JP2015164256A - Inverted l-shaped antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an antenna characteristic as compared to the inverted L-shaped antenna of the conventional method.SOLUTION: An inverted L-shaped antenna comprises: a ground conductor plate 10 which has a size dependent on a use frequency wavelength and which is held by ground potential; an inverted L-shaped antenna element 8 which includes an outer conductor 26, disposed on a plane in parallel with the ground conductor plate 10 and apart from the upper part of the ground conductor plate 10 with a first gap, and an inner conductor 24, a tip of which extends longer than the outer conductor 26 and which is disposed on the plane and spaced from the outer conductor 26 in a manner to be sandwiched with the outer conductor 26, and has a resonance frequency in the use frequency band; and an opposite conductor plate 17 which has a size to resonate with a resonance frequency substantially equivalent to the resonance frequency of the antenna element 8, and is disposed on a plane in parallel with the antenna element 8 apart from the upper part of the antenna element 8 with a second gap.

Description

  INDUSTRIAL APPLICABILITY The present invention improves an inverted L antenna suitable for application to an unbalanced ultra low profile inverted L antenna equipped in a 2.45 GHz band wireless communication system having a frequency range of 2.40 to 2.50 GHz. It is about.

  Conventionally, as a planar antenna used in wireless communication, for example, a microstrip antenna in which a square or circular patch conductor is printed on the surface of a square dielectric substrate is known. .

  FIG. 12 is a perspective view showing a configuration example of a planar antenna 300 according to a conventional example. A planar antenna 300 shown in FIG. 12 constitutes a microstrip antenna, and has a square dielectric substrate (hereinafter simply referred to as substrate 1), a ground conductor plate 2 having substantially the same shape, and an area of about 1/4 of the ground conductor plate 2. A square patch conductor plate 4 and a coaxial cable 5 as a feed line.

  In the figure, x is the width direction (x direction) of the substrate 1, y is the length direction (y direction) of the substrate 1, and is the direction in which the antenna current (hereinafter simply referred to as current) flows. z is the radiation direction of the electromagnetic wave, and the direction in which the directional gain is observed. sx is the length of the ground conductor plate 2 in the width direction, and sy is the length of the ground conductor plate 2 in the length direction. w is the length in the width direction of the patch conductor plate 4, and the lowercase l (el) is the length in the length direction of the ground conductor plate 2.

  The planar antenna 300 employs a structure in which an electromagnetic field is excited between the ground conductor plate 2 and the patch conductor plate 4. For example, the lengths sx and sy of one side of the ground conductor plate 2 are set to about one wavelength (λ) of the operating frequency, and the lengths w and l of one side of the patch conductor plate 4 are about half a wavelength (λ). λ / 2).

  In order to excite an electromagnetic field between the ground conductor plate 2 and the patch conductor plate 4, an electromagnetic wave is emitted from the opening at the end of the patch conductor plate 4. In the figure, 4a is a feeding point to which the inner conductor 5a of the coaxial cable 5 is connected. An outer conductor (not shown) of the coaxial cable 5 is connected to the ground conductor plate 2.

  However, the planar antenna 300 has a problem that the impedance characteristic becomes a narrow band because the thickness of the substrate 1 is sufficiently smaller than the wavelength. When a thick substrate is used to obtain a wide band, the feed line between the ground conductor plate 2 and the feed point 4a becomes long. Due to the inductance generated there, it is difficult to achieve impedance matching as an antenna, and the bandwidth is reduced. There is a problem that about 10% is the limit.

  In order to improve the problem of impedance matching, L-probe power feeding as shown in Non-Patent Document 1 has been proposed. According to this L-probe-fed microstrip antenna, the inner conductor, which is the feed line of the coaxial cable, is extended from the back of the ground conductor plate, bent in an inverted L shape, and the capacitance between the patch conductor and the parallel part is increased. It has a structure that cancels out the inductance generated in the inner conductor of the coaxial feeder.

  In order to improve the impedance matching problem, an inverted L-type antenna of Patent Document 1 has been proposed. Connect the outer conductor, which is the ground potential of the coaxial cable, to the ground conductor plate held at the ground potential, fold the coaxial cable at a predetermined distance above and parallel to the ground conductor plate surface. It is a structure that is arranged and further extended by exposing only the inner conductor from the middle of the parallel part.

  The position where the inner conductor is exposed is different from the L-probe-fed microstrip antenna of Non-Patent Document 1 described above. The inverted L-shaped antenna is small in size, with the length of the parallel portion of the coaxial cable being approximately ¼ wavelength (λ / 4) and the length of the ground conductor plate in this direction being approximately half wavelength (λ / 2). There are advantages you can do.

Japanese Patent Application Laid-Open No. 2011-08951

K. M. Luk, C. L. Mak, Y. L. Chow and K. F. Lee, “Broadband microstrip patch antenna” Electronics Letters vol.34, no.15, pp.1442-1443, July 1998.

The planar antenna according to the conventional example has the following problems.
i. The planar antenna 300 has a problem that the band is narrow as described above.

  ii. Both the planar antenna 300 and the L-probe-fed microstrip antenna of Non-Patent Document 1 require that the length of one side of the ground conductor plate 2 be about one wavelength, which increases the overall antenna and prevents miniaturization. There's a problem.

  iii. The inverted L-type antenna of Patent Document 1 has a problem that directivity characteristics in the radiation direction are not good because the radiation area of the antenna element is linear.

  Therefore, the present invention has been made in view of these points, and an object thereof is to provide an inverted L-type antenna that can improve directivity characteristics compared to a conventional inverted L-type antenna.

  In order to achieve the above object, an inverted L-type antenna according to the present invention includes a ground conductor plate having a size depending on a wavelength of a use frequency and held at a ground potential, as described in claim 1, An outer conductor disposed on a surface parallel to the ground conductor plate, separated from the upper portion of the ground conductor plate by a first gap, and spaced from the outer conductor on the surface and sandwiched by the outer conductor An inner conductor whose tip extends from the arranged outer conductor; a base end portion of the outer conductor is connected to a predetermined portion of the ground conductor plate; and a base end portion of the inner conductor is on the side of the ground conductor plate An inverted L-shaped antenna element that is connected to a power supply section provided in the antenna and has a resonance frequency in the band of the use frequency that is supplied to the inner conductor, and a size that resonates at a resonance frequency substantially equal to the resonance frequency of the antenna element. With a second gap above the antenna element. Those having a counter conductor plate arranged on the antenna element plane parallel.

  According to the inverted L-shaped antenna of the first aspect, the radiation area of the electromagnetic wave in the inverted L-shaped antenna element can be expanded (expanded) from a linear shape to a planar shape. Can be increased to the maximum.

  According to a second aspect of the present invention, in the inverted L-shaped antenna according to the first aspect, the first gap of the antenna element having the outer conductor and the inner conductor is formed of a dielectric having a relative dielectric constant higher than that of air. The inverted L-shaped antenna according to claim 1, wherein:

  The inverted L-type antenna according to claim 3 is the inverted L-type antenna according to claim 2, wherein the second gap of the antenna element having the outer conductor and the inner conductor is formed of a dielectric having a relative dielectric constant higher than that of air. .

  The inverted L-shaped antenna according to claim 4 is the grounded antenna according to claim 1, wherein the outer conductor and the inner conductor of the antenna element are bent at a position away from a predetermined position of the ground conductor plate by the first gap. It is arranged in parallel with the conductor plate.

  According to a fifth aspect of the present invention, in the inverted L-shaped antenna according to the fourth aspect, the outer conductor and the inner conductor are constituted by an outer conductor and an inner conductor of a coaxial cable.

  6. The inverted L-type antenna according to claim 6, wherein the antenna element is a coplanar line in which the outer conductor and the inner conductor are arranged at a predetermined interval in any one of claims 2 to 4. It is a thing.

  The inverted L-type antenna according to the present invention includes an opposing conductor plate having a size that resonates at a resonance frequency substantially equal to the resonance frequency of the inverted L-shaped antenna element whose base end is connected to the ground conductor plate. A counter conductor plate is disposed to face the upper portion of the antenna element.

  With this structure, the radiation area of the electromagnetic wave in the inverted L-shaped antenna element can be expanded (expanded) from a linear shape to a planar shape, so that the directional characteristic gain can be increased to the maximum as compared with the case where there is no opposing conductor plate. As a result, the directivity can be improved as compared with the conventional inverted L-type antenna. In addition, the size can be reduced as compared with the conventional planar antenna.

It is a perspective view which shows the structural example (the 1) of the inverted L-type antenna 100 as the 1st Embodiment of this invention. It is sectional drawing which shows the structural example (the 2) of the inverted L type antenna 100 containing the structure of the X1-X1 arrow line of FIG. It is a perspective view which shows the example of a dimension of each part of the inverted L type antenna 100, and its radiation principle. It is a graph which shows the S11 characteristic example at the time of changing the dimension dy of ay direction with the opposing conductor board 17. FIG. (A) And (B) is sectional drawing which shows the graph figure which shows the example of a radiation electric field directivity pattern (xz surface), and the structural example of the antenna element 8. FIG. (A) and (B) are the graphs which show the example of a radiation electric field directivity pattern (yz surface), and sectional drawing which shows the structural example of the antenna element 8. FIG. It is a perspective view which shows the structural example of the inverted L type | mold antenna 101 as a comparative example. (A) And (B) is a graph which shows the example of a radiation electric field directivity pattern (xz surface, yz surface) of the inverted L type antenna 101. FIG. 6 is a graph showing an example of directivity gain characteristics of the inverted L-type antenna 100. FIG. It is a perspective view which shows the structural example (the 1) of the inverted L type | mold antenna 200 as 2nd Embodiment. (A)-(C) are sectional drawings which show the structural example (the 2) of the inverted L type | mold antenna 200. FIG. It is a perspective view which shows the structural example of the planar antenna 300 which concerns on a prior art example.

  Embodiments of an inverted L antenna according to the present invention will be described below with reference to the drawings. The inverted L-type antenna 100 as the first embodiment shown in FIG. 1 is configured as an unbalanced feed ultra-low attitude inverted L-type antenna. The inverted L-type antenna 100 includes a ground conductor plate 10, an inverted L-shaped antenna element 8, and a rectangular opposing conductor plate 17.

  In the drawing, the x direction, the y direction, and the z direction are a three-dimensional coordinate system, and x is the width direction of the ground conductor plate 10 and the opposing conductor plate 17 and is a direction orthogonal to the y direction. y is the length direction of the ground conductor plate 10 and the opposing conductor plate 17 and is the direction in which the antenna current flows. z is a directivity direction, and is a radiation direction of electromagnetic waves. The z direction is a direction orthogonal to the x and y directions.

  The ground conductor plate 10 is composed of a finite conductor having a size that depends on the wavelength of the operating frequency, for example, a rectangular shape (vertical x horizontal) of a predetermined size, and holds at least the surface at the ground potential (ground potential portion). used. Specific examples of dimensions of the ground conductor plate 10 will be described later. A base end portion of the outer conductor 26 is connected to a predetermined position on the ground conductor plate 10, and an antenna element 8 that feeds power to the inner conductor 24 is provided. The antenna element 8 has an inverted L shape, and has a resonance frequency in the band of the used frequency, in this example, the 2.45 GHz band. For the inner conductor 24 and the outer conductor 26 of the antenna element 8, a semi-rigid coaxial cable (simply called the coaxial cable 20) having a characteristic impedance of 50Ω is used.

  The base end portion of the antenna element 8 is supported by connecting the outer conductor 26 of the coaxial cable 20 to a predetermined portion of the ground conductor plate 10. The inner conductor 24 is disposed at a distance from the outer conductor 26, and the tip extends beyond the outer conductor 26. The outer conductor 26 and the inner conductor 24 are bent at a predetermined distance from the predetermined position of the ground conductor plate 10, arranged in parallel near the ground conductor plate 10, and supplied with power to the inner conductor 24.

  The broken-line arrows shown in FIG. 1 are directed from the back surface side of the ground conductor plate 10 toward the connection portion 21 of the coaxial cable 20, and indicate a state where power is supplied from the back surface side. A transmission signal is supplied to the antenna element 8 during transmission, and a reception signal is extracted from the antenna element 8 during reception.

  On the upper portion of the antenna element 8, a counter conductor plate 17 is disposed at an upper position facing the ground conductor plate 10 with the antenna element 8 interposed therebetween. The opposing conductor plate 17 has a magnitude that resonates at a resonance frequency substantially equal to the resonance frequency of the antenna element 8, and insulation is maintained with respect to the ground conductor plate 10.

  For example, the opposing conductor plate 17 is constructed on a plurality of support portions 11a and 11b as shown in FIG. The support portions 11 a and 11 b are provided on both sides of the housing 11 for holding the ground conductor plate 10, for example. The housing 11 has holding portions 11 c and 11 d that hold the ground conductor plate 10. The opposing conductor plate 17 is installed on the support portions 11 a and 11 b at a position parallel to the ground conductor plate 10. Specific examples of dimensions of the opposing conductor plate 17 will be described later.

  Here, a configuration example of the inverted L-shaped antenna element 8 will be described with reference to FIG. In this example, in FIG. 2, a connection portion 21 connected to one end portion (base end side) of the coaxial cable 20 is provided at a predetermined position on the surface of the ground conductor plate 10. L0 shown in FIG. 2 is the length of the portion where the coaxial cable 20 is bent in an inverted L shape, and L1 is the length of the outer conductor 26 alone. Therefore, L0-L1 is the length of the portion where the inner conductor 24 is exposed.

  That is, the coaxial cable 20 is provided with an insulator (dielectric material) 25 shown in white in the drawing so as to surround the outside of the inner conductor 24 arranged at the center, and surrounds the outside of the insulator 25. Thus, the outer conductor 26 is arranged. The coaxial cable 20 is electrically connected between the surface of the ground conductor plate 10 and the outer conductor 26 at the connection portion 21 to the ground conductor plate 10, and the outer conductor 26 serves as a ground potential portion.

  The coaxial cable 20 having one end connected to the connection portion 21 is bent as a bent portion 22 at a position away from the surface of the ground conductor plate 10 by a predetermined length in the height direction. The front end side of the cable 20 is disposed so as to be parallel to the surface of the ground conductor plate 10. In the figure, h is a distance, which is the length between the surface of the ground conductor plate 10 and the center of the coaxial cable 20. For the distance h, for example, a signal of a use frequency transmitted and received by the inverted L antenna 100 is used. It is set to about 1/30 of one wavelength.

  The coaxial cable 20 is bent in an inverted L shape at a bent portion 22 and is extended in parallel and close to the ground conductor plate 10, and only the inner conductor 24 is extended to the length L0 to the inner conductor end 24 a. For the outer conductor 26 of the coaxial cable 20, the position of the length L 1 shorter than the length L 0 is used as the outer conductor end 23. At the position of the outer conductor end 23, the insulator 25 is also cut as an end. The position where the outer conductor 26 is cut becomes the feeding point of the antenna element 8.

  The length L0 from the bent portion 22 to the inner conductor end 24a is determined by the operating frequency. For example, it is set to about ¼ of one wavelength of a signal transmitted / received by the inverted L-type antenna 100. The inner conductor 24 thus extended and the outer conductor 26 having a length L1 function as the antenna element 8 of the inverted L-type antenna 100 of this example.

  The length L1 of the outer conductor 26 is set so that the impedance of the antenna element 8 becomes a desired value (here, characteristic impedance: 50Ω). The impedance of the antenna element 8 is performed by adjusting the length L0-L1 of the inner conductor 24. By adjusting this length L0-L1, impedance matching between the antenna element 8 and the feeding point can be achieved.

  Further, in FIG. 2, a connection portion 21 between the ground conductor plate 10 and the coaxial cable 20 is provided with a hole 20a penetrating from the front surface to the back surface, and the inner conductor 24 of the coaxial cable 20 is provided in the hole 20a. It has been passed. For example, the insulator 25 is also configured to pass through the hole 20a so that the inner conductor 24 does not electrically contact the surface of the ground conductor plate 10 or the like.

  Power is supplied using the outer conductor 26 and the inner conductor 24 drawn out to the back side of the ground conductor plate 10. The outer conductor 26 and the inner conductor 24 are connected to the signal processing circuit 3 shown in FIG. 2, and the signal processing circuit 3 performs a process of modulating a transmission signal at the time of transmission and a process of decoding a reception signal at the time of reception. .

  Next, with reference to FIG. 3, the example of a dimension of each part of the inverted L type antenna 100 and its radiation principle are demonstrated. In FIG. 3, pxm is a length from the connection portion 21 of the coaxial cable 20 to one end portion of the ground conductor plate 10. pxp is the length from the connecting portion 21 to the other end. In this example, the length pxm and the length pxp are set to the same dimension, and the length pxm + pxp indicates the width of the ground conductor plate 10 in the x direction (width direction).

  Pym is the length in the y-axis direction from the connecting portion 21 of the coaxial cable 20 to the end of the ground conductor plate 10 in the opposite direction in which the inner conductor 24 of the antenna element 8 extends. pyp is the length in the y-axis direction from the connecting portion 21 to the end of the ground conductor plate 10 in the direction in which the inner conductor 24 extends. In this example, the length pym and the length pyp are set to different dimensions, and the length pym + pyp indicates the dimension of the ground conductor plate 10 in the y direction (length direction).

  dx is the width of the counter conductor plate 17 in the x direction, and dy is the length of the counter conductor plate 17 in the y direction. dh is an inter-conductor distance between the ground conductor plate 10 and the counter conductor plate 17. The lengths dx and dy are set to dimensions that depend on the resonance frequency of the antenna element 8. This setting is for expanding (expanding) the linear radiation area to the planar radiation area.

  3 indicates the direction of current flowing through the ground conductor plate 10 and the coaxial cable 20. In the figure, I1 to I4 are currents flowing through the respective parts, and the current I1 is a current flowing through the inner conductor 24 in the y-axis direction.

  In this example, the length pxm and the length pxp are set equal to each other in the direction orthogonal to the longitudinal direction of the antenna element 8 on the surface of the ground conductor plate 10 (x-axis direction in FIG. 3). Therefore, the currents I2 in the x-axis direction cancel each other, the current in the x-axis direction becomes zero, and radiation due to the current I2 is suppressed.

  Then, by setting the lengths pym and pyp of the ground conductor plate 10 in the y-axis direction, adjustment is made so that the current in the y-axis direction on the conductor plate flows in the + y-axis direction. Here, the + y axis direction is a direction from the connection portion 21 of the coaxial cable 20 toward the inner conductor end portion 24a. That is, in this example, since the length pym is set smaller than ypp, the current I3 is larger than the current I4. Therefore, even if both cancel each other in the opposite direction, the y-axis direction on the conductor plate The total current flows in the + y-axis direction. Therefore, the radiation by the current I1 flowing in the + y axis direction through the inner conductor 24 is increased.

  The direction of the current I1 at the time of transmission / reception will be described in more detail. Inside the coaxial cable 20, a reverse current flows through the inner conductor 24 and the outer conductor 26 shown in FIG. And since the coaxial cable 20 of the position where the outer conductor 26 is arrange | positioned is shielded by the outer conductor 26, electromagnetic waves are not radiated | emitted.

  On the other hand, the current I1 flows out from the outer conductor end 23 by extending the inner conductor 24 to the outside. As a result, an electromagnetic field is radiated from the outer conductor end 23. An equal amount of current I 1 flows from the surface of the outer conductor 26 into the coaxial cable 20. If the inner conductor 24 is not extended from the outer conductor end 23, the electromagnetic field radiated from the outer conductor end 23 is almost zero (radiation principle).

  When receiving with the inverted L-shaped antenna 100, current flows on the inner conductor 24 extended from the outer conductor end 23 and the surface of the outer conductor 26 of the coaxial cable 20. As a result, a potential difference (voltage) is generated between the inner conductor 24 and the outer conductor 26 at the outer conductor end 23, whereby current I 1 flows into the coaxial cable 20 and reception is performed.

  Next, with reference to FIG. 4 to FIG. 6, antenna characteristics calculated in a specific dimension example of the inverted L-type antenna 100 will be described. The shape parameters of the inverted L antenna 100 were set as follows. As the radius of the coaxial cable constituting the antenna element 8, the radius from the connecting portion 21 to the outer conductor end 23 (feed point) is 1.095 mm, and the radius of the inner conductor 24 from the feed point to the tip is 0.255 mm. To do.

  Further, the width (pxm + pxp) of the ground conductor plate 10 in the x-axis direction shown in FIG. 1 is 0.36 times the signal wavelength λ (pxm + pxp), that is, the length pxm = pxp = 22 mm. The length of the ground conductor plate 10 in the y-axis direction is 0.51 times the signal wavelength λ (pym + pyp), that is, pym = 13 mm and yp = 50 mm. Further, the lengths L0 and L1 and the height h of the antenna element 8 are set to L0 = 39.8 mm, L1 = 17 mm, and h = 5.0 mm, respectively.

  The width dx in the x direction of the opposing conductor plate 17 is set to dx = 44 mm similarly to the width (pxm + pxp) of the ground conductor plate 10. The length dy in the y direction of the counter conductor plate 17 is shorter than the length pym + ypp of the ground conductor plate 10 and dy = 51.5 mm. The inter-conductor distance dh between the ground conductor plate 10 and the counter conductor plate 17 is set to dh = 10 mm, which is 0.08 times the signal wavelength λ. The inverted L-shaped antenna 100 was configured by setting these dimensions. After setting these parameters, antenna characteristics were obtained with the center frequency handled by the inverted L-type antenna 100 being 2.45 GHz.

  Here, an example of the S11 characteristic (voltage reflection coefficient) when the dimension dy in the y direction of the counter conductor plate 17 is changed will be described with reference to FIG. In FIG. 4, the vertical axis represents the voltage reflection coefficient S11 [dB], and S11 is an equal scale of 0, −10, −20, −30, −40, −50 [dB]. The horizontal axis represents the operating frequency [GHz]. In this example, the frequency used is 2.2 GHz to 3.0 GHz in equal divisions and in increments of 0.1 GHz. This is a calculation of the S11 characteristic when the dimension dy is changed in the operating frequency range of 2.2 GHz to 3.0 GHz. For the numerical analysis, an electromagnetic simulator "WIPL-D" based on the method of moments was used.

  The curve shown by the solid line is that the dimension dy of the opposing conductor plate 17 is 41.5 mm, the dimension L0 of the antenna element 8 is 30.0 mm, L1 is 9.0 mm, and the design frequency range is from the lower limit value 2.37 GHz to In the case of the upper limit value 2.53 GHz, the S11 vs. frequency characteristic has a return loss of −10 [dB] or less. A small resonance point (resonance frequency around 2.44 GHz) is obtained in the range of use frequency 2.37 GHz to 2.56 GHz, and a large resonance point (resonance frequency 2.86 GHz in the range of use frequency 2.64 GHz to 2.97 GHz. Near).

  The curve shown by the broken line shows that the dimensions of the opposing conductor plate 17 and the antenna element 8 are dy = 51.5 mm, L0 = 39.8 mm, L1 = 17.0 mm, and the design frequency range is 2.39 GHz to 2.51 GHz. In this case, the return loss = −10 [dB] or less is S11 versus frequency characteristics. A large resonance point (around the resonance frequency of 2.45 GHz) is obtained in the operating frequency range of 2.39 GHz to 2.50 GHz.

  The curve indicated by the alternate long and short dash line shows a return loss when the same dimensions are dy = 61.5 mm, L0 = 34.0 mm, L1 = 23.5 mm, and the design frequency range is 2.43 GHz to 2.48 GHz. = −10 [dB] or less is the S11 vs. frequency characteristic obtained. A large resonance point (around the resonance frequency of 2.45 GHz) is obtained in the range of the operating frequency from 2.43 GHz to 2.47 GHz.

  The above calculation results are classified into inverted L-type antennas 100 (A) to (C) and summarized in Table 1.

  According to Table 1, according to the inverted L-type antenna 100 (A) in which the opposing conductor plate 17 having dy = 41.5 mm is arranged, two resonances are caused around the resonance frequency of 2.44 GHz and around the resonance frequency of 2.86 GHz. Thus, it is possible to provide a wideband inverted L-type antenna 100. According to the inverted L-type antenna 100 (A), it was found that the maximum directivity gain = 8.26 [dB] was obtained near the use frequency of 2.98 GHz.

  Further, according to the inverted L-type antenna 100 (B) in which the opposing conductor plate 17 with dy = 51.5 mm is arranged, resonance is obtained in the vicinity of the resonance frequency of 2.45 GHz, and the inverted L-type antenna 100 for narrow band is provided. become able to. According to the inverted L-type antenna 100 (B), it was found that the maximum directivity gain = 8.10 [dB] was obtained near the use frequency of 2.45 GHz.

  Further, according to the inverted L-type antenna 100 (C) having the opposing conductor plate 17 with dy = 61.5 mm, resonance is obtained in the vicinity of the resonance frequency of 2.45 GHz, and the inverted L-type antenna 100 for narrow band is provided. become able to. That is, according to the inverted L-type antenna 100 (C), the length pmy + pyp of the ground conductor plate 10 and the length dy of the counter conductor plate 17 are substantially the same, and the resonance frequency is substantially equal. The band becomes narrow. Further, according to the inverted L-type antenna 100 (C), the maximum directivity gain = 6.67 [dB] was obtained in the vicinity of the use frequency of 2.19 GHz. It has been found that if dy is made too long, the radiation in the −z direction becomes too strong and the maximum directivity gain decreases.

  Here, with reference to FIG.5 and FIG.6, the example of the radiation electric field directivity pattern (xz surface, yz surface) of the inverted L type antenna 100 is demonstrated. In the circular graph shown in FIG. 5A, the horizontal axis represents the directional characteristic gain [dB] in the x direction of the antenna element 8, and the vertical axis represents the directional characteristic gain [dB] in the z direction. The directivity gain is -20, -10, -5, 0, 5, 10 [dB] on an even scale. In the cross-sectional view of the xz plane shown in FIG. 5B, the opposing conductor plate 17 having a width dx = 44 mm is disposed on the antenna element 8.

  A solid curve is a radiation electric field directivity pattern showing the magnetic characteristic Eφ in the xz plane of the antenna element 8. According to the radiation electric field directivity pattern of Eφ, it has the shape of a ridge facing upside down, and the directivity is largely spread in the direction of the opposing conductor plate 17. The maximum directivity gain in the z direction is 8 [dB].

  A broken curve is a radiation electric field directivity pattern indicating the electric field characteristic Eθ in the xz plane of the antenna element 8. The radiation field directivity pattern of Eθ has a shape similar to the symbol of infinity (∞). Both are antenna characteristics at a use frequency of 2.45 GHz and dy = 51.5 mm.

  In the circular graph shown in FIG. 6A, the horizontal axis represents the directional characteristic gain [dB] in the y direction of the antenna element 8, and the vertical axis represents the directional characteristic gain [dB] in the z direction. In the cross-sectional view of the yz plane shown in FIG. 6B, an opposing conductor plate 17 having a length dy = 51.5 mm is disposed on the antenna element 8. In the yz plane, the electric field characteristic Eφ is zero.

  A broken curve is a radiation electric field directivity pattern indicating the electric field characteristic Eθ on the yz plane of the antenna element 8. The radiated electric field directivity pattern of Eθ has a shape similar to an inverted ridge. It can be seen that current radiation contributes in the z-axis direction. Both are antenna characteristics at a use frequency of 2.45 GHz.

  In this way, by matching the resonance frequency depending on the dimensions dx and dy, which are the vertical and horizontal dimensions of the rectangular of the opposing conductor plate 17, with the resonance frequency of the inverted L-shaped antenna element 8, The voltage reflection coefficient (| S11 |) characteristic can be reduced to the minimum, and the directional characteristic gain can be increased to the maximum. With respect to the antenna element 8 that can obtain 8 dB as the directivity characteristic gain, it has been found that a directivity gain equivalent to that of a microstrip antenna having a size of about 6 times can be obtained.

  Here, with reference to FIG.7 and FIG.8, the inverted L type | mold antenna 101 as a comparative example and the inverted L type | mold antenna 100 which concern on this invention are compared. In this example, the antenna characteristics were compared between the inverted L-type antenna 101 without the opposing conductor plate 17 as shown in FIG. 7 and the inverted L-type antenna 100 with the opposing conductor plate 17 described above. The shape parameters of the inverted L-type antenna 101 as a comparative example are as follows. The inverted L-type antenna 101 is not only taken from the inverted L-type antenna 100 as the counter conductor plate 17, but also has a minimum | S11 | characteristic. Thus, the directional characteristic gain is set to be maximum.

  According to the inverted L-shaped antenna 101 shown in FIG. 7, the length pxm = pxp = 15 mm is set as the width (pxm + pxp) of the ground conductor plate 10 in the x-axis direction. The length of the ground conductor plate 10 in the y-axis direction is set to the length pym = 10 mm and yp = 50 mm. Further, the lengths L0 and L1 and the height h of the antenna element 8 of the inverted L-type antenna 101 are L0 = 31.6 mm, L1 = 22.8 mm, and h = 4.0 mm, respectively. The coaxial cable constituting the antenna element 8 of the inverted L antenna 101 was the same as that of the inverted L antenna 100.

  8A and 8B are graphs showing a radiation field directivity pattern example (xz plane) and a radiation field directivity pattern example (yz plane) of the unbalanced feed inverted L-type antenna 101 shown in FIG. 7 as a comparative example. In FIG. 8A, the solid curve is a radiation electric field directivity pattern indicating the electric field characteristic Eφ in the xz plane of the antenna element 8 of the inverted L-type antenna 101. According to the radiation electric field directivity pattern of Eφ, although it is slightly crushed, it has a substantially circular shape and has a large directivity in the z direction, but the inverted L antenna 100 shown in FIG. The maximum directional characteristic gain is about 4.8 [dB] smaller than the maximum directional characteristic gain in the z direction = 8 [dB].

  The dashed curve is a radiation electric field directivity pattern indicating the electric field characteristic Eθ in the xz plane of the antenna element 8 of the inverted L-type antenna 101. The radiated electric field directivity pattern of Eθ has the shape of an infinite (∞) symbol as in the inverted L-type antenna 100.

  Further, in the circular graph shown in FIG. 8B, the dashed curve is a radiation electric field directivity pattern indicating the electric field characteristic Eθ on the yz plane of the antenna element 8 of the inverted L-type antenna 101. The radiated electric field directivity pattern of Eθ has a shape of an inverted ridge, but the maximum directivity is larger than the maximum directional characteristic gain in the z direction of the inverted L-type antenna 100 shown in FIG. 6 = 8 [dB]. The characteristic gain is as low as about 4.8 [dB]. Both are antenna characteristics at a use frequency of 2.45 GHz.

  Both radiation electric field directivity patterns are slightly smaller than those of the inverted L-type antenna 100. This is because the inverted L-shaped antenna 101 shown in FIG. 7 does not have the opposing conductor plate 17 on the antenna element 8, so that the radiation area during transmission is small depending on the line shape of the inner conductor 24 and the directivity is extended. Probably not.

  On the other hand, according to this embodiment, the opposing conductor plate 17 exists on the antenna element 8 and the radiation area is expanded from the linear shape of the inner conductor 24 to the surface shape of the opposing conductor plate 17 during transmission. It is thought that the sex was extended. At the time of reception, compared to the inverted L-type antenna 101, the received power can be efficiently extracted from the inverted L-type antenna 100 captured on the surface of the opposing conductor plate 17.

Here, the directivity gain characteristic of the inverted L-type antenna 100 will be described with reference to FIG.
In FIG. 9, the vertical axis represents the directivity gain [dB] measured in the z direction of the inverted L antenna 100. The directivity gain is 7.00 to 9.00 [dB] on an even scale. The horizontal axis represents the operating frequency [GHz] of the inverted L-type antenna 100. The operating frequency [GHz] is 2.20 to 2.70 [GHz] in increments of 0.1 [GHz] on an equally divided scale.

  The solid curve is a pattern of calculated values indicating the directional characteristic gain [dB] in the z direction of the inverted L-type antenna 100 (gain characteristic pattern). According to this gain characteristic pattern, it has a gentle arc shape. The frequency bandwidth is 2.40 [GHz] to 2.50 [GHz], the center frequency is 2.45 GHz, the directivity gain is 8.10 [dB] or more, and the antenna element 8 in the z direction. It shows that the maximum directional characteristic gain at 8 is 8.10 [dB].

  As described above, according to the inverted L-type antenna 100 as the first embodiment, the resonance frequency (2.45 GHz) of the inverted L-shaped antenna element 8 in which the base end of the outer conductor 26 is connected to the ground conductor plate 10. A counter conductor plate 17 having a size (dx, dy) that resonates at substantially the same resonance frequency is provided, and the counter conductor plate 17 is disposed to face the upper portion of the antenna element 8.

  With this structure, the radiation area of the inverted L-shaped antenna element 8 can be expanded (expanded) from a linear shape to a planar shape, so that the directional characteristic gain can be increased to the maximum as compared with the case where the counter conductor plate 17 is not provided. As a result, the directivity characteristics can be improved as compared with the conventional inverted L-type antenna 101. Further, since the inverted L-shaped antenna element 8 is provided, the length of the ground conductor plate is about 1/3 of the length in the longitudinal direction ((pym + ypyp) = 63 mm) and the length in the short direction ((pxm + pxp). ) = 44 mm) is about ½ of the wavelength, and the area can be reduced to about 1/6 compared with a conventional flat antenna having a size of 1 wavelength × 1 wavelength, and can be greatly downsized. .

<Second Embodiment>
Next, with reference to FIGS. 10 and 11, structural examples (Nos. 1 and 2) of the inverted L-type antenna 200 as the second embodiment will be described. An inverted L-shaped antenna 200 shown in FIG. 10 has a dielectric substrate (hereinafter simply referred to as substrates 28 and 90) having a multilayer structure with a conductive pattern interposed therebetween, and a ground conductor plate 92 is disposed on the back surface 91b of the substrate 90. Then, flat conductive patterns 93, 94, 95 are coplanar on the surface 91a of the substrate 90 (position having a height h ′ (= the thickness of the substrate 90) from the ground conductor plate 92: see FIG. 11A). The example is arranged as a track.

  That is, as shown in FIG. 10, the ground conductor plate 92 is provided on almost the entire back surface 91 b of the substrate 90. The dimension of the ground conductor plate 92 in the y direction is a length pym ′ from one end, and a length pyp ′ in the y direction, that is, a length pym ′ + pyp ′. In the x direction, the lengths are pxm 'and pxp' from the center to the end, that is, the length pxm '+ pxp'.

  Conductive patterns 93, 94, 95 are provided on the surface 91 a of the substrate 90 in parallel in the y direction with the position of the length pym ′ as the base end from one end of the ground conductor plate 92. The length of the conductive pattern 93 is L0 ', and the length of the conductive patterns 94 and 95 is L1'.

  In the x-direction, the conductive pattern 93 is disposed at the center position of the ground conductor plate 92, and the conductive patterns 94 and 95 are disposed with a predetermined interval therebetween to form a coplanar line. Above the conductive patterns 93, 94, and 95, an opposing conductor plate 47 having a length dy ′ in the y direction and a length dx ′ in the x direction is disposed.

  Through holes 103, 104, and 105 shown in FIG. 11B are connected to the base ends of the conductive patterns 93, 94, and 95 (that is, the positions having a length pym 'from one end of the ground conductor plate 92), respectively. Yes. As shown in FIG. 11B, the penetrating portion 104 and the penetrating portion 105 are connected to the ground conductor plate 92. The through portion 103 is connected to the connection portion 97, and the electric wire 98 is connected to the connection portion 97. 11A and 11B, reference numerals 47a to 47d denote support portions that support the upper and lower edges of the substrate 90.

  FIG. 11C is a partially enlarged view of the plan view seen from the arrow A in FIG. 11A. A connection portion 97 is formed substantially concentrically with the through portion 103. The connection portion 97 and the ground conductor plate 92 are insulated by an annular gap. The electric wire 98 is connected to the connection portion 97. The signal processing circuit 3 is connected to the inverted L-type antenna 200 by the electric wire 99 connected to the electric wire 98 and the ground conductor plate 92.

  The inverted L-shaped antenna 200 is manufactured by printed circuit board technology. For the substrate 90 and the substrate 28, glass epoxy resin, ceramic, or the like, which is a dielectric having a higher dielectric constant than air, is used.

  A shape pattern composed of the connection portion 97 and the ground conductor plate 92 is formed on the back surface 91b of the substrate 90, and a shape pattern of the conductive patterns 93, 94, and 95 is formed on the surface 91a of the substrate 90, and the positions of the through portions 103, 104, and 105 are formed. A via hole is drilled and filled with a conductive material to form through-holes 103, 104, and 105 that connect the front and back surfaces.

  The thickness of the ground conductor plate 92 and the conductive patterns 93, 94, 95 is about 20 μm. Further, the area of the cross section orthogonal to the current flow direction of the through portions 103, 104, and 105 is set to be substantially equal to the area of the cross section orthogonal to the current flow direction of the conductive patterns 93, 94, and 95.

  The opposing conductor plate 47 is formed in a predetermined shape pattern on the surface of the substrate 28, that is, on the opposite surface to the conductive patterns 93, 94, 95 side. In FIG. 11A, the substrate 28 is constructed on the support portions 47a and 47b. However, the lower surface of the substrate 28 and the upper surfaces of the conductive patterns 93, 94, and 95 may be directly fixed.

  As described above, according to the inverted L-type antenna 200 as the second embodiment, the resonance frequency (2.P) of the inverted L-shaped antenna element 8 in which the base ends of the conductive patterns 94 and 95 are connected to the ground conductor plate 92. The counter conductor plate 47 having a size (dx ′, dy ′) that resonates at a resonance frequency substantially equal to 45 GHz) is provided, and the counter conductor plate 47 is disposed to face the upper portion of the antenna element 8.

  With this structure, the radiation area of the inverted L-shaped antenna element 8 can be expanded (expanded) from a linear shape to a planar shape, so that the directional characteristic gain can be increased to the maximum as compared with the case where the counter conductor plate 47 is not provided. As a result, the directivity can be improved as compared with the conventional inverted L-type antenna 101.

  Further, as shown in FIG. 10, the impedance L can be adjusted to 50Ω by adjusting the length L0 ′ of the conductive pattern 93 and the length L1 ′ of the conductive patterns 94 and 95. The length L0 'is set to be shorter than about 1/4 of one wavelength of a signal to be transmitted / received, for example. This is because the substrate 28 which is a dielectric is interposed between the conductive pattern 93 and the counter conductor plate 47 and does not have a space portion as in the first embodiment.

  Further, by setting the lengths pym ', pyp', pxm ', pxp' of the ground conductor plate 92 and the lengths dy ', dx' of the counter conductor plate 47, good characteristics can be obtained. These lengths can be reduced as compared with the inverted L-type antenna 100 described in the first embodiment by the interposition of the substrate 90 and the substrate 28 which are dielectric materials. Further, the distance between the ground conductor plate 92 and the conductive patterns 93, 94, 95, that is, the gap h ', and the distance between the ground conductor plate 92 and the opposing conductor plate 47, that is, the gap dh' can be reduced.

  Therefore, the size and thickness of the antenna can be further reduced, and a small, thin and high-performance unbalanced feeding ultra-low profile inverted L-type antenna can be provided.

  In each of the embodiments described so far, the antenna characteristics are improved by controlling the current on the ground conductor plate 92 by providing a slit on the surface of the ground conductor plate 92, for example. May be.

  The present invention is extremely suitable when applied to an ultra-low profile inverted L-type antenna equipped in a wireless communication system having a use center frequency of 2.45 GHz band, a mobile phone, or a wireless charging system of an automobile.

  DESCRIPTION OF SYMBOLS 3 ... Signal processing circuit, 8 ... Inverted L-shaped antenna element (antenna element part) 10, 40, 80 ... Grounding conductor plate, 11 ... Case, 90 ... Substrate (No. 1 dielectric substrate), 17, 47 ... opposing conductor plate, 20a ... hole, 21 ... connection point, 22 ... bent portion, 23 ... outer conductor end, 24 ... Inner conductor, 24a ... inner conductor tip, 25 ... insulator, 26 ... outer conductor, 28 ... substrate (second dielectric substrate), 47a-47d ... support, 93, 94, 95 ... conductive pattern, 97 ... connection part, 103, 104, 105 ... penetrating part, 100, 200 ... inverted L-type antenna

Claims (6)

A ground conductor plate having a size depending on the wavelength of the frequency used and held at the ground potential;
An outer conductor disposed on a plane parallel to the ground conductor plate and spaced apart from the outer conductor by a first gap at an upper portion of the ground conductor plate, and the outer conductor sandwiched between the outer conductors on the surface is spaced apart from the outer conductor. An inner conductor whose tip extends beyond the outer conductor, the base end of the outer conductor is connected to a predetermined location of the ground conductor plate, and the base end of the inner conductor is the ground conductor plate An inverted L-shaped antenna element that is connected to a power feeding unit provided on the side and is fed to the inner conductor and has a resonance frequency in a band of the use frequency;
A counter conductor plate having a magnitude that resonates at a resonance frequency substantially equal to the resonance frequency of the antenna element and disposed on a plane parallel to the antenna element, separated from the antenna element by a second gap; Inverted L-shaped antenna.   2. The inverted L-shaped antenna according to claim 1, wherein the first gap of the antenna element having the outer conductor and the inner conductor is formed of a dielectric having a relative dielectric constant higher than that of air.   The inverted L-shaped antenna according to claim 2, wherein the second gap of the antenna element having the outer conductor and the inner conductor is formed of a dielectric having a relative dielectric constant higher than that of air.   2. The inverted L shape according to claim 1, wherein an outer conductor and an inner conductor of the antenna element are bent at a position apart from the predetermined position of the ground conductor plate by the first gap and arranged in parallel with the ground conductor plate. antenna. The outer conductor and the inner conductor are
The inverted L-shaped antenna according to claim 4, wherein the inverted L-shaped antenna is configured by an outer conductor and an inner conductor of a coaxial cable. The antenna element is
The inverted L-shaped antenna according to any one of claims 2 to 4, wherein the inverted L-shaped antenna is configured by a coplanar line in which the outer conductor and the inner conductor are arranged with a predetermined gap therebetween.

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