JP2007028343A - Directivity variable antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a directivity variable antenna operable even at a several GHz band with nearly the same size as that of an omnidirectional antenna that can be operated at a frequency band lower than that of a prior art. <P>SOLUTION: The directivity variable antenna is provided with capacitors 8 for connecting an outer conductor 10 of a coaxial line 4 to ground in terms of a high frequency through a short-circuit line 7 formed of a conductor pattern on a dielectric film 9 formed on a ground plate 3 of the omnidirectional antenna element and the grounding position of the short-circuit line 7 at the side of the outer conductor 10 in terms of a high frequency is configured to be located on the ground plate 3 apart from the outer conductor 10 when viewed from a coaxial center axis of the coaxial line 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a variable directivity antenna capable of switching the directivity of an antenna, and is particularly suitable for a transmission / reception antenna for information equipment.

With the rapid development of wireless communication technology in recent years, products using wireless technology have started to spread widely, and great expectations are placed on expanding the transmission capacity of wireless communication paths. In recent years, research has been actively conducted to increase the transmission capacity by multiplexing multi-dimensional signals such as time, space, polarization, and code. Multiplexing by space is considered to be realized by an adaptive array antenna consisting of a plurality of omnidirectional antennas and a circuit that synthesizes the signal, but the size and spacing of each antenna increases. It was the cause that limited the application destination.
In particular, for use in a mobile communication terminal, it is desired that the size of the antenna be as small as possible. The directivity variable antenna can usually be made smaller than an adaptive array antenna because its directivity can be changed by a pair of antennas and a feeding circuit, and as a candidate for a small antenna that realizes multiplexing by space Although it is expected, there are few examples of research on the miniaturization of the variable directivity antenna, and its development has been expected.
An example of a conventional directional variable antenna is disclosed in Patent Document 1.
FIG. 8 is a diagram showing a configuration example of a directivity variable antenna disclosed in Patent Document 1. In FIG.
The antenna shown in FIG. 8 includes an antenna element 101, a reflective element 102 arranged in parallel to the antenna element 101, and directivity control means 103 that moves the reflective element 102 in an arc around the axis of the antenna element 101. Consists of The directivity control means 103 includes a rotation drive unit 103a and a connecting arm 103b, and an antenna element 101 is erected on the rotation drive unit 103a via an insulator (not shown). Further, the rotation drive unit 103a is attached to a conductor 104 such as a vehicle body, and the reflection element 102 is connected via a connection arm 103b. In addition, the coaxial feeder 105 electrically connects the antenna element 101 and the voltage source 106. Therefore, according to such a directivity variable antenna, the directivity can be directed to a specific direction by adjusting the positional relationship between the antenna element 101 and the reflective element 102. However, in the case of this directivity variable antenna, the antenna itself becomes much larger due to the addition of the reflective element 102.

Patent Document 2 discloses an example of a variable directivity antenna that can electrically switch directivity.
FIG. 9 is a diagram showing the configuration of the variable directivity antenna disclosed in Patent Document 2. In FIG.
In the variable directivity antenna shown in FIG. 9, a central drive element 112 and a parasitic element 113 are arranged on a circular ground conductor 111 and radially surrounding the drive element 112. An impedance load 114 is provided below the parasitic element 113, and the directivity is switched by switching the impedance of the impedance load 114. However, in the case of such a directivity variable antenna, the distance between the antenna central drive element 112 and the parasitic element 113 is a value of about λ / 4, and the whole antenna becomes 2λ or more.
Patent Document 3 discloses a similar example of a directivity variable antenna.
FIG. 10 is a diagram showing the configuration of the variable directivity antenna disclosed in Patent Document 3. In FIG.
In the variable directivity antenna shown in FIG. 10, a feeding antenna element A0 is arranged on a circular ground conductor 121, and parasitic variable reactance elements A1 to A6 are arranged at positions radially surrounding it. However, in the case of such a directivity variable antenna, the distance d between the feeding antenna element A0 and the parasitic variable reactance element is a value of about λ / 4, and the whole antenna is about λ.
As described above, the conventional directional variable antenna has a drawback that the shape is larger than that of the omnidirectional antenna. Therefore, a directional antenna that eliminates such drawbacks is disclosed in Patent Document 4.

Patent Document 4 discloses a variable directivity antenna having the same size as an omnidirectional antenna. Detailed characteristics of one implementation form of this antenna are disclosed in Non-Patent Document 1, and it is shown that the directivity is variable with a size equivalent to that of an omnidirectional antenna over a wide frequency band.
FIG. 11 is a diagram illustrating a configuration of a variable directivity antenna disclosed in Non-Patent Document 1. (a) is a cross-sectional view of the variable directivity antenna, and (b) is surrounded by a broken-line circle in (a). It is a top view of a part. The directivity variable antenna shown in FIG. 11 is configured such that the antenna directivity is changed by loading a short-circuit wire 132 on a feeding portion of a discone antenna 131 which is an omnidirectional antenna. Further, the reflection loss frequency characteristics of such a directivity variable antenna are shown in FIG. 12, and are the same over a wide frequency range regardless of the presence or absence of a short-circuit line. It can be seen that the reflection loss when loading is increased.
This is because the inductance generated by the short-circuit line increases with the frequency, but at a frequency of 10 GHz or less, the inductance is not sufficiently increased, and the effect of the short-circuit line has come out. Non-patent document 2 discloses a detailed examination result of the inductance generated by the short-circuit line.
Japanese Patent Laid-Open No. 06-350334 Japanese Patent Laid-Open No. 10-154911 JP 2001-24431 A JP 2004-304785 A Sakakibara, Hoshi, Sugai, Sato, “Proposal of antenna directivity control technology using coaxial short-circuit structure”, IEICE Tech. Bulletin, AP2003-274., 2004 Hagiwara, Hoshi, Aoi, “Inductance analysis by coaxial short circuit structure”, IEICE Technical Report, AP2004-82., 2004

The conventional variable directivity antenna shown in FIG. 11 can be configured with the same size as the omnidirectional antenna, but the reflection loss is reduced in a frequency band where the inductance generated by the short-circuit line cannot be sufficiently increased. Has become a cause of narrowing the bandwidth used. That is, it has become a cause of limiting the lower limit frequency band when the directional variable antenna is used in a broadband communication terminal or the like.
Therefore, the present invention has been made in view of the above points, and can operate a directional variable antenna having a size comparable to that of an omnidirectional antenna in a frequency band lower than that of a conventional antenna, which can operate in a few GHz band. An object of the present invention is to provide a variable directivity antenna.

In order to achieve the above object, the invention according to claim 1 is a non-directional antenna element comprising a ground plane and a radiating element, a coaxial line for feeding the antenna element, and a dielectric provided on the ground plane. A short-circuit wire formed by a conductor pattern on the film; and a capacitor for grounding the outer conductor side of the coaxial line at high frequency by the short-circuit wire; and high-frequency grounding on the outer conductor side of the short-circuit wire The variable-directivity antenna is characterized in that the position is on the ground plane outside the outer conductor when viewed from the coaxial central axis of the coaxial line.
According to a second aspect of the present invention, there is provided an omnidirectional antenna element comprising a ground plane and a radiating element, a coaxial line for feeding the antenna element, a short-circuit line for short-circuiting the inner conductor and the outer conductor of the coaxial line, A switch that switches a connection state between the inner conductor and the outer conductor by the short-circuit line between a short-circuit state and a non-short-circuit state, and the length of the short-circuit line between the inner conductor and the outer conductor of the coaxial line It features a longer directional variable antenna.
The invention according to claim 3 is the directivity variable antenna according to claim 1 or 2, wherein the central axis of the coaxial line, the connection point between the short-circuit line and the inner conductor, and the short-circuit line Connection points with the outer conductor are arranged side by side on a straight line.
According to a fourth aspect of the present invention, in the variable directivity antenna according to the first or second aspect, the short-circuit wire is bent in a meander shape.
According to a fifth aspect of the present invention, in the variable directivity antenna according to the second aspect, a material having a relative permeability greater than 1 is loaded in the vicinity of the short circuit line.

According to the first aspect of the present invention, a capacitor for grounding the outer conductor side of the coaxial line at high frequency by a short-circuit line formed by a conductor pattern on a dielectric film provided on the ground plane of the omnidirectional antenna element. In order to increase the inductance generated in the short-circuit wire, the high-frequency grounding position on the outer conductor side of the short-circuit wire is on the ground plane outside the outer conductor when viewed from the coaxial central axis of the coaxial line. Can do. As a result, it is possible to realize a directional variable antenna that has the same size as an omnidirectional antenna, can operate in a few GHz band, and operates in a lower frequency band. As a result, the variable directivity antenna can be used in a communication terminal or the like whose operating band is several GHz.
According to a second aspect of the present invention, the length of the short-circuit line for short-circuiting the inner conductor and the outer conductor of the coaxial line that feeds the non-directional antenna element composed of the ground plane and the radiating element is set between the inner conductor and the outer conductor of the coaxial line. It is possible to increase the inductance generated in the short-circuit wire by making the interval longer than the interval. As a result, it is possible to realize a variable directivity antenna that is comparable in size to an omnidirectional antenna, can operate in a few GHz band, and operates in a frequency band lower than the conventional one. As a result, the variable directivity antenna can be used in a communication terminal or the like whose operating band is several GHz.
Further, in the invention of claim 3, the coaxial line is formed by arranging the central axis of the coaxial line, the connection point between the short-circuit line and the inner conductor, and the connection point between the short-circuit line and the outer conductor in a straight line. It is possible to short-circuit in the electric field direction of the line, increase the length of the short-circuit line without greatly disturbing the electric field in the line, and further increase the generated inductance, so that it operates in a lower frequency band than before A directional variable antenna can be realized.
Further, in the invention of claim 4, since the short-circuit wire is bent in a meander shape and the length of the short-circuit wire is increased so that the generated inductance is increased, the directivity variable that operates in a lower frequency band than in the prior art. An antenna can be realized.
In the invention of claim 5, since a material having a relative permeability greater than 1 is loaded in the vicinity of the short-circuit line, the inductance generated in the short-circuit line can be further increased. A directional variable antenna can be realized.

Embodiments of a variable directivity antenna according to the present invention will be described below with reference to the drawings.
<First Embodiment>
First, the variable directivity antenna according to the first embodiment of the present invention will be described.
1A and 1B are diagrams for explaining a directivity variable antenna according to a first embodiment of the present invention. FIG. 1A is an overall perspective view, and FIG. 1B is a cross-sectional view in the direction of a coaxial central axis.
A variable directivity antenna 1 according to the first embodiment shown in FIG. 1 is constituted by a discone antenna that is fed by a coaxial line 4 and includes a radiator (radiating element) 2 and a ground plane 3. On the ground plane 3, a dielectric film 9 on which one electrode of a bias line 5, a switch 6, a short-circuit line 7 and a capacitor 8 is formed is affixed, and at the connection part between the coaxial line 4 and the discone antenna, It is comprised so that a short circuit can be turned ON / OFF electrically in four directions in the ground plane. The capacitor 8 is formed by a metal pattern on the dielectric film 9, and includes the electrode, the dielectric film 9, and the ground plane 3. The outer edge shape of the capacitor 8 is composed of a circular arc centered on the coaxial line 4 and a linear shape along the radiation direction, and is close to the coaxial line 4 and hardly disturbs the ground current that contributes to antenna radiation. .
A high-frequency grounding position on the outer conductor 10 side in the coaxial line 4 of the short-circuit line 7 is a connection portion with the capacitor 8, and this position is on the ground plane 3 outside the outer conductor 10 as viewed from the coaxial central axis. It has become. If comprised in this way, since the length of the short circuit wire 7 can be lengthened, the inductance which generate | occur | produces with the short circuit wire 7 can be increased greatly.
The switch 6 connected to the short-circuit line 7 employs a switch that can be electrically turned on / off. As the switch 6, for example, a diode switch, a MEMS switch, or the like can be considered. In the first embodiment, a PIN diode is used as the switch 6, and this switch 6 can be electrically controlled on and off using a control electrode (not shown here) from outside the antenna. Yes. If all the switches 6 are turned off, the electric field distribution of the coaxial line 4 is not disturbed, and the radiation pattern of the antenna remains omnidirectional.
On the other hand, when only one switch 6 is inserted, the electric field in the coaxial line is disturbed, and the radiation pattern of the antenna has directivity. Further, the directivity of the antenna can be switched by switching the switch 6 to be turned on.
FIG. 2 is a diagram illustrating an example of a switch.
In FIG. 2, A, B, and E are terminals, D is a PIN diode, C is a capacitor, L is an inductor, and R is a resistance. The terminal A is connected to the inner conductor (signal line) 11 of the coaxial line 4, the terminal B is connected to the outer conductor (ground conductor) 10 of the coaxial line 4, and the terminal E is connected to the bias line 5 on the dielectric film 9.
The PIN diode D is grounded by a capacitor C at a high frequency. By changing the value of the DC bias applied to the terminal E, the resistance value of the PIN diode D changes greatly, so that the switch 6 can be operated.

FIG. 3 is a diagram for explaining the directivity of the directivity variable antenna according to the first embodiment. FIG. 3 shows the antenna gain at an elevation angle of 45 degrees from the ground plane 3 for 360 degrees with reference to the switch 6 that turns on the radiator 2 as a reference (0 degree).
The solid line in the figure indicates the gain when one switch 6 in the direction of the angle of 0 degrees is turned on, and the dotted line indicates the gain when all the switches 6 are turned off. As is apparent from FIG. 3, when all the switches 6 are turned off, the gain becomes constant at any angle and becomes omnidirectional.
In addition, when the switch 6 is turned on, the directivity is changed and the radiation intensity in the direction opposite to that of the turned on switch is increased.
FIG. 4 shows the reflection loss characteristic of the variable directivity antenna according to the first embodiment.
The dotted line in the figure shows an example of the characteristic of a conventional directional variable antenna in which the short-circuit line 7 is connected linearly, and the solid line shows an example of the reflection loss characteristic when configured as in the first embodiment. .
As can be seen from FIG. 4, the directivity variable antenna according to the first embodiment has a reduced reflection loss of 10 GHz or less. Note that the reflection loss characteristic of the conventional directional antenna shown in FIG. 4 is different from the reflection loss characteristic of the conventional directional antenna shown in FIG. 12 is the reflection loss of the directional antenna with no dielectric film attached, whereas FIG.
Thus, according to the directivity variable antenna of the first embodiment, the directivity can be switched with the same size as that of a normal omnidirectional antenna. Further, the apparent length of the short-circuit line 7 is lengthened to greatly increase the inductance value of the short-circuit line 7 so that the reflection loss characteristic is improved. Thereby, the expansion of the operating band to the low frequency side can be realized.

<Second Embodiment>
FIGS. 5A and 5B are diagrams for explaining the directivity variable antenna according to the second embodiment. FIG. 5A is an overall perspective view, and FIG. 5B is a top view of a ground plane portion of the antenna power feeding unit. In addition, the same code | symbol is attached | subjected to the same site | part as FIG. 1, and description is abbreviate | omitted.
As shown in FIG. 5A, the variable directivity antenna 20 according to the second embodiment is also fed by the coaxial line 4 and is constituted by a discone antenna including the radiator 2 and the ground plane 3.
In addition, the short-circuit wire 21 and the switch 6 which are bent in a meander shape in four directions and have an effective length extended are connected to the coaxial line portion of the antenna feeding portion shown in FIG.
Here, the central axis 0 of the coaxial line 4, the connection point (connection point) between the short-circuit line 21 and the inner conductor 11, and the connection point (connection point) between the short-circuit line 21 and the outer conductor 10 are arranged in a straight line. Since the electric field direction of the TEM mode in the coaxial line 4 and the short circuit direction coincide with each other, the length of the short circuit line can be increased without greatly disturbing the electric field in the line other than the short circuit direction. it can. Therefore, even in such a configuration, the operating band can be expanded to the low frequency side.
Note that the switch 6 connected to the short-circuit line 21 is one that can be electrically turned on / off. As the switch 6, for example, a diode switch, a MEMS switch, or the like is conceivable.

<Third Embodiment>
6A and 6B are views for explaining a directivity variable antenna according to a third embodiment of the present invention, in which FIG. 6A is an overall perspective view, and FIG. 6B is a sectional view in the direction of a coaxial central axis. The same parts as those in FIGS. 1 and 5 are denoted by the same reference numerals and description thereof is omitted.
The directivity variable antenna 30 according to the third embodiment shown in FIG. 6 combines the characteristics of the directivity variable antenna 1 according to the first embodiment and the directivity variable antenna 20 according to the second embodiment. Is. That is, a bias line 5, a switch 6, a short-circuit line 21 that is bent into a meander shape and has an effective length extended, and a dielectric film 9 on which one electrode of the capacitor 8 is formed are pasted on the ground plane 3. Are configured.
If comprised in this way, the extension effect by having set the high frequency grounding position by the side of the outer conductor 10 of the short circuit wire 21 on the ground plane 3 outside the outer conductor 10 seeing from the coaxial central axis, and the short circuit wire 21 in the meander shape. The inductance of the short-circuit wire 21 can be greatly increased due to the extension effect resulting from the above. Therefore, in the case of such a configuration, the operating band can be further expanded to the low frequency side.

<Fourth Embodiment>
7A and 7B are views for explaining a directivity variable antenna according to a fourth embodiment of the present invention, in which FIG. 7A is an overall perspective view, and FIG. 7B is a sectional view in the direction of a coaxial central axis. In addition, the same code | symbol is attached | subjected to the same site | part as FIG. 1, and description is abbreviate | omitted.
In the directivity variable antenna 40 according to the fourth embodiment shown in FIG. 7, a high permeability material (for example, ferrite) 31 having a relative permeability greater than 1 is loaded on the coaxial line 4 near the short-circuit line 21. This is different from the directivity variable antenna 20 shown in FIG.
As described above, the inductance of the short-circuited wire 21 is increased by the increase in impedance of the short-circuited wire 21 due to the loading of the high permeability material 31 such as ferrite in the vicinity of the short-circuited wire 21 and the extension effect by forming the short-circuited wire 21 into the meander shape. Can be greatly increased. Therefore, even in such a configuration, the operating band can be expanded to the low frequency side. The fact that the inductance value of the short-circuit wire 21 depends on the magnetic permeability of the coaxial line portion has been elucidated by the analysis of Non-Patent Document 2.
5 to 7 also use PIN diodes as the switches 6. Similarly to the above, if all the switches 6 are turned OFF, the radiation pattern of the antenna becomes non-directional. When only one 6 is inserted, the radiation pattern of the antenna has directivity. It goes without saying that the antenna directivity can be switched by switching the switch 6 to be turned on.
Further, the present invention is by no means limited to the requirements shown here, such as the shape of the variable directivity antenna described in the present embodiment and combinations with other elements. These points can be changed within a range not impairing the gist of the present invention, and can be appropriately determined according to the application form.

The figure for demonstrating the directivity variable antenna which concerns on the 1st Embodiment of this invention. The figure which shows an example of a switch. The figure for demonstrating the directivity of the directivity variable antenna in 1st Embodiment. The figure which showed the reflection loss characteristic of the directivity variable antenna in 1st Embodiment. The figure for demonstrating the directivity variable antenna which concerns on the 2nd Embodiment of this invention. The figure for demonstrating the directivity variable antenna which concerns on the 3rd Embodiment of this invention. The figure for demonstrating the directivity variable antenna which concerns on the 4th Embodiment of this invention. The figure which showed the structural example of the directivity variable antenna currently disclosed by patent document 1. FIG. The figure which showed the structure of the directivity variable antenna currently disclosed by patent document 2. FIG. The figure which showed the structure of the directivity variable antenna currently disclosed by patent document 3. FIG. The figure which showed the structure of the directivity variable antenna currently disclosed by the nonpatent literature 1. FIG. The figure which shows the reflection loss characteristic of the conventional directional antenna (with a short circuit wire).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 20, 30, 40 ... Directional variable antenna, 2 ... Radiator, 3 ... Ground plane, 4 ... Coaxial line, 5 ... Bias line, 6 ... Switch, 7 ... Short circuit wire, 8 ... Capacitor, 9 ... Dielectric film DESCRIPTION OF SYMBOLS 10 ... Outer conductor, 11 ... Inner conductor, 21 ... Short circuit wire, 31 ... High magnetic permeability material

Claims (5)

  A non-directional antenna element comprising a ground plane and a radiation element; a coaxial line for feeding the antenna element; a short-circuit line formed by a conductor pattern on a dielectric film provided on the ground plane; and the short-circuit line And a capacitor for grounding the outer conductor side of the coaxial line at a high frequency, and a high-frequency grounding position on the outer conductor side of the short-circuit line is higher than the outer conductor when viewed from the coaxial central axis of the coaxial line. Further, the variable directivity antenna is configured to be on the outer ground plate.   A non-directional antenna element comprising a ground plane and a radiating element; a coaxial line that feeds the antenna element; a short-circuit line that short-circuits an inner conductor and an outer conductor of the coaxial line; A switch that switches a connection state between the outer conductor to a short-circuited state and a non-short-circuited state, and the length of the short-circuit line is longer than the interval between the inner conductor and the outer conductor of the coaxial line Variable antenna.   The directivity variable antenna according to claim 1 or 2, wherein a central axis of the coaxial line, a connection point between the short-circuit line and the inner conductor, and a connection point between the short-circuit line and the outer conductor are linear. Directivity variable antenna characterized by being arranged side by side.   The variable directivity antenna according to claim 1 or 2, wherein the short-circuit wire is bent in a meander shape.   The variable directivity antenna according to claim 2, wherein a material having a relative permeability greater than 1 is loaded in the vicinity of the short-circuit line.

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