WO2008146123A1

WO2008146123A1 - Antenna unit

Info

Publication number: WO2008146123A1
Application number: PCT/IB2008/001297
Authority: WO
Inventors: Hiroki Okada
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2007-05-25
Filing date: 2008-05-23
Publication date: 2008-12-04
Anticipated expiration: 2009-11-25
Also published as: JP2008294822A

Abstract

An antenna unit (1) for transmitting and receiving radio waves has an antenna element (2), a dielectric (3) provided near the antenna element (2), and a relative permittivity control portion (4) that changes the relative permittivity of the dielectric (3).

Description

ANTENNAUNIT

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to an antenna unit, and more particularly to an antenna unit that is able to change the resonance frequency of its antenna element and thus is compatible with many different communication medias. The invention also relates to a radio wave transmission and reception method of such an antenna unit.

2. Description of the Related Art

[0002] In recent years, various radio systems have been used in motor vehicles. In general, such radio systems in a motor vehicle transmit and receive radio waves via corresponding antenna units provided at the rear window glass. The reason for providing such antenna units at the rear window glass is to ensure that the driver can have a clear view ahead of the vehicle. Defogger patterns are also provided at the rear window glass. Therefore, antenna units for transmitting and receiving radio waves other than those for AM radio (e.g., radio waves for FM radio and analog TV) are provided in a narrow region other than where the defogger patterns are provided.

[0003] Meanwhile, it is expected that additional antennas for radio waves for new medias (e.g., radio waves for digital TV and digital radio) will be mounted in such a narrow area. However, it is difficult to secure a sufficient space for so many antennas.

[0004] In the following, an example antenna unit provided in a window glass of a motor vehicle will be described. Japanese Patent Application Publication No. 2005-33475 (JP-A-2005-33475) describes an antenna unit having an antenna element provided on the passenger compartment side face of an window glass and a dielectric provided between the antenna element and the window glass. The antenna element is a conductive member for transmitting and receiving radio waves. When the relative permittivity of the dielectric is εl and the relative permittivity of air is εo, ε₁ > εo is true.

[0005] When a radio wave passes through a dielectric, the wave length of the radio wave shortens. As such, if a dielectric is provided between an antenna element and a window glass as described in JP-A-2005-33475, the antenna element can be made shorter than it is when the dielectric is not provided.

[0006] However, the antenna unit described in JP-A-2005-33475 involves the following drawback. That is, the relative permittivity of the antenna unit described in JP-A-2005-33475 can not be changed once it is set in position on or near the window glass, and thus the frequency range of the radio waves that the antenna unit transits and receives can not be changed after its installation, and therefore an antenna unit needs to be provided for each communication media. According to this structure, if there are many communication medias, it is difficult to secure a sufficient space for so many antenna units in a rear window glass of a vehicle.

SUMMARY OF THE INVENTION

[0007] The invention provides an antenna device capable of making its antenna element compatible with many different communication medias by changing the resonance frequency of the antenna element without changing its length and shape and thus suitable to be provided at a rear window glass of a motor vehicle, or the like.

[0008] The first aspect of the invention relates to an antenna unit for transmitting and receiving radio waves, having: an antenna element; a dielectric provided near the antenna element; and a relative permittivity control portion that changes the relative permittivity of the dielectric.

[0009] According to the antenna unit described above, the resonance frequency of the antenna element is changed by changing the relative permittivity of the dielectric. More specifically, the resonance frequency of the antenna element decreases as the relative permittivity of the dielectric is increased, and the resonance frequency of the antenna element increases as the relative permittivity of the dielectric is reduced. By thus changing the resonance frequency of the antenna element, the frequency range of radio waves that the antenna transmits and receives can be changed.

[0010] The above-described antenna unit may be such that the relative permittivity control portion is adapted to adjust the resonance frequency of the antenna element by changing the relative permittivity of the dielectric.

[0011] According to this structure, a single antenna element can be made comparable with many different communication medias by adjusting the resonance frequency of the antenna element.

[0012] Further, the above-described antenna unit may be such that the relative permittivity control portion is adapted to change the relative permittivity of the dielectric by creating at least one of an electric field or a magnetic field on the dielectric.

[0013] In this case, the capability of changing the relative permittivity of the dielectric can be obtained with a simple structure.

[0014] In the above-described antenna unit, the relative permittivity control portion may include at least a pair of electrodes and the dielectric may be interposed between the electrodes, and the relative permittivity control portion may further include a power source from which voltage is applied to the electrodes, and the relative permittivity control portion may be adapted to change the relative permittivity of the dielectric by adjusting the voltage applied to the electrodes.

[0015] In this case, too, the capability of changing the relative permittivity of the dielectric can be obtained with a simple structure.

[0016] Further, the relative permittivity control portion may be adapted to change the relative permittivity of the dielectric by creating at least one of an electric field or a magnetic field on the dielectric, and the antenna unit may further include: a data storage storing a map defining a relation between the resonance frequency of the antenna element and control voltage required to create at least one of an electric field or a magnetic field corresponding to the resonance frequency of the antenna element; and a resonance frequency setting portion that, when controlling the resonance frequency of the antenna element to a target value, extracts a value of the control voltage corresponding to the target value of the resonance frequency from the map stored in the data storage and sets the extracted control voltage value to the relative permittivity control portion.

[0017] According to the above structure, in response to a specific communication media or channel being selected by the user, the relative permittivity control portion creates an electric field or a magnetic field having an appropriate strength based on the map stored in the data storage, which defines the relation between the resonance frequency of the antenna element and the control voltage required to create at least one of an electric field or a magnetic field corresponding to the resonance frequency of the antenna element on the dielectric.

[0018] Further, the above-described antenna unit may include a substrate made of an insulating material, and the dielectric and the antenna element may be provided on the substrate.

[0019] Further, the above-described antenna unit may be provided at an window glass of a vehicle, such a motor vehicle.

[0020] In this case, even if there are many communication medias, it is possible to produce an antenna unit comparable with them and then mount it at a rear window glass (e.g., rear window glass) of a vehicle, such as a motor vehicle, properly.

[0021] The dielectric and the antenna element may be in contact with the window glass.

[0022] According to this structure, the distance between the antenna element and the dielectric is zero or is as short as the thickness of the window glass, and this ensures that the resonance frequency of the antenna element changes sufficiently in response to the relative permittivity of the dielectric being changed.

[0023] Further, the above-described window glass may be a laminated glass and the dielectric may be provided between two glasses constituting the laminated glass.

[0024] According to this structure, the dielectric is provided between two glasses. Therefore, the dielectric is prevented from coming off from the glasses or prevented from deforming, which minimizes the possibility of deterioration of the performance of the antenna unit. Further, because such a dielectric is normally mounted in a laminated glass during an assembly -process in a factory, the dielectric can be more accurately positioned to achieve high radio-wave transmission and reception efficiencies than when it is attached on a glass by an user after purchasing of his or her motor vehicle.

[0025] Further, the dielectric may be provided on a passenger compartment side face of the window glass.

[0026] According to this structure, the dielectric is not exposed to wind and rain, and therefore its degradation can be minimized.

[0027] Further, the dielectric may be made of liquid crystals.

[0028] According to this structure, the anisotropic relative permittivity of liquid crystals enables precise control of the relative permittivity of the dielectric.

[0029] The second aspect of the invention relates to a radio wave transmission and reception method for an antenna unit having an antenna element, including: providing a dielectric near the antenna element; and creating at least one of an electric field and a magnetic field on the dielectric.

[0030] The above-described method may further include: inputting a target value of the resonance frequency of the antenna element; extracting, from a map defining a relation between the resonance frequency of the antenna element and control voltage required to create at least one of an electric field or a magnetic field corresponding to the resonance frequency of the antenna element, a value of the control voltage corresponding to the input target value of the resonance frequency of the antenna element; and applying the extracted value of the control voltage to at least a pair of electrodes between which the dielectric is interposed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a view schematically showing the configuration of an antenna unit according to the first example embodiment of the invention;

FIG. 2 is a cross-sectional view cutting through the antenna unit in FIG. 1 along the line H-II;

FIG. 3 is a graph illustrating the relation between the voltage applied between the electrodes and the relative permittivity of the dielectric;

FIG. 4 is a view illustrating how the molecular orientation of liquid crystal varies as the voltage applied to the dielectric made of liquid crystal is changed gradually;

FIG. 5 is a view illustrating how the molecular orientation of liquid crystal varies as the voltage applied to the dielectric made of liquid crystal is changed gradually;

FIG. 6 is a view illustrating how the molecular orientation of liquid crystal varies as the voltage applied to the dielectric made of liquid crystal is changed gradually;

FIG. 7 is a graph illustrating the relation between the relative permittivity of the dielectric and the resonance frequency of the antenna element;

FIG. 8 is a view showing an example of a map stored in a data storage;

FIG. 9 is a cross-sectional view showing an example of an antenna unit according to the second example embodiment of the invention; and

FIG. 10 is a cross-sectional view showing another example of the antenna unit according to the second example embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Hereinafter, an antenna unit 1 according to the first example embodiment of the invention will be described with reference to the drawings. FIG. 1 is an elevation view schematically showing the structure of the antenna unit 1. FIG. 2 is a cross-sectional view cutting through the antenna unit 1 along the line H-II in FIG. 1.

[0033] The following description refers to an example in which the antenna unit 1 is provided at the rear window glass of a motor vehicle (i.e., so-called in-glass antenna). In this example, referring to FIG. 1, an window glass 5 is a laminated glass constituted of two glasses 6, 7. The antenna unit 1 is constituted of an antenna element 2, a dielectric 3. a relative permittivity control portion 4, a data storage 9, a resonance frequency setting portion 11, and an input portion 21.

[0034] As will be described in detail below, the antenna unit 1 is capable of changing the resonance frequency of the antenna element 2 without changing its length, and therefore the antenna unit 1 is compatible with many different communication medias.

[0035] The antenna element 2 is a conductive member for transmitting and receiving radio waves. The antenna element 2 is formed in a specific pattern corresponding to the frequencies of the radio waves that it transmits and receives. In the illustrated example, the antenna element 2 is provided on the outer face of the outer glass 7 (i.e., the face of the outer glass 7 on the outside of the vehicle). Note that the antenna element 2 may alternatively be provided on the inner face of the inner glass 6 (i.e., the face of the inner glass 6 on the passenger compartment side). The antenna element 2 is formed by, for example, being patterned directly on the surface of the window glass 5. The length of the antenna element 2 is, for example, one-fourth the wave length corresponding to the center frequency of the variable resonance frequency range for the antenna element 2. When the antenna element 2 has such a length, it is normally a mono-pole antenna.

[0036] The dielectric 3 is provided near the antenna element 2. This sentence "the dielectric 3 is provided near the antenna element 2" represents that the dielectric 3 is provided within a region around the antenna element 2 where as the relative permittivity of the dielectric 3 changes, the resonance frequency of the antenna element 2 changes. The type of the dielectric 3 is not specifically limited. For example, the dielectric 3 may be made of liquid crystals. Liquid crystals have an anisotropic relative permittivity (the relative permittivity in the lateral direction of a liquid crystal and that in the longitudinal direction of the liquid crystal are different). Thus, as the orientation of the liquid crystal molecules changes in an electric field, the relative permittivity of the liquid crystal portion changes accordingly. In the example embodiment of the invention, this characteristic of liquid crystals is utilized.

[0037] Liquid crystals include, for example, N_p liquid crystals (positive liquid crystals) and N_n liquid crystals (negative liquid crystals). If the lateral relative permittivity of a liquid crystal is εl and the longitudinal relative permittivity of the liquid crystal is denoted ε2, εl < ε2 is true for N_p liquid crystals, and εl > ε2 is true for N_n liquid crystals. The dielectric 3 may be made of either of them.

[0038] The relative permittivity control portion 4 changes the relative permittivity of the dielectric 3. More specifically, the relative permittivity control portion 4 changes the relative permittivity of the dielectric 3 by creating an electric filed or a magnetic field on the dielectric 3. The following is an example case where the relative permittivity control portion 4 is adapted to change the relative permittivity of the dielectric 3 by creating an electric field on the dielectric 3. Referring to FIG. 1 and FIG. 2, the relative permittivity control portion 4 includes at least a pair of electrodes 8a and 8b that are arranged with the dielectric 3 interposed therebetween, a power source 22 for applying voltage between the electrodes 8a and 8b, and an electric cable 23 by which the electrodes 8a, 8b are connected to the power source 22. The relative permittivity control portion 4 changes the relative permittivity of the dielectric 3 by changing the voltage applied between the electrodes 8a and 8b.

[0039] FIG. 3 is a graph representing the relation between the voltage applied between the electrodes 8a and 8b and the relative permittivity of the dielectric 3. In FIG. 3, the solid curve represents data for a dielectric the relative permittivity of which decreases as the applied voltage increases, while the dotted curve represents data for another dielectric the relative permittivity of which increases as the applied voltage increases. The dielectric 3 may be made of either of them.

[0040] As shown in FIG. 1 and FIG. 2, the electrodes 8a, 8b are provided at the end faces of the dielectric 3 which are opposite each other. This arrangement enables to create an electric field on the dielectric 3 in parallel to the principal plane of the dielectric 3. Because the dielectric 3 is made of liquid crystals, the orientation of liquid crystal molecules varies in accordance with the voltage applied between the electrodes 8a and 8d. FIG. 4 to FIG. 6 illustrate an example of such variation of the orientation of liquid crystal molecules. [0041] FIG. 4 to FIG. 6 are views illustrating how the orientation of liquid crystal molecules varies in response to the voltage on the dielectric 3 being changed gradually. Here, referring to FIG. 4, it is assumed that all the liquid crystal molecules are oriented such that their major axes extend vertically as viewed in the drawings when Vl (e.g., OV) is being applied between the electrodes 8a and 8b. Then, referring to FIG. 5, as the voltage applied between the electrodes 8a and 8b is increased to V2, all the liquid crystal molecules turn, so that their major axes extend diagonally as viewed in the drawings. Then, referring to FIG. 6, as the voltage applied between the electrodes 8a and 8b is further increased to V3, all the liquid crystal molecules further turn, so that their major axes extend laterally as viewed in the drawings.

[0042] As such, the orientation of the liquid crystal molecules can be changed by changing the voltage applied between the electrodes 8a and 8b. As the orientation of the liquid crystal molecules changes, the relative permittivity of the dielectric 3 (the entire liquid crystal portion) changes accordingly, and as the relative permittivity of the dielectric 3 changes, the resonance frequency of the antenna element 2 changes accordingly. This is how the resonance frequency of the antenna element 2 is adjusted.

[0043] The graph of FIG. 7 illustrates the relation between the relative permittivity of the dielectric 3 and the resonance frequency of the antenna element 2. As is evident from this graph, the resonance frequency of the antenna element 2 decreases as the relative permittivity of the dielectric 3 increases.

[0044] The data storage 9 stores a map 10 (Refer to FIG. 8).

[0045] The map shown in FIG. 8 is one example of the map 10 stored in the data storage 9. Referring to^' FIG. 8, the map 10 defines the relation between the target value of the resonance frequency f_RES of the antenna element 2 and the value of voltage needed to be applied between the electrodes 8a and 8b to achieve the target value of the resonance frequency f_REs (will hereinafter be referred to as "control voltage V" where necessary), and so on.

[0046] The control voltage V changes in accordance with the target value of the resonance frequency f_REs and differs depending upon whether the relative permittivity control portion 4 is adapted to create an electric field or a magnetic field on the dielectric 3. In the case where the relative permittivity control portion 4 is adapted to create an electric field on the dielectric 3, the control voltage V is applied between the electrodes 8a and 8b shown in FIG. 1 and FIG. 2 (Refer to FIG. 8). On the other hand, in the case where the relative permittivity control portion 4 is adapted to create a magnetic field on the dielectric 3, the control voltage V is applied to an electromagnet coil (not shown in the drawings) provided near the dielectric 3.

[0047] In addition to the resonance frequency f_REs and the control voltage V, the map 10 may include information regarding the channel, control bit, and relative permittivity corresponding the resonance frequency f_REs and the control voltage V, and so on.

[0048] An input portion 21 is a portion to which an user (driver) inputs a request for selecting the communication media type or the channel. The structure of the input portion 21 is not specifically limited herein. For example, the input portion 21 may be a touch-panel type input portion.

[0049] In order to set the resonance frequency f_REs to the value corresponding to the communication media or channel selected by the user (will be referred to as "target resonance frequency fREs")_> the resonance frequency setting portion 11 extracts the value of the control voltage V corresponding to the target resonance frequency fβ_Es from the data storage 9 and sets the extracted value of the control voltage V to the relative permittivity control portion 4.

[0050] As such, owing to the data storage 9 and the resonance frequency setting portion 11, when the communication media or the channel is selected by the user, the relative permittivity control portion 4 creates an electric field or a magnetic filed with an appropriate strength using the map 10 on the dielectric 3.

[0051] Next, the operation of the antenna unit 1 of the first example embodiment will be described with reference to FIG. 1, FIG. 2, and FIG. 8. First, the user selects a desired communication media and selects a desired channel in the same communication media. Assuming that the user has just selected analog TV and channel 2 of the analog TV, the resonance frequency setting portion 11 first extracts, from the map 10 stored in the data storage 9, the value of the resonance frequency fβ_Es corresponding to channel 2 of analog TV and the value of the control voltage V needed to be applied between the electrodes 8a and 8b to achieve said value of the resonance frequency f_REs.

[0052] Subsequently, the resonance frequency setting portion 11 sets the extracted value of the control voltage V to the relative permittivity control portion 4, whereby voltage corresponding to channel 2 of analog TV is applied between the electrodes 8a and 8b. As the voltage is applied between the electrodes 8a and 8b, an electric field corresponding to channel 2 of analog TV is created on the dielectric 3. As the electric field is created on the dielectric 3, the relative permittivity of the dielectric 3 changes, so that the resonance frequency f_REs of the antenna element 2 changes to the frequency for channel 2 of analog TV which has been selected by the user. This is how the antenna unit 1 is set to receive the radio wave for the selected channel of the selected communication media.

[0053] The user can change the communication media or the channel by operating the input portion 21. For example, in the case where the user has newly selected A station of digital radio, the resonance frequency setting portion 11 extracts the value of the resonance frequency f_REs corresponding to the A station of the digital radio and the corresponding voltage to be applied between the electrodes 8a and 8b from the map 10 stored in the data storage 9. Then, as in the order described above, the relative permittivity of the dielectric 3 is changed, so that the resonance frequency f_REs of the antenna element 2 is changed to the frequency for the A station of the digital radio which has been selected by the user. This is how the antenna unit 1 is set to receive the ratio wave for the newly selected channel of the newly selected communication media.

[0054] As described above, the antenna unit 1 of the first example embodiment of the invention is capable of changing the resonance frequency range of the antenna element 2. Thus, the single antenna element 2 can be made compatible with many different communication medias. Thus, the antenna unit 1 is suitable to be provided at the rear glass of a motor vehicle, or the like. Further, the capability of changing the resonance frequency of the antenna element 2 eliminates the necessity of reducing the antenna gain when switching the communication media or the chancel to be received, and therefore the receiver sensitivity is always high regardless of which communication media or which channel is received.

[0055] Further, the antenna unit 1 may be adapted to change its radio wave transmission frequency by changing the resonance frequency f_REs of the antenna element 2 as in the foregoing structure for receiving radio waves. That is, the antenna unit 1 can be effectively used to transmit and receive radio waves for mobile phones, etc. When the antenna unit 1 is used for radio wave transmission and reception for mobile phones, etc, a glass substrate, or other insulator, may be used as a substrate for the antenna element 2 and the dielectric 3 instead of the window glass 5.

[0056] According to the first example embodiment of the invention, as described above, the resonance frequency of the antenna element 2 can be changed without changing its length. That is, the resonance frequency of the antenna element 2 can be changed without substantially changing the inpedance of the antenna element 2. Therefore, impedance matching can be performed without providing a circuit for impedance matching with coaxial cables, the transmitter, and the receiver, or by providing only a simple impedance matching circuit.

[0057] Hereinafter, an antenna unit according to the second example embodiment of the invention will be described with reference to the drawings. The cross-sectional view of FIG. 9 shows an example of the antenna unit of the second example embodiment. The cross-sectional view of FIG. 10 shows another example of the antenna unit of the second example embodiment. It is to be noted that the elements and structures identical to those of the antenna unit of the first example embodiment are denoted by the same numerals and their descriptions are not repeated again.

[0058] As described above, the dielectric 3 is provided in the laminated glass in the antenna unit 1 of the first example embodiment. Meanwhile, in the antenna unit 14 of the second example embodiment shown in FIG. 9, a dielectric 12 and electrodes 17a and 17b of a relative permittivity control portion 16 are provided on the passenger compartment side face of an window glass 13. While the antenna unit 14 is provided in a non-laminated glass, not a laminated glass, in the example illustrated in FIG. 9, the antenna unit 14 may alternatively be provided in a laminated glass. In the case where the antenna unit 14 is provided in a laminated glass, the antenna unit 14 may be provided on, for example, on the passenger compartment side face of the inner glass of the laminated glass.

[0059] In the second example embodiment, an antenna element 15 may either be provided on the passenger compartment side face or the outside face of the window glass 13. In the example illustrated in FIG. 9, the antenna element 15 is provided on the passenger compartment side face of the window glass 13. If the antenna element 15 is provided on the passenger compartment side face of the window glass 13, in view of the antenna gain, the antenna element 15 is preferably provided between the window glass 13 and the dielectric 12 as it is in the illustrated example. On the other hand, in the example illustrated in FIG. 10, an antenna element 18 is provided on the outside face of the window glass 13. Note that the input portion 21, the data storage 9, and the resonance frequency setting portion 11 may be provided in the antenna unit 1 of the second example embodiment as in the antenna unit 1 of the first example embodiment.

[0060] As such, the antenna units 14 and 19 of the second example embodiment can change the resonance frequency Ϊ_RES of each antenna element 15 and 18 as the antenna unit 1 of the first example embodiment does. Thus, the single antenna element 15, 18 can be used to receive radio waves for many different communication medias. Therefore, each antenna unit 14, 19 is suitable to be provided at the rear glass of a motor vehicle, or the like.

[0061] Note that the dielectric 3 in the first example embodiment and the dielectric 12 in the second example embodiment are not necessarily made of liquid crystals. For example, they may alternatively be made of a magnetic material (e.g., magnetic fluid) the relative permittivity of which changes in a magnetic field.

[0062] For example, the antenna units of the invention can be advantageously used as in-glass antenna units for motor vehicles, and the like.

[0063] While the invention has been described with reference to what are considered to be preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within scope of the invention.

Claims

1. An antenna unit for transmitting and receiving radio waves, characterized by comprising: an antenna element; a dielectric provided near the antenna element; and a relative permittivity control portion that changes the relative permittivity of the dielectric.

2. The antenna unit according to claim 1, wherein the relative permittivity control portion is adapted to adjust the resonance frequency of the antenna element by changing the relative permittivity of the dielectric.

3. The antenna unit according to claim 1 or 2, wherein the relative permittivity control portion is adapted to change the relative permittivity of the dielectric by creating at least one of an electric field or a magnetic field on the dielectric.

4. The antenna unit according to any one of claims 1 to 3, wherein the relative permittivity control portion includes at least a pair of electrodes between which the dielectric is interposed.

5. The antenna unit according to claim 4, wherein: the relative permittivity control portion includes a power source from which voltage is applied to the electrodes; and the relative permittivity control portion is adapted to change the relative permittivity of the dielectric by adjusting the voltage applied to the electrodes.

6. The antenna unit according to claim 2, wherein the relative permittivity control portion is adapted to change the relative permittivity of the dielectric by creating at least one of an electric field or a magnetic field on the dielectric, the antenna unit further comprising: a data storage storing a map defining a relation between the resonance frequency of the antenna element and control voltage required to create the at least one of an electric field or a magnetic field corresponding to the resonance frequency of the antenna element on the dielectric; and a resonance frequency setting portion that, when controlling the resonance frequency of the antenna element to a target value, extracts a value of the control voltage corresponding to the target value of the resonance frequency from the map stored in the data storage and sets the extracted control voltage value to the relative permittivity control portion.

7. An antenna unit according to any one of claims 1 to 6, further comprising: a substrate made of an insulating material, wherein the dielectric and the antenna element are provided on the substrate.

8. An antenna unit according to any one of claims 1 to 6, wherein the antenna unit is provided at an window glass of a vehicle.

9. The antenna unit according to claim 8, wherein the dielectric and the antenna element are in contact with the window glass.

10. The antenna unit according to claim 9, wherein: the window glass is a laminated glass; and the dielectric is provided between two glasses constituting the laminated glass.

11. The antenna unit according to claim 9, wherein the dielectric is provided on a passenger compartment side face of the window glass.

12. The antenna unit according to any one of claims 1 to 11, wherein the dielectric is made of liquid crystals.

13. A radio wave transmission and reception method for an antenna unit having an antenna element, characterized by comprising: providing a dielectric near the antenna element; and creating at least one of an electric field and a magnetic field on the dielectric.

14. The radio wave transmission and reception method according to claim 13, further comprising: inputting a target value of the resonance frequency of the antenna element; extracting, from a map defining a relation between the resonance frequency of the antenna element and control voltage required to create at least one of an electric field or a magnetic field corresponding to the resonance frequency of the antenna element, a value of the control voltage corresponding to the input target value of the resonance frequency of the antenna element; and applying the extracted value of the control voltage to at least a pair of electrodes between which the dielectric is interposed.