JP6399883B2 - Loop antenna - Google Patents

Description

  The present invention relates to a broadband loop antenna composed of a monopole element and two parasitic loop elements.

Conventionally, a loop antenna in which a monopole element is combined with a loop element so as to widen the operating frequency band of the monopole antenna has been proposed (see Non-Patent Document 1). A front view showing the configuration of the loop antenna is shown in FIG. 19, a side view thereof is shown in FIG. 20, a top view thereof is shown in FIG. 21, and a perspective view thereof is shown in FIG.
The loop antenna 100 shown in these drawings includes a monopole element 110, a loop element 111, and a ground plane 114. A monopole element 110 is provided upright on a rectangular conductive ground plane 114 that can be regarded as electrically infinite, and a rectangular half-loop loop element 111 is provided in the vicinity of the monopole element 110. Provided. A power feeding unit 113 that feeds power to the monopole element 110 is provided at the lower end of the monopole element 110. The loop element 111 is a parasitic element. The loop element 111 is electromagnetically coupled to the monopole element 110. Since the monopole element 110 and the loop element 111 operate in cooperation with the loop antenna 100, the loop element 111 operates in a wide band.

  The monopole element 110 has a length of hm10 and a line width of t12, and is arranged from the center of the loop element 111 at a position xm10 in the x-axis direction and ym10 in the y-axis direction. The loop element 111 has a horizontal portion length L10, a height h10, and a line width t11. When the design frequency of the loop antenna 100 is 5 GHz (free space wavelength λ = about 60 mm), the length hm10 of the monopole element 110 is about 0.233λ (about 14 mm), and its line width t12 is about 0.0013λ (about 0.08 mm), xm is about 0.083λ (about 5 mm), ym is about 0.0167λ (about 1 mm), the length L10 of the horizontal portion of the loop element 111 is about 0.33λ (20 mm), and its height FIG. 23 shows the frequency characteristics of the voltage standing wave ratio (VSWR) when h10 is about 0.167λ (about 10 mm) and the line width t11 is about 0.0013λ (about 0.08 mm). Referring to FIG. 23, the frequency f11 at which VSWR = 2 is about 4.00 GHz, f12 is about 5.32 GHz, and the center frequency fc is about 4.66 GHz. As a result, the relative bandwidth BW11 is about 28.33%. This specific band BW11 is about twice or more the specific band of the monopole element 110 alone. Further, the loop antenna 100 is almost omnidirectional in the xy plane.

The Institute of Electronics, Information and Communication Engineers Conference 2014 General Conference Proceedings B-1-121 “Monopole-fed Equivalent Loop Antenna”

  The conventional loop antenna 100 shown in FIGS. 19 to 23 is mainly used for a communication module and broadband communication. However, for these applications, a wider-band antenna is desired.

  Therefore, an object of the present invention is to provide a loop antenna that operates in a wide band with a small and simple structure.

  The loop antenna according to the present invention is installed on a ground plane in close proximity so as to be electromagnetically coupled to the monopole element fed to the lower end provided upright on the ground plane. An outer loop element, and an inner loop element that is disposed inside the outer loop element and is disposed in a plane of the outer loop element and is erected on the ground plane, and the monopole element is used Resonance characteristics that resonate in the middle of the frequency band, the outer loop element resonates at a lower frequency of the operating frequency band, and the inner loop element resonates at a higher frequency of the operating frequency band. It is the main feature that it is said.

  According to the present invention, even with a simple structure in which a monopole element, an outer loop element, and an inner loop element are provided upright on the ground plane, a specific band of about 29.5% or more can be obtained. It becomes like this. In addition, since it can be configured with a low-profile element having a simple structure on the ground plane, it is possible to provide a loop antenna that is excellent in miniaturization and suitable for mass production.

It is a front view which shows the structure of the loop antenna of the Example of this invention. It is a side view which shows the structure of the loop antenna of the Example of this invention. It is a top view which shows the structure of the loop antenna of the Example of this invention. It is a perspective view which shows the structure of the loop antenna of the Example of this invention. It is a figure which shows the frequency characteristic of VSWR of the loop antenna of the Example of this invention. It is a figure which shows the frequency characteristic of VSWR for demonstrating operation | movement of the loop antenna of the Example of this invention. It is a figure which shows the ratio band characteristic when the 1st parameter of the loop antenna of the Example of this invention is changed. It is a figure which shows the frequency characteristic of VSWR when the 1st parameter of the loop antenna of the Example of this invention is made into the 1st value. It is a figure which shows the frequency characteristic of VSWR when the 1st parameter of the loop antenna of the Example of this invention is made into the 2nd value. It is a figure which shows the ratio band characteristic when the 2nd parameter of the loop antenna of the Example of this invention is changed. It is a figure which shows the frequency characteristic of VSWR when the 2nd parameter of the loop antenna of the Example of this invention is made into the 1st value. It is a figure which shows the frequency characteristic of VSWR when the 2nd parameter of the loop antenna of the Example of this invention is made into the 2nd value. It is a figure which shows the ratio band characteristic when the 3rd parameter of the loop antenna of the Example of this invention is changed. It is a figure which shows the frequency characteristic of VSWR when the 3rd parameter of the loop antenna of the Example of this invention is made into the 1st value. It is a figure which shows the frequency characteristic of VSWR when the 3rd parameter of the loop antenna of the Example of this invention is made into the 2nd value. It is a figure which shows the ratio band characteristic when changing the 4th parameter of the loop antenna of the Example of this invention. It is a figure which shows the frequency characteristic of VSWR when the 4th parameter of the loop antenna of the Example of this invention is made into the 1st value. It is a figure which shows the frequency characteristic of VSWR when the 4th parameter of the loop antenna of the Example of this invention is made into the 2nd value. It is a front view which shows the structure of the conventional loop antenna. It is a side view which shows the structure of the conventional loop antenna. It is a top view which shows the structure of the conventional loop antenna. It is a perspective view which shows the structure of the conventional loop antenna. It is a figure which shows the frequency characteristic of VSWR of the conventional loop antenna.

FIG. 1 is a front view showing the configuration of the loop antenna 1 of the embodiment of the present invention, FIG. 2 is a side view thereof, FIG. 3 is a top view thereof, and FIG.
The loop antenna 1 according to the present invention shown in these drawings includes a monopole element 10, an outer loop element 11, an inner loop element 12, and a ground plane 14. A monopole element 10 is provided upright on a rectangular conductive ground plane 14 that can be regarded as electrically infinite, and a rectangular half-loop outer loop element 11 in the vicinity of the monopole element 10 and The inner loop element 12 is provided upright. A power feeding unit 13 that feeds power to the monopole element 10 is provided at the lower end of the monopole element 10, and both lower ends of the outer loop element and the inner loop element are electrically connected to the ground plane. The outer loop element 11 and the inner loop element 12 are arranged concentrically in substantially the same xz plane, and the inner loop element 12 overlaps with the outer loop element 11 as shown in FIGS. Are arranged as follows. The outer loop element 11 and the inner loop element 12 are parasitic elements. The outer loop element 11 and the inner loop element 12 are electromagnetically coupled to the monopole element 10, and in the loop antenna 1 according to the present invention, the monopole element 10, the outer loop element 11, and the inner loop element 12 cooperate. As a result, the loop antenna 1 according to the present invention operates in a wide band.

The monopole element 10 is made of a wire having a rectangular cross section, has a length (height) of hm, and a line width of t2. The center of the outer loop element 11 extends in the x-axis direction in the x-axis direction and the y-axis direction. It is arranged at the position of ym. Further, the outer loop element 11 is also made of a wire having a rectangular cross-sectional shape, the length of the horizontal portion is Lout, the height is hout, and the line width is t1. Further, the inner loop element 12 is also made of a wire having a rectangular cross section, the length of the horizontal portion is Lin, the height is fin, and the line width is t1.
When the design frequency of the loop antenna 1 according to the present invention is 5 GHz and the free space wavelength is λ (= about 60 mm), the length hm of the monopole element 10 is about 0.233λ (about 14 mm), and the line width thereof t2 is about 0.00133λ (about 0.08 mm), xm is about 0.0833λ (about 5 mm), ym is about 0.0167λ (about 1 mm), and the length Lout of the horizontal portion of the outer loop element 11 is about 0. .333λ (20 mm), its height hout is about 0.167λ (about 10 mm), its line width t1 is about 0.00133λ (about 0.08 mm), and the length Lin of the horizontal portion of the inner loop element 12 is about Voltage standing wave ratio (0.208λ (12.5 mm), its height hin is about 0.104λ (about 6.25 mm), and its line width t1 is about 0.00133λ (about 0.08 mm) ( VSWR) The frequency characteristics are shown in FIG. Referring to FIG. 5, the frequency f1 at which VSWR = 2 is about 4.05 GHz, f2 is about 6.52 GHz, and the center frequency fc is about 5.29 GHz. That is, the specific band BW1 can be a wide band of about 46.69%. The specific band BW1 is 1.6 times wider than the specific band BW11 of the conventional loop antenna 100. Although not shown, the loop antenna 1 according to the present invention has almost non-directionality in the xy plane. The ground plane 14 has a rectangular shape with a side of 3λ (180 mm) or more, and has a dimension that can be regarded as an electrically infinite size.

  FIG. 6 shows the frequency characteristics of VSWR for explaining the operation of the loop antenna 1 according to the present invention. FIG. 6 shows the frequency characteristics of VSWR when the dimensions of each part of the monopole element 10, the outer loop element 11, and the inner loop element 12 are set as described above. In FIG. 6, the VSWR characteristic indicated by the loop antenna 1 is indicated by a thin fine broken line. In FIG. 6, the resonance characteristic of the monopole element 10 is indicated by a thick alternate long and short dash line, and it is understood that the resonance characteristic resonates in the middle band in the VSWR characteristic indicated by the loop antenna 1. In FIG. 6, the resonance characteristic of the outer loop element 11 is indicated by a thick solid line, and is a resonance characteristic that resonates in a low band in the VSWR characteristic indicated by the loop antenna 1, and the resonance characteristic of the inner loop element 12 is thick. It is shown by a rough broken line, and it can be seen that the resonance characteristic resonates in a high band in the VSWR characteristic indicated by the loop antenna 1. The lower end of the monopole element 10 is supplied with power from the power supply unit 13, and the outer loop element 11 and the inner loop element 12 are electromagnetically coupled to the monopole element 10 to operate in cooperation. In the loop antenna 1, the resonance characteristics of the monopole element 10, the outer loop element, and the inner loop element are integrated. As a result, the loop antenna 1 according to the present invention operates in a wide band as shown in FIG. Further, the loop antenna 1 according to the present invention can be a small and low-profile loop antenna as shown in the above-described dimensions.

  Next, in the loop antenna 1 according to the present invention, the ratio band characteristics when the dimensions of each part of the outer loop element 11 and the inner loop element 12 are changed as parameters will be described. First, FIG. 7 shows the ratio band characteristics when the height hout of the outer loop element 11 is changed from 0.12λ to 0.23λ as the first parameter, and the dimensions of the respective parts excluding the height hout are set to the above values. . Referring to FIG. 7, when the height hout becomes about 0.133λ indicated by the mark A1, the specific band reaches about 29.5%, and as the height hout becomes longer, the specific band increases, and about 0 The peak value is about 49% at 163λ. When the height hout is further increased, the specific band is decreased, and when the height hout is about 0.181λ indicated by the mark B1, the specific band is decreased to about 29.5%, and the height hout is further increased. Then, the specific band further decreases, and when the height hout becomes about 0.23λ, the specific band becomes about 19%. Note that a 28.4% specific band obtained with the conventional loop antenna 100 is indicated by a broken line for comparison.

  As described above, the loop antenna 1 according to the present invention is the same as the conventional loop antenna 100 when the height hout of the outer loop element 11 is in the range of about 0.133λ (about 8 mm) to about 0.181λ (about 11 mm). A specific band of about 29.5% or more exceeding the obtained specific band can be obtained. Therefore, FIG. 8 shows the frequency characteristics of the VSWR when the height hout is about 0.133λ (about 8 mm), and FIG. 9 shows the frequency characteristics of the VSWR when the height hout is about 181λ (about 11 mm). Referring to FIGS. 8 and 9, when the height hout is about 0.133λ (about 8 mm) and about 0.181λ (about 11 mm), a wideband VSWR characteristic that can obtain a ratio band of about 29.5% or more is obtained. You can see that

  Next, the ratio when the length Lout of the horizontal portion of the outer loop element 11 is changed from 0.32λ to 0.40λ as the second parameter, and the dimensions of the respective portions excluding the length Lout of the horizontal portion are set to the above values. The band characteristics are shown in FIG. Referring to FIG. 10, when the length Lout of the horizontal portion is about 0.322λ indicated by the mark A2, the bandwidth reaches about 29.5%, and the bandwidth is improved as the length Lout of the horizontal portion increases. The maximum peak value is about 49% at about 0.334λ. When the length Lout of the horizontal portion is further increased, the specific band decreases and when the horizontal portion length Lout reaches about 0.347λ indicated by the mark B2, the specific band decreases to about 29.5%. When the length Lout of the horizontal portion is further increased, the specific bandwidth further decreases, and when the horizontal portion length Lout is about 0.353λ, the specific bandwidth is about 27%. As the length Lout of the horizontal portion is further increased, the specific band gradually increases, and when the length Lout of the horizontal portion becomes about 0.363λ indicated by the mark A3, the specific band is about 29.5. %, The ratio band is slightly improved as the horizontal portion length Lout is increased, and shows about 30.5% which is the second peak value at about 0.367λ. When the length Lout of the horizontal portion is further increased, the specific band decreases and when the horizontal portion length Lout reaches about 0.376λ indicated by the mark B3, the specific band decreases to about 29.5%. When the length Lout of the horizontal portion is further increased, the specific bandwidth further decreases, and when the horizontal portion length Lout is about 0.340λ, the specific bandwidth is about 27%. Note that a 28.4% specific band obtained with the conventional loop antenna 100 is indicated by a broken line for comparison.

  As described above, in the loop antenna 1 according to the present invention, the length Lout of the horizontal portion of the outer loop element 11 is in the range of about 0.322λ (about 19.3 mm) to about 0.347λ (about 21 mm), and In the range of about 0.363λ (about 21.8 mm) to about 0.376λ (about 22.5 mm), a specific band of about 29.5% or more exceeding the specific band obtained with the conventional loop antenna 100 can be obtained. it can. Therefore, FIG. 11 shows the frequency characteristics of the VSWR when the length Lout of the horizontal portion is about 0.350λ (about 21 mm), and FIG. 12 shows the frequency characteristics of the VSWR when the length Lout is about 0.383λ (about 23 mm). Referring to FIGS. 11 and 12, when the length Lout of the horizontal portion is about 0.350λ (about 21 mm), it has a broadband VSWR characteristic that can obtain a ratio band of about 29.5% or more. .383λ (about 23 mm) is outside the above range, but a broadband VSWR characteristic exceeding that of the conventional loop antenna 100 is obtained. However, the center frequency shifts to a high range.

  Next, FIG. 13 shows the ratio band characteristics when the height hin of the inner loop element 12 is changed from 0.03λ to 0.13λ as the third parameter, and the dimensions of the respective parts excluding the height hin are set to the above values. Show. Referring to FIG. 13, when the height hin becomes about 0.035λ indicated by the mark A4, the specific band reaches about 29.5%, and the specific band is maintained even if the height hin is increased. When the height hin exceeds about 0.09λ, it increases, and when it is about 0.106λ, it shows a peak value of about 49%. When the height hin is further increased, the specific band is decreased and when the height hin becomes about 0.126λ indicated by the mark B4, the specific band is decreased to about 29.5%, and the height hin is further increased. Then, the specific band further decreases, and when the height hin becomes about 0.13λ, the specific band becomes about 22%. Note that a 28.4% specific band obtained with the conventional loop antenna 100 is indicated by a broken line for comparison.

  As described above, the loop antenna 1 according to the present invention is a conventional loop antenna in which the inner loop element 12 has a height hin of about 0.035λ (about 2 mm) to about 0.126λ (about 7.56 mm). A ratio band of about 29.5% or more exceeding the ratio band obtained at 100 can be obtained. Therefore, FIG. 14 shows the frequency characteristics of the VSWR when the height is about 0.0375λ (about 2.25 mm), and FIG. 15 shows the frequency characteristics of the VSWR when the height is about 121λ (about 7.25 mm). Referring to FIGS. 14 and 15, when the height hin is about 0.0375λ (about 2.25 mm), a ratio band of about 29.5% can be obtained, but the center frequency becomes a VSWR characteristic that shifts to a low range, and about When 0.121λ (about 7.25 mm), it can be seen that the VSWR characteristic has a wide band that can obtain a ratio band of about 29.5% or more.

  Next, the ratio when the length Lin of the horizontal portion of the inner loop element 12 is changed from 0.11λ to 0.29λ as the fourth parameter, and the dimensions of the respective portions excluding the length Lin of the horizontal portion are set to the above values. The band characteristics are shown in FIG. Referring to FIG. 16, when the length Lin of the horizontal portion is about 0.118λ indicated by the mark A5, the specific bandwidth reaches about 29.5%, and even if the length Lin of the horizontal portion is increased, the specific bandwidth is Although it is maintained, it rises when the length Lin of the horizontal portion exceeds about 0.19λ, and shows a maximum peak value of about 49% at about 0.208λ. When the length Lin of the horizontal portion is further increased, the specific band decreases. However, when the length Lin of the horizontal portion exceeds about 0.24λ, it rises again and reaches the second peak value (about 36% when it is about 0.26λ). ). When the length Lin of the horizontal portion is further increased, the specific band decreases, and when the horizontal portion length Lin reaches about 0.285λ indicated by the mark B5, the specific band decreases to about 29.5%. . As the length Lout of the horizontal portion is further increased, the specific band is further reduced. When the horizontal portion length Lout is about 0.29λ, the specific band is about 28.5%. Note that a 28.4% specific band obtained with the conventional loop antenna 100 is indicated by a broken line for comparison.

  As described above, in the loop antenna 1 according to the present invention, the length Lin of the horizontal portion of the inner loop element 12 is about 0.118λ (about 7.1 mm) to about 0.285λ (about 17 mm). Thus, a specific band of about 29.5% or more exceeding the specific band obtained with the loop antenna 100 can be obtained. Therefore, FIG. 17 shows the frequency characteristics of the VSWR when the length Lin of the horizontal portion is about 0.125λ (about 7.5 mm), and FIG. 17 shows the frequency characteristics of the VSWR when the length Lin is about 0.275λ (about 16.5 mm). 18 shows. 17 and 18, when the length Lin of the horizontal portion of the inner loop element 12 is about 0.125λ (about 7.5 mm), a relative band of about 29.5% is obtained, but the center frequency is low. If the VSWR characteristic shifts to the range, and about 0.275λ (about 16.5 mm), a ratio band of about 29.5% or more is obtained, but the center frequency is a wide band VSWR characteristic slightly shifted to the high band. I understand that.

In the loop antenna according to the present invention described above, a specific band of about 29.5% or more can be obtained by disposing a low-profile inner loop element in the same plane as the outer loop element in the conventional loop antenna. Will be able to. In the loop antenna according to the present invention, when the wavelength of the center frequency of the use frequency band is λ, the height hout of the outer loop element is about 0.133λ to about 0.181λ, and the horizontal portion of the outer loop element is The length Lout is about 0.322λ to about 0.347λ and about 0.363λ to about 0.376λ, and the inner loop element height hin is about 0.035λ to about 0.126λ, and the length of the horizontal portion of the inner loop element When the thickness Lin is in the range of about 0.118λ to about 0.285λ, a specific band of about 29.5% or more can be obtained. In addition, since the loop antenna according to the present invention can be configured with a low-profile element having a simple structure on the ground plane, it is excellent in miniaturization and can be a loop antenna suitable for mass production. And since it can comprise with a simple design value, it can enable antenna commercialization by a short time design.
In the above description, the design frequency of the loop antenna according to the present invention is 5 GHz. However, the design is not limited to this, and the frequency may be a frequency used for a communication module or broadband communication. In addition, the outer loop element and the inner loop element are rectangular, but the present invention is not limited to this and may be polygonal or curved. Furthermore, the monopole element, the outer loop element, and the inner loop element can have a circular cross section, an elliptical shape, or a polygonal shape that is greater than or equal to a triangle, and can be a plate shape only for the monopole element. Furthermore, the loop antenna according to the present invention has a monopole element formed on one surface of a printed circuit board having a predetermined thickness with good high frequency characteristics such as a Teflon substrate, and an outer loop element and an inner loop element formed on the back surface thereof. A loop antenna can be configured by standing a printed circuit board on the ground plane. In this case, the thickness of the printed board is preferably about 1 mm in electrical length, and the physical length is set in consideration of the dielectric constant of the printed board.

DESCRIPTION OF SYMBOLS 1 Loop antenna, 10 Monopole element, 11 Outer loop element, 12 Inner loop element, 13 Feed part, 14 Ground plane, 100 Loop antenna, 110 Monopole element, 111 Loop element, 113 Feed part, 114 Ground plane

Claims (5)

A monopole element that is fed to the lower end provided upright on the ground plane;
An outer loop element erected on the ground plane proximate to electromagnetically couple to the monopole element;
An inner loop element disposed inside the outer loop element and disposed in a plane of the outer loop element and standing on the ground plane,
The monopole element has a resonance characteristic that resonates in the middle range of the used frequency band, the outer loop element has a resonance characteristic that resonates in the lower band of the used frequency band, and the inner loop element has a high characteristic in the used frequency band. A loop antenna characterized by having resonance characteristics that resonate in the region.   2. The loop antenna according to claim 1, wherein a height of the outer loop element is in a range of about 0.133λ to about 0.181λ, where λ is a wavelength of a center frequency of the use frequency band. .   When the wavelength of the center frequency of the use frequency band is λ, the length of the horizontal portion of the outer loop element is in the range of about 0.322λ to about 0.347λ and about 0.363λ to about 0.376λ. The loop antenna according to claim 1, wherein:   The loop antenna according to claim 1, wherein the height of the inner loop element is in the range of about 0.035λ to about 0.126λ, where λ is the wavelength of the center frequency of the use frequency band. .   The length of the horizontal portion of the inner loop element is in a range of about 0.118λ to about 0.285λ, where λ is a wavelength of a center frequency of the use frequency band. Loop antenna.

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