororesin and filler usable in the first dielectric layer 10. However, the material of the second dielectric layer 30 is not limited to this.

[0032] The second dielectric layer 30 may be formed to have a uniform dielectric constant in the thickness direction, or may be formed to have a uniform dielectric constant in the in-plane direction. In other words, in the present invention, the second dielectric layer 30 may be formed as a sheet having a uniform dielectric constant, or as a plate-like body with a greater thickness having a uniform dielectric constant. This eliminates the need for a convex lens shape, as in the antenna disclosed in Patent Document 1, allowing for a more compact patch antenna. Furthermore, this eliminates the need for a flat plate-like structure, as in a Fresnel lens, resulting in superior manufacturability. Additionally, it eliminates the need for a gradient in the dielectric constant in the in-plane direction, which also contributes to superior manufacturability.

[0033] When the second dielectric layer 30 contains, for example, a fluorine-based resin and a filler, similar to the first dielectric layer 10, the porosity of the second dielectric layer 30 is preferably 30% or more, more preferably 35% or more, even more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more, and is usually 80% or less, preferably 70% or less. Within this range, favorable properties such as the relative dielectric constant and expansion coefficient of the composite material can be ensured. As with the first dielectric layer 10, the porosity is a value calculated by measuring the bulk density and true density of the material to be the pore-containing layer and substituting them into the following formula: Porosity [%] = (1 - (bulk density [g / cm3] of material containing fluororesin and filler) 3 ] / True density of material containing fluororesin and filler [g / cm 3 ]))×100

[0034] A dielectric layer having a low dielectric constant suitable for improving antenna gain can be obtained by using, for example, a dielectric layer containing the fluorine-based resin and filler having the above-described configuration as the second dielectric layer 30. In addition, the expansion coefficient of the second dielectric layer 30 can be reduced, and damage, peeling, and the like caused by a difference with the expansion coefficient of the patch conductor 20 can be prevented.

[0035] To improve the antenna gain, the thickness of the second dielectric layer 30 is preferably 1.0 mm or more, more preferably 3.0 mm or more, and even more preferably 5.0 mm or more. The thickness of the second dielectric layer 30 is preferably 10 mm or less.

[0036] Although the mechanism by which the antenna gain is improved by providing a sheet-like second dielectric layer 30 with a uniform dielectric constant so as to cover the first surface 21 of the patch conductor 20 is unclear, it is thought that the electromagnetic waves radiated from the patch conductor 20 interact with the second dielectric layer 30 with a low dielectric constant to increase the directivity of the radiated electromagnetic waves, causing the second dielectric layer 30 to behave like a lens, thereby improving the antenna gain. Furthermore, according to this embodiment, the antenna can be miniaturized because a thin sheet-like second dielectric layer 30 is laminated on the patch conductor 20. Furthermore, since there is no need to form a flat plate-like structure like a Fresnel lens, the antenna is easy to manufacture. In addition, there is no need to form a gradient in the dielectric constant in the in-plane direction, which also provides excellent manufacturability.

[0037] <Ground layer> The ground layer 40 is a sheet-like conductor layer that is bonded to the second surface 12 of the first dielectric layer 10 and faces the patch conductor 20 across the first dielectric layer 10. The material of the ground layer 40 is not particularly limited as long as it is conductive, and examples include metals such as titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, and hafnium; and conductive metal oxides such as ITO, zinc oxide, and tin oxide. The ground layer 40 may also be made of a material containing two or more of these metals or metal oxides, or an alloy containing these metals as the main component.

[0038] <Power supply via> The power feed via 50 supplies power from, for example, a power feed line to the patch conductor 20. The power feed via 50 penetrates the first dielectric layer 10 and the ground layer 40. One end 51 of the power feed via 50 is electrically connected to the patch conductor 20. The other end 52 of the power feed via 50 is electrically connected to the power feed line. [Example]

[0039] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0040] <Sample> As with the patch antenna 1 according to the above embodiment, Examples 1 to 6 and Comparative Examples 1 to 3 were fabricated, each having a ground layer 40, a first dielectric layer 10, a patch conductor 20, and a second dielectric layer 30 laminated in this order. The relative permittivity and thickness of the second dielectric layer 30 in Examples 1 to 6 and Comparative Examples 2 to 3 are shown in Table 1. Note that Comparative Example 1 is a sample that does not have the second dielectric layer 30. In Table 1, the dielectric constant of Comparative Example 1 is set to 1, which is the dielectric constant of air, and the thickness is set to 0 mm. The relative permittivity of the first dielectric layer 10 in each of the samples of Examples 1 to 6 and Comparative Examples 1 to 3 was 1.88, and the thickness was 0.75 mm.

[0041] [Table 1]

[0042] <Evaluation of antenna gain> Table 2 shows the simulation results of the antenna gain for each sample of Examples 1 to 6 and Comparative Examples 1 to 3, and the improvement rate of the antenna gain relative to Comparative Example 1. Fig. 3 shows a graph comparing the antenna gain for Example 6 and Comparative Example 1. The horizontal axis of Fig. 3 represents the azimuth angle of the beam formed by the electromagnetic wave radiated from the patch conductor 20, and the vertical axis represents the antenna gain at each azimuth angle.

[0043] [Table 2]

[0044] As shown in Table 2, the antenna gain in Examples 1 to 6, which have a second dielectric layer 30 with a low dielectric constant of 3.5 or less, preferably 2.0 or less, and a thickness of 1 mm or more, was improved compared to the antenna gain in Comparative Example 1.

[0045] 3, the maximum gain of Example 6 was improved by about 1 dB compared to the maximum gain of Comparative Example 1. The beam width of Example 6 was also narrower than the beam width of Comparative Example 1. As described above, it was suggested that a patch antenna with improved directivity and antenna gain can be obtained by arranging the second dielectric layer 30 having a low dielectric constant of 3.5 or less and a thickness of 1 mm or more facing the first surface 21 of the patch conductor 20.

[0046] <Evaluation of Antenna Gain When the Thickness of the Second Dielectric Layer 30 is Varying> FIG. 4 shows the antenna gain when the thickness of the second dielectric layer 30 is changed in Example 9 (relative dielectric constant of the second dielectric layer 30: 1.5, relative dielectric constant of the first dielectric layer 10: 1.88), Example 10 (relative dielectric constant of the second dielectric layer 30: 2.0, relative dielectric constant of the first dielectric layer 10: 1.88), and Comparative Example 4 (relative dielectric constant of the second dielectric layer 30: 3.7, relative dielectric constant of the first dielectric layer 10: 1.88).

[0047] 4, in Examples 9 and 10, the antenna gain improved as the thickness of the second dielectric layer 30 increased. In contrast, in Comparative Example 4, the antenna gain decreased as the thickness of the second dielectric layer 30 increased.

[0048] FIG. 5 also shows the antenna gain when the thickness of the second dielectric layer 30 is changed in Example 11 (relative dielectric constant of the second dielectric layer 30: 1.5, relative dielectric constant of the first dielectric layer 10: 3.7), Example 12 (relative dielectric constant of the second dielectric layer 30: 2.0, relative dielectric constant of the first dielectric layer 10: 3.7), and Comparative Example 5 (relative dielectric constant of the second dielectric layer 30: 3.7, relative dielectric constant of the first dielectric layer 10: 3.7).

[0049] 5, in Examples 11 and 12, the antenna gain improved as the thickness of the second dielectric layer 30 increased. In contrast, in Comparative Example 5, the antenna gain decreased as the thickness of the second dielectric layer 30 increased. That is, a similar tendency was confirmed even when the relative dielectric constant of the first dielectric layer 10 was changed.

[0050] Aspects of the present disclosure are, for example, as follows. <1> a first dielectric layer; a patch conductor formed on the first dielectric layer; a second dielectric layer formed on the patch conductor; and The second dielectric layer has a relative dielectric constant of 3.5 or less. Patch antenna. <2> The thickness of the second dielectric layer is 1.0 mm or more. The aforementioned <1> The patch antenna according to claim 1. <3> At least one of the first dielectric layer and the second dielectric layer is an inorganic porous aggregate having pores constituted by a plurality of fine particles; fibrils made of fluorine-based resin; The aforementioned <1> or the above <2> The patch antenna according to claim 1. <4> The second dielectric layer has a relative dielectric constant of 2.0 or less. The aforementioned <1> From the above <3> 10. A patch antenna according to claim 9, wherein: [Explanation of symbols]

[0051] 1 patch antenna 10 First dielectric layer 20 patch conductors 30 Second dielectric layer 40 Ground Layer 50 Power supply vias

Claims

1. a first dielectric layer; a patch conductor formed on the first dielectric layer; a second dielectric layer formed on the patch conductor; and The second dielectric layer has a relative dielectric constant of 3.5 or less. Patch antenna.

2. The thickness of the second dielectric layer is 1.0 mm or more. The patch antenna of claim 1 .

3. At least one of the first dielectric layer and the second dielectric layer is an inorganic porous aggregate having pores constituted by a plurality of fine particles; fibrils made of fluorine-based resin; 3. The patch antenna according to claim 1, wherein:

4. The second dielectric layer has a relative dielectric constant of 2.0 or less.

3. The patch antenna according to claim 1 or 2.

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