JP2005020677A - Two-frequency sharing antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compose a two-frequency sharing dipole antenna. <P>SOLUTION: A first dipole antenna 2 including a first resonant frequency is composed of elements 7a, 7b and a transmission line 9, and a second dipole antenna 3 including a second resonant frequency (> the first resonant frequency) is composed of elements 8a, 8b and the transmission line 9. The transmission line 9 is composed of a coplanar strip 10 and a coplanar line 11 and connects the antenna to a coaxial cable 4. The transmission line 9 functions as a matching circuit which attains impedance matching between the antenna and the coaxial cable when operating in the first resonant frequency, and makes the coplanar line 11 function as a balun between the antenna and the coaxial cable 4 by making the impedance of the coplanar line 11 equal with that of the coaxial cable 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dual-frequency antenna, and more particularly to a dual-frequency dipole antenna.
[0002]
[Prior art]
Conventionally, an antenna obtained by deforming a monopole antenna into a flat shape using a thin copper plate or a printed board is used as an antenna attached to a window glass of an automobile, a deflector for preventing wind from being caught in an open car, or the like. The affixed antenna is connected to a mobile phone, a communication device or the like via a coaxial cable.
[0003]
On the other hand, the frequency bands used by mobile phones differ from country to country and often use two different frequency bands at the same time. For this reason, antenna manufacturers prepare multiple antennas with different antenna shapes for each destination. There is a need. For example, an a-shaped antenna is prepared for country A, and a b-shaped antenna is prepared for country B. Furthermore, in order to cover two frequency bands with one antenna, it is necessary to use a dual-frequency antenna that can be used by resonating at two frequencies.
[0004]
The following prior art discloses an example of a monopole antenna attached to a window glass of an automobile.
[0005]
[Patent Document 1]
JP-A-7-7318 [0006]
[Problems to be solved by the invention]
As described above, when a dual-frequency antenna is configured with a monopole antenna, it is necessary to prepare various types of shapes, which is disadvantageous for mass production.
[0007]
In addition, since a sufficiently large GND portion or GND pattern is required to operate as a monopole antenna, the occupied area of the entire antenna increases. For example, when affixed to a window glass of an automobile, The view from the room is limited.
[0008]
Furthermore, the gain of the monopole antenna is maximized when the GND size is infinite, but the size of the GND is limited by the size of the object to be pasted when pasting on the window glass or deflector of an automobile. As a result, a sufficient gain cannot be obtained.
[0009]
An object of the present invention is to provide a dual-frequency antenna that can obtain a sufficient gain even in a relatively small occupied area and is advantageous for mass production.
[0010]
[Means for Solving the Problems]
The present invention provides a first dipole antenna having a first resonance frequency, a second dipole antenna having a second resonance frequency higher than the first resonance frequency, and the first and second dipole antennas as coaxial antennas. A dual-frequency antenna having a transmission line for connection, wherein the transmission line constitutes an impedance matching circuit between the first and second dipole antennas and the coaxial cable, and the first And a balun between the second dipole antenna and the coaxial cable. Although the parallel two-wire line of the dipole antenna and the coaxial line of the coaxial cable have the same impedance, the current or voltage between the two parallel lines is balanced, whereas the voltage of the outer conductor of the coaxial line is Since it is always zero, if it is directly connected, power reflection or leakage occurs, so a balun is provided as a distributed constant type or lumped constant type matching circuit. In the present invention, the dipole antenna and the coaxial cable are connected by forming a balun in a part of the transmission line.
[0011]
In the present invention, the transmission line includes a first line portion and a second line portion, and the first line portion and the second line portion each have a first wavelength corresponding to the first resonance frequency. The impedance matching circuit between the first dipole antenna and the coaxial cable has a length of about 1/8, and the first line portion and the second line portion are respectively the second line portion and the second line portion. Having a length of about ¼ of the second wavelength corresponding to the resonance frequency, the first line portion constitutes the impedance matching circuit between the second dipole antenna and the second line portion; The second line portion may have the same impedance as the coaxial cable, and may constitute the balun between the second dipole antenna and the coaxial cable.
[0012]
In the present invention, the transmission line may also serve as the second dipole antenna having the second resonance frequency.
[0013]
In the present invention, the first dipole antenna, the second dipole antenna, and the transmission line may have a planar shape.
[0014]
Further, the present invention is a dual-frequency antenna that constitutes a dual-frequency dipole antenna by combining the first and second plate-like conductors, wherein the first and second plate-like conductors are The first plate-like conductive member has two antenna element portions each having a length corresponding to the first and second resonance frequencies, and a transmission line portion for connecting the antenna element portion and the coaxial cable. The transmission line portion of the body is connected to the inner conductor of the coaxial cable, the transmission line portion of the second plate-like conductor is connected to the outer conductor of the coaxial cable, and the first and second plate shapes The transmission line portion of the conductor constitutes an impedance matching circuit between the antenna element portion and the coaxial cable, and a balance / unbalance change between the antenna element portion and the coaxial cable. Characterized by a circuit.
[0015]
In the present invention, the transmission line unit includes a first line unit and a second line unit, and the first line unit and the second line unit each have a first wavelength corresponding to the first resonance frequency. The impedance matching circuit between the antenna element part and the coaxial cable, and the first line part and the second line part are respectively the second line part and the second line part. Having a length of about ¼ of the second wavelength corresponding to the resonance frequency, the first line portion constitutes the impedance matching circuit between the antenna element portion and the second line portion, and The second line portion may have the same impedance as that of the coaxial cable, and may constitute the balanced / unbalanced conversion circuit between the antenna element portion and the coaxial cable.
[0016]
In the present invention, the second line portion of the second plate-like conductor sandwiches the second line portion of the first plate-like conductor from the left and right, and the first plate-like conductor. You may provide so that the said 2nd track | line part may be straddled.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a plan view of a dual-frequency antenna 1 according to this embodiment. The plate-like conductors 2 and 3 are combined with each other to form a dual-frequency dipole antenna.
[0019]
The conductor 2 has antenna elements 7 a and 8 a and a transmission line 9. Elements 7a and 8a are both bent, and element 7a is longer than element 8a. The elements 7a and 8a are both connected to the transmission line 9 at one end. The transmission line 9 includes a coplanar strip 10 and a coplanar line 11. The coplanar strip 10 connects the elements 7 a and 8 a and the coplanar line 11, and the coplanar line 11 connects the coplanar strip 10 and the coaxial cable 4. The coplanar line 11 is composed of a pair of conductive plates (ground plates), and the pair of conductive plates has earth bridges 12 and 13 so as to straddle the coplanar line 11 of the conductor 3 described later. This earth bridge functions as an antenna characteristic adjustment GND, and functions as a fine adjustment of the resonance frequency and bandwidth of the antenna characteristic. Also, the lower conductive plate in the figure of the pair of conductive plates is formed longer along the line direction of the coplanar line 11 than the upper conductive plate, and functions as a stub for adjusting antenna characteristics. The pair of conductive plates of the coplanar line 11 is connected to the outer conductor 5 of the coaxial cable 4. The conductor 2 constitutes the first dipole antenna 2.
[0020]
On the other hand, the conductor 3 includes antenna elements 7 b and 8 b and a transmission line 9. Elements 7b and 8b are both bent, and element 7b is longer than element 8b. The element 7b is paired with the element 7a to constitute the first dipole antenna 2, and the element 8b is paired with the element 8a to constitute the second dipole antenna 3. The elements 7b and 8b are both connected to the transmission line 9 at one end. The transmission line 9 includes a coplanar strip 10 and a coplanar line 11. The coplanar strip 10 connects the elements 7 b and 8 b and the coplanar line 11, and the coplanar line 11 connects the coplanar strip 10 and the coaxial cable 4. The conductor 3 constitutes the second dipole antenna 3. The transmission line 9 of the second dipole antenna 3 and the transmission line 9 of the first dipole antenna 2 are electrically insulated from each other, and the earth bridges 12 and 13 in the transmission line 9 of the first dipole antenna 2 and the second dipole antenna. 3 transmission lines 9 are electrically insulated. The transmission line 9 of the second dipole antenna 3 is connected to the inner conductor 6 of the coaxial cable 4.
[0021]
The dual-frequency antenna 1 shown in FIG. 1 is used by being attached to, for example, a car deflector. The other end of the coaxial cable 4 is connected to a mobile phone or other communication device.
[0022]
FIG. 2 is an exploded perspective view of the dual-frequency antenna shown in FIG. The deflector 14 is a wind entanglement prevention plate provided in the automobile. Instead of the deflector 14, it may be a window glass of an automobile. The antenna protection sheet 16 is bonded to the deflector 14 via the adhesive 15. The plate-like conductor 2 is provided in the shape of the antenna protection sheet 16, and the plate-like conductor 3 is provided via the antenna protection sheet 17. The positional relationship between the conductor 2 and the conductor 3 is as shown in FIG. 1, and the elements 7a and 7b face each other, and the elements 8a and 8b face each other. A cover 19 that protects the entire antenna is provided on the conductor 3 via an antenna protection sheet 18.
[0023]
The dual-frequency shared antenna 1 of the present embodiment covers the first resonance frequency with the first dipole antenna 2 and covers the second resonance frequency with the second dipole antenna 3. The first resonance frequency band can be an AMPS band of 800 MHz, for example, and the second resonance frequency band can be a PCS band of 1900 MHz, for example.
[0024]
In the following, description will be made separately on the case of operating at the first resonance frequency (low frequency band) and the case of operating at the second resonance frequency (high frequency band).
[0025]
FIG. 3 shows the configuration of the dual-frequency antenna 1 when operating in the low frequency band. The total length (that is, the sum of the lengths of the elements 7a and 7b) L1 of the first dipole antenna 2 composed of the elements 7a and 7b is set to ½ of the first wavelength λ1 corresponding to the first resonance frequency. . At this time, part of the current flowing through the antenna also flows through the elements 8a and 8b, but the elements 8a and 8b function as an open stub that adjusts the antenna characteristics in the low frequency band.
[0026]
The total length L2 of the transmission line 9, that is, the sum of the length L3 of the coplanar strip 10 and the length L4 of the coplanar line 11 is set to ¼ of the first wavelength λ1. Specifically, the length L3 of the coplanar strip 10 is set to 1/8 of the first wavelength λ1, and the length L4 of the coplanar line 11 is set to 1/8 of the first wavelength λ1. An impedance matching circuit that matches the impedance between the elements 7a and 7b of the first dipole antenna 2 and the coaxial cable 4 by setting the total length L2 of the transmission line 9 to 1/4 of the first wavelength λ1. Function as.
[0027]
The earth bridge 13 functions to adjust the antenna characteristics, and the resonance frequency and bandwidth of the antenna can be finely adjusted by adjusting the distance L5 from the earth bridge 12.
[0028]
FIG. 4 shows frequency characteristics of the dual-frequency antenna 1 according to this embodiment. For comparison, the figure also shows the frequency characteristics of a conventional monopole antenna. The dual-frequency antenna 1 of this embodiment has a gain equal to or higher than that of the conventional antenna in the low frequency band (800 MHz).
[0029]
FIG. 5 shows a configuration of the dual frequency antenna 1 when operating in a high frequency band. The total length (that is, the sum of the lengths of the elements 8a and 8b) L6 of the second dipole antenna 3 composed of the elements 8a and 8b is set to ½ of the second wavelength λ2 corresponding to the second resonance frequency. .
[0030]
When the length L7 of the coplanar strip 10 constituting the transmission line 9 is set to ¼ of the second wavelength λ2, the impedance of the elements 8a and 8b is Z _L , and the impedance of the coplanar line 11 is Z _in , the coplanar strip 10 Is set to be (Z _in · Z _L ) ^0.5 , thereby functioning as an impedance matching circuit for matching the impedances of the elements 8a and 8b and the coplanar line 11. Specifically, in the cross-sectional configuration of the coplanar strip 10 shown in FIG. 6, the impedance is set to a desired value by adjusting the dielectric constant εr, thickness h, line width W, etc. of the substrate.
[0031]
The length L8 of the coplanar line 11 constituting the transmission line 9 is set to ¼ of the second wavelength λ2, and is set to have the same impedance as that of the coaxial cable 4. Specifically, in the cross-sectional configuration of the coplanar line 11 shown in FIG. 7, the impedance is set to a desired value by adjusting the dielectric constant εr and thickness h of the substrate, the width W of the line, and the like. By setting L8 to λ2 · 1/4, the coplanar line 11 forms a super-top balun that is a distributed constant balun (see FIG. 13), and is a dipole antenna that is a balanced transmission line and an unbalanced transmission line. It functions as a balanced / unbalanced conversion circuit for converting a transmission mode between the coaxial cable 4 and the coaxial cable 4.
[0032]
FIG. 8 shows the frequency characteristics of the dual-frequency shared antenna 1 according to this embodiment. For comparison, the figure also shows the frequency characteristics of a conventional monopole antenna. The dual-frequency shared antenna 1 of this embodiment has a gain equal to or higher than that of the conventional antenna in a high frequency band (1900 MHz).
[0033]
The size and function of each part are summarized as follows.
[0034]
<Coplanar strip 10>
Length = λ1 · 1/8 = λ2 · 1/4
Function: impedance matching circuit between the first dipole antenna 2 and the coaxial cable 4 in the low frequency band, and impedance matching circuit in the high frequency band
<Coplanar track 11>
Length = λ1 · 1/8 = λ2 · 1/4
Function: impedance matching circuit between the first dipole antenna 2 and the coaxial cable 4 in the low frequency band, and a balun between the second dipole antenna 3 and the coaxial cable 4 in the high frequency band
In this way, the first dipole antennas 2 and 3 are configured, and the common transmission line 9 is made to function as an impedance matching circuit and a balun between the coaxial cable 4, so that the dual frequency antenna 1 can be configured with a simple configuration. Can be configured. In this embodiment, since the dipole antennas 2 and 3 are used, a large GND area as in the case of using a monopole antenna is not required, so that a good field of view can be secured even when pasted on a car deflector or window glass. can do. In addition, an antenna gain necessary for communication can be obtained even in a limited pasting area. In addition, since the balun or balanced / unbalanced conversion circuit necessary for connecting the dipole antenna to the coaxial cable is constituted by the coplanar line 11 of the planar circuit, the entire antenna is planarized and applied to a car deflector or window glass. Can be pasted.
[0037]
Furthermore, in this embodiment, by increasing the thickness of the conductor plate of the first dipole antennas 2 and 3, it is possible to widen the frequency characteristics, so that a single dual-frequency shared antenna 1 uses different frequencies. It can handle multiple destinations, which is advantageous for mass production.
[0038]
As mentioned above, although embodiment of this invention was described, this invention can be variously changed without being limited to this.
[0039]
For example, in this embodiment, as shown in FIG. 2, the conductors 2 and 3 are sequentially laminated via the protective sheets 16, 17, and 18, but the conductor 2 is formed on the surface of the printed circuit board and the back surface is formed. The conductor 3 may be formed.
[0040]
FIG. 9 shows a configuration example using a printed circuit board. The conductor 2, that is, the first dipole antenna 2 is formed on the surface of the printed circuit board 20, and the conductor 3, that is, the second dipole antenna 3 is formed on the back surface of the printed circuit board 20. Each of the conductors 2 and 3 is formed by a circuit patterning technique.
[0041]
In the present embodiment, the earth bridges 12 and 13 are used. However, since at least one earth bridge may be provided, for example, only a single earth bridge 12 as shown in FIG. 10 may be used. .
[0042]
In this embodiment, the elements 7a and 7b constitute the first dipole antenna 2, and the elements 8a and 8b constitute the second dipole antenna 3. However, the elements 8a and 8b may be constituted by the transmission line 9. Is possible.
[0043]
FIG. 11 shows a case in which the elements 8 a and 8 b in FIG. 1 are eliminated and a transmission line 9 constituted by a coplanar strip 10 and a coplanar line 11 is substituted. Since the condition to be satisfied by the total length L2 of the transmission line 9 is ½ of the second wavelength λ2 corresponding to the second resonance frequency, L2 = λ1 · ¼ = λ2 · 1/2.
[0044]
FIG. 12 shows the frequency characteristics of the dual-frequency shared antenna 1 shown in FIG. The vertical axis represents the amount of reflection (dB), and the lower the amount of reflection, the more resonance occurs. It can be seen that resonance occurs not only in the 800 MHz band but also in 1900 MHz, and operates in a low frequency band and a high frequency band.
[0045]
In the present embodiment, the elements 7a, 7b, 8a, 8b are bent, but may be linear or looped.
[0046]
The conductors 2 and 3 may be made of conductive resin instead of metal.
[0047]
In this embodiment, the impedance of the coplanar line 11 is set to be the same as the impedance of the coaxial cable 4 in the high frequency band, but the impedance of the coplanar line 11 is not the same as the impedance of the coaxial cable 4. It may function as an impedance matching circuit that matches the impedance between the strip 10 and the coaxial cable 4. In this case, the coplanar strip 10 and the coplanar line 11 constitute a multistage impedance conversion circuit for obtaining impedance matching between the elements 8 a and 8 b and the coaxial cable 4.
[0048]
Further, in the present embodiment, the coplanar strip 10 and the coplanar line 11 are formed on the same plane, but may be formed on different planes.
[0049]
The dual-frequency antenna according to the present embodiment is a planar antenna and can be attached to a car deflector, a window glass, or the like, but of course is not limited to this and can be provided on an arbitrary object.
[0050]
【The invention's effect】
According to the present invention, since a large GND space is not required as in the case of a monopole antenna, the occupied area of the entire antenna can be reduced. Further, a sufficient gain can be ensured with a small occupied area.
[Brief description of the drawings]
FIG. 1 is a plan view of a dual-frequency antenna according to an embodiment.
FIG. 2 is an exploded perspective view of the dual frequency antenna shown in FIG.
FIG. 3 is an explanatory diagram of a size during operation in a low frequency band.
FIG. 4 is a graph showing frequency characteristics in a low frequency band.
FIG. 5 is an explanatory diagram of a size during operation in a high frequency band.
FIG. 6 is a cross-sectional configuration diagram of a coplanar strip.
FIG. 7 is a cross-sectional configuration diagram of a coplanar line.
FIG. 8 is a graph showing frequency characteristics in a high frequency band.
FIG. 9 is a plan view of another dual-frequency antenna according to the embodiment.
FIG. 10 is a plan view of another dual-frequency antenna according to the embodiment.
FIG. 11 is a plan view of another dual-frequency antenna according to the embodiment.
12 is a graph showing frequency characteristics of the dual-frequency antenna shown in FIG.
FIG. 13 is an explanatory diagram of a super top type balun.
[Explanation of symbols]
1 dual frequency antenna, 2 first dipole antenna (conductor), 3 second dipole antenna (conductor), 4 coaxial cable, 5 outer conductor of coaxial cable, 6 inner conductor of coaxial cable, 7a, 7b, 8a, 8b element, 9 transmission line, 10 coplanar strip, 11 coplanar line.

Claims (7)

A first dipole antenna having a first resonance frequency;
A second dipole antenna having a second resonance frequency higher than the first resonance frequency;
A transmission line for connecting the first and second dipole antennas to a coaxial antenna;
A dual-frequency antenna having
The transmission line constitutes an impedance matching circuit between the first and second dipole antennas and the coaxial cable, and constitutes a balun between the first and second dipole antennas and the coaxial cable. A dual-frequency antenna. The antenna of claim 1, wherein
The transmission line has a first line part and a second line part,
Each of the first line portion and the second line portion has a length of about 1/8 of the first wavelength corresponding to the first resonance frequency, and is formed between the first dipole antenna and the coaxial cable. The impedance matching circuit between,
Each of the first line portion and the second line portion has a length of about ¼ of a second wavelength corresponding to the second resonance frequency, and the first line portion is the second dipole antenna. And the second line portion, and the second line portion has the same impedance as the coaxial cable, and the balun between the second dipole antenna and the coaxial cable is formed. A dual-frequency antenna that is configured. The antenna according to any one of claims 1 and 2,
The dual-frequency antenna according to claim 1, wherein the transmission line also serves as the second dipole antenna having the second resonance frequency. The antenna according to any one of claims 1 to 3,
The dual-frequency antenna according to claim 1, wherein the first dipole antenna, the second dipole antenna, and the transmission line have a planar shape. A dual-frequency antenna that combines a first and a second plate-like conductor to form a dual-frequency dipole antenna,
The first and second plate-like conductors each have two antenna element portions each having a length corresponding to the first and second resonance frequencies;
A transmission line portion connecting the antenna element portion and the coaxial cable;
Have
The transmission line portion of the first plate-like conductor is connected to an inner conductor of the coaxial cable;
The transmission line portion of the second plate-like conductor is connected to an outer conductor of the coaxial cable;
The transmission line portions of the first and second plate-like conductors constitute an impedance matching circuit between the antenna element portion and the coaxial cable, and between the antenna element portion and the coaxial cable. A dual-frequency antenna comprising a balance-unbalance conversion circuit. The antenna according to claim 5, wherein
The transmission line part has a first line part and a second line part,
Each of the first line portion and the second line portion has a length of about 1/8 of the first wavelength corresponding to the first resonance frequency, and is between the antenna element portion and the coaxial cable. The impedance matching circuit of
Each of the first line portion and the second line portion has a length of about ¼ of a second wavelength corresponding to the second resonance frequency, and the first line portion and the antenna element portion The impedance matching circuit between the second line portion and the second line portion has the same impedance as the coaxial cable, and the balanced / unbalanced conversion between the antenna element portion and the coaxial cable. A dual-frequency shared antenna comprising a circuit. The apparatus of claim 6.
The second line portion of the second plate-like conductor sandwiches the second line portion of the first plate-like conductor from the left and right, and the second line portion of the first plate-like conductor. A dual-frequency antenna that is provided so as to straddle the antenna.

Images