JP4299206B2 - Biconical antenna - Google Patents

Description

  The present invention relates to a biconical antenna for performing wireless communication.

In recent years, UWB (Ultra
Wideband) is attracting attention (see Non-Patent Document 1 and Non-Patent Document 2). UWB uses a pulse having a width of only about 1 ns in a band of 3.1 GHz to 10.6 GHz. When viewed in terms of frequency, it looks like it occupies a very wide band of several GHz width. Therefore, high-speed communication can be performed.

  Since the communicable distance in UWB is short, use for a wireless interface for performing data transmission between a computer and peripheral devices is considered (see Non-Patent Document 3 and Non-Patent Document 4).

  An antenna used in UWB is a biconical antenna. Regarding the biconical antenna, Patent Document 1 and Patent Document 2 disclose the structure thereof.

  As shown in FIG. 11, a general biconical antenna 40 has truncated cone-shaped metals 42 and 44 opposed via a gap G. One of them is a power feeding part 42 and the other is a ground part 44. The power feeding unit 42 is connected to the central conductor 30 of the coaxial cable 34. The ground portion 44 is connected to the shield conductor 32 of the coaxial cable 34. Radiation or reception of electromagnetic waves is performed on the side surface (inclined surface) of the power supply unit 42.

  As described above, it is considered to use UWB in a computer. Therefore, it is necessary to attach the antenna 40 to the computer, and it is desirable to reduce the size. In particular, when it is attached to a notebook computer, it is desired to reduce the size of the antenna. For example, in Patent Document 2, the length of the gap is several centimeters, and other portions are about tens of centimeters, which is very large. Patent Document 1 does not describe the size. Patent Document 1 and Patent Document 2 do not describe that an antenna is miniaturized and used as a wireless interface of a computer. With the prior art, the computer's wireless interface using the biconical antenna 40 must be abandoned.

  The UWB frequency band is a microwave band as described above. Therefore, the manufacturing of the antenna 40 requires considerable accuracy. When the antenna 40 is manufactured, if the error of the shape / dimension of the antenna 40 occurs or the surface of the antenna 40 is scratched, the antenna characteristics change. When metal is cut into a truncated cone shape or the antenna 40 is assembled, extremely precise manufacturing is required.

JP 2001-185942 A JP-A-9-8550 Nikkei Electronics 2003 2-17 no.841 Nikkei Business Publications, Inc. NIKKEIMICRODEVICES 2003.8 No.218 Nikkei Business Publications, Inc. Nikkei Electronics 2004 2-16 no.867 Nikkei BP Nikkei Electronics 2004 3-15 no.869 Nikkei Business Publications, Inc.

  An object of the present invention is to provide a biconical antenna that is reduced in size and weight and can be manufactured with high precision so that it can be used as a wireless interface of a computer or the like.

  The gist of the biconical antenna of the present invention is a dielectric having a truncated cone-shaped cavity from the upper surface and the lower surface of the cylindrical shape toward the center, and the planes of the top portions of the truncated cone shape facing each other in parallel. And a power feeding portion that is a conductor film provided on the inner surface of the cavity on the upper surface side, and a ground portion that is a conductor film provided on the inner surface of the cavity on the lower surface side.

  The power feeding part is higher than the ground part.

  A cylindrical dielectric attached to the lower surface; and a ground reinforcing portion that is a conductor film provided on the inner surface of the cylindrical shape and connected to the ground portion.

  A disc-shaped cavity provided at the top of the truncated cone shape on the upper surface side; and a reflector that is a conductor film provided on the inner surface of the disc-shaped cavity.

  In the present invention, since the gap between the power feeding portion and the ground portion is filled with a dielectric, the antenna is downsized. Further, since the inside of the power feeding portion and the ground portion is made hollow, the antenna becomes light. Furthermore, since the conductor film constituting the power feeding portion and the ground portion can be formed by electroless copper plating, the shape accuracy is improved and it is suitable as a high-frequency antenna.

  Next, an embodiment of the biconical antenna of the present invention will be described with reference to the drawings.

  The biconical antenna 10a according to the present invention shown in FIG. 1 has frustoconical cavities 14a and 16a from the upper surface A and the lower surface B of the columnar shape toward the center, and the planes of the top portions C and D of the frustoconical shape. The dielectric 12a facing each other in parallel, the power feeding portion 18a which is a conductor film provided on the inner surface of the cavity 14a on the upper surface A side, and the conductor film provided on the inner surface of the cavity 16a on the lower surface B side And a ground portion 20a.

  Compared to the conventional case, since the space between the power feeding portion 18a and the ground portion 20a is filled with the dielectric 12a, the shape of the entire antenna is reduced in size. This is because the dielectric constant of the dielectric 12a is higher than that of air, and the wavelength of the electromagnetic wave in the antenna can be shortened. In addition, as shown in FIG. 1, between the electric power feeding part 18a and the ground part 20a includes between the frustoconical inclined surfaces.

  The relative dielectric constant of the dielectric 12a is, for example, 3.6. An epoxy resin or the like can be used as the dielectric 12a, but other resins may be used as long as they have the same dielectric constant.

  Moreover, the inside of the electric power feeding part 18a and the ground part 20a becomes the cavity 14a, 16a. This is because the electromagnetic wave can only enter the conductor up to the thickness δ of the skin shown in Equation 1, so that it is not necessary to fill the inside with the conductor. In Equation 1, μ is the magnetic permeability of the conductor, f is the frequency, and σ is the conductivity of the conductor. The antenna 10a is reduced in weight by making the inside into the cavities 114a and 16a.

  The conductor film is made of copper or gold. The film thickness is at least equal to or greater than the skin thickness δ. For example, the film thickness is set to 0.1 μm or more.

  The power feeding portion 18a is higher than the ground portion 20a. A general biconical antenna has the same height of the feeding portion and the ground portion, but it has been found by various simulations that the diameter of the cylindrical shape is reduced by changing the height. Suitable for antenna miniaturization.

  The biconical antenna 10a includes a cylindrical dielectric 13a attached to the lower surface B, and a ground reinforcing portion 24a that is a conductor film provided on the cylindrical inner surface and connected to the ground portion 20a. For example, the diameter of the bottom surface of the ground portion 20a and the diameter of the ground reinforcing portion 24a are the same. The ground portion 20a is smaller than the power feeding portion 18a, and the reduced portion is compensated by the ground reinforcing portion 24a.

  It has a disk-shaped cavity 26a provided at the top C of the truncated cone shape on the upper surface A, and a reflector 28a that is a conductor film provided on the inner surface of the disk-shaped cavity 26a.

  The biconical antenna 10a includes a coaxial cable 34 having a center conductor 30, an insulator covering the center conductor 30, and a shield conductor 32 covering the insulator. One end of the coaxial cable 34 is inserted into the cavities 16a and 22a of the ground portion 20a (including the ground reinforcing portion 24a), the center conductor 30 is connected to the power feeding portion 18a, and the shield conductor 32 is connected to the ground portion 20a. The center conductor 30 and the ground part 20a are insulated.

  A connector 36 is connected to the other end of the coaxial cable 34 so that the biconical antenna 10a can be connected to various circuits.

  An example of the shape of the biconical antenna 10a is shown below. The diameters of the top part C and the bottom part A of the power feeding part 20a are 11.0 mm and 2.8 mm, respectively. The height of the power feeding unit 18a is 8.0 mm. The diameters of the top part D and the bottom part B of the ground part 20a are 2.8 mm and 9.4 mm, respectively. The height of the ground portion 20a is 5.0 mm. The diameter and height of the reflector 28a are 2.8 mm and 1.0 mm, respectively. The diameter and height of the ground reinforcing portion 24a are 9.4 mm and 13.0 mm, respectively. A gap G between the power feeding unit 18a and the ground unit 20a is 2.8 mm.

  The voltage standing wave ratio (VSWR) of the above-described biconical antenna 10a is obtained by simulation. The result is shown in FIG. The simulator used is Ansoft HFSS. The simulation is performed by terminating the coaxial cable 36 at the lower end E of the ground reinforcing portion 24a. In the UWB band, VSWR is 2 or less. In addition, the VSWR rapidly increases when the band is outside the UWB band. Only the band necessary for using the antenna 10a can be used, indicating that the antenna characteristics are good. The VSWR can be used as an antenna better as it approaches 1, and there is no practical problem if it is 2 or less.

  The results of simulation with various changes in the shape and relative dielectric constant of the antenna 10a are shown below. The simulator is the same as above.

  FIG. 3 shows simulation results in which the relative dielectric constant of the dielectric 12a is variously changed. A relative dielectric constant of 3.6 is the best, and a good antenna characteristic is exhibited even at 3.0 or 4.0. It can be seen that desired antenna characteristics cannot be obtained simply by increasing the relative dielectric constant.

  FIG. 4 shows a simulation result when the gap G is changed. The best antenna characteristics are shown when the gap G is 2.8 mm. It can be seen that the antenna characteristics deteriorate when the gap G is too wide or narrower than 2.8 mm.

  FIG. 5 shows a simulation result when the height of the power supply unit 18a is changed. The antenna characteristics are best when the height of the power feeding portion 18a is 8.0 mm. When the height is lowered, the antenna characteristics are deteriorated on the low frequency side, and when the height is increased, the antenna characteristics are deteriorated on the high frequency side.

  FIG. 6 shows a simulation result when the height of the ground portion 20a is changed. The antenna characteristics are good when the height of the ground portion 20a is 5 or 6 mm, and even 7 mm is good. In consideration of miniaturization of the antenna, 5 mm is preferable. Further, when the height is lowered, the antenna characteristics are deteriorated on the low frequency side.

  FIG. 7 shows a simulation result when the height of the ground reinforcing portion 24a is changed. The antenna characteristic is the best when the height of the ground reinforcing portion 24a is 13 mm or 15 mm. Considering miniaturization of the antenna 10a, 13 mm is preferable.

  FIG. 8 shows a simulation result when the width of the biconical antenna 10a, in other words, the diameter of the frustoconical bottom A of the power feeding portion 18a is changed. 11 mm is the best, and even 10 mm and 12 mm are good antenna characteristics. At 9.0 mm, the VSWR becomes 2 or more in the intermediate frequency band, and the antenna characteristics deteriorate.

  FIG. 9 shows a simulation result when the height of the reflector 28a is changed. The antenna characteristics are good when the height of the reflector 28a is 1.0 or 1.5 mm. Considering miniaturization of the antenna 10a, 1.0 mm is preferable. When the height of the reflector 28a is lowered, the antenna characteristics are deteriorated on the high frequency side, and when it is increased, the antenna characteristics are deteriorated on the low frequency side.

  Next, the manufacturing method of the biconical antenna 10a of this invention is demonstrated. The biconical antenna 10a is manufactured by the following steps (1) to (4).

  (1) The dielectric 12a having a truncated cone-shaped cavity from the cylindrical upper surface A and the lower surface B toward the center is formed by lathe processing (small volume production) or mold forming (mass production). On the lower surface B, a cylindrical dielectric 13a is integrated with the dielectric 12a and is formed at the same time.

  (2) Conductive films are formed on the inner surfaces of the frustoconical cavities 14a and 16a by electroless copper plating. The conductor film has a power supply portion 18a on the upper surface side and a ground portion 20a on the lower surface side. When electroless copper plating is performed, lift-off resist is applied to portions other than the power supply portion 18a, the ground portion 20a, and the ground reinforcement portion 24a. After the electroless copper plating, the lift-off resist is removed, and plating other than the power feeding portion 18a is removed. If the film thickness is thin due to electroless copper plating, electrolytic copper plating may be applied based on the plating. Moreover, you may comprise the electric power feeding part 18a with the electrode which punched the copper plate with the metal mold | die. Perform final finishing by removing burrs and adjusting differences in dimensions as necessary.

  (3) A coaxial probe 34 is prepared, the coaxial probe 34 is inserted into the cavities 16a and 22a from the cavity on the lower side E (B), the central conductor 30 is connected to the power feeding portion 18a, and the shield conductor 32 is connected to the ground portion. Connect to 20a.

  (4) A connector 36 is attached to the coaxial probe 34. Thereby, the antenna 10a is completed.

  The biconical antenna 10a of the present invention forms the power feeding portion 18a and the ground portion 20a by electroless copper plating. Therefore, the power feeding portion 18a and the like have a higher shape accuracy than being cut out from a conductor, and are suitable for a high-frequency antenna. In addition, there is an advantage that mass production is easier than cutting a conductor to make a power feeding part.

  Although the electroless copper plating is performed in the step (2), a conductive film may be formed by vapor deposition of gold or the like. Like the plating, the power feeding portion 18a and the like can be formed with high accuracy.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment. For example, as shown in FIG. 10, a power supply unit 18b and a ground unit 20b may be a biconical antenna 10b having a target shape. The power feeding portion 18b and the ground portion 20b are formed of a conductor film similarly to the above-described embodiment, and the insides are cavities 14b and 16b. The conductor film is also formed by electroless copper plating. By electroless copper plating or the like, the antenna 10b has a high dimensional accuracy and is suitable as a high-frequency antenna.

  The diameter of the reflector 28a in FIG. 1 may be variously changed. A certain frequency band can be cut by the reflector 28a. 10 may be provided with a reflector at the top C as in FIG. 1, and the diameter of the reflector may be variously changed. Moreover, in FIG. 1, the structure without the reflector 28a may be sufficient.

  The dielectric 12a may use alumina or the like in addition to using an epoxy resin. In this case, the step (1) is a step of placing alumina in a mold shown in FIG.

  The cavities 14a and 14b of the power feeding portion 18a and the ground portion 20a in FIG. 1 have different bottom sizes, but may be the same.

  In addition, the present invention can be carried out in a mode in which various improvements, modifications, and changes are added based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

It is a figure which shows the structure of the biconical antenna of this invention. It is a figure which shows the simulation result of VSWR of the biconical antenna of FIG. It is a figure which shows the simulation result of VSWR when the dielectric constant of a dielectric material is changed variously. It is a figure which shows the simulation result of VSWR when a gap is changed. It is a figure which shows the simulation result of VSWR at the time of changing the height of an electric power feeding part. It is a figure which shows the simulation result of VSWR when changing the height of a ground part. It is a figure which shows the simulation result of VSWR at the time of changing the height of a ground reinforcement part. It is a figure which shows the VSWR simulation result when changing the diameter of the bottom part of the truncated cone shape of the electric power feeding part of a biconical antenna. It is a figure which shows the simulation result of VSWR when changing the height of a reflector. It is a figure which shows the structure of the biconical antenna in which the electric power feeding part and a ground part are object. It is a figure which shows the structure of the conventional biconical antenna.

Explanation of symbols

10a, 10b, 40: Biconical antenna 12a, 12b, 13a: Dielectric 14a, 4b, 16a, 16b, 22a, 26a: Cavity 18a, 18b, 42: Power feeding unit 20a, 20b, 44: Ground unit 24a: Ground reinforcement Part 28a: Reflector 30: Center conductor 32: Shield conductor 34: Coaxial cable 36: Connector

Claims (3)

A dielectric having a frustoconical cavity toward the center from each of the columnar upper surface and the lower surface, the planes of the tops of the frustoconical shapes facing each other in parallel;
A power feeding part that is a conductor film provided on the inner surface of the cavity on the upper surface side;
A ground portion which is a conductor film provided on the inner surface of the cavity on the lower surface side;
A biconical antenna having
The height of the power feeding part is higher than the height of the ground part,
The inner surface connected to the ground part which is a conductor film provided on the inner surface of the cavity on the lower surface side is a cylindrical ground reinforcing part of the conductor film, and
A columnar cavity provided at the top of the truncated cone shape on the upper surface side;
And a reflector made of a conductor film provided on an inner surface of the cylindrical cavity. The biconical antenna according to claim 1, wherein
The height of the power feeding part is 8 mm,
The diameter of the bottom of the frustoconical shape of the feeding portion, which is a frustoconical shape that becomes the width of the biconical antenna, is 11 mm;
The height of the frustum-shaped ground part is 5 mm,
The height of the cylindrical ground reinforcing portion is 13 mm,
The cylindrical ground reinforcing portion has a diameter of 9.4 mm,
The height of the cylindrical reflector is 1 mm,
The biconical antenna according to claim 1, wherein the cylindrical reflector has a diameter of 2.8 mm. Biconical antenna according to claim 1 and / or 2,
The biconical antenna, wherein the dielectric is an epoxy resin.

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