JP2006060384A - Variable frequency type antenna and wireless communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable frequency type antenna providing temperature compensation without narrowing a variable range of a resonance frequency by using a base body formed of a material having temperature characteristics reverse to temperature characteristics of a varicap diode etc., and also to provide a wireless communication device. <P>SOLUTION: The variable frequency type antenna 1 comprises a radiation electrode 2, the base body 3, and a frequency varying circuit 4. The frequency varying circuit 4 has the varicap diode 40 and can vary the resonance frequency of the radiation electrode 2 by varying a control voltage V applied to the varicap diode 40. The base body 3 is formed of a dielectric whose dielectric constant decreases according as temperature rises. Consequently, a decrement (or an increment) of the resonance frequency accompanying a rise (or a fall) in temperature of the varicap diode 40 can be compensated with an increase (or a decrease) of the resonance frequency accompanying a temperature rise (or a fall) in dielectric constant of the base body 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a variable frequency antenna and a wireless communication device capable of adjusting a resonance frequency, and more particularly to a variable frequency antenna and a wireless communication device having a temperature compensation function.

Conventionally, as this type of variable frequency antenna, for example, there are technologies disclosed in Patent Document 1 and Patent Document 2.
FIG. 10 is a schematic diagram showing the electrical configuration of these conventional variable frequency antennas.
As shown in FIG. 10, this frequency variable antenna is a planar antenna, and the varicap diode 101 is connected to the radiating electrode 100 of the inverted F antenna, and the voltage applied to the RFC 102 is changed to change the frequency of the radiating electrode 100. The resonance frequency can be changed. Furthermore, a temperature compensating capacitor 103 is connected in series with the varicap diode 101 so as to suppress temperature fluctuation of the resonance frequency. Specifically, since the capacitance value of the varicap diode 101 increases as the temperature rises, by connecting the capacitor 103 whose capacitance value decreases as the temperature rises, the entire capacitance value of the capacitor 103 and the varicap diode 101 is the expected value. The temperature fluctuation of the resonance frequency is suppressed so as not to deviate from the above.

JP 09-307344 A Japanese Patent Laid-Open No. 10-028013

However, the conventional frequency variable antenna described above has the following problems.
The capacitor 103 changes a capacitance value with respect to a temperature change, and does not change the capacitance value due to a change in voltage applied via the RFC 102. On the other hand, the varicap diode 101 has a function of greatly changing the capacitance value by changing the applied voltage. Therefore, even if the voltage applied to the varicap diode 101 is changed in a certain constant temperature state, the capacitance value of the capacitor 103 is fixed, and only the capacitance value of the varicap diode 101 changes.
By the way, if the capacitor 103 connected in series with the varicap diode 101 is not a value close to the capacitance value of the varicap diode 101, the object of compensating for the temperature change of the varicap diode 101 cannot be achieved. Therefore, as described above, if the capacitance value of the capacitor 103 is a fixed value, a change in the capacitance value of the capacitor 103 cannot be increased, and as a result, the variable range of the resonance frequency becomes narrow. is there.

  The present invention has been made in order to solve the above-described problems. By using a substrate formed of a material having a temperature characteristic opposite to that of the varicap diode, the variable range of the resonance frequency can be reduced. An object of the present invention is to provide a variable frequency antenna and a wireless communication device that can perform temperature compensation.

In order to solve the above problems, the invention according to claim 1 changes a voltage applied to a radiating electrode having a power feeding portion and formed on a substrate, and a varicap diode electrically connected to the radiating electrode. Thus, a variable frequency antenna having a frequency variable circuit that changes the resonance frequency of the radiation electrode by changing the capacitance value of the varicap diode, and the dielectric constant of the base decreases with increasing temperature. By forming it with a dielectric material, the resonance frequency drop due to the increase in the capacitance value of the varicap diode with temperature rise is offset by the increase in resonance frequency due to the decrease in dielectric constant due to temperature rise. .
With this configuration, when a high-frequency signal having a resonance frequency is sent from the power feeding unit to the radiation electrode, the high-frequency signal is radiated from the radiation electrode as a radio wave. Further, the resonance frequency of the radiation electrode can be changed by changing the voltage applied to the varicap diode of the frequency variable circuit. By the way, when the temperature rises, the capacitance value of the varicap diode of the frequency variable circuit increases, and the resonance frequency of the radiation electrode may decrease. However, in the present invention, the base is formed of a dielectric whose dielectric constant decreases in response to a temperature rise, so that when the temperature rises, the dielectric constant of the base decreases and acts to increase the resonance frequency. . As a result, the increase in the resonance frequency cancels the decrease in the resonance frequency due to the increase in the capacitance value of the varicap diode, and the temperature variation of the resonance frequency is suppressed.

In the invention of claim 2, the radiation electrode is formed in a planar shape, the feeding portion is formed of the first electrode disposed on the base in the vicinity of the radiation electrode, and the frequency variable circuit is disposed in the vicinity of the radiation electrode. The second electrode arranged on the base is connected to the second electrode.
With this configuration, it is possible to form a frequency variable type planar antenna.

In the invention of claim 3, the radiation electrode is formed in a loop shape, the base part of the radiation electrode is used as a power supply part, and the tip part of the radiation electrode is arranged opposite to the power supply part with a certain gap, and a frequency variable circuit is provided. The configuration is such that it is disposed on the loop path of the radiation electrode.
With this configuration, a variable frequency hula hoop antenna can be formed.

According to a fourth aspect of the present invention, there is provided a radiation electrode which is formed in a loop shape on a base body with a base portion as a power feeding portion and whose front end portion is opposed to the power feeding portion with a certain gap, and on a loop path of the radiation electrode. A frequency variable circuit comprising a frequency variable circuit for changing a resonance frequency of the radiation electrode by changing a capacitance value of the varicap diode by changing a voltage applied to the varicap diode interposed and electrically connected to the radiation electrode. By providing a dielectric whose dielectric constant decreases in response to a rise in temperature in the gap between the feeding part and the tip of the radiation electrode, the capacitance of the varicap diode increases with the rise in temperature. The structure is such that the decrease in the resonance frequency is offset by the increase in the resonance frequency due to the decrease in the dielectric constant of the dielectric as the temperature rises.
With this configuration, when the temperature rises, the capacitance value of the varicap diode increases and attempts to lower the resonance frequency. However, in the gap between the feeding portion and the tip of the radiation electrode, a dielectric is formed corresponding to the temperature rise. Since the dielectric whose rate decreases is provided, the capacitance between the gaps decreases as the temperature rises, and acts to increase the resonance frequency. As a result, the decrease in the resonance frequency due to the increase in the capacitance value of the varicap diode due to the temperature rise is canceled out, and the temperature fluctuation of the resonance frequency is suppressed.

  According to a fifth aspect of the present invention, there is provided a radio communication apparatus comprising the variable frequency antenna according to any one of the first to fourth aspects.

  As described above in detail, according to the variable frequency antenna according to the first to third aspects of the present invention, the temperature compensation is performed by utilizing the temperature characteristics of the substrate. Such a separate capacitor is not required, and the number of parts can be reduced. Further, since the fixed capacitance capacitor is not required, there is no restriction on the variable range of the capacitance value of the varicap diode, and as a result, there is an excellent effect that the resonance frequency can be changed in a wide band.

  According to the variable frequency antenna according to the fourth aspect of the present invention, the temperature compensation function can be obtained simply by providing a dielectric whose dielectric constant decreases in response to a temperature rise in the gap between the feeding portion and the tip of the radiation electrode. Therefore, it is easy to add a temperature compensation function. As a result, the cost of the product can be reduced.

  Further, according to the wireless communication device of the invention of claim 5, since the variable frequency antenna according to any of claims 1 to 4 is provided, stable communication can be performed in a wide frequency band. it can.

  The best mode of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway perspective view showing a wireless communication device having a variable frequency antenna according to a first embodiment of the present invention.
As shown in FIG. 1, the wireless communication device has a structure in which the variable frequency antenna 1 of this embodiment is attached to a circuit board 11 housed in a case 10.
Specifically, a ground region 11a and a non-ground region 11b are provided on the surface of the circuit board 11 (front side surface in FIG. 1), and a BB portion (baseband portion) necessary for wireless communication is indicated by a one-dot chain line. 12 and an RF unit (high frequency transmission / reception unit) 13 are mounted on the ground region 11 a and serve as a power feeding means for the frequency variable antenna 1.

The variable frequency antenna 1 is attached to the non-ground region 11b of the circuit board 11 as described above.
FIG. 2 is an enlarged perspective view showing the variable frequency antenna 1, and FIG. 3 is a plan view showing an expanded peripheral surface of the variable frequency antenna 1.
As shown in FIGS. 2 and 3, the frequency variable antenna 1 is a planar antenna and includes a radiation electrode 2, a base 3, and a frequency variable circuit 4.

  The radiation electrode 2 has a rectangular planar shape, and is formed on the upper surface 30 of the dice base 3. Reference numeral 20 denotes a power feeding unit for the radiation electrode 2, and the power feeding unit 20 is a long electrode (first electrode) formed across the upper surface 30 and the side surface 31 of the base 3. The power feeding unit 20 has a tip provided close to the radiation electrode 2 with a predetermined gap, and a predetermined capacity is secured between the radiation electrode 2 and the power feeding unit 20.

The frequency variable circuit 4 is a circuit that can change the resonance frequency of the radiation electrode 2, and is interposed between the radiation electrode 2 and the ground region 11a. Specifically, a long electrode (second electrode) 21 is formed across the upper surface 30 and the side surface 32 of the base 3, and this electrode 21 is a radiation electrode with the tip thereof having a predetermined gap. 2, a predetermined capacity is secured between the radiation electrode 2 and the electrode 21. The frequency variable circuit 4 is connected to such an electrode 21.
That is, as shown in FIG. 3, the frequency variable circuit 4 includes a varicap diode 40, the cathode side of the varicap diode 40 is connected to the electrode 21, and the anode side is grounded to the ground region 11a. A high frequency choke coil component 41 is connected to the cathode side of the varicap diode 40. With this structure, by changing the control voltage V applied to the varicap diode 40 through the high frequency choke coil component 41, the capacitance value of the varicap diode 40 changes, the electrical length of the radiating electrode 2 changes, and the radiating electrode 2 The resonance frequency also changes corresponding to the capacitance value.

In the varicap diode 40 as described above, when the ambient temperature rises (or falls), the capacitance value of the varicap diode 40 also increases (or decreases) correspondingly. The resonance frequency of the radiation electrode 2 becomes lower (or higher) as the capacitance value of the varicap diode 40 increases (or decreases). Therefore, when the ambient temperature changes, the resonance frequency of the radiation electrode 2 changes from the desired value. It will shift.
Therefore, in this embodiment, the substrate 3 is provided with a temperature compensation function for suppressing fluctuations in the resonance frequency.
That is, the substrate 3 is formed of a dielectric whose dielectric constant decreases in response to a temperature rise. Here, a dielectric that can control the fluctuation of the resonance frequency is used even if the same material is changed by changing the mixing ratio. In the radiation electrode 2, a wavelength shortening effect is generated by the dielectric constant of the substrate 3, and the higher the dielectric constant, the lower the resonance frequency of the radiation electrode 2. Therefore, by forming the base body 3 with a dielectric material whose dielectric constant decreases in response to the temperature rise, it is possible to obtain the radiation electrode 2 whose resonance frequency increases with the temperature rise of the base body 3.

FIG. 4 is a diagram for explaining the temperature compensation function of the substrate 3.
As indicated by the broken characteristic line S4 in FIG. 4, it is assumed that the resonance frequency of the varicap diode 40 with respect to the temperature change decreases with the inclination θ. In this case, as shown by the solid characteristic line S3, a dielectric having a dielectric constant whose inclination of the resonance frequency with respect to a temperature change increases by θ is adopted as the base 3.
As a result, as shown by a point P, when the resonance frequency is the desired value f0 at the temperature T0, when the temperature rises to “T1”, the resonance frequency becomes as shown by the point P1 on the characteristic line S4. As the temperature of the varicap diode 40 increases, it tends to decrease by “Δf”. However, as indicated by a point P2 on the characteristic line S3, the resonance frequency tends to increase by “Δf” as the temperature of the substrate 3 rises. Therefore, the resonance frequency decreases as the temperature of the varicap diode 40 increases. The increase in the resonance frequency accompanying the temperature rise of the base 3 is canceled out, and the resonance frequency is maintained at the desired value f0 as indicated by a point p3.

The operation and effect of this embodiment will be described.
FIG. 5 is a diagram for explaining a wide band using a variable frequency antenna.
When a high-frequency signal is sent from the RF unit 13 shown in FIG. 1 to the radiation electrode 2 through the power feeding unit 20 of the variable frequency antenna 1, the high-frequency signal is radiated from the radiation electrode 2 as a radio wave at a predetermined resonance frequency.
Further, the resonant frequency of the radiation electrode 2 can be changed by changing the control voltage V applied to the varicap diode 40 of the frequency variable circuit 4. Specifically, by changing the control voltage V applied to the varicap diode 40 of the frequency variable circuit 4, the resonance frequency of the radiation electrode 2 is changed from the frequency f0 to the frequencies f1, f2, f3, as shown in FIG. It can be changed to f4. Therefore, when the frequency variable circuit 4 is not used, the frequency bandwidth of the frequency variable antenna 1 is the narrow bandwidth h that the radiation electrode 2 has. On the other hand, when the frequency variable circuit 4 is used, The communicable frequency band becomes a wide bandwidth H corresponding to the variable width of the resonance frequency of the radiation electrode 2, and the frequency variable antenna 1 can be widened.

By the way, when the temperature of the varicap diode 40 of the frequency variable circuit 4 rises, the capacitance value of the varicap diode 40 increases and the resonance frequency of the radiation electrode 2 may be lower than the desired value f0. However, as described with reference to FIG. 4, in this embodiment, the decrease in the resonance frequency due to the increase in the capacitance value of the varicap diode 40 due to the temperature rise is offset by the increase in the resonance frequency due to the substrate 3. Is suppressed, and the resonance frequency of the radiation electrode 2 is maintained at the desired resonance frequency f0.
As described above, according to the variable frequency antenna 1 of this embodiment, the temperature compensation is performed using the temperature characteristics of the base 3, so that a separate capacitor such as a conventional variable frequency antenna is required. And not. Therefore, the number of parts can be reduced accordingly. Further, since the fixed capacitance capacitor is not required, the variable range of the capacitance value of the varicap diode 40 is not limited, and the resonance frequency can be changed in a wide band as shown in FIG.
As a result, stable communication can be performed in a wide frequency band by using a wireless communication device including the variable frequency antenna 1 of this embodiment.

Next explained is the second embodiment of the invention.
FIG. 6 is a perspective view showing a variable frequency antenna according to a second embodiment of the present invention, and FIG. 7 is a circuit diagram showing a variable frequency circuit applied to the second embodiment.
The variable frequency antenna 1-1 of this embodiment is a hula hoop antenna, and the radiation electrode 2 is formed in a loop shape. Specifically, as shown in FIG. 6, the radiation electrode 2 is formed on the base 3 in an outward loop shape (inverted C shape), and the base of the radiation electrode 2 is used as the power feeding unit 20. And the front-end | tip part 22 of the radiation electrode 2 was opposingly arranged in the vicinity of the electric power feeding part 20, and the fixed gap G was provided between these electric power feeding parts 20 and the front-end | tip part 22, and was made into the capacitive coupling state.

  The substrate 3 on which the radiation electrode 2 is formed is formed of a dielectric whose dielectric constant decreases in response to a temperature rise, as in the first embodiment.

Further, the frequency variable circuit 4 is interposed on the loop path of the radiation electrode 2 at a position close to the power feeding unit 20.
In this embodiment, as shown in FIG. 7, the variable frequency circuit 4 includes a chip capacitor component 42 and a chip inductor component 43 connected in series to the radiation electrode 2, and a varicap diode 40 is connected to the chip capacitor component 42 and the chip inductor. The structure is such that the parts 43 are connected in parallel to the series connection body. With this structure, the resonance frequency of the radiation electrode 2 can be changed by changing the control voltage V applied to the varicap diode 40.

Also in this embodiment, the dielectric substrate 3 has a temperature compensation function for the varicap diode 40, as in the first embodiment. In this embodiment, however, the varicap diode 40 and A frequency variable circuit 4 including a high-frequency choke coil component 41, a chip capacitor component 42, and a chip inductor component 43 is interposed in the loop-shaped radiation electrode 2, and the frequency variable circuit 4 is close to the power feeding unit 20 having a large current distribution. Since it is arranged at a position, the resonance frequency of the radiation electrode 2 can be changed in a wider range than in the first embodiment.
Since other configurations, operations, and effects are the same as those in the first embodiment, description thereof is omitted.

Next explained is the third embodiment of the invention.
FIG. 8 is a perspective view showing a variable frequency antenna according to a third embodiment of the present invention, and FIG. 9 is a cross-sectional view taken along line AA in FIG.
The frequency variable antenna of this embodiment is also a hula hoop antenna as in the second embodiment, but differs from the second embodiment in that temperature compensation is performed not by the substrate but by another temperature compensating member.

That is, as shown in FIG. 8, the variable frequency antenna 1-2 includes a loop-shaped radiation electrode 2 having a gap G between the tip portion 22 and the power feeding portion 20, and the frequency variable circuit of the second embodiment. The radiation electrode 2 and the frequency variable circuit 4 are formed on a dielectric substrate 3 'whose dielectric constant does not depend on the temperature rise.
Then, the temperature compensating member 5 was placed between the power feeding unit 20 and the tip 22 as shown by a two-dot chain line in FIG. Here, the temperature compensating member 5 is formed of a dielectric whose dielectric constant decreases in response to a temperature rise. As shown in FIG. 9, the temperature compensation member 5 is pasted in a state where it is in contact with the power feeding portion 20 and the tip portion 22. However, since the capacitance value of the gap G portion is changed more positively, The member 5 was pasted only on the gap G.

  With such a configuration, when the temperature rises, the capacitance value of the varicap diode 40 of the frequency variable circuit 4 increases and attempts to lower the resonance frequency. On the other hand, as the temperature rises, the dielectric constant of the temperature compensating member 5 decreases. Accordingly, as the temperature rises, the capacitance between the gaps G between the power feeding unit 20 and the tip 22 becomes smaller and acts to increase the resonance frequency. As a result, the decrease in the resonance frequency due to the increase in the capacitance value of the varicap diode 40 due to the temperature rise is offset by the increase in the resonance frequency due to the decrease in the capacitance value between the gaps G, and the temperature fluctuation of the resonance frequency is suppressed. It becomes.

As described above, according to the variable frequency antenna 1-2 of this embodiment, the temperature compensation function can be obtained only by providing the temperature compensating member 5 having a small and simple structure between the power feeding portion 20 and the tip portion 22. Therefore, it is easy to add a temperature compensation function, and the cost of the product can be reduced accordingly.
Other configurations, operations, and effects are the same as those in the first and second embodiments, and thus description thereof is omitted.

In addition, this invention is not limited to the said Example, A various deformation | transformation and change are possible within the range of the summary of invention.
For example, in the above-described embodiments, examples of planar antennas and hula-hoop antennas have been shown and described. However, the present invention can of course be applied to any surface-mounted antenna having a dielectric as a base.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway perspective view showing a wireless communication device including a variable frequency antenna according to a first embodiment of the present invention. It is a perspective view which expands and shows a frequency variable type antenna. It is a top view which expand | deploys and shows the surrounding surface of a frequency variable type | mold antenna. FIG. 4 is a diagram for explaining a temperature compensation function of a substrate 3. It is a diagram for demonstrating the broadening by a frequency variable type | mold antenna. It is a perspective view which shows the frequency variable type antenna which concerns on 2nd Example of this invention. It is a circuit diagram which shows the frequency variable circuit applied to 2nd Example. It is a perspective view which shows the frequency variable type antenna which concerns on 3rd Example of this invention. It is arrow AA sectional drawing of FIG. It is the schematic which shows the electrical structure of the conventional frequency variable type | mold antenna.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1-1,1-2 ... Frequency variable type antenna, 2 ... Radiation electrode, 3, 3 '... Base | substrate, 4 ... Frequency variable circuit, 5 ... Temperature compensation member, 10 ... Case, 11 ... Circuit board, 11a ... ground area, 11b ... non-ground area, 12 ... BB part, 13 ... RF part, 20 ... feeding part, 21 ... electrode, 22 ... tip part, 30 ... upper surface, 31 ... side face, 32 ... side face, 40 ... varicap Diode: 41 ... high frequency choke coil component, 42 ... chip capacitor component, 43 ... chip inductor component.

Claims (5)

The capacitance value of the varicap diode is changed by changing the voltage applied to the radiating electrode having a power feeding portion and formed on the substrate and the varicap diode electrically connected to the radiating electrode. A variable frequency antenna having a frequency variable circuit that changes a resonance frequency of an electrode;
By forming the substrate with a dielectric whose dielectric constant decreases in response to a temperature rise,
A structure in which a decrease in resonance frequency due to an increase in capacitance value of the varicap diode due to a temperature rise is offset by an increase in resonance frequency due to a decrease in the dielectric constant of the dielectric due to temperature rise,
This is a variable frequency antenna. The radiating electrode is formed in a planar shape, and the feeding portion is formed of a first electrode disposed on the base in the vicinity of the radiating electrode,
The frequency variable circuit was connected to a second electrode disposed on the base in proximity to the radiation electrode.
The frequency variable antenna according to claim 1, wherein: The radiating electrode is formed in a loop shape, the base of the radiating electrode is used as the feeding portion, and the tip of the radiating electrode is arranged opposite to the feeding portion in the vicinity of the feeding portion,
The frequency variable circuit is interposed on the loop path of the radiation electrode.
The frequency variable antenna according to claim 1, wherein: A radiation electrode which is formed in a loop shape on the base body with the base portion as a power feeding portion, and whose tip is opposed to the power feeding portion in the vicinity of the power feeding portion, and a radiation electrode interposed on the loop path of the radiation electrode. A variable frequency antenna comprising a frequency variable circuit that changes a capacitance value of a varicap diode by changing a voltage applied to a varicap diode electrically connected to the varicap diode and changes a resonance frequency of the radiation electrode. ,
By providing a dielectric whose dielectric constant decreases in response to a temperature rise in the gap between the feeding portion and the tip of the radiation electrode,
A structure in which a decrease in resonance frequency due to an increase in capacitance value of the varicap diode due to a temperature rise is offset by an increase in resonance frequency due to a decrease in the dielectric constant of the dielectric due to temperature rise,
This is a variable frequency antenna. The frequency variable antenna according to any one of claims 1 to 4, comprising:
A wireless communication device.

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