Antenna and manufacturing method thereof

Abstract

To provide an antenna which suppresses an electromagnetic wave leaking from an EBG structure of an EBG reflector plate and the ground by applying a metamaterial technique, and a manufacturing method of the same.SOLUTION: An antenna having a small-sized structure comprises: an antenna element 1 which radiates an electromagnetic field in both front and rear directions; an EBG reflector plate 2 which reflects the radiation to the rear side of the antenna element 1 to the front side; and a dielectric material layer 4 which captures and suppresses the electromagnetic wave leaking from the EBG reflector plate 2 to the rear side. By suppressing the leaking electromagnetic wave radiated to the rear side from the EBG reflector plate 2 by the dielectric material layer 4, the electromagnetic field is radiated in a single direction while having the small reflection area. Since the electromagnetic wave leaking to the rear side from the EBG reflector plate 2 is captured and suppressed by providing the dielectric material layer 4, the antenna can be mounted in contact with a metal portion or the like even if the metal portion exists in an antenna mounting area of a device, and thereby restrictions on antenna mounting can be eliminated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an antenna that suppresses backward radiation from an antenna element and a method for manufacturing the same. [Background technology]

[0002] Due to the high mounting density, it is difficult to secure a sufficient antenna installation area, and there is a demand for antennas to be smaller, lighter, and thinner. To meet this demand, antennas with low profile structures have been developed, and one such antenna is the inverted-F antenna (Patent Document 1).

[0003] In Patent Document 1, electromagnetic waves are radiated from a pair of antenna elements, and an EBG plate is disposed behind the inverted-F antenna element in order to suppress coupling of the electromagnetic waves from the pair of antenna elements.

[0004] In Patent Document 1, in order to suppress coupling of electromagnetic waves from a pair of antenna elements, the distance between the antenna elements and the EBG plate is set to 1 / 4λ (λ is the wavelength of the frequency used). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5112204 [Patent Document 2] Patent No. 5527316 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, the EBG plate is disposed behind a pair of antenna elements, and no attention is paid to the periodic boundary condition at the edge of the EBG plate.

[0007] As a result, electromagnetic waves may leak out from the edges of the EBG plate in Patent Document 1, potentially generating an electric field from the EBG plate toward the ground behind it, leaving the problem that these leaking electromagnetic waves may affect forward radiation from the antenna element.

[0008] Patent Document 2 achieves a low-profile antenna by adopting a three-layer structure in which the antenna element, the mushroom-type periodic structure, and the ground are formed.

[0009] In order to achieve a low-profile antenna, Patent Document 2 employs a structure in which a resonator is used to keep the area occupied by the mushroom-shaped periodic structure equal to or smaller than the size of the antenna element.

[0010] Patent Document 2 does not pay attention to the periodic boundary conditions at the edges of the mushroom-shaped periodic structure, and therefore the problem remains that electromagnetic waves leak out from the edges of the mushroom-shaped periodic structure, generating an electric field toward the rear ground, and this leaked electromagnetic wave affects the forward radiation from the antenna element.

[0011] The installation conditions for wireless terminals in IoT / M2M, which have been expanding in recent years, have made it difficult to secure an optimal installation location for antennas, as seen in typical LPWA (Low Power Wide Area: trademark) systems, where they are attached directly to metal devices or installed in locations with metal parts or water nearby. As a result, the radio wave transmission and reception environment is in the worst possible condition, which adversely affects antennas.

[0012] In Patent Document 2, no measures are taken to prevent backward leakage of electromagnetic waves from the mushroom-shaped periodic structure, so when the ground is mounted close to a metal part in the antenna mounting area of ​​a device, the leaked electromagnetic waves are reflected forward as reflected waves of opposite phase, resulting in a deterioration of the antenna gain. Therefore, there is a problem that the mounting location when installing the antenna of Patent Document 2 in a device is limited.

[0013] An object of the present invention is to provide an antenna that applies metamaterial technology to suppress electromagnetic waves leaking from an EBG structure of an EBG reflector and a ground, and a method for manufacturing the same. [Means for solving the problem]

[0014] Generally, an antenna with a small reflector radiates electromagnetic fields in both directions (+ / -z direction). This bidirectional radiation changes to unidirectional radiation as the reflector's reflective area increases, but an increase in the reflector area also means an increase in the antenna volume. The present invention provides an antenna that has a small reflecting area yet radiates an electromagnetic field in a single direction.

[0015] Specifically, in order to achieve the above-mentioned object, the antenna of the present invention is an antenna having a small structure, characterized in that it has an antenna element that radiates an electromagnetic field in both forward and backward directions, an EBG reflector that reflects the backward radiation of the antenna element forward, and a dielectric layer that captures and suppresses electromagnetic waves that leak backward from the EBG reflector.

[0016] The antenna is characterized in that the dielectric layer has a metal surface facing the ground of the EBG reflector.

[0017] The antenna is characterized in that the electromagnetic wave reflecting surface of the EBG reflector is set to be wider than the radiation surface of the antenna element.

[0018] The antenna is characterized in that the metal surface of the dielectric layer has a planar structure made of a metal plate.

[0019] The antenna is characterized in that the dielectric layer has a dielectric between the ground of the EBG reflector and the metal plate, and has a structure that attenuates the leakage electromagnetic waves while suppressing radiation.

[0020] The antenna is characterized in that an inverted F antenna element having a patch-shaped radiation surface is used as the antenna element.

[0021] The antenna is characterized in that the metal surface of the dielectric layer has a cavity structure consisting of a planar structure made of a metal plate and a side structure raised from the edge of the planar structure.

[0022] The antenna is characterized in that the distance between the radiation surface of the antenna element and the reflection surface of the EBG reflector and the thickness dimension of the dielectric layer are each set to 1 / 4λ (λ is the wavelength of the frequency used) or less.

[0023] The antenna is characterized in that a coaxial cable is arranged along the ground of the EBG reflector, the inner conductor of the coaxial cable is connected to the power supply part of the antenna element, and the outer conductor of the coaxial cable is connected to the ground of the EBG reflector.

[0024] The antenna is characterized in that the minimum dimension of the metal plate of the dielectric layer is set to be approximately the same as the dimension of the ground of the EBG reflector.

[0025] The method for manufacturing an antenna having a small structure according to the present invention is characterized by carrying out the following assembly steps: forming an antenna element that radiates an electromagnetic field in both forward and backward directions using a first dielectric substrate as a core material; forming an EBG reflector that reflects backward radiation from the antenna element forward using a second dielectric substrate as a core material; forming a dielectric layer that captures and suppresses electromagnetic waves leaking backward from the EBG reflector using a third dielectric substrate as a core material; and stacking the antenna element, the EBG reflector, and the dielectric layer into a three-layer structure.

[0026] The method for manufacturing the antenna is characterized by carrying out the following assembly steps: an assembly step of forming the feeding section and the grounding section of the antenna element toward the ground of the EBG reflector; an assembly step of forming a countersink in at least one of the facing end faces of the second dielectric substrate and the third dielectric substrate to receive a coaxial cable and lead it out of the dielectric substrate, and a countersink to couple the coaxial cable to the antenna element; and an assembly step of receiving the coaxial cable in the countersink and connecting the inner core wire to the feeding section within the countersink, and connecting the matching adjustment grounding section to the ground of the EBG reflector within the countersink. [Effects of the Invention]

[0027] As described above, according to the present invention, there is provided an antenna element that radiates an electromagnetic field in both forward and backward directions, an EBG reflector that reflects the backward radiation of the antenna element forward, and a dielectric layer that has a metal surface facing the EBG reflector and captures and suppresses electromagnetic waves leaking backward from the EBG reflector. The reflective area of ​​an EBG reflector is inversely proportional to the amount of radiation behind the antenna element, but by adopting the EBG reflector of the present invention, the reflective area is reduced, and by adding the dielectric layer, it is possible to radiate an electromagnetic field in one direction while maintaining a small reflective area.

[0028] Furthermore, according to the present invention, by providing the dielectric layer, electromagnetic waves leaking backward from the EBG reflector are captured and suppressed, so that even if there are metal parts in the antenna mounting area of ​​the device, the antenna can be mounted in contact with the device, which not only eliminates the restrictions imposed on antenna mounting, but also makes it possible to reduce the effective height dimension of the antenna and achieve miniaturization. Furthermore, it is possible to suppress leakage electromagnetic waves leaking backward from the EBG reflector while maintaining a compact structure, and there is no risk of a decrease in antenna gain in the forward direction, making it possible to achieve stable communication. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a perspective view showing an antenna according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view of the antenna according to the embodiment of the present invention, seen from the bottom side. [Figure 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 1 is a plan view showing an EBG reflector according to an embodiment of the present invention. [Figure 5] FIG. 2 is a perspective view showing the relationship between an antenna element and an EBG reflector in the embodiment of the present invention. [Figure 6] FIG. 2 is a perspective view illustrating an example of a dielectric layer in an antenna according to an embodiment of the present invention. [Figure 7] 10(a) and 10(b) are characteristic diagrams showing the results of simulating the radiation pattern in the elevation plane of the antenna according to the embodiment of the present invention. [Figure 8] For comparison, (a) and (b) are characteristic diagrams showing the results of simulating the radiation pattern in the elevation plane of an antenna that does not have a dielectric layer. [Figure 9] 10A and 10B are characteristic diagrams showing the results of simulating the frequency response of the VSWR and the gain in the forward direction of the antenna according to the embodiment of the present invention and an antenna for comparison. [Figure 10] FIG. 10 is a cross-sectional view showing another example of a dielectric layer in the antenna according to the embodiment of the present invention. [Figure 11] FIG. 10 is a perspective view showing another example of a dielectric layer in the antenna according to the embodiment of the present invention. [Figure 12] 1(a), 1(b), 1(c), and 1(d) are perspective views showing the state of the dielectric substrates during the manufacturing process of the antenna according to the present invention, disassembled into individual dielectric substrates. [Figure 13] 13 is a perspective view showing an antenna manufactured by the method for manufacturing a feed structure to an antenna according to the embodiment of the present invention shown in FIG. 12. FIG. [Figure 14] 14(a) is a cross-sectional view showing the internal structure of the antenna according to the embodiment of the present invention shown in FIG. 13, and FIG. 14(b) is a characteristic diagram showing a simulated radiation pattern. [Figure 15] FIG. 1A is a plan view showing a state in which an antenna according to an embodiment of the present invention is installed on a metal plate, and FIG. 1B is a characteristic diagram showing a simulated radiation pattern. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0031] Generally, antennas with small reflectors radiate electromagnetic fields in both directions (±z direction), but this bidirectional radiation changes to unidirectional radiation as the reflector's reflective area increases. Therefore, an increase in the reflector area means an increase in the antenna volume. In other words, the reflective area of ​​the EBG reflector and the amount of radiation to the rear of the antenna element are inversely proportional to each other. In order to achieve a compact antenna structure, the present invention provides an EBG reflector that applies metamaterial technology, thereby reducing the reflection area and making the antenna smaller than when an EBG reflector is not provided.Furthermore, by suppressing the leakage electromagnetic waves that radiate backward from the EBG reflector, it is possible to radiate an electromagnetic field in one direction while maintaining a small reflection area.

[0032] Since the reflective area of ​​the EBG reflector and the amount of radiation behind the antenna element are inversely proportional, the use of an EBG reflector can make the antenna smaller. However, on the other hand, since the reflective area of ​​the EBG reflector is reduced compared to when no EBG reflector is provided, the amount of leakage electromagnetic waves radiated behind the EBG reflector increases. Therefore, if metamaterial technology is adopted in which the reflection area of ​​the EBG reflector is set smaller than the radiation area of ​​the antenna element shown in Patent Document 2, it is impossible to suppress the radiation of electromagnetic waves in one direction due to the inverse proportional relationship described above, and the backward radiation of leaked electromagnetic waves will increase by the amount of the reduced reflection area.

[0033] Therefore, the present invention provides a dielectric layer behind the EBG reflector, and by using this dielectric layer to suppress the leakage electromagnetic waves that radiate backward from the EBG reflector, it is possible to radiate an electromagnetic field in one direction while having a small reflection area, in other words, it is possible to suppress the backward radiation of leakage electromagnetic waves and radiate an electromagnetic field in one direction while having a small reflection area.

[0034] According to the present invention, by providing the dielectric layer, electromagnetic waves leaking backward from the EBG reflector are captured and suppressed, so even if a metal part is present in the antenna mounting area of ​​the device, the antenna can be mounted in contact with the metal part, which not only eliminates the restrictions imposed on antenna mounting, but also enables the effective height dimension of the antenna to be kept low and made smaller, makes it possible to suppress leakage electromagnetic waves leaking backward from the EBG reflector, and increase the antenna gain in the forward direction.

[0035] Specifically, as shown in Figures 1 and 3, the antenna according to an embodiment of the present invention is an antenna with a small structure, and includes an antenna element 1 that radiates an electromagnetic field in both forward and backward directions, an EBG reflector 2 that reflects backward radiation from the antenna element 1 forward, and a dielectric layer 4 that captures and suppresses electromagnetic waves leaking backward from the EBG reflector 2.

[0036] In the following description, an inverted-F antenna element having a low-profile structure with a patch-like plane is used as the antenna element 1, and the antenna element 1 will be referred to as an inverted-F antenna element 1.

[0037] As shown in Figures 1, 2 and 3, the antenna according to an embodiment of the present invention has a three-layer structure in which an inverted-F antenna element 1 is arranged on the top layer, an EBG reflector 2 is arranged on the layer below that, and a dielectric layer 4 is arranged on the layer below that.

[0038] 1, 2 and 3, the patch-shaped radiation surface 1a of the inverted-F antenna element 1 is formed on the upper surface of a dielectric substrate 5, and an EBG reflector 2 is disposed on the lower surface of the dielectric substrate 5. Furthermore, as shown in FIGS. 1, 2 and 3, a dielectric substrate 6 is disposed below the dielectric substrate 5, and a ground 3 is formed on the lower surface of the dielectric substrate 6.

[0039] 1, 3, and 5, the inverted-F antenna element 1 is composed of a patch-shaped radiating surface 1a formed on the upper surface of a dielectric substrate 5, a feeder 1b that penetrates the dielectric substrate 5 from top to bottom and is connected to the patch-shaped radiating surface 1a at its upper end, and a matching-adjustment grounding portion 1c that penetrates the dielectric substrate 5 from top to bottom and is connected to the patch-shaped radiating surface 1a at its upper end and to the ground 3 at its lower end. An inner conductor 12a of a coaxial cable 12 (described below) is connected to the feeder 1b of the inverted-F antenna element 1, and an outer conductor 12b of the coaxial cable 12 (described below) is connected to the matching-adjustment grounding portion 1c, so that data to be transmitted is transmitted to the inverted-F antenna element 1, and received data received by the inverted-F antenna element 1 is taken out via the coaxial cable 12.

[0040] The dielectric substrate 5 has the characteristics of thickness B and relative dielectric constant εr, and when the operating frequency is 5.15 GHz, the thickness B is set to 1.6 mm and the relative dielectric constant εr is set to 2.33. However, the operating frequency is not limited to 5.15 GHz, and similarly, the thickness B is not limited to 1.6 mm and the relative dielectric constant εr is not limited to 2.33. The dielectric substrate 6 has the characteristics of thickness B and relative dielectric constant εr, and when the operating frequency is 5.15 GHz, the thickness B is set to 1.6 mm and the relative dielectric constant εr is set to 2.6. However, the operating frequency is not limited to 5.15 GHz, and similarly, the thickness B is not limited to 1.6 mm and the relative dielectric constant εr is not limited to 2.33. If the wavelength of the operating frequency is λ, then a thickness of 1.6 mm is approximately 1 / 36.4λ.

[0041] As is clear from the above dimensional relationships, the thickness B of the dielectric substrates 5 and 6 is related to the wavelength λ of the operating frequency, and it is desirable to set the thickness of the dielectric substrates 5, 6 to approximately 1 / 4λ or less of the wavelength λ of the operating frequency. If the wavelength of the operating (design) frequency is λ, it is particularly desirable to set the thickness to 1 / 10λ or less in order to achieve compactness.

[0042] As described above, the thickness B of the dielectric substrate 5 is set to 1 / 4λ or less, so that the radiation surface 1a of the antenna element 1 is positioned close to the reflection surface 2a of the EBG reflector 2, and the distance between the radiation surface 1a of the antenna element 1 and the reflection surface 2a of the EBG reflector 2 is set to 1 / 4λ or less.

[0043] As shown in FIG. 5, the feed portion 1b and the ground portion 1c of the inverted-F antenna 1 are insulated from the EBG reflecting substrate 2 (the reflecting element 2b described below) and penetrate the dielectric substrate 6 in the vertical direction.

[0044] In the embodiment shown in Figure 1, an inverted F antenna element is used as the antenna element 1, but this is not limited to this and it may be a linear radiation type antenna element or an antenna that radiates linearly polarized or circularly polarized electromagnetic waves, and is not limited to an inverted F antenna.In short, any configuration that radiates electromagnetic waves in both forward and backward directions is acceptable.

[0045] A specific description will be given of the EBG reflector 2. The EBG reflector 2 has a reflecting element 2b that forms a reflecting surface 2a that reflects the electromagnetic waves radiated backward from the inverted-F antenna element 1 forward (in the +z direction), and a via 2c that passes through the dielectric substrate 6 from top to bottom and connects the reflecting surface 2a to the ground 3.

[0046] 1, 3 and 4, six reflective elements 2b that form the reflective surface 2a are formed in a periodic arrangement on the upper surface of the dielectric substrate 6, electrically insulated from one another. The multiple reflective elements 2b are connected in parallel to the ground 3 by vias 2c that penetrate the dielectric substrate 6 in the vertical direction, and the reflective elements 2b, vias 2c and ground 3 form a mushroom-shaped element.

[0047] The periodically arranged mushroom-shaped elements form an artificial magnetic wall, which in turn forms an EBG reflector 2 that reflects the electromagnetic waves radiated backward from the inverted-F antenna element 1 forward.

[0048] In an embodiment of the present invention, by employing the EBG reflector 2, the area of ​​the reflecting surface 2a that reflects the radiated electromagnetic waves radiated backward from the antenna element 1 in the forward direction (+z direction) is reduced compared to when the EBG reflector 2 is not provided. The area of ​​the reflecting surface 2a of the EBG reflector 2 is reduced by the amount by which the EBG reflector 2 is provided, but since the area of ​​the reflecting surface 2a of the EBG reflector 2 and the amount of radiation backward from the radiation surface 1a of the antenna element 1 are inversely proportional to each other, the area S1 of the reflecting surface 2a of the EBG reflector 2 is set to be larger than the area S2 of the radiation surface 1a of the antenna element 1 in order to reduce the amount of radiation backward from the radiation surface 1a of the antenna element 1 as quickly as possible.

[0049] In the embodiment shown in the figure, six reflecting elements 2b of the EBG reflector 2 are formed on the dielectric substrate 6, but the number of reflecting elements 2b installed on the EBG reflector 2 is not limited to six, and although the reflecting elements 2b of the EBG reflecting substrate 2 shown in the figure are shaped like a square, this is not limited to this and they may be shaped like a rectangle or a polygon, and are not limited to the shape shown in the figure. The reflecting elements 2b of the multiple EBG reflectors 2 are formed on the top surface of the dielectric substrate 6, insulated from each other, as shown in Figure 4.

[0050] This embodiment of the present invention has a dielectric layer 4 with a metal surface 4a facing the EBG reflector 2, and by capturing and suppressing electromagnetic waves leaking backward from the EBG reflector 2, it achieves an increase in antenna gain in the forward direction (+z direction) of the antenna element 1.

[0051] The structure of the dielectric layer 4 will be described in detail. As shown in Figures 1, 2, 3, and 6, the dielectric layer 4 has a flat metal plate 7 that forms the metal surface 4a facing the ground 3 of the EBG reflector 2, and this metal plate 7 forms the metal surface 4a with a planar structure. As shown in Figure 3, the minimum dimensions of the metal plate 7 are set to be approximately the same as the dimensions of the ground 3. These dimension settings are intended to stabilize the impedance of the antenna, and the dimensions of the metal plate 7 may be larger than the dimensions of the ground 3 within the range in which the impedance is stabilized.

[0052] Next, embodiments of the dielectric layer 4 will be described in detail with reference to FIGS. 3, 4, 6, 9, 10 and 11. FIG.

[0053] The dielectric layer 4 according to the embodiment shown in Figures 3 and 6 has a ground 3 formed on the upper surface of a dielectric substrate 9 and a flat metal plate 7 formed on the lower surface thereof, thereby having the dielectric substrate 9, which is a dielectric, between the ground 3 and the metal plate 7 of the EBG reflector 2, and constructing a structure that captures and attenuates leakage electromagnetic waves leaking from the EBG reflector 2. The dielectric substrate 9 has the characteristics of thickness B and relative dielectric constant εr, and when the operating frequency is 5.15 GHz, the thickness B is set to 1.6 mm and the relative dielectric constant εr is set to 2.33. However, the operating frequency is not limited to 5.15 GHz, and similarly, the thickness B is not limited to 1.6 mm and the relative dielectric constant εr is not limited to 2.33. Furthermore, it is sufficient that the end surface of the metal plate 7 facing the ground 3 is flat, and it is acceptable for the opposite surface to have irregularities, etc. If the wavelength of the design (used) frequency is λ, then a thickness of 1.6 mm is approximately 1 / 36.4λ.

[0054] As is clear from the above dimensional relationships, the thickness B of the dielectric substrate 9 is related to the wavelength λ of the operating frequency, and it is desirable to set the thickness of the dielectric substrate 9 to approximately 1 / 4λ or less of the wavelength λ of the operating frequency. If the wavelength of the operating (design) frequency is λ, it is particularly desirable to set the thickness to 1 / 10λ or less in order to achieve miniaturization.

[0055] As described above, the thickness B of the dielectric substrate 9 is set to 1 / 4λ or less, and the ground 3 and the metal plate 7 are formed on either side of the dielectric substrate 9, so the thickness dimension of the dielectric layer 4 is set to approximately 1 / 4λ or less.

[0056] The dielectric layer 4 according to the embodiment shown in Figures 10 and 11 forms a cavity structure 11 consisting of a combination of a planar metal surface 4a made of a flat metal plate 7 formed on the underside of a dielectric substrate 9 and a metal surface 4b made of a side wall 10 formed by raising the periphery of the metal plate 7 toward the ground 3.

[0057] 10 and 11, the dielectric layer 4 has a side wall 10 that rises toward the ground 3 side, ensuring a gap d between them, and captures and suppresses electromagnetic waves leaked from the EBG reflector 2 based on the relationship between the relative permittivity ε of the dielectric substrate 9 and the gap d. The energy density is high inside the cavity structure 11, and Joule loss due to the leakage electromagnetic waves flowing on the metal plate 7, side wall 10, and surface of the ground 3, and heat loss due to dielectric loss in the dielectric caused by the electric field, etc., increase, and the energy of the leakage electromagnetic waves leaking from the EBG reflector 2 is converted into heat and attenuated.

[0058] The effect of suppressing leakage electromagnetic waves by the dielectric layer 4 according to the embodiment shown in FIGS. 3 and 6 will be described based on the results of a simulation.

[0059] As shown in Fig. 3, excitation is performed from the feeding point 1b of the inverted antenna element 1. The excitation frequency is set to 5.15 GHz, the thickness B of the dielectric substrate 5 is set to 1.6 mm, and the relative dielectric constant εr is set to 2.33, and the thickness B of the dielectric substrate 6 is set to 1.6 mm, and the relative dielectric constant εr is set to 2.6. Furthermore, the thickness B of the dielectric substrate 9 is set to be the same as the thicknesses of the dielectric substrates 5 and 6.

[0060] 7(a) and 7(b) show the characteristics of the simulation results of the radiation pattern in the elevation plane of the antenna according to the embodiment of the present invention. For comparison, FIGS. 8(a) and 8(b) show the simulation results of the radiation pattern in the elevation plane of an antenna not equipped with the dielectric layer 4.

[0061] The solid line in Figure 7(a) represents the θ-direction component Eθ of the electric field in the antenna according to the embodiment of the present invention, and the dotted line in Figure 7(b) represents the φ-direction component Eφ of the electric field in the antenna according to the embodiment of the present invention.

[0062] The solid line in FIG. 8(a) represents the θ-direction component Eθ of the electric field in the comparative antenna, and the dotted line in FIG. 8(b) represents the φ-direction component Eφ of the electric field in the conventional comparative antenna.

[0063] As shown in Figure 7, it is clear from the elevation in-plane radiation pattern of the antenna additionally equipped with the dielectric layer 4 of the embodiment of the present invention that radiation backward (-z direction) from the EBG structure is suppressed.

[0064] Furthermore, the gain of antenna element 1 in the forward direction (+z direction) increased by approximately 2.2 dB, and the gain at the operating frequency of 5.15 GHz was approximately 5.9 dBi. The 3 dB drop frequency fractional bandwidth of the gain was approximately 20%.

[0065] P1 in Figure 9 shows the frequency response of the voltage standing wave ratio (VSWR) in the antenna according to the embodiment of the present invention, and P2 in Figure 9 shows the frequency response of the voltage standing wave ratio (VSWR) in the comparative antenna.

[0066] Antennas are required to have a voltage standing wave ratio (VSWR) of 2 or less. As is clear from Fig. 9, the antenna according to the embodiment of the present invention has a VSWR of 2 or less around the design frequency of 5.15 GHz. Furthermore, as is clear from Fig. 9, in the embodiment of the present invention, the frequency ratio bandwidth in which the VSWR is 2 or less is approximately 7%.

[0067] Next, a power feeding structure for the antenna element 1 in the antenna according to the present invention will be described with reference to FIGS.

[0068] 13 and 14(a), power is fed to the antenna element 1 via a coaxial cable 12. As shown in Fig. 13, the coaxial cable 12 is arranged along the ground 3 of the EBG reflector 2, with an inner conductor 12a of the coaxial cable 12 connected to the power feed portion 1b of the antenna element 1 and an outer conductor 12b of the coaxial cable 12 connected to the ground 3 of the EBG reflector 2.

[0069] The coaxial cable 12 is led out from the mating surfaces of the dielectric substrate 6 and the dielectric substrate 9 along the ground 3 of the EBG reflector 2. The lead-out direction H of the coaxial cable 12 is not limited to the direction shown in FIG. 13 .

[0070] Next, a method for manufacturing an antenna according to the present invention will be described with reference to Fig. 12. Figs. 12(a), (b), (c), and (d) show the state of disassembled dielectric substrates during the manufacturing process of the antenna manufacturing method. Fig. 12(a) shows the state of the dielectric substrate 5 forming the antenna element 1, viewed from an oblique direction. Fig. 12(b) shows the state of the dielectric substrate 6 forming the EBG reflector 2 and the ground 3, viewed from an oblique direction. Fig. 12(c) shows the state of the dielectric substrate 6 of Fig. 12(b), rotated around the rotation axis x so that the ground 3 faces upward, viewed from an oblique direction. Fig. 12(d) shows the state of the dielectric substrate 9 forming the dielectric layer 4, viewed from an oblique direction.

[0071] As shown in Fig. 12(a), an assembly step is performed to form an antenna element 1 that radiates an electromagnetic field in both forward and backward directions using a first dielectric substrate as a core material. Specifically, as shown in Fig. 12(a), a patch-like radiation surface 1a of the inverted-F antenna element 1 is formed on the upper surface of a dielectric substrate 5 serving as the first dielectric substrate. As an example, the patch-like radiation surface 1a is formed on the upper surface of the dielectric substrate 5 by etching.

[0072] 12(b) are then opened in the patch-shaped radiation surface 1a of the dielectric substrate 5. One of the through holes T1 is for forming the power supply portion 1b of the inverted-F antenna element 1, and the remaining through hole T2 is for forming the matching adjustment ground portion 1c of the inverted-F antenna element 1.

[0073] As shown in Figures 12(b) and 12(c), an assembly step is performed to form an EBG reflector 2 that uses a second dielectric substrate as a core material and reflects backward radiation from the antenna element 1 forward. Specifically, as shown in Figure 12(b), six reflecting elements 2b that constitute the reflecting surface 2a of the EBG reflector 2 are formed on the upper surface of a dielectric substrate 6 that serves as the second dielectric substrate. The six reflecting elements 2b are insulated from one another. As an example, the six reflecting elements 2b are formed on the upper surface of the dielectric substrate 6 by etching. Adjacent reflecting elements 2b are also separated and insulated by etching. Spaces 17 are also formed by etching at locations corresponding to the through holes T1 and T2 in the dielectric substrate 5, separating them from adjacent reflecting elements 2b.

[0074] As shown in FIG. 12(c), a ground 3 is formed over the entire surface of the dielectric substrate 6 opposite to the surface on which the reflecting element 2b is formed.

[0075] As shown in Figure 12(b), after forming the reflecting element 2b, or when forming the reflecting element 2b, a through hole T3 is opened in each reflecting element 2b, penetrating vertically through the dielectric substrate 6 as shown in Figures 12(b) and (c), and through holes T4 and T5 are opened in the space 17 shown in Figure 12(b), penetrating vertically through the dielectric substrate 6, communicating with the through holes T1 and T2 of the dielectric substrate 5 shown in Figure 12(a).

[0076] As shown in Figure 12(c), ground 3 is formed over the entire surface of dielectric substrate 6 opposite to the surface on which reflecting element 2b is formed. When forming ground 3, as shown in Figure 12(c), space 18 is formed in the location of through hole T4 in dielectric substrate 6, and the opening portion of through hole T4 in dielectric substrate 6 is separated and insulated from ground 3. When forming ground 3, through hole 5 is formed in dielectric substrate 6 with the opening end of through hole T5 connected to ground 3, as shown in Figure 12(c).

[0077] 12(b) and 12(c), vias 2c are formed in the dielectric substrate 6 by filling the through holes T3 in the dielectric substrate 6 with gold plating, and multiple reflecting elements 2b in the dielectric substrate 6 are connected in parallel to the ground 3 by the vias 2c. Here, the reflecting elements 2b, vias 2c and ground 3 in the dielectric substrate 6 shown in FIGS. 12(b) and 12(c) constitute an EBG reflector 2 of a mushroom-shaped element.

[0078] Through holes T1 and T2 in dielectric substrate 5 shown in Figure 12(a) and through holes T4 and T5 in dielectric substrate 6 shown in Figure 12(b) are filled with gold plating to form power supply portion 1b and matching adjustment ground portion 1c shown in Figure 3 on dielectric substrates 5 and 6. Because space 17 is provided in dielectric substrate 6, power supply portion 1b and matching adjustment ground portion 1c are insulated from reflecting element 2b. Because space 18 is provided in dielectric substrate 6, power supply portion 1b is insulated from ground 3 of dielectric substrate 6. Because the open end of through hole T5 is connected to ground 3, matching adjustment ground portion 1c is formed in a state where it is connected to ground 3.

[0079] 3 and 13, the upper end of the power supply section 1b is connected to the patch-shaped radiating surface 1a shown in Fig. 12(a), and the lower end is insulated from the ground 3. The upper end of the matching adjustment ground section 1c is connected to the reflecting element 2b shown in Fig. 12(b), and the lower end is connected to the ground 3, as shown in Fig. 3 and 13. Here, the patch-shaped radiation surface 1a, the power supply portion 1b, and the matching adjustment ground portion 1c constitute the antenna element 1. Although the antenna element 1 shown in Fig. 13 uses an inverted-F antenna element, antenna elements other than the inverted-F antenna element may be used as long as the antenna element 1 is configured to radiate electromagnetic waves in the forward and backward directions.

[0080] As shown in Fig. 12(d), an assembly step is performed in which a third dielectric substrate is used as a core material to form a dielectric layer 4 that captures and suppresses electromagnetic waves leaking backward from the EBG reflector 2. More specifically, as shown in Fig. 12(d), a metal surface 4a is formed on the entire surface of a dielectric substrate 9 serving as the third dielectric substrate. 12(d), the metal surface 4a of the dielectric substrate 9 is formed of a metal plate 7. The metal plate 7 is formed by plating the dielectric substrate 9 with gold or by attaching a metal foil to the dielectric substrate 9.

[0081] After the above assembly steps, an assembly step is carried out in which the antenna element 1, EBG reflector 2, and dielectric layer 4 are laminated into a three-layer structure. Specifically, as shown in Fig. 12(d), the metal plate 7 is positioned on the bottom surface and laminated on the dielectric substrate 9, and as shown in Fig. 12(b), the reflector 2b is positioned on the top surface and laminated on the dielectric substrate 6. When laminating, the dielectric substrate 6 and the dielectric substrate 9 are positioned so that the gold plating in the through hole T3 of the dielectric substrate 6 and the ground 3 of the dielectric substrate 9 are connected, and then the dielectric substrates 6 and 9 are laminated and joined together. When laminating, the dielectric substrates 5 and 6 are joined by positioning the gold plating in the through holes T1 and T2 of the dielectric substrate 5 and the gold plating in the through holes T4 and T5 of the dielectric substrate 6. When stacked in a three-layer structure, the gold plating in through hole T5 of dielectric substrate 6 is connected to ground 3 of dielectric substrate 6, and the gold plating in through hole T4 of dielectric substrate 6 is separated from ground 3 by space 18.

[0082] In the illustrated embodiment, through holes T1, T2, T3, T4, and T5 are formed in each of the dielectric substrates 5, 6, and 9, but this is not limited to this. After the dielectric substrates 5, 6, and 9 are stacked, the through holes may be formed continuously across these dielectric substrates 5, 6, and 9, and gold plating may be continuously filled into these through holes T1, T2, T3, T4, and T5. In the illustrated embodiment, a plurality of antenna elements 1 are formed on the dielectric substrate 5, a plurality of EBG reflectors 2 are formed on the dielectric substrate 6 corresponding to the antenna elements 1 on the dielectric substrate 5, and the dielectric substrates 5, 6, and 9 are stacked and then separated individually on a unit basis of antenna element 1 to construct an antenna. The assembly steps do not have to be performed in the order described, and it is possible to perform the assembly step of forming the antenna element 1 on the dielectric substrate 5, the assembly step of forming the EBG reflector 2 on the dielectric substrate 6, and the assembly step of forming the dielectric layer 4 on the dielectric substrate 9 in a sequentially changed order in consideration of manufacturing efficiency.

[0083] Next, the state of the dielectric substrate during the manufacturing process of the structure for connecting the coaxial cable 12 to the antenna element 1 will be described with reference to FIGS. 12(a), 12(b), and 12(c).

[0084] 12(a), 12(b), and 12(c), an assembly step is performed in which the feed portion 1a and the matching adjustment ground portion 1b of the antenna element 1 are formed toward the ground 3 of the EBG reflector 2. Specifically, as described above, through holes T1, T2, T4, and T5 are formed in the dielectric substrate 5 shown in Fig. 12(a) and the dielectric substrate 6 shown in Fig. 12(b), and gold plating is filled into the through holes T1, T2, T4, and T5, and the feed portion 1b and the matching adjustment ground portion 1c connected to the patch-shaped radiating surface 1a of the antenna element 1 are formed toward the ground 3 of the dielectric substrate 9 shown in Fig. 12(d).

[0085] As shown in Figure 12(b), a countersink 14 for receiving a coaxial cable 12 is formed on the surface of the dielectric substrate 6 opposite the reflecting element 2b, and a countersink 13 reaching the feeding portion 1b of the antenna element 1 is formed in the dielectric substrate 6 so as to communicate with the countersink 14. As shown in Fig. 12(c), a countersink 14 for receiving a coaxial cable 12 is formed on the surface of the dielectric substrate 9 on which the ground 3 is formed, and a countersink 13 for receiving the feeding part 1b of the antenna element 1 is formed in the dielectric substrate 6 so as to communicate with the countersink 14. As shown in Fig. 12(d), the end of the countersink 13 in the dielectric substrate 9 is opened into a space 18 in the dielectric substrate 9, and a part 15 is mounted in the countersink 14 and connected to the ground 3.

[0086] As shown in FIG. 13, a coaxial cable 12 is sandwiched and supported between a counterbore 14 in the dielectric substrate 6 and a counterbore 14 in the dielectric substrate 9, and the coaxial cable 12 is led out along the ground 3 of the dielectric substrate 9 to the outside. The inner conductor 12a of the coaxial cable 12 is received in the counterbore 13 of the dielectric substrate 6 shown in Figure 12(b) and the counterbore 13 of the dielectric substrate 9 shown in Figure 12(c), and the inner conductor 12a of the coaxial cable 12 is connected to the power supply part 1b of the antenna element 1 in the space 18 formed by the opening of the counterbore 13 of the dielectric substrate 9. 12(d), the external conductor 12b of the coaxial cable 12 is connected to part 15 of the dielectric substrate 9, and the external conductor 12b of the coaxial cable 12 is connected to the ground 3 by part 15. When the external conductor 12b of the coaxial cable 12 is connected to the ground 3 by part 15, the soldering points of part 15 and the external conductor 12b are accommodated within a recess 19 formed in the dielectric substrate 9, thereby tightly adhering the dielectric substrate 6 and the dielectric substrate 9.

[0087] In the embodiment, the structure in which the coaxial cable 12 is attached via the part 15 is illustrated, but it is desirable to suppress the influence of the part 15 by controlling the amount of penetration of the part 15 into the dielectric substrate 6. Furthermore, the connection structure is not limited to using the part 15, and the coaxial cable and the antenna element may be joined by point joining, crimping joining, or the like.

[0088] Through the above manufacturing process, the antenna shown in FIG. 13 is completed.

[0089] In the embodiment shown in Figures 12 and 13, the countersunk holes 13, 14 are formed in both the dielectric substrate 6 and the dielectric substrate 9, but this is not limited to this. It is also possible to form a countersunk hole 14 for receiving the coaxial cable 12 and leading it out of the dielectric substrates 5, 6, and a countersunk hole 13 for connecting the coaxial cable 12 to the antenna element 1, on at least one of the facing end faces of the dielectric substrate 6 shown in Figure 12(b) and the dielectric substrate 9 shown in Figure 12(c).

[0090] The antenna shown in Fig. 14(a) is completed through the manufacturing process shown in Fig. 12 and Fig. 13. The results of simulating the radiation pattern of the antenna shown in Fig. 14(a) are shown in Fig. 14(b). As is clear from a comparison of the characteristics shown in Figure 14(a) and Figure 7(a), even if power is fed to the antenna element 1 using the feed structure using the coaxial cable 12 shown in Figure 14(a), a radiation pattern within a practical range is obtained, and no problems arise from adopting the feed structure shown in Figure 14(a).

[0091] FIG. 15(b) shows the results of a simulation of an antenna according to an embodiment of the present invention, which employs a power supply structure using a coaxial cable 12 as shown in FIG. 14(a), mounted directly on an external metal plate 16 as shown in FIG. 15(a). As is clear from a comparison of the characteristics shown in Figure 15(a) and Figure 7(a), even if antenna element 1 equipped with the feed structure using the coaxial cable shown in Figure 15(a) is mounted directly on an external metal plate (metal device), a radiation pattern within a practical range is obtained, and no problems arise from adopting the feed structure shown in Figure 15(a).

[0092] As seen in typical LPWA (Low Power Wide Area: trademark) systems, it can be attached directly to metal devices or installed in locations where there are metal parts or water nearby, ensuring stable antenna installation at all times.

[0093] From the results of the above simulation, it was found that by adding the dielectric layer 4 of the embodiment of the present invention, radiation in the backward direction (-z direction) can be suppressed and the gain in the forward direction (+z direction) can be increased by approximately 2.2 dB.

[0094] The above results show the same tendency in the antenna additionally equipped with the dielectric layer 4 according to the embodiment of the present invention shown in FIGS.

[0095] As described above, according to the embodiment of the present invention, the leakage electromagnetic waves leaking from the EBG structure are captured and suppressed by the dielectric layer, and the leakage electromagnetic waves from the EBG structure are attenuated, so that they do not affect the electromagnetic waves radiated forward from the antenna element, and the desired radiation pattern can be ensured, and stable communication can be achieved without risk of a decrease in the gain of the antenna element.

[0096] Furthermore, by setting the distance between the antenna element and the EBG reflector, the distance between the EBG reflector and the ground, and the distance between the ground and the metal plate to 1 / 4λ or less (λ: wavelength of the frequency used), the distance between the antenna element and the metal surface of the dielectric layer can be narrowed, which contributes to a lower profile of the antenna.

[0097] Furthermore, in the embodiment of the present invention, the dielectric layer suppresses leakage of electromagnetic waves from the EBG structure. The installation conditions for wireless terminals in IoT / M2M, which have been expanding in popularity in recent years, require that they be attached directly to metal devices or installed in locations where there are metal parts or water nearby, as seen in typical LPWA (Low Power Wide Area: trademark) systems. However, in embodiments of the present invention, even if the metal plate with the dielectric layer is mounted close to the metal device or in contact with the metal device, the effect of leakage electromagnetic waves on the antenna gain can be suppressed, and the terminals can be installed without being affected by the radio wave transmission / reception environment. [Industrial Applicability]

[0098] The present invention has the advantage that not only can it satisfy the installation condition of a low profile, but also it can significantly ease the installation conditions of wireless terminals in IoT / M2M, which has become increasingly popular in recent years. [Explanation of symbols]

[0099] 1 antenna element 1a Patch-shaped radiating surface 1b Power supply unit 1c Matching adjustment ground 2 EBG reflector 2a Reflecting surface of EBG reflector 3 grand 4 Dielectric Layer 4a metal surface 5,6,9 Dielectric substrate 7 metal plate 10 side wall 11 Cavity structure

Claims

1. An antenna having a compact structure, an antenna element that radiates electromagnetic fields in both forward and backward directions; an EBG reflector that reflects radiation emitted backward from the antenna element forward; a dielectric layer that captures and suppresses electromagnetic waves leaking backward from the EBG reflector, The dielectric layer is The antenna has a metal surface facing the ground of the EBG reflector.

2. An antenna as described in claim 1, wherein the metal surface of the dielectric layer is a planar structure made of a metal plate.

3. The dielectric layer 3. The antenna according to claim 2, further comprising a dielectric between the ground of the EBG reflector and the metal plate, and configured to attenuate electromagnetic waves leaking backward from the EBG reflector while suppressing radiation.

4. The metal surface of the dielectric layer is 2. The antenna according to claim 1, wherein the antenna has a cavity structure formed by a combination of a planar structure made of a metal plate and a side structure standing up from an edge of the planar structure.

5. An antenna described in any one of claims 1 to 3, wherein the distance between the radiation surface of the antenna element and the reflection surface of the EBG reflector, and the thickness dimension of the dielectric layer are each set to 1 / 4λ (λ: wavelength of the frequency used) or less.

6. An antenna as described in claim 2, characterized in that the minimum dimension of the metal plate of the dielectric layer is set to be approximately the same as the dimension of the ground of the EBG reflector.

7. An antenna having a compact structure, an antenna element that radiates electromagnetic fields in both forward and backward directions; an EBG reflector that reflects radiation emitted backward from the antenna element forward; a dielectric layer that captures and suppresses electromagnetic waves leaking backward from the EBG reflector, a coaxial cable is arranged along the ground of the EBG reflector; an inner conductor of the coaxial cable connected to a feed portion of the antenna element; and an outer conductor of the coaxial cable is connected to the ground of the EBG reflector.

8. A method for manufacturing an antenna having a compact structure, comprising: an assembly step of forming an antenna element that radiates an electromagnetic field in both forward and backward directions using the first dielectric substrate as a core material; an assembly step of forming an EBG reflector using a second dielectric substrate as a core material to reflect radiation emitted backward from the antenna element forward; an assembly step of using a third dielectric substrate as a core material, forming a metal surface of the third dielectric substrate facing the ground of the EBG reflector, and forming a dielectric layer that captures and suppresses electromagnetic waves leaking backward from the EBG reflector; and an assembly step of laminating the antenna element, the EBG reflector, and the dielectric layer into a three-layer structure.

9. A method for manufacturing an antenna having a compact structure, comprising: an assembly step of forming an antenna element that radiates an electromagnetic field in both forward and backward directions using the first dielectric substrate as a core material; an assembly step of forming an EBG reflector using a second dielectric substrate as a core material to reflect radiation emitted backward from the antenna element forward; an assembly step of forming a dielectric layer using a third dielectric substrate as a core material to capture and suppress electromagnetic waves leaking backward from the EBG reflector; an assembly step of forming a feeding portion and a matching adjustment ground portion of the antenna element toward the ground of the EBG reflector; an assembly step of forming a counterbore in at least one of the facing end surfaces of the second dielectric substrate and the third dielectric substrate, the counterbore for receiving a coaxial cable and leading it out of the dielectric substrate, and the counterbore for coupling the coaxial cable and the antenna element; an assembly step of receiving the coaxial cable into the countersink, connecting the inner core wire to the power supply unit within the countersink, and connecting the matching adjustment ground unit to the ground of the EBG reflector within the countersink; and an assembly step of laminating the antenna element, the EBG reflector, and the dielectric layer into a three-layer structure.

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