JPH07297627A - Antenna device - Google Patents

Abstract

PURPOSE:To provide an antenna device which contains such a structure that can switch the resonance frequency of antenna despite the use of a compact antenna that has the comparatively small band width. CONSTITUTION:This antenna device can switch the resonance frequency and includes an antenna main body 11 which has the capacity C1 among a distribution inductance component L1, an impedance adjustment inductance component L2 and a ground potential. Then the capacitor C2 and a diode D1 are connected in series to each other and in parallel to the capacity C1, and the voltage is applied to a connection point 16 between the C2 and the D1 so that the D1 is turned on or off. Thus the resonance frequency is switched by the changeover carried out between the ON and OFF states of the D1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency antenna device, and more particularly to an antenna device having a structure in which the resonance frequency can be switched so that it can be used in a plurality of frequency bands.

[0002]

2. Description of the Related Art In mobile communication devices, there is a demand for smaller antenna devices. An inverted F-type antenna device is known as a small-sized antenna device used for this type of application.

An example of the inverted F type antenna device is K. Fujimot.
o, A. Henderson, K. Hirasawa and JR James, "Small Aentennas" (Research Studies Press Lt.
d., England). An example of this inverted F type antenna device will be described with reference to FIG. The inverted F type antenna device 1 has a rectangular metal plate 2 that functions as a radiation unit. From one side edge of the metal plate 2, a ground terminal 3 formed by being bent so as to be orthogonal to the metal plate 2 is provided. Further, the power supply terminal 4 is formed by bending a part of the metal plate from the other side edge of the metal plate 2.

Since the inverted F type antenna device 1 has the structure as described above, the ground terminal 3 and the power feeding terminal 4 are inserted into the through holes (plurality) provided in the printed circuit board so that the printed circuit board can be mounted on the printed circuit board. Can be implemented.

[0005]

However, the conventional small-sized antenna including the above-mentioned inverted F type antenna device does not have a sufficiently wide bandwidth, and therefore, when used in a mobile communication device, it has a transmitting side and a receiving side. Only one frequency band on the side could be covered. That is, in the portable mobile communication device, as shown in FIG. 2, when the frequency band Tx on the transmission side and the frequency band Rx on the reception side are separated by the frequency indicated by A in FIG. In order to enable transmission and reception with, the antenna device is required to have a bandwidth shown by B in FIG. However, the conventional small-sized antenna device cannot satisfy such a bandwidth B.

Therefore, in the case of a system such as a PHP (Personal Handyphone) having the same frequency on the transmission side and the reception side, the transmission frequency and Although it was possible to cover the reception frequency, there was no small antenna device capable of covering the frequency bands of both the transmission side and the reception side in a system having different transmission frequencies and reception frequencies.

Therefore, there has been a demand for the appearance of an antenna device which is compact and has a function capable of switching the resonance frequency of the antenna. An object of the present invention is to provide an antenna device that satisfies the above-mentioned demands and that has a structure capable of switching the resonance frequency of the antenna while using a small antenna having a relatively narrow bandwidth.

[0008]

According to a broad aspect of the present invention, there is provided an antenna main body having a power feeding portion and a portion connected to the ground potential, and an electrostatic capacitance between the antenna main body and the ground potential. On the other hand, a capacitance means connected between the antenna body and the ground potential so as to be parallel to each other and for adding a capacitance in parallel to the capacitance, and the capacitance for switching the resonance frequency of the antenna device. An antenna device is provided, which is connected to the means and comprises a switching means enabling the value of the capacitance of the capacitance means to be changed.

In a particular aspect of the antenna device of the present invention, the capacitance means has capacitors connected in series with each other and an element whose capacitance is changed, and the capacitance is changed. The switching means is connected to the element whose capacitance is changed so as to change the capacitance of the element. In this case, the capacitor functions to prevent the current given from the switching means from flowing to the antenna body side.

Further, according to a more specific aspect of the present invention, the element whose capacitance is changed is composed of a diode, and the switching means includes the diode at a connection point between the capacitor and the diode. It is configured by a voltage supply circuit that supplies a first or second voltage that is turned on or off. In this structure, when the diode is turned on, the diode becomes conductive. Therefore, the capacitance component of the entire antenna device has an electrostatic capacitance between the antenna device and the ground potential and a capacitance of the capacitor. It is determined by the capacity connected in parallel. On the other hand,
When the diode is turned off, the capacitance of the diode itself is added to the capacitor in series. Therefore, the capacitance of the entire antenna device is determined by the capacitance in which the antenna body has a ground potential and the capacitance in which the series capacitance of the capacitor and the diode are connected in parallel. In this way, the resonance frequency of the antenna device is switched by turning the diode on or off.

According to yet another specific aspect of the present invention, the capacitance means includes a first capacitor, a diode connected in series with the first capacitor, and a diode connected in series with the diode. And a second capacitor, the switching means mutually connecting a first connection point between the first capacitor and the diode and a second connection point between the diode and the second capacitor to each other. The voltage supply circuit is configured to apply voltages of different polarities and to invert the polarities of the voltages applied to the first and second connection points. Here, by inverting the polarities of the voltages applied to the first and second connection points, the diode is turned on or off, whereby the resonance frequency of the antenna device is switched.

The antenna device used in the antenna device of the present invention is a conventionally known rod antenna or inverted F antenna.
Type antenna or the like can be used, but preferably,
A dielectric substrate, a ground electrode formed on at least one of a side surface and a bottom surface of the dielectric substrate, and a low conductor fixed to the dielectric substrate such that one main surface faces the upper surface of the dielectric substrate. An antenna main body is used, which includes a radiator made of a lossy material and a power feeding unit provided on at least one of a side surface and a bottom surface of a laminated body formed of the dielectric substrate and the radiator.

[0013]

In the present invention, the capacity of the capacity means is changed by the switching means. Therefore, the capacitance of the capacitance means that is added in parallel to the electrostatic capacitance that the antenna body has with the ground potential is switched. On the other hand, the resonance frequency of the antenna device is determined by the inductance value of the inductance component of the antenna body and the capacitance value between the antenna body and the ground potential. In the antenna device of the present invention, the capacitance of the capacitance device is changed by the switching device, so that the resonance frequency of the antenna device is switched.

Therefore, even when the antenna main body is constructed by using a small antenna having a narrow bandwidth, the resonance frequency can be switched, so that it can be suitably used in a system having different transmission frequencies and reception frequencies.

Therefore, according to the present invention, it is possible to provide a small antenna device which is most suitable for a system such as a mobile phone having different transmission frequencies and reception frequencies.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a schematic block diagram of an antenna device of the present invention. In this antenna device, the power supply terminal F
It has an antenna body 11 having the above, a capacitance means 12 connected to the antenna body 11, and a switching means 13 for switching the capacitance of the capacitance means 12. The antenna body 11 is
It has a power feeding portion 14 and a portion 15 connected to the ground potential. Further, as shown by the broken line in FIG. 3, the antenna body 11 has a capacitance C ₁ with the ground potential. The capacitance C ₁ is composed of a capacitor element incorporated in the antenna main body and / or a distributed capacitance that the antenna main body 11 has between the antenna main body 11 and the ground potential, which will be described later in a specific embodiment.

The capacitance means 12 is connected to the antenna main body 11 and the graph.
Connected to the ground potential, and therefore the capacitance C
₁Are connected in parallel to. The capacity means 12 is
Quantity C ₁Function to add capacity in parallel to
The capacity of one itself is switched by the switching means 13.
It is configured to Therefore, the
Between the antenna body 11 and the ground potential in the antenna device
The total electrostatic capacity of the
Switched by switching the capacity of the means 12
It

Therefore, in the antenna device of this embodiment, the resonance frequency can be switched by switching the capacity of the capacity means 12 by the switching means 13.
This makes it possible to construct an antenna device that can be used in a plurality of bands.

FIG. 4 is a circuit diagram showing a specific embodiment of the antenna device of the present invention shown in FIG. In the present embodiment, the antenna body 11 has a distributed inductance component L ₁ of a portion that radiates an electromagnetic wave, an impedance adjustment distributed inductance component L _2, and a capacitance C ₁ .
The capacitance C ₁ refers to the capacitance that the antenna body 11 has with the ground potential. A capacitor element connected to the ground potential may be provided in the antenna body 11 in order to adjust the resonance frequency. In that case, the capacitance of the capacitor element is also the capacitance C mentioned above. _Make up ₁ . However, when the above capacitor element is not provided in the antenna body 11, the capacitance C ₁ is formed by the distributed capacitance between the antenna body 11 and the ground potential.

Between the antenna body 11 and the ground potential
Is the capacitor C₂And diode D ₁And are connected in series
Has been done. This capacitor C₂And diode D
₁Constitute the above-mentioned capacitance means 12. From Figure 4
As is clear, capacitor C₂And diode D₁so
The configured capacity is the capacity in the antenna body 11 described above.
C₁And are connected in parallel.

A resistor R ₁ is provided between the connection point 16 between the capacitor element C ₂ and the diode D ₁ and the input terminal 17.
Are connected. A resistor R ₂ is connected between the end of the resistor R _{1 on} the side opposite to the input terminal 17 and the ground potential. The resistors R ₁ and R ₂ are connected to divide the pulse voltage applied from the input terminal 17 and to apply a pulse voltage of an appropriate magnitude to the connection point 16.

Pulse voltage applied to the connection point 16
Is a diode D when "high" ₁Is turned on
As in the case of “low” voltage, the diode D₁But
Diode D so that it is turned off₁Threshold voltage
Is set based on. In addition, the resistance R₁And resistance R₂
Is the diode D₁ON state or
A pulse voltage that turns off is applied to the connection point 16.
Thus, the resistance values of both are selected.

A trigger pulse power supply (not shown) is connected to the input terminal 17, and a pulse voltage is applied from the power supply. Next, the switching operation of the resonance frequency in the antenna device of the embodiment shown in FIG. 4 will be described.

The resonance frequency f ₀ of the antenna body 11 having the inductance components L ₁ and L ₂ and the capacitance C ₁ is
The inductance value of the inductance components L ₁ and L ₂ is L
It represents ₁ and L _2, when representing the capacitance of the capacitor C ₁ likewise in C _1,

[0025]

[Equation 1]

Is represented by Therefore, it is understood that the resonance frequency f ₀ can be moved by adjusting the capacitance C ₁ . On the other hand, in this embodiment, the antenna body 11 is
The capacitor C ₂ and the diode D ₁ described above are connected to. In addition, the capacitor C ₂ and the diode D
_A pulse voltage is applied to the capacitive means constituted by ₁ through resistors R ₁ and R ₂ . Accordingly, the diode D ₁ is turned on if the voltage of the "high" is given from the input terminal 17, the diode D ₁ becomes conductive. Therefore, the resonance frequency f _ON of the antenna device in which the diode is in the ON state is equal to the capacitance of the capacitor C _2.
Expressed as ₂ ,

[0027]

[Equation 2]

[0028] On the other hand, from input terminal 17 "low"
When the voltage of ₁Is off
It becomes a state. Therefore, the part that constitutes the capacitance means 12
Capacity C_xIs the diode D₁In the non-conducting state of
The capacitance is C_DAnd when

[0029]

[Equation 3]

It becomes Therefore, the resonance frequency f _OFF of the antenna device when the diode D ₁ is off is

[0031]

[Equation 4]

It becomes That is, when the diode D ₁ is turned on, only the capacitor C ₂ is connected in parallel with the capacitance C ₁ . Therefore, the capacity C ₁
The overall capacitance of the capacitive means connected in parallel with is increased, and the overall resonance frequency is reduced.

On the other hand, when a low voltage is applied from the input terminal 17, the diode D ₁ is turned off and the capacitance connected in parallel with the capacitance C ₁ becomes C _x . Therefore, the capacitance of the capacitance means connected in parallel with the capacitor C ₁ is reduced, and the resonance frequency of the antenna device is increased.

Therefore, in the antenna device of this embodiment, the resonance frequency of the antenna device is switched by applying the voltage of "high" or "low" from the input terminal 17.

Usually, in a system in which the transmission frequency and the reception frequency are different, the transmission frequency is set in the frequency region lower than the reception frequency. This is because the design of the amplifier for obtaining the output required for transmission is easier on the low frequency side than on the high frequency side. Therefore, in the antenna device of the present embodiment, preferably, a “high” voltage is applied from the input terminal 17 during transmission, and the diode D ₁ is turned on. Further, at the time of reception, a "low" voltage is applied to the input terminal 17, and the diode D ₁ is turned off.

As described above, in the antenna device of this embodiment, the reception frequency of the antenna device can be switched by switching the pulse voltage applied from the input terminal 17. Therefore, the antenna body 11 can be preferably used in a system having different transmission frequencies and reception frequencies. In this case, an arbitrary antenna such as a conventionally known rod antenna or inverted F-type antenna can be used as the antenna body. Therefore, it is small,
In addition, it is possible to easily provide an antenna device that can switch the resonance frequency.

Next, a specific structural example of the antenna device of this embodiment will be described with reference to FIGS. FIG. 5 is a perspective view showing a radiator used in the antenna device of this embodiment. The radiator 21 is configured by bending a plate-shaped member made of a metal material such as copper or a copper alloy as illustrated. In addition, as the radiator 21,
Other materials may be used as long as they have a low conductor loss, such as the above metals.

The radiator 21 has a radiator 22 having a rectangular planar shape. A first fixing portion 23 is formed so as to extend from one short side of the radiating portion 22 toward the dielectric substrate side described later. Further, from the other short side of the radiating portion 22,
The second fixing portion 24 is formed by bending. A power supply terminal 25 and a ground terminal 26 are integrally formed with the fixed portion 23 at the tip of the first fixed portion 23. Also,
A capacitance connection terminal 27 is formed integrally with the fixed portion 24 on the tip side of the second fixed portion 24.

Further, locking pieces 2 are provided on both sides of the fixed portion 23.
8, 29 have locking pieces 30, 31 on both sides of the fixed portion 24.
Are respectively hung from the side edges on the short side of the radiating portion 22.

On the other hand, reinforcing pieces 32, 33 are formed by bending from both side edges on the long side of the radiating portion 22 in order to enhance mechanical strength. FIG. 6 shows the radiator 21.
It is a perspective view for demonstrating the dielectric substrate 41 combined with and the component mounted on the dielectric substrate 41. The dielectric substrate 41 has a substantially rectangular parallelepiped shape as illustrated.
The dielectric substrate 41 can be made of an appropriate dielectric material such as dielectric ceramics or synthetic resin. In this embodiment, the dielectric substrate 41 is formed by using the ceramics integrated firing technique.

One side surface 41 on the long side of the dielectric substrate 41
A ground electrode 42a and a terminal electrode 43 are formed on a. The terminal electrode 43 is the voltage input terminal 17 described above.
Equivalent to. The other side surface 41 facing the side surface 41a
A ground electrode 42b is formed on b.

A power supply electrode 44 and a ground electrode 45 are formed at a predetermined distance on one side surface 41c on the short side of the dielectric substrate 41. In addition, the dielectric substrate 41
A connection electrode 46 is formed on the other side surface 41d on the short side.

A circuit pattern 47 is formed on the dielectric substrate 41.
Is formed by forming a conductive film. Also,
Each chip type electronic component forming the diode D ₁ and the resistors R ₁ and R ₂ shown in FIG. 4 is mounted and electrically connected by the circuit pattern 47. In FIG. 6, the chip type electronic components showing the diode D ₁ and the resistors R ₁ and R ₂ are indicated by the same reference symbols.

On the upper surface of the dielectric substrate 41,
A capacitance extracting electrode 48 for forming a capacitor is formed. The connection electrode 46 formed on the side surface 41d is formed so as not to be electrically connected to the capacitance extraction electrode 48. That is, as shown in the cross-sectional view of the portion where the capacitance extracting electrode 48 is formed in FIG.
The capacitance extracting electrode 48 and the connection electrode 46 are formed so as not to reach the edge of the dielectric substrate 41 so that they are not electrically connected.

In the dielectric substrate 41, at an intermediate height position,
A capacitance extracting electrode 49 is formed so as to overlap with the capacitance extracting electrode 48 via the dielectric substrate layer, and a ground electrode 50 is formed at a position lower than the capacitance extracting electrode 49. In addition, the capacitance extraction electrode 49
Are drawn out to the side surface 41d so as to be electrically connected to the above-mentioned connection electrode 46. On the other hand, the ground electrode 50 is formed in a size below the dielectric substrate 41 so as to extend over substantially the entire plane of the dielectric substrate 41, and is electrically connected to the aforementioned ground electrodes 42a and 42b. ing.

Therefore, as shown in FIG. 7, by the capacitance extracting electrode 48 and the capacitance extracting electrode 49, as shown in FIG.
The capacitor C ₂ shown in FIG. Further, the capacitor constituted by the capacitance extracting electrode 49 and the ground electrode 50 constitutes a part of the capacitance C ₁ in the antenna body 11 in the embodiment shown in FIG.

In the antenna device of this embodiment, the radiator 21 is fixed to the dielectric substrate 41 described above. At the time of fixing, the dielectric substrate 41 is inserted between the first and second fixing portions 23 and 24, and the ground terminal 26 and the connection terminal 27 are inserted.
Is soldered to the ground electrode 45 and the connection electrode 46 provided on the dielectric substrate 41. FIG. 8 is a perspective view showing the outer appearance of the antenna device of this embodiment obtained in this way.

The slits 26a, 2 are formed at the tips of the first and second fixing portions 23, 24 of the radiator 21 shown in FIG.
4a is formed. These slits 24a, 26a
Functions as a solder paste injecting section. That is,
The tip of the dispenser for applying the solder paste can be inserted through the slits 24a and 26a to surely attach the solder paste to the ground electrode 45 and the connection electrode 46 of the dielectric substrate 41. Therefore, the fixed portion 23,
When joining 24 to the dielectric substrate 41, the solder paste is surely spread by heating in the space between the fixing portions 23 and 24 and the side surface of the dielectric substrate 41, so that the joining area between them is increased. You can

Instead of the slits 24a and 26a, a through hole into which the tip of the solder dispenser can be inserted may be formed. As shown in FIG. 8, in the antenna device 51 of the present embodiment, the tips of the locking pieces 28, 29, 31 are brought into contact with the upper surface of the dielectric substrate 41, and the radiator 2 of the radiator 21 is contacted.
A space layer X having a predetermined thickness is formed between the upper layer 2 and the upper surface of the dielectric substrate 41.

Therefore, the space layer X suppresses the loss of radiated radio waves, thereby increasing the antenna gain. In the antenna device of the present embodiment shown in FIG. 8, as described above, on the side surface of the structure in which the radiator 32 is fixed to the dielectric substrate 41, the power supply terminal 25 as the power supply unit, the ground terminal 26, and the capacitance of the capacitance means. Terminal electrode 4 for switching
3 is formed, the bottom surface of the dielectric substrate 41 can be used for surface mounting on the printed circuit board.

Therefore, even though the antenna device 51 is a small-sized antenna device that can be surface-mounted on a printed circuit board, the frequency band can be switched by applying a "high" or "low" voltage from the terminal electrode 43. Can be provided.

FIG. 9 shows the reflection loss-frequency characteristics of the antenna device 51. In the reflection loss-frequency characteristics shown in FIG. 9, the frequency position shown by arrow A, that is, 1.670 G
Resonance points are shown at the position of Hz and the frequency position indicated by the broken arrow B, that is, the position of 1.770 GHz.
The resonance points indicated by the arrows A and B are the above-mentioned terminal electrodes 4
3 (input terminal 17 in the circuit diagram shown in FIG. 4) is applied by applying a “high” or “low” voltage, respectively. The characteristics shown in FIG. 9 show the case where +3 V is applied as the above “high” voltage and −3 V is applied as the “low” voltage, and the resistance R ₁ in FIG. 4 is 3.3 k.
Ω, resistance R ₂ = 47 kΩ, capacitance C ₁ = 1.0 pF, capacitance of capacitor C ₂ = 0.5 pF, capacitance D _x of diode D ₁ in OFF state C _x = 1.02 pF, inductance L
_This is the characteristic when the sum of ₁ and the inductance L ₂ = 6.055 mH.

As is apparent from FIG. 9, in this antenna device 51, when a "high" voltage is applied from the terminal electrode 43, the resonance frequency becomes 1.670 GHz, and the "low" voltage from the terminal electrode 43. When is applied, 1.
The resonant frequency will be switched to 770 GHz. Therefore, the antenna device 51 can be suitably used for a mobile communication device having a transmission frequency of 1.670 GHz and a reception frequency of 1.770 GHz.

FIG. 10 shows an arrangement according to the second embodiment of the present invention.
It is a circuit diagram of an antenna device. In the second embodiment,
Capacity C of the main body 11₁In parallel with the ground potential
Between the first capacitor C₂And diode D₁Alone
Without the second capacitor C₃Are connected. Sanawa
The capacitance means is a first capacitor connected in series with each other.
Sensor C₂, Diode D₁And the second capacitor C₃so
It is configured. And the first capacitor C₂And die
Aether D₁Connection point 61 between the diode D and₁And the
2 capacitors C₃Between the connection point 62 and
And the diode D ₁In parallel with R₂Is connected
Between the first connection point 61 and the pulse voltage supply terminal 63
Between resistance R₁Are connected. Also, the second connection point 6
2 is a second input terminal 64 for applying a pulse voltage
It is connected to the.

In the antenna device of the second embodiment, the above-mentioned pattern is used.
The negative voltage input terminals 63 and 64 have different polarities.
Pressure is applied. In addition, the + voltage is input to the input terminal 63.
If a negative voltage is applied to the input terminal 64, the
De D₁The voltage of the above different polarity so that
Is selected. Therefore, as described above, the input terminal 63
From the input terminal 64 is applied from the input terminal 64
By the diode D₁Is turned on, in which case
The capacitance of the capacitance means is the first capacitor C ₂Capacity
And the second capacitor C₃To be determined by the capacity of
become.

On the other hand, when switching to increase the resonance frequency of the antenna, the polarities of the voltages applied to the input terminals 63 and 64 are reversed. That is, + to the input terminal 64
Is applied to the input terminal 63, whereby the diode D ₁ is turned off. In this case, the capacitance of the capacitance means is equal to that of the first capacitor C ₂ and the second capacitor C ₂ .
Not only the capacitor C _{3 of the above} , but the capacitance of the diode D _{1 in} the non-conducting state is added. Therefore, as in the case of the first embodiment, by inverting the polarities of the voltages applied from the input terminals 63 and 64, the resonance frequency of the antenna device can be switched as in the first embodiment.

As described above, the first and second input terminals 6
In the second embodiment having Nos. 3 and 64, voltages of different polarities are input to the first and second input terminals 63 and 64. Such an input voltage is the output of the control unit that controls the antenna device. Can be suitably used.

The second capacitor C ₃ in the second embodiment is provided to separate the diode D ₁ from the ground potential when applying voltages having different polarities as described above.

In the antenna devices of the first and second embodiments,
Although the configuration has been described in which the resonance frequency of the antenna device is switched in two stages, the antenna device of the present invention can be configured so that the resonance frequency can be switched in multiple stages of three or more stages. For example, in the third embodiment shown in FIG. 11, a plurality of capacitance means and resonance frequency switching circuits shown in the first embodiment are connected to the antenna main body 11, whereby a plurality of resonance frequencies of 3 or more are provided. It is configured to be switched to a stage. Since the capacitance means and the resonance frequency switching circuit of each stage in the third embodiment are the same as those in the first embodiment, the same parts are designated by the same reference numerals and reference numbers. The detailed description is omitted by using the description given in the first embodiment.

As is apparent from FIG. 11, in the structure in which the plurality of capacitance means and the frequency switching circuit are connected to the antenna body 11, the capacitance of the connected capacitance means can be switched in multiple stages. It can be suitably used for communication devices having a large number of reception frequencies such as channels of a television receiver.

[Brief description of drawings]

FIG. 1 is a perspective view showing a conventional inverted F-type antenna.

FIG. 2 is a schematic diagram for explaining a bandwidth required for an antenna in a system in which a transmission frequency and a reception frequency are different.

FIG. 3 is a schematic block diagram of an antenna device of the present invention.

FIG. 4 is a circuit diagram of an antenna device according to an embodiment of the present invention.

FIG. 5 is a perspective view showing a radiator used in an embodiment of the present invention.

FIG. 6 is a perspective view showing a main part of an antenna device used in an embodiment of the present invention.

FIG. 7 is a partial cutaway sectional view for explaining a capacitor formed in the dielectric substrate of FIG.

FIG. 8 is a perspective view showing the outer appearance of the antenna device according to the embodiment of the present invention.

FIG. 9 is a reflection loss of the antenna device according to the embodiment of the present invention.
The figure which shows a frequency characteristic.

FIG. 10 is a circuit diagram of an antenna device according to a second embodiment of the present invention.

FIG. 11 is a circuit diagram of an antenna device according to a third embodiment of the present invention.

[Explanation of symbols]

11 ... antenna main body 12 ... capacitance means 13 ... switching means C ₁ ... diode C ₃ to form a capacitor D ₁ ... capacitance means for forming the capacitor C ₂ ... capacitance means having between the ground electrode of the antenna main body … Second capacitors L ₁ , L ₂ … Inductance component of the antenna body

Claims (4)

[Claims] 1. An antenna main body having a power feeding section and a portion connected to the ground potential, and an antenna main body and a ground potential so that the antenna main body is parallel to a capacitance between the antenna main body and the ground potential. An antenna device, which is connected between the capacitor device and the capacitor device for adding a capacitance, and a switching device for switching the value of the capacitance of the capacitor device in order to change the resonance frequency of the antenna device. . 2. The capacitance means includes a capacitor connected in series with each other and an element whose capacitance is changed, and the capacitance of the element whose capacitance is changed is changed.
The antenna device according to claim 1, wherein the switching means is connected to an element whose capacitance is changed. 3. The element whose capacitance is changed is a diode, and the switching means applies a first voltage or a second voltage for turning on or off the diode to a connection point between the capacitor and the diode. The antenna device according to claim 2, which is a voltage supply circuit. 4. The capacitance means includes a first capacitor,
A first capacitor connected in series with the diode; and a second capacitor connected in series with the diode, wherein the switching means has a first connection between the first capacitor and the diode. Point, the diode and the second
A voltage supply circuit configured to apply voltages of different polarities to the second connection point between the first and second capacitors and to invert the polarities of the voltages applied to the first and second connection points. The antenna device according to claim 1.