JP4087623B2 - Planar antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a planar antenna used for transmission / reception of a wireless LAN or the like.
[0002]
[Prior art]
A so-called microstrip antenna in which patch-shaped radiating elements are arranged in parallel on a ground plate via a dielectric layer can be thinly formed due to its structure. For this reason, as a transmission / reception antenna used in a high use frequency band such as a wireless LAN, a planar antenna constituted by using a microstrip antenna as an antenna portion and covering the antenna portion with a radome has been widely used.
[0003]
This conventional planar antenna is provided with a coaxial cable plug composed of a central conductor and a threaded portion around the center conductor, and is fed by a feed line such as a coaxial cable via the coaxial cable plug. The outer conductor of the coaxial cable is connected to the ground plate via the threaded portion of the coaxial cable plug, while the core wire of the coaxial cable is connected to the central conductor of the coaxial cable plug. Furthermore, the central conductor of the coaxial cable plug protrudes from the back surface to the radiation surface side through the insertion hole of the ground plate, and is connected to the feeding point of the radiation element by soldering across the dielectric layer made of air. In such a conventional planar antenna, stray capacitance is generated where the central conductor of the coaxial cable plug crosses the dielectric layer. Therefore, when this antenna is used in a high frequency band, the stray capacitance is There was a risk of adverse effects on radiation characteristics.
[0004]
FIG. 10 shows the vertical polarization vertical plane directivity when a conventional planar antenna is actually formed to be usable in the 2 GHz band (center frequency f ₀ = 2.45 GHz), which is the frequency band used in the wireless LAN system. It is a directivity characteristic diagram. From this figure, in the conventional planar antenna, the directivity peak position P2 (shown by a black circle) is tilted upward at a tilt angle θ2 of about 3 ° with respect to the front direction of the antenna (the vertical direction of the radiating element surface). It can be seen that the shift occurs in the direction (antenna radiation direction). According to this conventional planar antenna, the radiation direction is generated in a direction different from the front direction, so that the directivity characteristic is not vertically symmetrical, and the radiation characteristic for the transmitting / receiving device arranged in the front direction is deteriorated. there were.
[0005]
[Problems to be solved by the invention]
In view of these problems, an object of the present invention is to realize a planar antenna that can correct the peak position of the directivity characteristic and improve the radiation characteristic in the front direction.
[0006]
[Means for Solving the Problems]
A planar antenna according to a first aspect of the present invention includes a patch-shaped radiating element, a ground plate disposed so as to face the back of the radiating element via a dielectric layer, and a dielectric layer from the back surface of the ground plate. A planar antenna comprising a feed line connected to a feed point of a radiating element ,
While the plate thickness of the radiating element is constant, the ground plate is formed in an inclined plate shape with a predetermined inclination angle so that the surface facing the back of the radiating element is inclined with respect to the back surface, and the radiating element and the ground plate Are arranged such that the surfaces facing each other are inclined and non-parallel to the center line direction of the radiating element passing through the feed point position of the radiating element, and the radiating surface of the radiating element and the back surface of the ground plate body, Arranged so as to be orthogonal to the front direction.
[0008]
A planar antenna according to a second aspect of the present invention is configured by arranging a patch-shaped parasitic element in parallel with a radiation surface of a radiation element via a dielectric layer.
[0009]
According to a third aspect of the present invention, there is provided a planar antenna including at least one convex ground wall disposed on the front surface of the ground plate so as to surround the radiating element.
[0010]
According to a fourth aspect of the present invention, there is provided a planar antenna comprising: an inner ground wall disposed so as to surround substantially the entire circumference of the radiating element; and an outer ground wall concentrically disposed outside the inner ground wall. It consists of the body.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of a planar antenna according to the present invention. 1A is a front view of the planar antenna 1a, FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A, and FIG. 1C is BB of FIG. FIG. This planar antenna 1a is made of a synthetic resin formed so as to cover the entire radiation surface side of the antenna portion 10 formed so as to be able to transmit and receive linearly polarized waves in a frequency band of 2.4 GHz used in a wireless LAN or the like. And the radome 20.
[0014]
The antenna unit 10 includes a ground plate 11 formed in a substantially square shape, a convex ground wall 12 provided on the surface of the ground plate 11, and a length L1 that is approximately 0.5 times the wavelength λ used. The radiating element 13 is formed in a square plate shape, and the parasitic element 19 is formed in a rectangular plate shape. The patch-shaped radiating element 13 is formed in a thin plate shape made of a conductive material such as iron surface-treated by galvanization or the like, for example, and is arranged so as to be orthogonal to the front direction of the planar antenna 1a. The ground plate 11 is disposed on the back of the radiating element 13 so as to face the radiating element 13 via a spacer 14a having a length L2. The ground plate 11 is formed of a conductive material such as an aluminum alloy for die casting so that the plate thickness increases from the upper side to the lower side. The ground plate 11 is formed in an inclined plate shape with an inclination angle θ1 of approximately 4 °, and the back surface of the ground plate 11 is disposed so as to be orthogonal to the front direction.
[0015]
The spacer 14a protrudes from the center of the ground plate 11 so as to coincide with the front direction. The spacer 14a passes through the radiating element 13 and the ground plate 11 facing the radiating element 13 so that the surfaces facing each other pass through the feed point position of the radiating element 13. A first dielectric that is arranged so as to be non-parallel with an inclination angle θ1 of approximately 4 ° in the linear direction, and air having a layer width L2 between the ground plate 11 and the radiating element 13 as a dielectric. Layer 15a is formed. Furthermore, the spacer 14a fixes the central portion of the radiating element 13 so that the sides of the ground plate 11 and the radiating element 13 are parallel to each other.
[0016]
A parasitic element 19 is arranged on the radiation surface of the radiation element 13 so as to be orthogonal to the front direction via a spacer 14b having a length L6 projecting from the center of the radiation surface in the front direction. The parasitic element 19 is configured such that the short side has a length L7 that is approximately 0.4 times the use wavelength λ, and the long side has a length L8 that is approximately 0.5 times the use wavelength λ. Similarly to the radiating element 13, the parasitic element 19 is formed into a thin plate shape, that is, a patch shape by a conductive material such as iron surface-treated by galvanization or the like. The spacer 14 b arranges the radiating element 13 and the parasitic element 19 in parallel, and forms a second dielectric layer 15 b using air having a layer width L 6 as a dielectric between the radiating element 13 and the parasitic element 19. is doing. In addition, the spacer 14 b is fixed to the center of the parasitic element 19 with a screw 17 so that the sides of the radiating element 13 and the horizontally long parasitic element 19 are parallel to each other.
[0017]
Further, a plate-like ground wall 12 is provided on the ground plate 11 so as to surround the radiating element 13 over the entire circumference laterally from the peripheral edge of the radiating element 13 on the front side thereof. The earth wall body 12 is formed of a conductive material such as an aluminum alloy for die casting, for example, and is integrally connected to the earth plate body 11 by connection means such as molding by a mold. The earth wall 12 is composed of two groups, an inner earth wall 12a and an outer earth wall 12b. The inner ground wall 12a is disposed concentrically with the radiating element 13 with a distance L3 from the peripheral edge of the radiating element 13. The outer ground wall body 12b is disposed concentrically with the inner ground wall body 12a with a distance L4 outward from the inner ground wall body 12a and along the peripheral edge of the ground plate body 11. ing. The inner ground wall body 12a and the outer ground wall body 12b are both protruded from the ground plate 11 in the front direction at a height H1.
[0018]
Further, on the back surface of the ground plate 11, a mounting bracket 25 for fixing the antenna post and the antenna 1 a is provided. An F-shaped coaxial cable plug 26 to which, for example, a coaxial cable (not shown) is connected as a feed line is projected below the mounting bracket 25. The outer conductor 26b of the coaxial cable plug 26 is connected to the ground plate 11 by connection means such as integral molding with a mold or screwing with a screw. The central conductor 26a of the coaxial cable plug 26 passes through the through hole 27 of the ground plate 11 provided coaxially with the outer conductor 26b and the inner insulator 26c, and is covered with the inner insulator 26c. The leading end portion of the central conductor 26a penetrating the one dielectric layer 15a is connected to a predetermined feeding point 21 of the radiating element 13 by a connecting means such as soldering.
[0019]
The position of the feeding point 21 defined by the radiating element 13 is defined as a position where the planar antenna 1a can radiate vertical polarization. That is, in the state where the front direction of the planar antenna 1a is horizontally oriented, the four sides around the antenna are arranged in the horizontal direction and the vertical direction, respectively, and the feeding point 21 is on the vertical center line of the radiating element 13 and the radiating element. It is defined at a position below the center of 13.
[0020]
The planar antenna 1a having the above configuration is configured by covering the entire front side of the ground plate 11 with the radome 20 including the ground wall 12, the radiating element 13, and the parasitic element 19, and exposing the back surface of the ground plate 11. Consists of states. The radome 20 is attached to the ground plate 11 in close contact with the outer peripheral surface of the outer ground wall 12b. The planar antenna 1a is installed by attaching the mounting bracket 25 to a support member such as an antenna column in an outdoor or indoor environment with the front direction of the antenna facing the transmission or reception antenna of the other party.
[0021]
When the planar antenna 1 a is installed outdoors, the outer ground wall 12 b also functions as a waterproof wall that prevents inundation of rainwater or the like from the joint between the ground plate 11 and the radome 20. It is most preferable that the inner ground wall body 12a and the outer ground wall body 12b are disposed on the ground plate body 11 without interruption, but as shown in the present embodiment, Water drain grooves 18a and 18b may be provided at the center of the lower side of the inner ground wall body 12a and the outer ground wall body 12b so as to provide a drainage channel to the outside.
[0022]
FIG. 2 is a directivity characteristic diagram in the vertical polarization vertical plane when the above-described planar antenna 1a is used for wireless LAN (center frequency f ₀ = 2.45 GHz). From this characteristic diagram, compared to the conventional directivity characteristic diagram of FIG. 10, the peak position P1 (illustrated by a black circle) of the directivity characteristic of the planar antenna 1a moves in the front direction, and the radiation direction is equal to the front direction. You can see that it is suitable. Furthermore, it can be seen that the FB ratio in the conventional characteristic diagram (front / rear ratio in directivity characteristics, hereinafter the same) is 13 dB, whereas the planar antenna 1a is 16 dB, and the FB ratio can be improved by about 3 dB. Here, in order for the conventional planar antenna to improve the FB ratio to 16 dB, it has been confirmed that the surface area of the ground plate needs to be increased to at least about 2.1 times the area.
[0023]
Note that the wavelength used is λ, the length of the spacer 14a, that is, the layer width L2 of the dielectric layer is approximately 0.06λ, and the distance L3 between the radiating element 13 and the inner ground wall 12a is approximately 0.1λ or more. The distance L4 between the wall 12a and the outer ground wall 12b is 0.02λ to 0.1λ, and the height of the ground wall 12 from the ground plate 11, that is, the height of the inner ground wall 12a and the outer ground wall 12b. The planar antenna 1a may be configured within a range of the set dimensions of 0.05λ to 0.1λ.
[0024]
As described above, in the planar antenna 1a of the first embodiment, since the radiating element 13 and the ground plate 11 are arranged in non-parallel, it is desired to shift the directivity characteristic peak position caused by the stray capacitance of the feeder line. Thus, it is possible to correct the radiation characteristic in the front direction of the antenna. In particular, since the radiating element 13 and the ground plate 11 are arranged non-parallel at an inclination angle θ1 of approximately 4 ° so as to be inclined in the center line direction of the radiating element 13 passing through the feeding point 21, the coaxial cable plug The directivity characteristic generated at the tilt angle of about 3 ° from the front direction due to the stray capacitance generated in the portion across the first dielectric layer 15a of the central conductor 26a of the 26 central conductors 26a has the directivity characteristic so as to coincide with the front direction. The peak position P1 can be moved. Therefore, it is possible to improve the radiation characteristic in the front direction by making the directivity characteristic vertically symmetric.
[0025]
Further, since the plate-like inner ground wall body 12a and outer ground wall body 12b are provided so as to surround the radiating element 13 laterally from the peripheral edge of the radiating element 13 on the ground plate body 11, the ground plate body 11 Can be increased to a suitable area for obtaining the required radiation characteristics. Therefore, the FB ratio as the radiation characteristic can be improved without increasing the outer dimension of the ground plate 11, and the antenna having the radiation characteristic comparable to the conventional one can be reduced in size. Further, since the inner ground wall 12a and the outer ground wall 12b serve as a reinforcing material for improving the structural strength of the ground plate 11, the ground plate 11 can be formed thin, and the planar antenna 1a can be reduced in weight. Can be Furthermore, since the parasitic parasitic element 19 having a different size from that of the radiation element 13 is arranged in parallel via the second dielectric layer 15b, the specific bandwidth can be widened.
[0026]
FIG. 3 is a cross-sectional view of an essential part showing a modified example of the first embodiment. In the planar antenna 1b of FIG. 3, the outer ground wall 12b is removed, and a parallel ground wall 12c having a width L5 is formed from the entire circumference of the protruding end of the inner ground wall 12a to the outside in parallel to the ground plate 11. Projected.
[0027]
The same effect as the antenna 1a of FIG. 1 can be obtained also by the planar antenna 1b. The width L5 of the parallel ground wall 12c is formed to be equal to the distance L4 between the inner ground wall 12a and the outer ground wall 12b in the antenna 1a, and is in the range of 0.02λ to 0.1λ (operating wavelength λ). Can be set.
[0028]
FIG. 4 shows a second embodiment of the planar antenna according to the present invention. The planar antenna 1c is configured by removing the parasitic element 19 from the planar antenna 1a described as the first embodiment. Other configurations are the same as those of the planar antenna 1a. According to the planar antenna 1c, the directivity characteristic can be corrected so that the radiation direction coincides with the front direction, and the radiation characteristic in the front direction can be improved, similarly to the planar antenna 1a of the first embodiment. it can. In addition, since the ground wall 12 is disposed on the ground plate 11, the surface area of the ground plate 11 on the side where the radiating element is disposed can be increased, the FB ratio is improved, and the entire antenna is reduced in size and weight. can do.
[0029]
In addition, this invention is not limited to the said embodiment, As shown in the following (1)-(6), the shape and structure of each part are suitably changed in the range which does not deviate from the meaning of this invention. It is also possible to implement.
(1) The planar antenna according to the present invention is configured with a shape and dimension corresponding to other system operating frequencies such as IMT2000.
(2) As shown in the planar antenna 1d in FIG. 5, the ground plate 11 is made uniform in thickness to form an inclined surface having an inclination angle θ1. Also with this configuration, it is possible to obtain the same effects as the planar antenna 1a of FIG. Furthermore, the volume of the ground plate 11 can be reduced to reduce the manufacturing cost.
[0030]
(3) As shown in the planar antenna 1e in FIG. 6, the ground wall 12 is constituted by a bar 12d having a substantially square cross section. Also with this configuration, the surface area of the ground plate 11 on the radiation element arrangement surface side can be increased, and the FB ratio as radiation characteristics can be improved.
(4) The earth wall body 12 is not only constituted by two groups of the inner earth wall body 12a and the outer earth wall body 12b, but is constituted by one group or plural groups such as three or four groups. And disposing concentrically with the radiating element 13 on the ground plate 11. For example, in the planar antenna 1f of FIG. 7, the earth wall 12 is composed of three earth walls 12e, 12f, and 12g. Also with this configuration, it is possible to obtain the same effects as the planar antenna 1a of FIG.
[0031]
(5) In the first embodiment, instead of the first dielectric layer 15a and the second dielectric layer 15b made of air formed by the spacers 14a and 14b, at least one dielectric layer is made of a printed circuit board. For example, when a printed circuit board is used as the second dielectric layer 15b, patch-like radiating elements made of copper foil or the like and parasitic elements are printed on both surfaces of the printed circuit board, and the printed circuit board is interposed via the spacer 14a. The planar antenna may be configured by being disposed on the ground plate 11.
(6) In the second embodiment, instead of the dielectric layer made of air formed by the spacers 14a, the patch-like radiating elements are arranged on the ground plate 11 through the dielectric layer made of a printed board. In this case, the patch-like radiating element may be printed on a printed board using a copper foil or the like.
[0032]
(7) For example, like the planar antennas 1g and 1h in FIGS. 8A and 8B, a pair of cutout portions 30 or a pair of protruding piece portions 31 are provided at the diagonal portions of the square plate-like radiation element 13. By providing, the antenna unit 10 is configured to be able to radiate right-handed circularly polarized waves. Moreover, the notch part 30 and the protrusion piece part 31 are provided in the other diagonal part, and the antenna part 10 is comprised so that a left-handed circularly polarized wave can be radiated | emitted.
(8) The earth plate 11, the radiating element 13, and the earth wall 12 are each formed in a circular shape, and the round radome 20 is attached to the earth plate 11, and the round planar antenna 1k in FIG. To configure.
(9) The coaxial cable plug 26 is configured using not only the F type but also the TNC type, NC type, N type, and the like.
[0033]
【The invention's effect】
As described in detail above, according to the first aspect of the present invention, the radiating element and the ground plate are arranged non-parallel, and the radiating surface of the radiating element and the back of the ground plate are orthogonal to the front direction. having disposed the displacement of the peak position of the directional characteristics caused by stray capacitance feed line has become possible to correct the desired position, it is possible to improve the radiation characteristic in the front direction. In addition, since the radiating element and the ground plate are arranged so as to be inclined in the direction of the center line of the radiating element that passes through the feeding point position of the radiating element, the peak position of the directivity characteristic is corrected so as to coincide with the front direction. Can do. Therefore, it is possible to improve the radiation characteristic in the front direction by making the directivity characteristic vertically symmetric.
[0035]
According to the second aspect of the present invention, since the patch-shaped parasitic element is arranged in parallel to the radiation surface of the radiation element via the dielectric layer, the usable frequency band can be widened.
[0036]
According to the invention of claim 3 , since at least one convex ground wall body is disposed on the front surface of the ground plate so as to surround the radiation element, the surface area of the ground plate on the radiation element arrangement surface side is reduced. The radiation characteristic can be improved without increasing the outer dimension of the ground plate. That is, an antenna having radiation characteristics comparable to the conventional one can be made smaller than the conventional one. In addition, since the earth wall serves as a reinforcing material that improves the structural strength of the earth plate, the earth plate can be formed thin to reduce the weight of the entire antenna.
[0037]
According to the fourth aspect of the present invention, since the earth wall body is constituted by the inner earth wall body and the outer earth wall body, a suitable surface area for obtaining required radiation characteristics can be ensured.
[Brief description of the drawings]
FIGS. 1A and 1B show a planar antenna according to a first embodiment of the present invention, in which FIG. 1A is a front view, FIG. 1B is a sectional view taken along line AA, and FIG. .
2 is a directivity characteristic diagram of the planar antenna of FIG. 1; FIG.
FIG. 3 is a cross-sectional view of a principal part showing a modification of the planar antenna of FIG.
4A and 4B show a planar antenna according to a second embodiment of the present invention, in which FIG. 4A is a front view, and FIG.
5 is a cross-sectional view of a main part showing a modification of the planar antenna in FIG. 1. FIG.
6 is a cross-sectional view of a principal part showing a modification of the planar antenna of FIG. 1. FIG.
7 is a cross-sectional view of a main part showing a modification of the planar antenna of FIG. 1. FIG.
FIGS. 8A and 8B are front views showing a modification of the planar antenna according to the present invention.
FIG. 9 is a front view showing a modified example of the planar antenna according to the present invention.
FIG. 10 is a directivity characteristic diagram of a conventional planar antenna.
[Explanation of symbols]
1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1k ··· Planar antenna, 11 · · Earth plate, 12 · · Earth wall, 12a · · Inside earth wall, 12b · · · Outside earth wall Body 13 .. radiating element 15a .. first dielectric layer 15b .. second dielectric layer 19 .. parasitic element 21.

Claims (4)

A patch-shaped radiating element, a grounding plate disposed on the back of the radiating element via a dielectric layer, and a power supply connected to the feeding point of the radiating element across the dielectric layer from the back of the grounding plate A planar antenna comprising a track ,
While making the plate thickness of the radiating element constant, the ground plate is formed in an inclined plate shape with a predetermined inclination angle so that the surface facing the back of the radiating element is inclined with respect to the back surface,
The radiating element and the ground plate are arranged such that surfaces facing each other are inclined and non-parallel in the direction of the center line of the radiating element passing through the feeding point position of the radiating element,
The planar antenna formed by arrange | positioning the radiation | emission surface of the said radiation | emission element, and the back surface of the said earthing | grounding board body so as to be orthogonal to a front direction. 2. The planar antenna according to claim 1, wherein the patch-shaped parasitic element is arranged in parallel to the radiation surface of the radiation element via a dielectric layer. The planar antenna according to claim 1 or 2 , wherein at least one convex ground wall is disposed on the front surface of the ground plate so as to surround the radiating element. The earth wall, and the inner ground wall which is arranged so as to surround substantially the entire circumference of the radiating element, according to claim 3 comprising consist of an outer ground wall which is arranged concentrically outside the inner earth wall A planar antenna according to claim 1.

Images