JP2018117253A - antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of improving antenna characteristics.SOLUTION: An antenna 100 includes a dielectric substrate 10. A first ground element 20a and a second ground element 20b are arranged on the rear face 14 side of the dielectric substrate 10. A slit 22 is formed in the first ground element 20a and the second ground element 20b. A feeding element 30 is arranged on the surface 12 side of the dielectric substrate 10. A feeding point 40 is connected with the feeding element 30. The feeding point 40 is arranged on the slit 22 side relative to the feeding element 30.SELECTED DRAWING: Figure 1

Description

  The present invention relates to antenna technology, and more particularly to an antenna in which a feed element is disposed on a dielectric substrate.

  An example for miniaturizing an antenna is a microstrip antenna. In order to vary the directivity of the microstrip antenna, a plurality of parasitic elements are arranged around each side of the substantially rectangular microstrip antenna, and the electrical length of each parasitic element is switched (for example, see Patent Document 1). ).

JP2012-120150A

  If the distance between the microstrip antenna and the parasitic element is wide, the gain improvement effect is small even if the parasitic element is arranged.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a technique for improving antenna characteristics.

  In order to solve the above problems, an antenna according to an aspect of the present invention includes a dielectric substrate, a ground element disposed on the first surface side of the dielectric substrate, a slit formed in the ground element, and a dielectric substrate. A power feeding element disposed on the second surface side of the power supply, and a power feeding point connected to the power feeding element. The feeding point is arranged on the slit side with respect to the feeding element.

  According to the present invention, antenna characteristics can be improved.

FIGS. 1A to 1B are plan views showing the structure of an antenna according to an embodiment of the present invention. It is sectional drawing which shows the structure of the antenna of Fig.1 (a)-(b). FIGS. 3A to 3B are diagrams showing a change in relative gain with respect to the diameter of the hole in FIG. It is a figure which shows the change of the relative gain with respect to the movement distance of the hole of Fig.1 (a). It is a figure which shows the structural example of the circuit part of Fig.1 (a). FIGS. 6A to 6F are diagrams showing the effect of the shape of the parasitic element in FIG. FIGS. 7A to 7C are views showing the effect of the parasitic element arrangement shown in FIG. It is a figure which shows the effect by the size of the parasitic element of Fig.1 (a). FIGS. 9A to 9F are diagrams showing the effects of the arrangement and size of the parasitic elements in FIG. FIGS. 10A to 10E are diagrams showing another effect due to the size of the parasitic element in FIG. FIGS. 11A to 11D are perspective views showing another structure of the antenna shown in FIGS. FIGS. 12A and 12B are perspective views showing another structure of the antenna of FIG. It is a figure which shows the effect by arrangement | positioning of the feed point and slit of Fig.1 (a).

  Before specifically describing the embodiment of the present invention, an outline of the present embodiment will be described. The embodiment relates to an antenna in which a feeding element is arranged on the front surface of a dielectric substrate and a ground element is arranged on the back surface. An example of the antenna is a microstrip antenna used for an on-board unit of an ETC (Electronic Toll Collection System), and a resonance frequency thereof is a 5.8 GHz band. As described above, the present embodiment aims to improve the antenna characteristics (antenna gain, antenna efficiency), and is specifically described by at least one of the following (1) to (3).

  (1) The antenna is provided with a notification circuit for notifying the ETC on-board device that the antenna is connected to the ETC on-board device. When the notification circuit is installed in the vicinity of the microstrip line connecting the feeding element and the feeding point, the mismatch impedance increases due to the influence of the input impedance starting from the feeding point, and the antenna gain decreases. If the notification circuit is arranged around the outer edge portion of the feed element as a radiation source in this way, the antenna characteristics are deteriorated. In this embodiment, a hole is provided in the vicinity of the central portion of the power feeding element, and the notification circuit is arranged so as to be surrounded by the power feeding element. Thereby, since the influence on the input impedance is reduced, the antenna characteristics are improved.

  (2) When a plurality of parasitic elements, which are parasitic elements, are arranged around the feeding element, the effect of improving the antenna gain is small if the distance between the feeding element and the parasitic element is wide. The interval should be narrowed to some extent. However, since the parasitic element also resonates at the resonance frequency when the interval is narrowed, the effective resonance frequency is lowered by electromagnetic coupling between the parasitic element and the feeder element. As a result, the antenna gain at the desired resonance frequency is reduced. In the present embodiment, the size of the feed element is determined so that the resonance frequency of the feed element is higher than a desired resonance frequency. A plurality of parasitic elements are arranged while the interval between such feeder elements is narrowed to some extent. As a result, the effective resonance frequency is in the vicinity of the desired band, and the antenna gain at the desired resonance frequency is improved.

  (3) The power feeding element is generally arranged so as to overlap the central portion of the ground element. This is to form the antenna directivity in the zenith direction by diffracting the radio wave radiated from the power feeding element from the end of the ground element at an equal distance. Considering this, it is preferable that the dielectric substrate has a substantially square shape. On the other hand, when an electric circuit other than the power feeding element is mounted on the surface of the dielectric substrate, the dielectric substrate has a substantially rectangular shape instead of a substantially square shape. If the ground element has a substantially rectangular shape according to the mounting part of the electric circuit, the distance from the antenna element to the ground element becomes non-uniform, and components that cancel out the phase are generated. The antenna gain in the zenith direction is reduced. In this embodiment, the ground potential is separated into the first ground element and the second ground element by forming a slit in the ground element. In addition, the first ground element has a substantially square shape, and the power feeding element is overlapped at the center thereof. Furthermore, the feeding point is arranged on the slit side. As a result, the current flowing in the longitudinal direction of the dielectric substrate is reduced, so that the above-described directivity pattern is not easily broken.

  In the following description, “parallel” and “orthogonal” include not only perfect parallel and orthogonal, but also a case of deviating from parallel within an error range. Further, “substantially” means that they are the same in an approximate range.

  1A to 1B are plan views showing the structure of an antenna 100 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the structure of the antenna 100. As shown in FIGS. 1A to 1B and FIG. 2, an orthogonal coordinate system including an x-axis, a y-axis, and a z-axis is defined. The x axis and the y axis are orthogonal to each other in the plane of the antenna 100. The z axis is perpendicular to the x axis and the y axis. The positive directions of the x-axis, y-axis, and z-axis are defined in the directions of the arrows in FIGS. 1A to 1B and FIG. 2, and the negative direction is in the direction opposite to the arrows. It is prescribed. Of the two main surfaces forming the antenna 100 and parallel to the xy plane, the main plane disposed on the positive direction side of the z-axis is the surface 12 and is negative on the z-axis. The main plane disposed on the direction side is the back surface 14. When the back surface 14 is called the first surface, the front surface 12 is called the second surface.

  The antenna 100 includes a dielectric substrate 10, a first ground element 20a, a second ground element 20b, which are collectively referred to as a ground element 20, a slit 22, a feeding element 30, a hole 32, a land part 34, a circuit part 36, and a microstrip line. 38, feeding point 40, electric circuit section 42, first parasitic element 50a, second parasitic element 50b, third parasitic element 50c, fourth parasitic element 50d, fifth parasitic element collectively referred to as parasitic element 50. It includes a feeding element 50e and a sixth parasitic element 50f. The number of parasitic elements 50 is not limited to “6”.

  The dielectric substrate 10 is formed in a plate shape, and has a rectangular front surface 12 and a back surface 14 that are longer in the x-axis direction than in the y-axis direction. On the back surface 14 of the antenna 100, a first ground element 20a is disposed on the positive direction side of the x axis, and the first ground element 20a has a substantially square shape. In addition, on the back surface 14 of the antenna 100, the second ground element 20b is disposed on the negative direction side of the x axis. Here, the slit 22 is disposed between the first ground element 20a and the second ground element 20b. The slit 22 is formed in the ground element 20, and the back surface 14 of the dielectric substrate 10 is exposed in the slit 22. Thus, the ground potential of the second ground element 20b is separated from the first ground element 20a with the slit 22 as a boundary.

  In the surface 12 of the dielectric substrate 10, a portion overlapping with the first ground element 20 a is defined as the first region 24, and a portion overlapping with the second ground element 20 b is defined as the second region 26. 24 and the second region 26 are also separated with the slit 22 as a boundary. On the surface 12 of the dielectric substrate 10, a power supply element 30 having a substantially square shape is disposed near the central portion of the first region 24. Therefore, the power feeding element 30 is disposed so as to overlap the first ground element 20 a on a projection plane (hereinafter simply referred to as “projection plane”) parallel to the front surface 12 or the back surface 14. The feed element 30 may be called a microstrip antenna or a patch antenna.

  A hole portion 32 is disposed near the central portion inside the power feeding element 30, and a land portion 34 is disposed near the central portion inside the hole portion 32. The land portion 34 is a conductor having a cylindrical shape, and the height in the z-axis direction is close to the thickness of the power feeding element 30. Moreover, since the hole part 32 is enclosed by the electric power feeding element 30 in circular arc shape, it opens in donut shape. In addition, the shape of the hole part 32 and the land part 34 is not limited to these. A through-hole portion 46 formed of a conductor is disposed so as to penetrate the dielectric substrate 10 from the surface on the negative z-axis side of the land portion 34 to the surface on the positive z-axis side of the first ground element 20a. The through-hole portion 46 electrically connects the first ground element 20a and the land portion 34.

  A circuit portion 36 is disposed between the power feeding element 30 and the land portion 34. The configuration of the circuit unit 36 may be arbitrary. For example, when the circuit unit 36 is a notification circuit, the resistance element corresponds to the circuit unit 36. The circuit unit 36 may be a semiconductor element, reactance, or the like. The power feeding element 30 and the land portion 34 are electrically connected by such a circuit portion 36. In addition, on the surface 12 of the dielectric substrate 10, a plurality of parasitic elements 50 are arranged around the feeder element 30. The shape of each parasitic element 50 may not be the same.

  The microstrip line 38 connected to the outer edge portion of the feeding element 30 on the negative direction side of the x axis extends in the direction of the slit 22. A feeding point 40 is disposed at the slit 22 side end of the microstrip line 38. Therefore, the feeding point 40 is connected to the feeding element 30 via the microstrip line 38 and is disposed on the slit 22 side with respect to the feeding element 30. One end of a coaxial cable 44 is connected to the feeding point 40. The other end of the coaxial cable 44 is connected to, for example, an ETC on-vehicle device (not shown). With such a configuration, the feeding element 30 is fed from the feeding point 40, and the antenna 100 transmits and receives an ETC signal and inputs and outputs the signal to and from the ETC on-vehicle device via the coaxial cable 44.

  In the second region 26 on the surface 12 of the dielectric substrate 10, an electric circuit portion 42 having a substantially rectangular shape is disposed. Therefore, the electric circuit unit 42 is disposed so as to overlap the second ground element 20b on the projection surface. Any circuit can be used as the electric circuit section 42. For the sake of clarity, a structure in which the second region 26 is omitted may also be referred to as the antenna 100.

  So far, the basic structure of the antenna 100 has been described. Hereinafter, the structure of the antenna 100 will be described in more detail. In particular, here, (1) the arrangement of the circuit unit 36, (2) the shape and arrangement of the feeding element 30 and the parasitic element 50, and (3) the structure including the second region 26 will be described in this order. The characteristics shown below are the results of simulation.

(1) Arrangement of Circuit Unit 36 First, the diameter of the hole 32 when the circuit unit 36 is arranged will be described. 3A to 3B show changes in relative gain with respect to the diameter of the hole portion 32. FIG. FIG. 3A shows a change in relative gain when the diameter of the hole 32 arranged at the center of the feeding element 30 in FIG. 1A is changed. The center of the feed element 30 is a position connecting the midpoint of the feed element 30 in the x-axis direction and the midpoint of the y-axis direction. Here, the horizontal axis indicates the hole diameter, and the vertical axis indicates the relative gain. As shown in the figure, when the hole diameter is larger than 3 mm, the relative gain decreases. FIG. 3B shows the relationship between the wavelength and the length when the desired resonance frequency is set in the 5.8 GHz band. Referring to this, based on FIG. 3A, the diameter of the hole 32 is set to a length equal to or less than 1/8 of the wavelength at the resonance frequency of the antenna 100.

  Next, the position of the hole 32 when the circuit part 36 is arranged will be described. FIG. 4 shows a change in relative gain with respect to the movement distance of the hole 32. This can be said to be a change in relative gain with respect to the moving distance of the circuit unit 36. Here, from the center of the feeding element 30 in FIG. 1A, the positive direction of the x axis (+ x axis direction 200), the negative direction of the y axis (−y axis direction 202), and the positive direction of the y axis (+ y axis direction 204). ), A change in relative gain when the hole 32 is moved in the negative x-axis direction (−x-axis direction 206) is shown. The relative gain is shown on the basis of the case where the hole 32 is arranged at the center of the feed element 30. When the hole 32 or the circuit part 36 is shifted from the center, the relative gain tends to decrease. Therefore, the hole 32 is formed within a moving distance from the center of the feeding element 30 to about 1.2 mm, that is, a length up to 1/20 of the wavelength at the resonance frequency of the antenna 100.

  Further, a structure in the case where no resistance element, semiconductor element, reactance, or the like is used as the circuit unit 36 will be described. FIG. 5 shows a structural example of the circuit part 36 and shows a top view of the surface 12. The circuit portion 36 is formed as a stub pattern extending from the power feeding element 30 onto the hole portion 32 and continues to the land portion 34. The circuit part 36 having such a stub pattern becomes high impedance in a desired frequency band due to an inductive reactance component. Thus, the one where the impedance of the circuit part 36 is high is preferable.

(2) Shape and Arrangement of Feeding Element 30 and Parasitic Element 50 FIGS. 6A to 6F show the effect of the shape of the parasitic element 50. 6A to 6C are top views showing the structure of a conventional antenna 170 to be compared with the antenna 100. FIG. In these antennas 170, the portion of the second region 26 in FIG. 1A is omitted. In the antenna 170 of FIG. 6A, the feed element 130 is disposed at the center portion of the dielectric substrate 110. Here, the dielectric substrate 110 and the power feeding element 130 correspond to the dielectric substrate 10 and the power feeding element 30. In the feed element 130, the outer edge portion in the x-axis direction and the outer edge portion in the y-axis direction intersect, and at least one of the lengths is set to a length that is ½ of the wavelength λ at the resonance frequency of the antenna 170. The

  In the antenna 170 of FIG. 6B, in addition to the structure of FIG. 6A, the first parasitic element 150a to the eighth parasitic element 150h, which are collectively referred to as the parasitic element 150, are arranged around the feeder element 130. Is done. Here, the parasitic element 150 is formed in a rod shape such that an outer edge portion facing the feeding element 130 becomes long. The diodes arranged between adjacent parasitic elements 150 are electrically insulated, and the distance between the feeding element 130 and the parasitic element 150 is approximately 1 / wavelength λ at the resonance frequency of the antenna 170. 4 length. In the antenna 170 of FIG. 6C, the distance between the feeding element 130 and the parasitic element 150 in FIG. 6B is set to about 1/20 of the wavelength λ at the resonance frequency of the antenna 170. . That is, in FIG. 6C, the distance between the feed element 130 and the parasitic element 150 is narrower than that in FIG. 6B.

  In FIG. 6 (d), the antenna 100 of FIG. 1 (a) is shown modified to facilitate comparison with FIG. 6 (c). Here, the first parasitic element 50 a to the eighth parasitic element 50 h, which are collectively referred to as the parasitic element 50, are arranged around the feeder element 30. Further, in the power feeding element 30, the outer edge portion in the x-axis direction and the outer edge portion in the y-axis direction intersect, and at least one length thereof, that is, at least one length in the x-axis direction and the y-axis direction is The length of the antenna 100 is shorter than a half of the wavelength λ at the resonance frequency. That is, the length of the power feeding element 30 is shorter than the length of the power feeding element 130 in the x-axis direction or the y-axis direction. Further, in each parasitic element 50, the length of the outer edge portion on the side facing the feeding element 30 is made shorter than the length of the feeding element 30 in the same direction as the outer edge portion. For example, the length of the first parasitic element 50 a in the x-axis direction is shorter than ½ of the length of the power feeding element 30 in the x-axis direction. Note that the distance between the feeding element 30 and the parasitic element 50 is about 1/20 of the wavelength λ at the resonance frequency of the antenna 100, as in FIG.

  Hereinafter, in order to clarify the explanation, FIGS. 6A to 6D are referred to as a structure A, a structure B, a structure C, and a structure D, respectively. FIG. 6E shows VSWR (Voltage Standing Wave Ratio) when the frequency is changed. It can be said that the lower the VSWR, the better the characteristics. A band including the resonance frequency of the antenna 170 and the antenna 100 is shown as a desired band. On the other hand, FIG. 6F shows the antenna gain when the frequency is changed. It can be said that the higher the antenna gain, the better the characteristics. In these, the structure B characteristic 212 is substantially the same as the structure A characteristic 210. This is because the parasitic element 150 does not contribute to the improvement of the characteristics because the distance between the feeder element 130 and the parasitic element 150 is too large in FIG.

  In the structure C characteristic 214, the antenna gain is improved at a frequency lower than the desired band as compared with the structure A characteristic 210 and the structure B characteristic 212, but the antenna gain is not improved in the desired band. This is because since the distance between the feeding element 130 and the parasitic element 150 is narrow, it can be considered that the effective length of the feeding element 130 is equivalently increased, and this reduces the effective resonance frequency. is there.

  In the structure D characteristic 216, both the VSWR and the antenna gain are improved in the desired band as compared with the structure A characteristic 210 to the structure C characteristic 214. This can be said to improve the antenna gain without changing the radiation pattern in the desired band. Again, since the distance between the feed element 30 and the parasitic element 50 is narrow, it can be considered that the effective length of the feed element 30 is equivalently increased. However, since the length of the feed element 30 is set to be a resonance frequency higher than the desired band, it resonates in the desired band when the parasitic element 50 is disposed. As described above, the length of the feeding element 30 in the x-axis direction or the y-axis direction is shorter than the length of ½ of the wavelength λ at the resonance frequency of the antenna 100. Further, in each parasitic element 50, the length of the outer edge portion on the side facing the feeding element 30 is made shorter than the length of the feeding element 30 in the same direction as the outer edge portion.

  FIGS. 7A to 7C are views showing the effect of the parasitic element arrangement shown in FIG. In FIG. 7A, the distance between the feed element 30 and the parasitic element 50 is set to a length of about 1/20 of the wavelength λ at the resonance frequency of the antenna 100. In FIG. 7B, the distance between the feeding element 30 and the parasitic element 50 is set to about ５ of the wavelength λ at the resonance frequency of the antenna 100. Here, this distance will be described. FIG. 7C shows the effect obtained by the placement of the parasitic element 50, the horizontal axis indicates the distance in units of the wavelength λ, and the vertical axis indicates the antenna when the parasitic element 50 is not disposed. Indicates the amount of gain improvement. In each parasitic element 50, the length of the outer edge portion facing the feeding element 30 is set to ¼ of the wavelength λ at the resonance frequency of the antenna 100. As the distance increases, the antenna gain improvement decreases. Therefore, the interval between each of the plurality of parasitic elements 50 and the feeding element 30 is made shorter than 1/10 of the wavelength at the resonance frequency of the antenna 100.

  Next, the length of the outer edge of the parasitic element 50 on the non-facing side with respect to the feeding element 30 will be described. This corresponds to the length in the y-axis direction of the first parasitic element 50a in FIG. FIG. 8 shows the effect due to the size of the parasitic element 50, the horizontal axis indicates the length in units of the wavelength λ, and the vertical axis indicates the antenna gain improvement in the case where the parasitic element 50 is not disposed. Indicates the amount. Here, the distance between the feeding element 30 and the parasitic element 50 is set to 1/50 of the wavelength λ at the resonance frequency of the antenna 100, and the length of the outer edge of the parasitic element 50 on the side facing the feeding element 30. The length is ¼ of the wavelength λ at the resonance frequency of the antenna 100. Under such circumstances, the antenna gain improvement amount increases as the length of the outer edge of the parasitic element 50 on the non-opposing side with respect to the feeding element 30 increases. When the length is 0.38λ, the antenna gain improvement is maximized. Furthermore, when the length approaches ½ of the wavelength λ, the antenna gain improvement amount rapidly decreases.

  This is because the parasitic element 50 does not resonate in the desired band if the length of the parasitic element 50 on the non-opposite side of the feeding element 30 is about ¼ of the wavelength λ. The electric field concentrates in the vicinity of the feeding element 30 as a part. However, if the length is about ½ of the wavelength λ, the parasitic element 50 operates as an antenna that resonates in a desired band. This is because the electric field is strongly distributed, affecting the current distribution, and disturbing the radiation pattern and the impedance of the antenna. In summary, the length of the parasitic element 50 on the side not facing the feeding element 30 is made shorter than the length of at least one feeding element 30 in the x-axis direction and the y-axis direction, and the resonance frequency of the antenna 100 is also reduced. The length is 1/5 or more of the wavelength at.

  Next, the arrangement of the parasitic element 50 will be described. FIGS. 9A to 9F show another effect depending on the arrangement and size of the parasitic element 50. 9 (a) corresponds to FIG. 6 (a), FIG. 9 (b) corresponds to FIG. 6 (c), and FIG. 9 (c) corresponds to FIG. 6 (d). 9A to 9B, the length of the feed element 130 in the x-axis direction or the y-axis direction is ½ of the wavelength λ at the resonance frequency of the antenna 170, as in FIG. 6D. Shorter than the length. Here, for clarity of explanation, FIGS. 9A to 9C are also referred to as the structure A, the structure C, and the structure D, respectively.

  In FIG. 9D, a seventh parasitic element 50g and an eighth parasitic element 50h are added as compared to FIG. 9C. Specifically, the seventh parasitic element 50g is arranged so as to be in contact with the corner portion C1 of the feeding element 30 on the positive direction side of the x axis and the positive direction side of the y axis. Further, the eighth parasitic element 50h is arranged so as to be in contact with the corner portion C2 on the positive direction side of the x axis and the negative direction side of the y axis in the power supply element 30. That is, the second parasitic element 50b, the seventh parasitic element 50g, and the third feeder element 30c are arranged so as to surround the corner C1 of the feeder element 30, and the fourth parasitic element 50d and the eighth parasitic element 50h. The fifth parasitic element 50e is disposed so as to surround the corner portion C2 of the feeder element 30. As described above, in FIG. 9D, the number of parasitic elements 50 is larger than that in FIG. 9C, and the total element area of the parasitic elements 50 is increased. Here, FIG. 9D is referred to as a structure E.

  FIG. 9E shows the antenna gain improvement amounts of the structures C, D, and E with respect to the structure A, and FIG. 9F shows the efficiency improvement amounts of the structures C, D, and E with respect to the structure A. . In the structure D, the antenna gain improvement amount and the efficiency improvement amount are larger than those in the structure C. Further, in the structure E, the amount of improvement in antenna gain is comparable to that in the structure D, but the amount of improvement in efficiency is large. Therefore, by increasing the element area of the parasitic element 50, the antenna gain and efficiency are improved.

  Next, the size of the parasitic element 50 will be described. FIGS. 10A to 10E show another effect depending on the size of the parasitic element 50. FIG. 10A shows a structure in which the parasitic element 50 shown in FIG. 9E is brought close to the shape of the parasitic element 50 shown in FIG. As described above, the length of the outer edge portion of the parasitic element 50 on the side facing the feeding element 30 is made shorter than the length of the feeding element 30 in the same direction as the outer edge portion. Therefore, the length in the x-axis direction of the first parasitic element 50a and the fifth parasitic element 50e is shorter than the length in the x-axis direction of the feed element 30 and the length of the third parasitic element 50c in the y-axis direction. This is shorter than the length of the feed element 30 in the y-axis direction. Here, FIG. 10A is referred to as a structure F.

  FIG. 10B shows the structure of the antenna 170 to be compared with FIG. The length of the outer edge portion of the parasitic element 150 on the side facing the feeding element 130 is made equal to the length of the feeding element 130 in the same direction as the outer edge portion. Therefore, the length of the first parasitic element 150a and the fifth parasitic element 150e in the x-axis direction is equal to the length of the feeder element 130 in the x-axis direction, and the length of the fifth parasitic element 150c in the y-axis direction. The length is made equal to the length of the feed element 130 in the y-axis direction. Here, FIG. 10B is referred to as a structure G.

  FIG. 10C shows the VSWR when the frequency is changed with respect to the structure F. FIG. The parasitic element 50 resonates near P1. Since the frequency of P1 is far from the desired band, the VSWR in the desired band is not affected. On the other hand, FIG. 10D shows the VSWR when the frequency is changed with respect to the structure G. The resonance by the parasitic element 150 resonates in the vicinity of P2, that is, in the vicinity of the resonance frequency of the feeder element 130. For this reason, the VSWR in the desired band deteriorates due to resonance of the parasitic element 150. FIG. 10E shows the antenna gain improvement amount in the desired band for the structures F and G. Here, when the antenna gain improvement amount is smaller than 0 dB, it indicates that the characteristic is deteriorated. For the same reason as described above, the antenna gain improvement amount of the structure F is larger than the antenna gain improvement amount of the structure G.

  Various modifications of the antenna 100 described so far will be described. FIGS. 11A to 11D are perspective views showing another structure of the antenna 100. FIG. FIG. 11A is a perspective view of the antenna 100 according to the first modification when viewed from the front surface 12, and FIG. 11B illustrates the antenna 100 according to the first modification with the back surface 14. It is a perspective view at the time of seeing from. For these, the microstrip line 138 is not used, and feeding by the feeding point 40 is performed from the back surface 14 side.

  FIG. 11C is a perspective view when the antenna 100 according to the second modification is viewed from the surface 12, and FIG. 11D illustrates the antenna 100 according to the third modification as the surface 12. It is a perspective view at the time of seeing from. In these, the 1st perturbation part 60a and the 2nd perturbation part 60b are provided in the corner | angular part which opposed on the diagonal in the electric power feeding element 30. FIG. The first perturbation unit 60 a and the second perturbation unit 60 b are collectively referred to as the perturbation unit 60, and have a shape in which corner portions of the feed element 30 are cut out. The radio wave radiated from the antenna 100 is circularly polarized by the perturbation unit 60. In FIG. 11C, the microstrip line 38 is disposed, and in FIG. 11D, the microstrip line 38 is not used, and power feeding by the feeding point 40 is performed from the back surface 14 side.

  12A and 12B are perspective views showing the structure of the antenna 100. Specifically, FIG. 12A shows the antenna 100 according to the fourth modification, and FIG. ) Shows the antenna 100 according to the fifth modification. Until now, the plurality of parasitic elements 50 are arranged in a single layer at least at a part around the feeding element 30. On the other hand, in FIGS. 12A to 12B, the plurality of parasitic elements 50 are doubled at least partially around the feeding element 30. For example, in FIG. 12A, two parasitic elements 50, a first parasitic element 50a and a seventh parasitic element 50g, are arranged side by side from the feeding element 30 in the positive direction of the y-axis. With such a structure, the parasitic element 50 is disposed close to the end of the dielectric substrate 10 and the antenna gain is improved. In FIG. 12A, the microstrip line 38 is arranged, and in FIG. 12B, the microstrip line 38 is not used, and power feeding by the feeding point 40 is performed from the back surface 14 side.

(3) Structure including the second region 26 In the description so far, the second region 26 is omitted from the antenna 100 of FIG. Hereinafter, the structure of the antenna 100 including the second region 26 will be described. FIG. 13 shows the effect of the arrangement of the feeding point 40 and the slit 22. Here, four structures will be described. Structure H to structure J indicate the structure of the antenna 170 to be compared with the antenna 100. The structure H is an antenna 170 having the same structure as that shown in FIGS. 6 (a) and 9 (a). The microstrip line 138 extends from the feed element 130 in the negative direction of the y axis, and connects the feed point 140 at the end opposite to the feed element 130 side. In addition, the ground element 120 is disposed on the opposite side of the dielectric substrate 110 from the power feeding element 130. Here, the ground element 120, the microstrip line 138, and the feeding point 140 correspond to the ground element 20, the microstrip line 38, and the feeding point 40. As described above, the antenna directivity in the zenith direction is formed by the current distribution of the structure H.

  The dielectric substrate 110 in the structure I has a shape longer in the x-axis direction than in the y-axis direction, like the dielectric substrate 10 in FIG. The ground element 120 also has a shape that is long in the x-axis direction in accordance with the shape of the dielectric substrate 110. In the current distribution of structure I, the ground current (A3) in the vicinity of the feeding point 140 flows in the negative direction of the x axis along the outer edge portion of the dielectric substrate 110 extending in the x axis direction (A1, A2). In the radiation of radio waves from A1, A2, and A3 due to the ground current, as described above, the distance from the radiation end of the antenna element to the diffraction end of the ground element is non-uniform, so that components that cancel each other out are generated. As a result, the antenna directivity in the zenith direction is lost, and the antenna gain in the zenith direction is reduced.

  Dielectric substrate 110 in structure J has the same shape as dielectric substrate 110 in structure I. On the other hand, instead of the ground element 120, a first ground element 120 a and a second ground element 120 b are arranged, and the ground potential is separated by the slit 122. The first ground element 120 a side is a first region 124, and the second ground element 120 b side is a second region 126. Here, the first ground element 120a, the second ground element 120b, the slit 122, the first region 124, and the second region 126 are the first ground element 20a, the second ground element 20b, the slit 22, the first region 24, the first region 24, and the second region 126, respectively. 2 corresponding to area 26. In the current distribution of the structure J, the ground flowing in the negative direction of the x-axis along the outer edge portion of the dielectric substrate 110 extending in the x-axis direction due to the separation of the first ground element 120a and the second ground element 120b by the slit 122. The current (A1, A2) is smaller than in the case of structure I. As a result, the components that cancel each other out are reduced, and the collapse of the antenna directivity in the zenith direction is suppressed.

  The structure K corresponds to a structure in which the parasitic element 50 is omitted from the antenna 100 in FIG. The microstrip line 38 extends from the feeding element 30 in the negative direction of the x-axis, and connects the feeding point 40 at the end opposite to the feeding element 30 side. In the current distribution of the structure K, the ground current (A4) in the vicinity of the slit 22 is increased by arranging the feeding point 40 in the vicinity of the slit 22. However, the ground currents (A1, A2) flowing in the negative x-axis direction along the outer edge of the dielectric substrate 10 extending in the x-axis direction are smaller than in the case of the structure J. As a result, the components that cancel each other are further reduced, and the antenna directivity in the zenith direction is further prevented from being collapsed, so that the antenna gain in the zenith direction becomes close to that of the structure H.

  According to the present embodiment, since the circuit portion is surrounded by the power feeding element, disturbance of input characteristics and radiation characteristics can be suppressed even when the circuit portion is arranged. In addition, since disturbance of input characteristics and radiation characteristics is suppressed, antenna characteristics (antenna gain, antenna efficiency) can be improved. Further, since the through hole portion is arranged, the ground element and the land portion can be electrically connected. Further, since the diameter of the hole is set to a length of 1/8 or less of the wavelength at the resonance frequency of the antenna, the influence on the electromagnetic field of the antenna can be reduced. In addition, since the influence of the antenna on the electromagnetic field is reduced, the influence of the hole can be reduced. Moreover, since the diameter of the hole is set to 1/8 or less of the wavelength at the resonance frequency of the antenna, the input characteristics and the radiation characteristics can be kept high. In addition, since the input characteristics and radiation characteristics are kept high, the influence of the hole can be reduced.

  Further, since the impedance of the circuit unit is increased, the power feeding element and the ground element can be separated at high frequency. In addition, since the power feeding element and the ground element are separated in a high frequency manner, disturbance of input characteristics and radiation characteristics can be suppressed. In addition, since the hole is formed in the range of the length from the center of the feed element to 1/20 of the wavelength at the resonance frequency of the antenna, the change in the resonance frequency of the antenna can be reduced. Moreover, since the change of the resonance frequency of this antenna is reduced, disturbance of input characteristics and radiation characteristics can be suppressed. In addition, since the circuit portion is formed as a stub pattern, the number of circuit components can be reduced while maintaining the antenna characteristics. Further, since the number of circuit components is reduced, the cost can be reduced.

  In addition, since the length of the feed element is shorter than ½ of the wavelength at the resonance frequency of the antenna, and the length of the parasitic element is shorter than the length of the feed element, Resonance with the element can be suppressed. In addition, since the resonance between the feeding element and the parasitic element at the resonance frequency is suppressed, the antenna characteristics can be improved. Further, since the interval between the parasitic element and the feeding element is made shorter than 1/10 of the wavelength at the resonance frequency of the antenna, the parasitic element can be used as a reflector. In addition, since the parasitic element is used as the reflector, the antenna characteristics can be improved. In addition, since the length of the outer edge portion of the parasitic element on the non-opposing side with respect to the feeding element is shorter than the length of the feeding element, resonance between the feeding element and the parasitic element at the resonance frequency can be suppressed. Further, since the length of the outer edge portion of the parasitic element on the non-facing side with respect to the feeding element is not less than 1/5 of the wavelength at the resonance frequency of the antenna, the antenna characteristics can be improved. In addition, since the parasitic element is disposed so as to surround the corner of the feeder element, the element area can be increased. Moreover, since a perturbation part is added, it can respond to circular polarization.

  Further, since the slit is formed in the ground element and the power feeding element is arranged on the slit side, the ground current can be reduced. In addition, since the ground current is reduced, the radiation of components that cancel each other out is reduced. Further, since the radiation of components that cancel each other is reduced, the antenna characteristics can be improved. Further, since the slit is widened to some extent, the ground current flowing through the second ground element can be reduced. In addition, since the ground current flowing through the second ground element is reduced, the antenna characteristics in the zenith direction can be improved. In addition, since the ground potential is separated into the first ground element and the second ground element, the ground current that radiates components that cancel each other is reduced, and the antenna characteristics can be improved. In addition, since the electric circuit portion is mounted in a region overlapping with the second ground element, the usage of the antenna can be expanded.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements, and such modifications are also within the scope of the present invention.

The outline of one embodiment of the present invention is as follows.
(Item 1-1)
A dielectric substrate;
A ground element disposed on the first surface side of the dielectric substrate;
A feed element disposed on the second surface side of the dielectric substrate;
A hole disposed inside the feeding element;
A land portion disposed inside the hole portion;
A circuit unit disposed between the feeding element and the land unit;
An antenna comprising:

  According to this aspect, since the circuit unit is arranged at a position that does not affect the input impedance, the antenna characteristics can be improved.

(Item 1-2)
Item 11. The antenna according to Item 1-1, further comprising a through-hole portion that penetrates the dielectric substrate and connects the ground element and the land portion. In this case, since the through hole portion is disposed, the ground element and the land portion can be electrically connected.
(Item 1-3)
Item 11. The antenna according to item 1-1 or item 1-2, wherein the diameter of the hole is a length of 1/8 or less of the wavelength at the resonance frequency of the antenna. In this case, since the diameter of the hole is set to a length of 1/8 or less of the wavelength at the resonance frequency of the antenna, the influence of the hole can be reduced.
(Item 1-4)
Any one of Items 1-1 to 1-3, wherein the hole is formed within a length range from the center of the feeding element to 1/20 of a wavelength at a resonance frequency of the antenna. The antenna according to Crab. In this case, since the hole is formed within the length range from the center of the feed element to 1/20 of the wavelength at the resonance frequency of the antenna, the influence of the hole can be reduced.
(Item 1-5)
The antenna according to any one of Items 1-1 to 1-4, wherein the circuit unit is formed as a stub pattern. In this case, since the circuit portion is formed as a stub pattern, the number of circuit components can be reduced.

(Item 2-1)
An antenna,
A dielectric substrate;
A feed element disposed on one side of the dielectric substrate;
A plurality of parasitic elements arranged around the feeding element,
The length of the feed element in the direction of at least one of the two outer edges intersecting the feed element is shorter than the length of ½ of the wavelength at the resonance frequency of the antenna,
In each of the plurality of parasitic elements, the length of the outer edge portion on the side facing the feeding element is shorter than the length of the feeding element.

  According to this aspect, since the length of the feed element is shorter than ½ of the wavelength at the resonance frequency of the antenna and the length of the parasitic element is shorter than the length of the feed element, the antenna characteristics can be improved. .

(Item 2-2)
Item 2. The antenna according to Item 2-1, wherein an interval between each of the plurality of parasitic elements and the power supply element is shorter than 1/10 of a wavelength at a resonance frequency of the antenna. In this case, since the distance between the parasitic element and the feeding element is shorter than 1/10 of the wavelength at the resonance frequency of the antenna, the parasitic element can be used as a reflector.
(Item 2-3)
Item 2-1 or Item 2-2 is characterized in that, in each of the plurality of parasitic elements, the length of the outer edge portion on the non-opposing side with respect to the feeder element is shorter than the length of the feeder element. Antenna. In this case, since the length of the outer edge portion of the parasitic element on the non-opposing side with respect to the feeding element is shorter than the length of the feeding element, the antenna characteristics can be improved.
(Item 2-4)
Item 2 is characterized in that, in each of the plurality of parasitic elements, the length of the outer edge portion on the non-opposing side to the feeding element is 1/5 or more of the wavelength at the resonance frequency of the antenna. -3 antenna. In this case, since the length of the outer edge portion of the parasitic element on the non-opposite side to the feeding element is 1/5 or more of the wavelength at the resonance frequency of the antenna, the antenna characteristics can be improved.
(Item 2-5)
The antenna according to any one of Items 2-1 to 2-4, wherein the parasitic element is disposed so as to surround a corner portion of the feeder element. In this case, since the parasitic element is arranged so as to surround the corner of the feeder element, the element area can be increased.

(Item 3-1)
A dielectric substrate;
A ground element disposed on the first surface side of the dielectric substrate;
A slit formed in the ground element;
A feed element disposed on the second surface side of the dielectric substrate;
A feeding point connected to the feeding element,
The antenna, wherein the feeding point is disposed on the slit side with respect to the feeding element.

  According to this aspect, since the slit is formed in the ground element and the feed element is arranged on the slit side, the ground current that radiates components that cancel out the phases is reduced, and the antenna characteristics can be improved.

(Item 3-2)
The ground element is
A first ground element;
A second ground element having a ground potential separated from the first ground element with the slit as a boundary;
The antenna according to item 3-1, wherein the first ground element is disposed so as to overlap the power feeding element on a projection plane parallel to the first surface or the second surface. In this case, since the ground potential is separated into the first ground element and the second ground element, the ground current that radiates components that cancel each other is reduced, and the antenna characteristics can be improved.
(Item 3-3)
An electric circuit part formed on the second surface side of the dielectric substrate;
Item 3. The antenna according to Item 3-2, wherein the electric circuit unit is disposed so as to overlap the second ground element on a projection plane parallel to the first surface or the second surface. In this case, since the electric circuit portion is mounted in a region overlapping with the second ground element, the usage application of the antenna can be expanded.

  In the embodiment of the present invention, a hole 32 and a land 34 are formed in the power feeding element 30, and a circuit unit 36 is connected thereto. However, the present invention is not limited to this. For example, the hole 32, the land 34, and the circuit 36 may not be included. According to this modification, the structure of the antenna 100 can be simplified.

  In the embodiment of the present invention, a plurality of parasitic elements 50 are arranged around the feeding element 30. However, the present invention is not limited to this. For example, the plurality of parasitic elements 50 may not be arranged. According to this modification, the structure of the antenna 100 can be simplified.

  In the embodiment of the present invention, the dielectric substrate 10 includes the second ground element 20b, the second region 26, and the electric circuit unit 42. However, the present invention is not limited to this. For example, the second ground element 20b, the second region 26, and the electric circuit unit 42 may not be disposed. At that time, the dielectric substrate 10 has a substantially square shape. According to this modification, the structure of the antenna 100 can be simplified.

  In this embodiment, the slit 22 is formed so as to penetrate the dielectric substrate 10 in the y-axis direction. However, the present invention is not limited to this. For example, the slit 22 may not penetrate the dielectric substrate 10 in the y-axis direction. At that time, a part of the first ground element 20a and the second ground element 20b are connected. According to this modification, the degree of freedom of structure can be improved.

  In the embodiment of the present invention, the antenna 100 is used in an ETC vehicle-mounted device, and the resonance frequency of the antenna 100 is assumed to be in the 5.8 GHz band. However, the present invention is not limited to this. For example, the usage of the antenna 100 and the resonance frequency may be other than these. According to this modification, the application range of the antenna 100 can be expanded.

  DESCRIPTION OF SYMBOLS 10 Dielectric substrate, 12 surface, 14 back surface, 20 ground element, 22 slit, 24 1st area | region, 26 2nd area | region, 30 feeder element, 32 hole part, 34 land part, 36 circuit part, 38 microstrip line, 40 Feeding point, 42 electrical circuit part, 44 coaxial cable, 46 through-hole part, 50 parasitic element, 60 perturbation part, 100 antenna.

Claims (3)

A dielectric substrate;
A ground element disposed on the first surface side of the dielectric substrate;
A slit formed in the ground element;
A feed element disposed on the second surface side of the dielectric substrate;
A feeding point connected to the feeding element,
The antenna, wherein the feeding point is disposed on the slit side with respect to the feeding element. The ground element is
A first ground element;
A second ground element having a ground potential separated from the first ground element with the slit as a boundary;
2. The antenna according to claim 1, wherein the first ground element is disposed so as to overlap the feeding element on a projection plane parallel to the first surface or the second surface. An electric circuit part formed on the second surface side of the dielectric substrate;
3. The antenna according to claim 2, wherein the electrical circuit unit is disposed to overlap the second ground element on a projection plane parallel to the first surface or the second surface.