Antenna apparatus

In an antenna apparatus, a radiation element includes a perturbation element. A first power feeding line has a first end connected to the radiation element and is configured to feed power to the radiation element. A second power feeding line has a first end configured to feed power to the radiation element through electromagnetic coupling. The radiation element, the first power feeding line and the second power feeding line are arranged on a same plane to constitute a balance type antenna.

BACKGROUND

The present invention is related to an antenna apparatus. More specifically, the present invention is directed to an antenna apparatus which is used as a global positioning system (GPS) antenna, and the like.

As is well known in this technical field, the GPS (Global Positioning System) corresponds to a satellite positioning system with employment of artificial satellites. In the GPS system, electromagnetic waves (GPS signals) having frequencies of approximately 1.57 GHz are received from 4 sets, or more sets of artificial satellites among 24 sets of artificial satellites which are orbiting the earth; positional relationships and temporal errors between these artificial satellites and a moving object are measured based upon the received electromagnetic waves; and a position and an altitude of the moving object on a map can be calculated based upon the basic idea of the trigonometrical survey.

Very recently, the GPS systems are utilized in vehicle navigation systems capable of detecting positions of traveling automobiles, namely, are widely popularized. Vehicle navigation apparatuses are arranged by GPS-purpose antennas, processing apparatuses, display apparatuses, and the like. The GPS-purpose antennas are employed in order to receive GPS signals. The processing apparatuses process the GPS signals received by the GPS-purpose antennases so as to detect present positions of vehicles. The display apparatuses display the present position of the vehicles detected by the processing apparatuses on maps.

On the other hand, in connection with the progress of current compact communication appliances (for example, GPS type vehicle navigation apparatuses, portable type navigation apparatuses, satellite waves receivers, etc.) such as mobile communication appliances, compactnesses and high performance as to antenna apparatuses utilized in these communication appliances are required.

Among these antenna apparatuses, plane type antenna apparatuses (for instance, circular polarized patch antenna, etc.) have such merits that antenna structures thereof are made slim and compact, and these plane type antenna apparatuses can be comparatively easily manufactured in the form of integrated circuits in combination with semiconductor circuits. As a result, these plane type antenna apparatuses are widely employed as antennas utilized in compact communication apparatuses.

As such plane type antenna apparatuses, for instance, antenna apparatuses having the below-mentioned antenna structures are known (refer to, for example, patent document 1): That is, these antenna apparatuses are equipped with circular polarized antenna elements, and circuit boards in which LNA (Low Noise Amplifiers) are formed on rear planes thereof. The circular polarized antenna elements are formed by so-called “patch antenna element.” The circular polarized antenna elements contain dielectric substrates which are manufactured by high dielectric materials such as ceramics. While radiation elements are formed on front surfaces of the dielectric substrates, ground patterns are formed on rear surfaces of the dielectric substrates. Pin holes penetrated from the front surfaces through the rear surfaces of the dielectric substrates are formed in the dielectric substrates. Power feeding pins penetrate through the pin holes, while the power feeding pins connect the radiation elements to the circuit boards. In the plane type antenna apparatuses equipped with the above-described antenna structures, since electric capacitances of antennas can be secured based upon the dielectric substrates made of the high dielectric materials, resonant frequencies of these antennas are lowered, so that the plane type antenna apparatuses can be made compact. In such patch antenna elements, since ground patterns are provided opposite to radiation elements, gains along directions of high elevation angles become high.

In any case, as GPS-purpose antennas, circular polarized antenna elements are used. In other words, GPS signals correspond to circular polarized waves. Further, circular polarized waves are also utilized in the field of ETC signals.

As is well known, an ETC (Electronic Toll Collection) system corresponds to such a system developed as the measure capable of relaxing traffic jams occurred in tool gates where tools as to toll roads (speedways, etc.) are paid. In other words, the above-described ETC system implies such a system that payments of tools are automatically accomplished by utilizing wireless communications at tool gates of speedways. In the above-explained ETC system, ETC signals are communicated in bidirectional communication manners between road-sided antennas equipped in gates installed at tool gates, and gate-passing vehicles equipped with on-vehicle communication appliances having ETC-purpose antennas so as to acquire vehicle information about these gate-passing vehicles, so that the ETC system can execute toll paying business for speedways without stopping the gate-passing vehicles.

There are some possibilities that ETC-purpose antennas are mounted on interior portions of vehicles. For instance, certain ETC-purpose antennas may be set on dashboards under certain angled conditions, or some ETC-purpose antennas may be set on glass of windshields. Also, mounting of ETC-purpose antennas in advance is popularized. That is to say, ETC-purpose antennas are mounted on interior portions of vehicles in factories of vehicle manufactures. In this factory mounting case, there are many cases that these ETC-purpose antennas are installed under such a condition that the ETC-purpose antennas are embedded in rear sides of room mirrors, and embedded under dashboards.

Also, circular polarized plane antennas (curl antenna elements) are known in which circular polarized waves are radiated by elements having spiral shapes.

Referring toFIG. 1andFIG. 2, a description is made of a conventional cud antenna element.

The curl antenna element60is constructed by employing a spiral (whirling) radiation element (antenna element)62, a ground plate64located opposite to the radiation element61, and a power feeding portion66raised from the ground plate64along a vertical direction. The ground plate64and the spiral-shaped radiation element62are arranged substantially parallel to each other. A feeding point66aof the power feeding portion66is provided at a near center of the ground plate64. It should be noted that an insulator64asuch as a through hole is provided at a center portion of the ground plate64. As a consequence, the feeding point66ais not electrically connected to the ground plate64. In any case, the conventional curl antenna element60is an antenna element having a three-dimensional structure.

It should also be noted that curl antenna elements are disclosed in, for instance, a patent document 2 and a patent document 3. While the curl antenna elements disclosed in these patent documents 2 and 3 have three-dimensional structures, since these antenna elements have ground planes which are located opposite to antenna elements in a parallel manner, impedances can be readily matched with each other. Also, the curl antenna elements disclosed in these patent documents 2 and 3 constitute such directional antennas having high gains along zenithal directions thereof due to the ground planes located opposite to the antenna elements.

The above-described patch antenna elements and curl antenna elements are manufactured in the three-dimensional structures, so that thicknesses of antenna elements thereof become bulky. As a result, these patch antenna elements and curl antenna elements can be hardly made thinner. That is to say, in such a case that ground planes located opposite to antenna elements cannot be installed, the patch antenna elements and the curl antenna elements cannot be used as circular polarized antenna elements.

To solve this problem, as the circular polarized antenna elements, film antennas are known which are adhered to windshields of vehicles (refer to, for example, patent document 4). The film antenna disclosed in the patent document 4 is equipped with a single loop-shaped film antenna capable of receiving circular polarized waves on a transparent film. This circular polarized antenna element corresponds to a right-hand polarized antenna equipped with a loop antenna and a non-power feeding element. While edge portions of the loop antenna in the power feeding side are formed in land shapes, these land shapes construct a first power feeding terminal and a second power feeding terminal. The first and second power feeding terminals are connected to first and second connection terminals of a connector which contains a low noise amplifier (LNA) circuit. The connector is connected to a coaxial cable. As a consequence, the first power feeding terminal is connected via the LNA circuit to an inner conductor of the coaxial cable, and the second power feeding terminal is connected to an outer conductor of the coaxial cable.

It should also be noted that as on-vehicle type antenna apparatuses, on-vehicle type digital terrestrial antenna apparatuses used so as to receive digital terrestrial broadcasting waves are known.

[Patent Document 1] Japanese Patent Publication No. 2001-339232 A

[Patent Document 2] Japanese Patent Publication No. 2007-235460 A

[Patent Document 3] Japanese Patent Publication No. 2003-218632 A

[Patent Document 4] Japanese Patent Publication No. 2006-013696 A

In the case that such an antenna apparatus which requires a ground plane located opposite to a radiation element (curl antenna element), as disclosed in the above-described patent documents 2 and 3, is manufactured with employment of a film antenna structure as disclosed in the patent document 4, in the film antenna, the ground plane located opposite to the radiation element cannot be formed, so that impedance matching of the radiation element with respect to the ground plane becomes very difficult.

SUMMARY

It is therefore one advantageous aspect of the present invention to provide an antenna apparatus capable of achieving better impedance matching with respect to a radiation element which requires a ground plane (for example, curl antenna element) as a film antenna, even in such a case that the ground plane located opposite to the radiation element cannot be sufficiently secured.

It is also one advantageous aspect of the present invention to provide a composite antenna apparatus which is operable as both a GPS-purpose antenna and a digital terrestrial broadcasting receiving-purpose antenna.

According to one aspect of the invention, there is provided an antenna apparatus comprising:

a radiation element including a perturbation element;

a first power feeding line, having a first end connected to the radiation element and configured to feed power to the radiation element; and

a second power feeding line, having a first end configured to feed power to the radiation element through electromagnetic coupling,

wherein the radiation element, the first power feeding line and the second power feeding line are arranged on a same plane to constitute a balance type antenna.

The antenna apparatus may be configured such that: the second power feeding line has a part extending parallel to the first power feeding line.

The antenna apparatus may further comprise: a transparent substrate on which the radiation element, the first power feeding line and the second feeding line are provided.

The antenna apparatus may be configured such that: the transparent substrate is a resin film.

The antenna apparatus may be configured such that: the transparent substrate is a glass plate.

The antenna apparatus may further comprise: a transparent substrate in which the radiation element, the first power feeding line and the second feeding line are embedded.

The antenna apparatus may be configured such that: the transparent substrate is a glass plate.

The antenna apparatus may be configured such that: the antenna apparatus is configured to serve as a GPS antenna receiving a GPS signal of a 1.57 GHz frequency band.

The antenna apparatus may be configured such that: the second power feeding line is disposed adjacent to the first power feeding line; the second power feeding line has a part extending parallel to the first power feeding line; the antenna apparatus is configured to serve as a balance type antenna when a second end of the first power feeding line and a second end of the second power feeding line are electrically disconnected; and the antenna apparatus is configured to serve as a monopole antenna when the second end of the first power feeding line and the second end of the second power feeding line are electrically connected.

The antenna apparatus may further comprise: a resonant circuit, electrically connecting the second end of the first power feeding line and the second end of the second power feeding line in a parallel manner, and configured to electrically connect or disconnect the second end of the first power feeding line and the second end of the second power feeding line in accordance with a frequency band received by the antenna apparatus.

The antenna apparatus may be configured such that: the balance type antenna is configured to serve as a GPS antenna receiving a GPS signal of a 1.57 GHz frequency band; and the monopole antenna is configured to serve as a digital terrestrial antenna receiving digital terrestrial broadcasting signal.

The antenna apparatus may be configured such that: the radiation element is curl-shaped.

The antenna apparatus may be configured such that: the electromagnetic coupling is established at a position adjacent to the first end of the first power feeding line.

DETAILED DESCRIPTION OF EXEMPLIFIED EMBODIMENTS

Exemplified embodiments of the invention will be described below in detail with reference to the accompanying drawings

Referring toFIG. 3, a description is made of an antenna apparatus10according to a first embodiment of the present invention. The antenna apparatus10shown in this drawing corresponds to a GPS-purpose antenna capable of receiving GPS signals transmitted from GPS satellites.

The antenna apparatus10shown in the drawings is constructed of a film antenna. In other words, the antenna apparatus10is constructed by employing a transparent resin film11, and a GPS antenna pattern20formed on the resin film11. The GPS antenna pattern20is formed on the same plane.

The GPS antenna pattern20is arranged by a curl-shaped radiation element (antenna element)21having a perturbation element211, a first power feeding line22, and a second power feeding line23. The first power feeding line22is employed in order to directly feed electric power to the curl-shaped radiation element21. While the second power feeding line23is elongated parallel to the first power feeding line22and is approximated thereto, the second power feeding line23is employed in order to feed electric power with respect to the radiation element21through electromagnetic coupling. The power feeding operation by the second power feeding line23by utilizing the electromagnetic coupling is performed in order to easily adjust impedance matching of the antenna apparatus10.

The first power feeding line22and the second power feeding line23, which are shown in the drawings, are elongated shorter than a dimension (diameter) of the radiation element21.

The radiation element21shown in the drawing has a quadrangle (rhombic). In other words, the radiation element21has a first edge21-1, a second edge21-2, a third edge21-3, and a fourth edge21-4along a clockwise direction in this order from a tip22aof the first power feeding line22. One edge of the above-described perturbation element211is connected to a tip21-4aof the fourth edge21-4. In other words, the perturbation element211is provided inside the first edge21-1of the radiation element21. Both the first edge21-1and the fourth edge21-4are provided at positions which are approximated to both the first power feeding line22and the second power feeding line23, whereas both the second edge21-2and the third edge21-3are provided at positions which are separated far from the first power feeding line22and the second power feeding line23. As a consequence, both the first edge21-1and the fourth edge21-4are provided in a portion lower than a dashed line “A” ofFIG. 3, whereas the second edge21-2and the third edge21-3are provided in a portion higher than the dashed line “A.” In the above-described exemplification, such a case is described that the radiation element21is provided along the clockwise direction, and the right spiral circular polarized waves are received by the radiation element21. In the case that left-hand circular polarized waves are received, the radiation element21is arranged in a counterclockwise direction.

A first feeding point26is formed at a root portion of the first power feeding line22, and a second feeding point27is formed at a root portion of the second power feeding line23. A balun (balanced to unbalanced transformer)29is arranged between the first and second feeding points26and27, and also, an intermediate terminal29aso as to perform an unbalanced power feeding-to-balanced power feeding conversion between the intermediate terminal29a, and the first and second feeding points26and27, so that electric power is supplied to the first feeding point26and the second feeding point27, respectively. The balun29is mounted on a circuit board provided in a connector40(refer toFIG. 5), which will be discussed later.

In the example shown in the drawing, while the electric power is directly fed from the first power feeding line22to the first edge21-1of the radiation element21, the electric power is fed by utilizing the electromagnetic coupling from the second power feeding line23to the fourth edge21-4of the radiation element21. The second power feeding line23has an electromagnetic coupling portion231which is electromagnetically coupled to the fourth edge21-4of the radiator element21.

As previously described, the balance type GPS pattern20is constructed by employing the radiation element21, the first power feeding line22, and the second power feeding line23. Since the GPS antenna pattern20is manufactured in the form of the balance type GPS antenna, such a ground plane located opposite to the radiation element21is no longer required.

In the above-described antenna apparatus10shown inFIG. 3, an impedance thereof is adjusted by the second power feeding line23. An axial ratio thereof is adjusted by the perturbation element211. And a reception frequency thereof is adjusted by an outer circumferential length of the radiation element21. As a consequence, the antenna apparatus10can be easily designed.

Next, feeding of the electric power by utilizing the electromagnetic coupling effect achieved in the antenna apparatus10according to the first embodiment of the present invention will be described in more detail.

Currents are concentrated in both the first edge21-1and the fourth edge21-4of the radiation element21, which are located in the portion lower than the dashed line “A” ofFIG. 3. As a consequence, a more effect of the power feeding may be obtained if the power feeding line23provided for adjusting the antenna impedance is electromagnetically coupled with either the first edge21-1or the fourth edge21-4.

Conversely, current distributions are small in both the second edge21-2and the third edge21-3of the radiation element21, which are located in the portion higher than the dashed line “A” ofFIG. 3. As a consequence, when the power feeding line23for adjusting the impedance is electromagnetically coupled to either the second edge21-2or the third edge21-3, an effect of the power feeding becomes small, as compared with such a case that the second power feeding line23for adjusting the impedance is electromagnetically coupled to either the first edge21-1or the fourth edge21-4.

As a consequence, if the first edge21-1and the fourth edge21-4of the radiation element21can be selected, then the impedance adjustment may be carried out at any position of these first and fourth edges21-1and21-4. For instance, the second power feeding line23for adjusting the impedance may be set at such positions indicated by other dashed lines shown inFIG. 3.

In the antenna apparatus10shown inFIG. 3, an impedance adjusting operation is carried out as follows: That is, an inductance component “L” of an impedance can be adjusted by adjusting a length “a” of the above-described electromagnetic coupling portion231of the second power feeding line23. Also, a capacitance component “C” of the impedance can be adjusted by adjusting a gap width “b” between the fourth edge21-4of the radiation element21and the electromagnetic coupling portion231of the second power feeding line23. Thus, impedance matching of the antenna apparatus10can be easily adjusted in the above-described manner.

As can be understood fromFIG. 4, a zenithal direction is a direction which the gain is high along in the antenna apparatus10. In other words, the antenna apparatus10can be made very thin, and corresponds to such a directional antenna whose gain is high along the zenithal direction.

Referring toFIG. 5, the antenna apparatus10is installed on an inner side of the glass30such as a windshield of an automobile by utilizing a pressure sensible double-sided adhesive tape.

In this drawing, a connector (amplifier unit)40is connected to both the first feeding point26and the second feeding point27of the antenna apparatus10, and a coaxial cable50is connected to this connector (amplifier unit)40.

As previously described, the connector (amplifier unit)40contains the above-described balun29(refer toFIG. 3) mounted on the circuit board (not shown) arranged inside the connector50. The connector40contains a low noise amplifier (LNA) circuit (not shown), and a ground pattern (not shown), which are formed on the circuit board. The intermediate terminal29a(refer toFIG. 3) of the balun29is connected to an input terminal of this LNA circuit.

On the other hand, although not shown in the drawing, as is well known in this technical field, the coaxial cable50has an inner conductor located at a center, and an outer conductor having a cylindrical shape. An output terminal of the LNA circuit is connected to the inner conductor of the coaxial cable50, and the above-described ground pattern formed on the circuit board is connected to the outer conductor of the coaxial cable50.

In the antenna apparatus10shown inFIG. 5, the GPS antenna pattern20is formed on the resin film11. In contrast to this antenna structure, alternatively, the GPS antenna pattern20may be directly embedded in the windshield30of the automobile. Such an alternative antenna apparatus is referred to as a glass-printed antenna.

The antenna apparatus (film antenna)10shown inFIG. 3is marketed as an optional component of a vehicle dealer. As a consequence, the antenna apparatus (film antenna)10is not mounted in a manufacturing stage of a factory, but is commercially marketed as an appendix component provided by a vehicle dealer. In contrast to the film antenna10, the above-explained glass-printed antenna corresponds to such a GPS-purpose antenna which is mounted by a manufacturing step in a factory, and therefore, is commercially available as an OEM component.

In the above-described glass-printed antenna, at an edge portion of the glass30, a first signal line terminal (not shown) is connected to the first feeding point26, and a second signal line (not shown) is connected to the second feeding point27. A connector (not shown) which comprises the balun29and the LNA circuit (not shown) is mounted on these first and second signal line terminals. In other words, the connector (amplifier unit) is inserted into the first and second signal line terminals.

In the glass-printed antenna having the above-described antenna structure, since printed patterns such as an AM/FM radio and a rear defogger are formed and at the same time the GPS antenna pattern20is printed on the glass30, cost (manufacturing step number) required for forming the GPS antenna is not newly produced. Also, since the connector (amplifier unit) may be merely mounted on the glass30, the mounting shape thereof need not be changed with respect to each of vehicles. In other words, a degree at which antenna products are commonly manufactured can be improved. Furthermore, the amplifier unit is mounted on the glass30when the glass30is supplied from a glass manufacturer, so that a total number of mounting steps related to the GPS antenna can be reduced in an automobile manufacturer. Since the glass-printed antenna is employed, a good appearance of the interior portion of the vehicle can be maintained in the stylish manner, as compared with such a case that the film antenna is adhered on the glass in the post stage.

Alternatively, the amplifier unit (connector) is not installed immediately under the glass30, but the amplifier unit may be alternatively installed at a remote place by deriving the connector from the glass30by connecting a lead wire (coaxial signal line) to the connector (namely, amplifier unit).

Referring toFIG. 6, a description is made of a composite antenna apparatus10A according to a second embodiment of the present invention. The composite antenna apparatus10A shown in this drawing corresponds to such a composite antenna apparatus formed by combining a GPS-purpose antenna capable of receiving GPS signals transmitted from GPS satellites with a digital terrestrial broadcast receiving-purpose antenna for receiving digital TV signals in frequency ranges used in digital terrestrial broadcasting systems.

The composite antenna apparatus10A shown in the drawing is constructed of a film antenna. In other words, the composite antenna apparatus10A is constructed by employing a transparent resin film (not shown), and a composite antenna pattern20A formed on the transparent resin film. The composite antenna pattern20A is formed on the same plane.

The composite antenna pattern20A is arranged by a curl-shaped radiation element (antenna element)21having a perturbation element211, a first power feeding line22A, and a second power feeding line23A. The first power feeding line22A is employed in order to directly feed electric power to the curl-shaped radiation element21. While the second power feeding line23A is elongated parallel to the first power feeding line22A and is approximated thereto, the second power feeding line23A is employed in order to feed electric power with respect to the radiation element21through electromagnetic coupling.

While the composite antenna pattern20A shown in the drawing is different from the GPS antenna pattern20shown inFIG. 3, the first power feeding line22A and the second power feeding line23A are elongated longer than a dimension (diameter) of the radiation element21.

In other words, in the GPS antenna pattern20shown inFIG. 3, a distance defined from root portions of the first and second power feeding lines22and23up to a top of the radiation element21is 63 mm, whereas in the composite antenna pattern20A ofFIG. 6, a distance “L” defined from root portions of the first and second power feeding lines22A and23A up to a top of the radiation element21is 120 mm. As previously described, the lengths of the first and second power feeding lines22A and23A are made longer in order that a total length of the composite antenna pattern20A is made nearly equal to a ¼ wavelength of the frequency band of 600 MHz.

Since a structure of the radiation element21shown inFIG. 6is identical to that of the radiation element21shown inFIG. 3, a detailed explanation thereof will be omitted.

A first feeding point26is formed at a root portion of the first power feeding line22A, and a second feeding point27is formed at a root portion of the second power feeding line23A. A balun (not shown), as shown inFIG. 3, is arranged between the first and second feeding points26and27.

Referring toFIG. 7in addition toFIG. 6, a parallel resonant circuit60having a predetermined frequency band is inserted between the first feeding point26and the second feeding point27. In the example shown in these drawings, the predetermined frequency band is selected to be 1.5 GHz. As a consequence, this parallel resonant circuit60is designed in such a manner that the circuit between the first and second feeding points26and27are opened at the predetermined frequency band (namely, 1.5 GHz band), and the circuit between the first and second feeding points26and27is short-circuited in a frequency range other than the predetermined frequency range (1.5 GHz band).

Since the circuit between the first and second feeding points26and27is opened, a balance type antenna pattern20A is constructed by utilizing the radiation element21, the first power feeding line22A, and the second power feeding line23A, whereas since the circuit between the first and second feeding points26and27is short-circuited, the antenna pattern20A can be operated as a monopole antenna.

In the antenna apparatus10A shown in the drawings, the balance type antenna pattern20A is used as such a GPS-purpose antenna for receiving GPS signals whose predetermined frequency band is selected to be approximately 1.57 GHz, whereas the monopole antenna is used as a digital terrestrial broadcast receiving-purpose antenna for receiving digital terrestrial TV broadcasting signals in the use frequency band.

It should also be understood that as shown inFIG. 7, a matching coil62is connected to the first feeding point26.

FIG. 8andFIG. 9show simulation results as to a radiation characteristic of the antenna apparatus10A shown inFIG. 6when the circuit between the first and second feeding points26and27is opened. InFIG. 8, an abscissa indicates a frequency in the unit of “GHz”, and an ordinate indicates an axial ratio in the unit of “dB.” InFIG. 9, a chain line indicates a gain characteristic of a right-hand circular polarized wave “RHCP”, and a solid line indicates a gain characteristic of a left-hand circular polarized wave “LHCP”

As can be understood fromFIG. 8, the axial ratio is small at a frequency (approximately 1.57 GHz) of a GPS signal. Also, as can be understood fromFIG. 9, the gain of the right-hand circular polarized wave “RHCP” is high along the zenithal direction (namely, zero degree).

FIG. 10andFIG. 11show simulation results as to a radiation characteristic of the antenna apparatus10A shown inFIG. 6when the circuit between the first and second feeding points26and27is short-circuited. That is, InFIG. 10, an abscissa indicates a frequency in the unit of “GHz”, and an ordinate indicates VSWR. InFIG. 11, a chain line indicates a gain characteristic of a vertical polarized wave, and a solid line indicates a gain characteristic horizontal polarized wave.

As can be understood fromFIG. 10, the VSWR is small in the frequency band (470 MHz to 770 MHz) used in the digital terrestrial broadcasting system. Also, as can be understood fromFIG. 11, the gain of the horizontal polarized wave is high in the use frequency band.

As can be understood from the foregoing description, since the circuit between the first feeding point26and the second feeding point27is opened and closed, the antenna apparatus10A can be operated as the composite antenna apparatus.

Although the preferred embodiments of the present invention is described, the present invention is not limited only to the above-described embodiments. For instance, in the above-described embodiments, as the radiation element (antenna element)21, although such a curl-shaped antenna element having the quadrangle (rhombic) form is used, the present invention is not limited only to the antenna elements such shapes. In other words, the form of the radiation element (antenna element)21is not limited only to the quadrangle (rhombic), but curl-shaped antenna elements having circular, polygonal, and other forms may be alternatively used. Although in the above-described embodiments, the balun29is arranged between the intermediate terminal29a, and both the first and second feeding points26and27so as to feed the electric power to the first and second feeding points26and27. Alternatively, the electric power may be fed to the first and second feeding points26and27without employing the balun29.

The radiation element21may be formed so as to have a shape other than the curled-shape. The radiation element21, the first power feeding line22and the second feeding line23may be provided on a transparent substrate such as a glass. The radiation element21, the first power feeding line22and the second feeding line23may be embedded in a transparent substrate which is other than a glass.