JP2005101995A - Wideband antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wideband antenna which is reduced in size and weight in comparison with a conventional discone antenna while maintaining an input impedance. <P>SOLUTION: The antenna is provided with a cone whose top is composed of a supply point, a radiating conductor composed of a structure which is formed by sequentially adhering and integrating m (m≥1) pieces of truncated cones and/or cylindrical objects to the bottom of the cone and a flat conductor including the supply point in the radiating conductor. Alternatively, the wideband antenna is provided with an n-angular pyramid (n≥3) whose top is composed of a supply point, a radiating conductor composed of a structure which is formed by sequentially adhering and integrating m (m≥1) pieces of frustums of n-angular pyramid and/or n-angular prisms to the bottom of the n-angular pyramid and a flat conductor including the supply point in the radiating conductor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a broadband antenna used in a wireless LAN base station and UWB.

  Currently, wireless LANs using the 2.4 GHz band and the 5 GHz band are becoming popular. A patch antenna is mainly used in these systems. However, a system using both frequency bands has been studied, and in this case, since two antennas corresponding to each frequency are required, a wider-band antenna is required. UWB technology using 3 to 10 GHz is also open to the private sector in the United States, and a broadband antenna suitable for this is demanded. As an antenna exhibiting wideband characteristics, a discone antenna, a self-complementary antenna, and a log periodic antenna are known. In particular, a discone antenna is known to have a very wide band (see Non-Patent Document 1).

  As shown in FIG. 6, this discone antenna is formed of a disk (disk) 5 made of a metal conductor and a cone (cone) 6 made of a metal conductor, the signal conductor of the coaxial line is the cone 6, and the ground is It is connected to the disk 5 and used. The size of this antenna is determined by the minimum frequency f to be used. If the wavelength at this time is λ, the apex angle θ of the cone 6 is about 30 °, the diameter of the disk 5 ≧ 0.15λ, Select height ≧ 0.2λ (Reference 1). On the other hand, when this antenna is installed on a system casing or indoor ceiling, the casing or ceiling is the ground, and a signal line is connected to the conical section. At this time, since the ground plane is generally wide, the input impedance changes, and the apex angle of the cone 6 needs to be about 45 °. This increases the diameter of the antenna. Specifically, when the lowest frequency used is 3 GHz, the height of the cone 6 needs to be 20 mm and the diameter of the cone needs to be 40 mm.

In order to solve such a problem, an antenna is proposed in which the outer peripheral conductor is a semi-spheroid 7 as shown in FIG. 7 instead of the cone 6 as shown in FIG. 6 (Patent Document 1). . This antenna is superior to the conventional discone antenna of FIG. 6 in that the antenna diameter can be reduced.
Antenna Engineering Handbook The Institute of Electronics, Information and Communication Engineers March 5, 1999 First edition, 10th edition, published by Ohmsha p128 JP-A-9-153727

  However, since the antenna of FIG. 7 suitable for miniaturization uses a half-spheroid 7 instead of the cone 6 of the discone antenna of FIG. 6, the contact angle between the disk 5 and the half-spheroid 7 There is a problem that φ becomes small, and as a result, the input impedance becomes small and the reflection characteristics deteriorate.

  Further, since the feed line to the antenna (in this case, the coaxial line) is generally 50Ω, it is desirable that the input impedance of the antenna is also 50Ω. Of course, such a broadband antenna cannot make 500Ω over the entire desired band, but it is desirable to make it as close to 50Ω as possible. However, when the input impedance deviates greatly from 50Ω as in the case of the antenna described above, there is a problem that the reflection loss increases due to the impedance mismatch and the antenna characteristics deteriorate.

  The present invention has been devised to solve such conventional problems, and an object of the present invention is to provide a broadband antenna that is smaller and lighter than the conventional discone antenna while maintaining good reflection characteristics. It is in.

  The broadband antenna of the present invention is a radiating conductor comprising a conical body whose top is a feeding point and a structure in which m (m ≧ 1) frustums and / or cylindrical bodies are sequentially bonded and integrated to the bottom of the conical body. And a planar conductor including the feeding point in the radiation conductor.

  In addition, another broadband antenna of the present invention includes an n-pyramid (n ≧ 3) whose top is a feeding point, and m (m ≧ 1) n-pyramidal frustums and / or n-prisms at the bottom of the n-pyramid. And a planar conductor including the feeding point in the radiation conductor.

  The reflection characteristics can be appropriately controlled by adjusting the angle of the top of the cone or the n-pyramid. Further, by making the m-th column a cylinder or an n-prism, the size can be further reduced.

  According to the broadband antenna of the present invention, a planar conductor serving as a ground is obtained by using a structure in which a radiating conductor is combined with a cone, a truncated cone or a cylinder, or an n-sided pyramid, an n-sided pyramid, an n-sided pyramid and an n-sided prism. Since the contact angle φ can be determined by the cone or the apex angle θ of the pyramid, the antenna can be miniaturized without reducing the contact angle θ. The structure of the radiator can be reduced in size and weight while maintaining the characteristics.

  Hereinafter, the broadband antenna of the present invention will be described with reference to the drawings.

FIG. 1A is a plan view showing an example of an embodiment of a broadband antenna of the present invention, and FIG. 1B is a schematic sectional view taken along line x ₁ -x ₁ . According to the broadband antenna A of FIG. 1, the signal conductor 1 is formed at the portion of the planar conductor 2 forming the ground so as not to contact the planar conductor 2, and the radiation conductor 3 is formed at the tip thereof. .

  According to this antenna A, the radiating conductor 3 is formed by a cone 3a and a structure in which a truncated cone 3b is integrally joined to the bottom of the cone 3a.

  According to such a broadband antenna, the high-frequency signal that has entered from the signal conductor 1 generates an electric field between the radiating conductor 3 and the planar conductor 2 and radiates vertically polarized radio waves in the space.

  In addition, the radiation conductor 3 should just be a conductor only in the side surface of the structure, and the inside may be a dielectric material, may be hollow, or may be a conductor.

  The input impedance to the antenna is determined by the size of the planar conductor 2 and the apex angle of the cone 3a. That is, when the diameter of the planar conductor 2 forming the ground is as large as λ, the characteristic of VSWR ≦ 2 is obtained from the lowest usable frequency when the apex angle of the cone 3a is approximately 90 °. When the diameter of the planar conductor 2 is as small as 0.15λ, when the apex angle of the cone 3a is approximately 60 °, the characteristic of VSWR ≦ 2 is obtained from the lowest usable frequency. Therefore, the apex angle of the cone 3a is actually determined by the size of the planar conductor forming the ground.

  The height of the cone 3a and the height of the truncated cone 3b must be appropriately determined by an electromagnetic field simulator or the like, but the overall height must be 0.2λ or more (λ is the wavelength at the lowest usable frequency). .

Figure 2 is a plan view showing an example of another embodiment of the antenna of the present invention (a) and a schematic cross-sectional view at the x ₂ -x ₂ (b). According to the broadband antenna B of FIG. 2, the radiation conductor 3 is formed by a structure in which a cone 3a and a cylindrical body 3c are integrally joined to the bottom of the cone 3a.

  Such a broadband antenna has a function similar to that of the antenna A, but the portion connected to the bottom of the cone 3a has a cylindrical shape. As a result, the outermost diameter of the antenna B can be made smaller, and the antenna can be downsized.

Figure 3 is a plan view showing an example of yet another embodiment of the antenna of the present invention (a) and a schematic cross-sectional view of the x ₃ -x ₃ (b). According to the broadband antenna C of FIG. 3, the radiation conductor 3 is formed by a structure in which a cone 3a, a truncated cone 3b, and a column 3c are integrally joined.

  Such a broadband antenna has a function similar to that of the antenna A, but the portion connected to the bottom of the cone 3a has a truncated cone shape and a cylindrical shape. As a result, the outermost diameter of the antenna B can be made smaller, and the antenna can be downsized.

Figure 4 is a plan view showing an example of another embodiment of the antenna of the present invention (a) and a schematic cross-sectional view of the x ₄ -x ₄ (b). According to the broadband antenna D of FIG. 4, the radiation conductor 3 is formed of a structure in which a triangular pyramid 4a, a triangular frustum 4b, and a triangular prism 4c are integrally joined.

  As described above, the same effects as described above can be obtained not only by the cone 3a, the truncated cone 3b, and the column 3c of FIGS. 1 to 4, but also by the n-shaped pyramid 4a, the n-shaped truncated pyramid 4b, and the n-shaped prism 4c. Play.

  Each of the antennas A, B, C, and D is an example (m = 1, 2) in which the cone 3a, the truncated cone 3b, and the cylinder 3c are combined, but this combination is not limited to these. For example, 3a-3b-3b, 3a-3b-3c-3b, 3a-3c-3b, 3a-3c- using two or more of the truncated cone 3b and the cylinder 3c with respect to the cone 3a. Various combinations such as 3b-3c, 3a-3b-3c-3b-3c, etc. may be made with m ≧ 3.

  In the above example, the conical body 3a, the truncated cone 3b, and the column 3c are described as separate bodies and joined and integrated. However, all of these shapes form the outer wall of the radiation conductor 3. As long as the outer wall has the above-described structure, there is no problem even if it is a separate body or an integral body having the above outer wall surface.

  Even if it is a case where it is a case where it is constituted by n pyramid 4a, n pyramid frustum 4b, and n prism 4c, the above-mentioned other mode has the same effect. Further, although the case where n = 3 has been described with reference to FIG. 4, even if n ≧ 4, the effect of the present invention is not substantially different.

  Further, in FIG. 1 to FIG. 4, m = 1 or 2 has been described, but there is no problem even if three or more frustums 3b and n-pyramidal frustums 4b are stacked.

  Next, FIG. 5 shows the result of calculation of reflection characteristics for the embodiment shown in FIGS.

  In the embodiment of FIG. 1, the height of the cone 3a is 7 mm, the diameter of its bottom surface is 12 mm, the height of the truncated cone 3b is 15 mm, and the diameter of its bottom surface is 16 mm. In the embodiment of FIG. 2, the height of the cone 3a is 7 mm, the diameter of the bottom surface is 12 mm, and the height of the cylinder 3c is 15 mm. In the embodiment of FIG. 3, the height of the cone 3a is 5 mm, the diameter of its bottom surface is 6 mm, the height of the truncated cone 3b is 4 mm, the diameter of its bottom surface is 12 mm, and the height of the cylinder 3c is 13 mm. In the embodiment of FIG. 4, the height of the regular triangular pyramid 4 a is 7 mm, one side of the bottom surface is 12 mm, and the height of the triangular prism 4 c is 15 mm. In all cases, the size of the ground conductor 2 was 50 mm square.

  The solid line in FIG. 5 is an embodiment of the form shown in FIG. 1, the dotted line is the embodiment of the form shown in FIG. 2, the alternate long and short dash line is the embodiment of the form shown in FIG. 3, and the broken line is the embodiment of the form shown in FIG. In general, the range indicating the frequency band of the antenna is often expressed in a region where VSWR is 2 or less, that is, a reflection characteristic of −9.54 dB or less. In all cases of this embodiment, good reflection characteristics are obtained in the region of about 3 GHz to 10 GHz or more. That is, it can be seen that the antenna has a broadband characteristic.

It is the top view (a) and sectional drawing (b) which show an example of embodiment of the wideband antenna in this invention. It is the top view (a) and sectional drawing (b) which show an example of other embodiment of the wideband antenna in this invention. It is the top view (a) and sectional drawing (b) which show an example of other embodiment of the wideband antenna in this invention. It is the top view (a) and sectional drawing (b) which show an example of other embodiment of the wideband antenna in this invention. FIG. 5 is a reflection characteristic of the embodiment of the wideband antenna shown in FIGS. It is the top view (a) and sectional drawing (b) which show the conventional wideband antenna. It is the top view (a) and sectional drawing (b) which show the other conventional broadband antenna.

Explanation of symbols

1 Signal conductor 2 Ground conductor 3 Radiation conductor 4 Radiation conductor

Claims (6)

A conical body having a feeding point at the top, a radiating conductor composed of a structure in which m (m ≧ 1) frustums and / or cylindrical bodies are sequentially bonded and integrated at the bottom of the conical body, and the radiating conductor in the radiating conductor A broadband antenna comprising a planar conductor including a feeding point. The broadband antenna according to claim 2, wherein the reflection characteristic is controlled by an angle of a top portion of the conical surface. The broadband antenna according to claim 1 or 2, wherein the m-th is formed by a cylindrical body. Radiation composed of an n-pyramid (n ≧ 3) whose top is a feeding point and a structure in which m (m ≧ 1) n-pyramids and / or n-prisms are sequentially bonded and integrated at the bottom of the n-pyramid. A broadband antenna comprising a conductor and a planar conductor including the feeding point in the radiation conductor. 4. The broadband antenna according to claim 3, wherein the reflection characteristic is controlled by the angle of the apex of the n-pyramidal surface. The broadband antenna according to claim 1 or 2, wherein the m-th is formed by an m-prism.

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