Coupling degree adjustment circuit, antenna device, and wireless communication device

A dielectric body includes a first radiating element on a first side and a second radiating element on a second side. The first radiating element and the second radiating element are linear conductors that each extend from a first end to a second end (an open end), and are parallel or substantially parallel to each other in a direction from the first end to the second end. The first end of the first radiating element is connected to a first port of a coupling degree adjustment circuit, and the first end of the second radiating element is connected to a second port of the coupling degree adjustment circuit. The first radiating element and the second radiating element are mainly coupled to each other in the coupling degree adjustment circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a coupling degree adjustment circuit, an antenna device for multiband, and a communication terminal apparatus equipped with the antenna device.

2. Description of the Related Art

Japanese Unexamined Patent Application Publication No. H06-069715 and Patent Literature Japanese Unexamined Patent Application Publication No. 2003-008326 disclose multiple resonant antennas in which a radiating element and a radiating element are coupled to each other for the purpose of expanding applicable frequency bands. In these multiple resonant antennas, a feeding element and a non-feeding element are parallel to each other in a region in which a magnetic field component is increased and are made magnetically coupled to each other so that each element can act as a radiating element.

The typical configuration of the conventional multiple resonant antennas as disclosed in Japanese Unexamined Patent Application Publication No. H06-069715 and Japanese Unexamined Patent Application Publication No. 2003-008326, as illustrated inFIG. 1A, includes a first radiating element RE1as a feeding element, and a second radiating element RE2as a non-feeding element, makes the vicinity of a feeding portion of the first radiating element RE1and the vicinity of a ground end of the second radiating element RE2close and in parallel to each other so as to cause the elements to be magnetically coupled to each other.

When a resonant frequency of the first radiating element RE1is set to f1 and a resonant frequency of the second radiating element RE2is set to f2, and the first radiating element RE1and the second radiating element RE2are coupled to each other, as illustrated inFIG. 1B, the second radiating element RE2resonates at f2. The return loss characteristic of this whole multiple resonant antenna shows the combination of a resonance characteristic of the first radiating element RE1and a resonance characteristic of the second radiating element RE2, as illustrated as the solid line ofFIG. 1B, and becomes a characteristic as illustrated by a solid line.

However, the strength of coupling between the first radiating element RE1and the second radiating element RE2is determined not only by a distance between the elements but under a condition in which the vicinity of a feeding portion of the first radiating element RE1and the vicinity of a ground end of the second radiating element RE2are close to each other and also arranged in parallel to each other. Therefore, the flexibility of the pattern of the first radiating element RE1and the second radiating element RE2is low. In addition, when the first radiating element RE1and the second radiating element RE2are arranged too close to each other, it becomes impossible to match a feeding circuit and the multiple resonant antenna and further, when other components (especially a metal article) exist near a portion in which the elements are parallel (a portion in which the elements are magnetically coupled), a problem that the degree of coupling of the first radiating element RE1and the second radiating element RE2may change arises.

SUMMARY OF THE INVENTION

In view of the above problems, preferred embodiments of the present invention provide a coupling degree adjustment circuit and an antenna device that increase design flexibility of a radiating element pattern and setting a degree of coupling between two radiating elements regardless of whether the radiating elements are close or not close, and a communication terminal apparatus equipped with the antenna device.

A coupling degree adjustment circuit according to a preferred embodiment of the present invention includes a primary side circuit that includes a first coil element and is connected to a first radiating element; and a secondary side circuit that includes a second coil element electromagnetically coupled to the first coil element, and is connected to a second radiating element.

An antenna device according to a preferred embodiment of the present invention includes a first radiating element; a second radiating element, and a coupling degree adjustment circuit connected between the first radiating element and the second radiating element, and a feeding circuit, the coupling degree adjustment circuit including a primary side circuit that includes a first coil element and is connected to the first radiating element; and a secondary side circuit that includes a second coil element electromagnetically coupled to the first coil element, and is connected to the second radiating element.

A communication terminal apparatus according to a preferred embodiment of the present invention includes an antenna device including a first radiating element; a second radiating element, and a coupling degree adjustment circuit connected between the first radiating element and the second radiating element, and a feeding circuit, the coupling degree adjustment circuit including a primary side circuit that includes a first coil element and is connected to the first radiating element; and a secondary side circuit that includes a second coil element electromagnetically coupled to the first coil element, and is connected to the second radiating element.

According to various preferred embodiments of the present invention, since it is not necessary to arrange a first radiating element and a second radiating element parallel to each other, the design flexibility of those patterns is increased. In addition, even if the first radiating element and the second radiating element are arranged close to each other, a degree of coupling can be set to a predetermined degree of coupling, so that a feeding circuit and a multiple resonant antenna can be easily matched.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

FIG. 2AandFIG. 2Bare circuit diagrams of an antenna device101of a first preferred embodiment of the present invention. InFIG. 2A, a portion of a coupling degree adjustment circuit21is simplified and illustrated. InFIG. 2B, the configuration of the coupling degree adjustment circuit21is more specifically illustrated. This antenna device101includes the coupling degree adjustment circuit21, a first radiating element11, and a second radiating element12. The first radiating element11is connected to a first port (a feeding port) P1of the coupling degree adjustment circuit21. The second radiating element12is connected to a second port P2of the coupling degree adjustment circuit21.

The coupling degree adjustment circuit21includes a primary side circuit including a first coil element L1, and a secondary side circuit including a second coil element L2. The first coil element L1is connected to a first radiating element11, and the second coil element L2is connected to a second radiating element12.

The coupling degree adjustment circuit21includes the first coil element L1and the second coil element L2that are electromagnetically coupled to each other. Thus, the first radiating element11and the second radiating element12are coupled through the coupling degree adjustment circuit21. Then, a degree of coupling of the first radiating element11and the second radiating element12can be defined by a degree of coupling of the coupling degree adjustment circuit21. The degree of coupling of the coupling degree adjustment circuit21can be defined by, for example, a coil distance between the first coil element L1and the second coil element L2. While the electromagnetic field coupling of each coil element is coupling that is mainly performed through a magnetic field, electric field coupling may be partially included.

In particular, the operations of the coupling degree adjustment circuit21will be described with reference toFIG. 2B. As illustrated inFIG. 2B, the first coil element L1includes coil elements L1aand L1b, and the second coil element L2includes coil elements L2aand L2b. When a current is supplied from a feeding circuit30in a direction indicated by arrow a in the figure, a current flows in the coil element L1ain a direction indicated by arrow b in the figure and also a current flows in the coil element L1bin a direction indicated by arrow c in the figure. Those currents generate a magnetic flux passing through a closed magnetic circuit, as indicated by arrow A in the figure.

Since the coil element L1aand the coil element L2ashare a coil winding axis, and the conductor patterns of these two coil elements are parallel or substantially parallel to each other in a plan view state (a state in which the elements are viewed in a direction of the coil winding axis), a magnetic field generated as a result of flowing of the current b in the coil element L1ais coupled to the coil element L2aand thus an induced current d flows in the coil element L2ain an opposite direction. Similarly, since the coil element L1band the coil element L2bshare a coil winding axis and are parallel or substantially parallel to each other, a magnetic field generated as a result of flowing of the current c in the coil element L1bis coupled to the coil element L2band thus an induced current e flows in the coil element L2bin an opposite direction. Those currents generate a magnetic flux passing through a closed magnetic circuit, as indicated by arrow B in the figure.

Since the magnetic flux passing through the closed magnetic circuit by the coil elements L1aand L1band the magnetic flux passing through the closed magnetic circuit by the coil elements L2aand L2brepel each other, an equivalent magnetic barrier MW is generated between the first coil element L1and the second coil element L2.

The coil element L1aand the coil element L2aare also coupled to each other through an electric field. Similarly, the coil element L1band the coil element L2bare also coupled to each other through an electric field. Accordingly, when alternating-current signals flow in the coil element L1aand the coil element L1b, electric-field coupling causes currents to be excited in the coil element L2aand the coil element L2b. Capacitors Ca and Cb inFIG. 2Beach symbolically represent coupling capacitances for the electric-field coupling.

When an alternating current flows in the first coil element L1, the direction of a current flowing in the second coil element L2as a result of the coupling through the magnetic field and the direction of a current flowing into the second coil element L2as a result of the coupling through the electric field are the same. Accordingly, the first coil element L1and the second coil element L2are coupled to each other strongly through both the magnetic field and the electric field. In other words, it is possible to reduce the amount of loss and to transmit high frequency energy.

FIG. 3is a view illustrating a more specific example of a configuration of the antenna device of the first preferred embodiment of the present invention. In this example, a rectangular or substantially rectangular parallelepiped shaped dielectric body10includes a primary side PS on which the first radiating element11is provided, and a secondary side SS on which the second radiating element12is provided. The first radiating element11and the second radiating element12preferably are L-shaped or substantially L-shaped linear conductors that each extend from a first end to a second end (an open end). The first radiating element11and the second radiating element12are parallel or substantially parallel to each other in a direction from the first end to the second end (the open end), respectively. When the resonant frequency of the first radiating element11is represented by f1 and the resonant frequency of the second radiating element12is represented by f2 and a relationship f1<f2 is satisfied, the second radiating element12is shorter than the first radiating element11.

The first end of the first radiating element11is connected to a first port P1of the coupling degree adjustment circuit21, and the first end of the second radiating element12is connected to a second port P2of the coupling degree adjustment circuit21. While the degree of coupling (without passing through the coupling degree adjustment circuit21) between the first radiating element11and the second radiating element12preferably is about 0.2 to about 0.3, for example, the degree of coupling of the coupling degree adjustment circuit21preferably is not less than about 0.5 (desirably not less than about 0.7), for example. In this way, the degree of coupling between a primary side circuit and a secondary side circuit is higher than the degree of coupling between the first radiating element and the second radiating element without passing through the coupling degree adjustment circuit, so that the first radiating element11and the second radiating element12are mainly coupled to each other with the degree adjustment circuit21.

It is to be noted that although it has been necessary to adjust a distance (a thickness of the dielectric body10) between the first radiating element11and the second radiating element12in the conventional technique in order to adjust the degree of coupling between the first radiating element11and the second radiating element12formed in the dielectric body10, according to a preferred embodiment of the present invention, a degree of coupling between the first coil element L1and the second coil element L2of the coupling degree adjustment circuit21can be used to adjust the degree of coupling between the first radiating element11and the second radiating element12. Therefore, the pattern of the first radiating element11and the second radiating element12to the dielectric body10, and the dielectric body10have a high flexibility in design.

Second Preferred Embodiment

FIG. 4Ais a configuration view of an antenna device102of a second preferred embodiment of the present invention. The antenna device102includes the coupling degree adjustment circuit21, a first radiating element11, and a second radiating element12. The coupling degree adjustment circuit21includes a primary side circuit including the first coil element L1and a secondary side circuit including the second coil element L2, and the first coil element L1and the second coil element L2are electromagnetically coupled to each other.

A rectangular or substantially rectangular parallelepiped shaped dielectric body10includes a primary side PS on which a first radiating element11and a third radiating element13are provided; and a secondary side SS on which a second radiating element12is provided. The first radiating element11and the second radiating element12are conductors preferably each having a rectangular or substantially rectangular spiral shape. This first radiating element11and the second radiating element12are parallel or substantially parallel to each other in a direction from the first end to the second end (the open end), respectively. The third radiating element13is also a conductor having a rectangular or substantially rectangular spiral shape. The first end of the third radiating element13is arranged on a side far apart each other from the first end of the first radiating element11and the second radiating element12. The third radiating element13is coupled to the first radiating element11through an electromagnetic field.

The first radiating element11is connected to a first port (a feeding port) P1of the coupling degree adjustment circuit21. The second radiating element12is connected to a second port P2of the coupling degree adjustment circuit21. Thus, the first radiating element11and the second radiating element12are coupled through the coupling degree adjustment circuit21. Then, the degree of coupling of the first radiating element11and the second radiating element12is determined by the degree of coupling of the coupling degree adjustment circuit21. In addition, since being partially close to each other, the first radiating element11and the third radiating element13are electromagnetically coupled. Then, the degree of coupling of the first radiating element11and the third radiating element13, if each of the patterns are not changed, is determined by a mutual close distance.

When the resonant frequency of the first radiating element11is represented by f1, the resonant frequency of the second radiating element12is represented by f2, and the resonant frequency of the third radiating element13is represented by f3, the relationship f3<f1<f2 is satisfied in this example.

FIG. 4Bshows a return loss characteristic of the antenna device102as viewed from a feeding circuit. The return loss characteristic of this antenna device are illustrated by combination of the resonance characteristic of the first radiating element RE1, the resonance characteristic of second radiating element RE2, and the resonance characteristic of third radiating element RE3that are illustrated by a dashed line inFIG. 4B, and becomes a frequency characteristic of a wide band as illustrated by the solid line ofFIG. 4B.

Third Preferred Embodiment

FIG. 5is a configuration view of an antenna device103A according to a third preferred embodiment of the present invention. This antenna device103A includes a coupling degree adjustment circuit23A, a first radiating element11, and a second radiating element12. The coupling degree adjustment circuit23A includes a primary side circuit including a first coil element L1and a secondary side circuit including a second coil element L2, and the first coil element L1and the second coil element L2are electromagnetically coupled to each other. The first radiating element11is provided on a primary side PS of a rectangular or substantially rectangular parallelepiped shaped dielectric body10, and the second radiating element12is provided on a secondary side SS of the dielectric body10. The first radiating element11and the second radiating element12preferably are L-shaped or substantially L-shaped linear conductors that each extend from a first end to a second end (an open end). The first radiating element11and the second radiating element12are parallel or substantially parallel to each other in a direction from the first end to the second end (the open end), respectively.

The coupling degree adjustment circuit23A is connected between the first radiating element11and the second radiating element12, and a feeding circuit30. A first matching circuit91is connected between the first coil element L1of the coupling degree adjustment circuit23A and the first radiating element11. In addition, a second matching circuit92is connected between the second coil element L2of the coupling degree adjustment circuit23A and the second radiating element12. The first matching circuit91matches the impedance of the first coil element L1of the coupling degree adjustment circuit23A and the impedance of the first radiating element11. The second matching circuit92matches the impedance of the second coil element L2of the coupling degree adjustment circuit23A and the impedance of the second radiating element12.

Thus, the first radiating element11and the second radiating element12are coupled through the coupling degree adjustment circuit23A. Then, the degree of coupling of the first radiating element11and the second radiating element12is determined by the degree of coupling of the coupling degree adjustment circuit23A.

As described above, the first matching circuit91provided between the first coil element L1of the coupling degree adjustment circuit23A and the first radiating element11can match the impedance of the first coil element L1of the coupling degree adjustment circuit23A and the impedance of the first radiating element11according to the characteristic of the first radiating element11. Similarly, the second matching circuit92provided between the second coil element L2of the coupling degree adjustment circuit23A and the second radiating element12can match the impedance of the second coil element L2of the coupling degree adjustment circuit23A and the impedance of the second radiating element12according to the characteristic of the second radiating element12. It is to be noted that these matching circuits may be preferably defined by a single element of an inductor or a capacitor, and may be preferably defined by an LC resonance circuit (a n-type, a T-type, a series-connected type, a parallel-connected type, and the like). The same may be applied to the preferred embodiments as described below.

FIG. 6is a configuration view of an antenna device103B according to the third preferred embodiment of the present invention. This antenna device103B includes a coupling degree adjustment circuit23B, the first radiating element11, and the second radiating element12. The coupling degree adjustment circuit23B includes the primary side circuit including the first coil element L1and the secondary side circuit including the second coil element L2, and the first coil element L1and the second coil element L2are electromagnetically coupled to each other.

The coupling degree adjustment circuit23B is connected between the first radiating element11and the second radiating element12, and the feeding circuit30. A first matching circuit91is connected between the first coil element L1of the coupling degree adjustment circuit23B and the first radiating element11. In addition, a second matching circuit92is connected between the second coil element L2of the coupling degree adjustment circuit23B and the second radiating element12. Furthermore, a third matching circuit93is connected between the first coil element L1of the coupling degree adjustment circuit23B and the feeding circuit30. This third matching circuit93matches the impedance of the first coil element L1of the coupling degree adjustment circuit23B and the impedance of the feeding circuit30. The other configurations and operations are the same as those of the antenna device103A.

FIG. 7is a configuration view of an antenna device103C according to the third preferred embodiment of the present invention. This antenna device103C includes a coupling degree adjustment circuit23C, the first radiating element11, and the second radiating element12. The coupling degree adjustment circuit23C includes the primary side circuit including the first coil element L1and the secondary side circuit including the second coil element L2, and the first coil element L1and the second coil element L2are electromagnetically coupled to each other.

The coupling degree adjustment circuit23C is connected between the first radiating element11and the second radiating element12, and the feeding circuit30. A first matching circuit91is connected between the first coil element L1of the coupling degree adjustment circuit23C and the first radiating element11. In addition, a second matching circuit92is connected between the second coil element L2of the coupling degree adjustment circuit23C and the second radiating element12. Moreover, a third matching circuit93is connected between the first coil element L1of the coupling degree adjustment circuit23C and the feeding circuit30. In addition, a fourth matching circuit94is connected between the first coil element L1of the coupling degree adjustment circuit23C and ground. Furthermore, a fifth matching circuit95is connected between the second coil element L2of the coupling degree adjustment circuit23C and the ground. The first matching circuit91, the third matching circuit93, and the fourth matching circuit94provide impedance matching between the first coil element L1of the coupling degree adjustment circuit23C and the feeding circuit30, and impedance matching between the first coil element L1and the first radiating element11. The second matching circuit92and the fifth matching circuit95provide impedance matching between the second coil element L2of the coupling degree adjustment circuit23C and the second radiating element12. The other configurations and operations are the same as those of the antenna devices103A and103B.

FIG. 8is a configuration view of an antenna device103D according to the third preferred embodiment of the present invention. The antenna device103D includes a coupling degree adjustment circuit23D, the first radiating element11, and the second radiating element12. The coupling degree adjustment circuit23D includes the primary side circuit including the first coil element L1and the secondary side circuit including the second coil element L2, and the first coil element L1and the second coil element L2are electromagnetically coupled to each other.

A sixth matching circuit96is connected between the first coil element L1and the second coil element L2. In addition, a seventh matching circuit97is connected in shunt between the first coil element L1and the feeding circuit30. Further, an eighth matching circuit98is connected in shunt between the second coil element L2and the second radiating element12.

The sixth matching circuit96matches the first coil element L1and the second coil element L2. The seventh matching circuit97together with the matching circuits91,93, and94matches the feeding circuit30and the first coil element L1. The eighth matching circuit98together with the matching circuits92and95matches the second coil element L2and the second radiating element12.

Fourth Preferred Embodiment

FIG. 9is a circuit diagram of an antenna device104equipped with a coupling degree adjustment circuit24of a fourth preferred embodiment of the present invention. In the fourth preferred embodiment, the primary side coil and the secondary side coil of the coupling degree adjustment circuit24are respectively defined by two coil elements. Then, the primary side circuit of the coupling degree adjustment circuit24is connected in series between the feeding circuit30and the first radiating element11, and the second radiating element12is connected to the secondary side circuit of the coupling degree adjustment circuit24.

In this example, the primary side coil and the secondary side coil are coupled (tightly coupled) to each other with a high degree of coupling. In other words, the primary side coil includes a coil element L1aand a coil element L1b, which are connected in series to each other and are wound so as to define a closed magnetic circuit. In addition, the secondary side coil includes a coil element L2aand a coil element L2b, which are connected in series to each other and are wound so as to define the closed magnetic circuit. In other words, the coil element L1aand the coil element L1bare coupled to each other in an opposite phase (additive polarity coupling) and the coil element L2aand the coil element L2bare coupled to each other in an opposite phase (additive polarity coupling).

In addition, it is preferable that the coil element L1aand the coil element L2abe coupled to each other in the same phase (subtractive polarity coupling) and the coil element L1band the coil element L2bare coupled to each other in the same phase (subtractive polarity coupling).

FIG. 10is a view illustrating an example of conductor patterns of individual layers when the coupling degree adjustment circuit24according to the fourth preferred embodiment of the present invention is configured in a multilayer substrate, that is a laminate in which a plurality of dielectric layers or magnetic layers are laminated on each other. Each of the individual layers is defined either by a dielectric sheet or a magnetic sheet and a conductor pattern is provided on each of base material layers51ato51f.

In a range illustrated inFIG. 10, a conductor pattern74is provided on the base material layer51a. A conductor pattern72is provided on the base material layer51b, and conductor patterns71and73are provided on the base material layer51c. Conductor patterns61and63are provided on the base material layer51d, a conductor pattern62is provided on the base material layer51e, and a feeding terminal41, a ground terminal43, an antenna terminal42as a connection port of the first radiating element, and an antenna terminal44as a connection port of the second radiating element are provided on the lower surface of the base material layer51f, respectively. Dashed lines extending vertically inFIG. 10represent via electrodes that provide inter-layer connections between the conductor pattern and the conductor pattern.

As illustrated inFIG. 10, the right half of the conductor pattern72, and the conductor pattern71define the coil element L1a. In a similar manner, the left half of the conductor pattern72, and the conductor pattern73define the coil element L1b. In addition, the conductor pattern61and the right half of the conductor pattern62define the coil element L2a. Furthermore, the left half of the conductor pattern62, and the conductor pattern63define the coil element L2b.

InFIG. 10, ellipses indicated by a dashed line represent closed magnetic circuits. A closed magnetic circuit CM12interlinks with the coil elements L1aand L2b. A closed magnetic circuit CM34also interlinks with the coil elements L2aand L2b.

InFIG. 10, since the magnetic flux passing through the closed magnetic circuit CM12and the magnetic flux passing through the closed magnetic circuit CM34repel each other, a magnetic barrier is generated between the closed magnetic circuits CM12and CM34. This magnetic barrier increases the confinement property of the magnetic flux of the closed magnetic circuits CM12and CM34. As a result, it is possible to cause the magnetic barrier to act as a transformer having a sufficiently large coupling coefficient.

In addition, the coil element L1aand the coil element L2aare also coupled to each other through an electric field. Similarly, the coil element L1band the coil element L2bare coupled to each other through the electric field. Accordingly, when alternating-current signals flow in the coil element L1aand the coil element L1b, electric-field coupling causes currents to be excited in the coil element L2aand the coil element L2b.

When an alternating current flows in the first coil element L1, the direction of a current flowing in the second coil element L2as a result of the coupling the magnetic field and the direction of a current flowing in through the second coil element L2as a result of the coupling through the electric field are the same. Thus, the first coil element L1and the second coil element L2are strongly coupled to each other through both the magnetic field and the electric field.

Fifth Preferred Embodiment

FIG. 11is a circuit diagram of an antenna device105equipped with a coupling degree adjustment circuit25of a fifth preferred embodiment of the present invention. In the fifth preferred embodiment, the primary side coil of the coupling degree adjustment circuit25preferably includes four coil elements L1a, L1b, L1c, and L1d, and a secondary side coil preferably includes two coil elements L2aand L2b. The primary side circuit of the coupling degree adjustment circuit25is connected in series between the feeding circuit30and the first radiating element11, and the second radiating element12is connected to the secondary side circuit of the coupling degree adjustment circuit25.

The coil elements L1aand L1bare electromagnetically coupled to each other in opposite phases. In addition, the coil elements L1cand Lid are electromagnetically coupled to each other in opposite phases. Furthermore, the coil elements L2aand L2bare electromagnetically coupled to each other in opposite phases. The coil elements L2aand L1aare electromagnetically coupled to each other in the same phase and the coil elements L2aand L1care also electromagnetically coupled to each other in the same phase. In addition, the coil elements L2band L1bare electromagnetically coupled to each other in the same phase and the coil elements L2band Lid are also electromagnetically coupled to each other in the same phase.

FIG. 12is an exploded perspective view of the coupling degree adjustment circuit25of the fifth preferred embodiment of the present invention. As illustrated inFIG. 12, base material layers51ato51kare each defined by a magnetic sheet, and a conductor pattern is provided on each of the base material layers51bto51k. A conductor pattern73is provided on the base material layer51b, conductor patterns72and74are provided on the base material layer51c, conductor patterns71and75are provided on the base material layer51d, a conductor pattern83is provided on the base material layer51e, conductor patterns82and84are provided on the base material layer51f, conductor patterns81and85are provided on the base material layer51g, conductor patterns61and65are provided on the base material layer51h, conductor patterns62and64are provided on the base material layer51i, and a conductor pattern63is provided on the base material layer51j. On the lower surface of the base material layer51k, a feeding terminal41, a ground terminal43, an antenna terminal42as a connection port of the first radiating element, an antenna terminal44as a connection port of the second radiating element, and the like are provided. Lines extending vertically inFIG. 12represent via electrodes that provide inter-layer connections between the conductor pattern and the conductor pattern.

InFIG. 12, the conductor patterns61to65define the coil elements L1aand L1b, and the conductor patterns71to75define the coil elements L1cand L1d. In addition, the conductor patterns81to85define the coil elements L2aand L2b.

In this fifth preferred embodiment of the present invention, the secondary side coils (L2a, L2b) are disposed so as to be sandwiched by the primary side coils (L1a, L1b) and (L1C, L1d), so that the primary side coils (L1a, L1b, L1c, L1d) and the secondary side coils (L2a, L2b) are more tightly coupled. That is, the leakage magnetic field is reduced and the energy transmission loss of high-frequency signals between the primary side coils and the secondary side coils is reduced.

Sixth Preferred Embodiment

FIG. 13is a perspective view of a main portion of an antenna device106according to a sixth preferred embodiment of the present invention.FIG. 14is a circuit diagram of the antenna device106.

According to the sixth preferred embodiment of the present invention, a first radiating element11, a second radiating element12, and a third radiating element13are provided. A coupling degree adjustment circuit26A is connected between the feeding portion of these radiating elements11,12, and13, and a feeding circuit30.

The coupling degree adjustment circuit26A includes a matching circuit93, a coupling element20, and coil elements L1and L3. The coupling element20includes a primary side circuit including a coil element L2and a secondary side circuit including a coil element L4, and the coil element L2and the coil element L4are electromagnetically coupled to each other. A reactance element15is inserted between the coil element L2and the second radiating element12. Similarly, a reactance element16is inserted between the coil element L4and the third radiating element13.

Between the first radiating element11and a matching circuit93, a series circuit defined by the coil elements L1and L3is connected, and the coupling element20is connected between the connection point and ground.

By the circuit illustrated inFIG. 14, the degree of coupling between the second radiating element12and the third radiating element13can be defined by mutual induction M24between the coil elements L2and L4of the coupling element20.

FIG. 15shows a return loss characteristic of the antenna device106as viewed from the feeding circuit. InFIG. 15, “Low Band” indicates a return loss characteristic by the first radiating element11and “High Band” indicates a return loss characteristic by the second radiating element12and the third radiating element13. In other words, the first radiating element11covers a low band, and the second radiating element12and the third radiating element13cover a high band. The bandwidth of the high band can be defined by a length of the second radiating element12, a length of the third radiating element13, a reactance of the reactance elements15and16, and a degree of coupling of the coupling element20.

In this way, a plurality of radiating elements may be connected to the primary side circuit of a coupling degree adjustment circuit (26A). In addition, the plurality of radiating elements may be connected to the secondary side circuit of the coupling degree adjustment circuit.

Seventh Preferred Embodiment

FIG. 16is a circuit diagram of an antenna device107according to a seventh preferred embodiment of the present invention. According to the seventh preferred embodiment of the present invention, three radiating elements11,12, and13are provided. A coupling degree adjustment circuit26B is connected between the feeding portion of these radiating elements11,12, and13, and a feeding circuit30.

The coupling degree adjustment circuit26B includes a matching circuit93, a coupling element19, and coil elements L1and L2. The coupling element19includes a primary side circuit including a coil element L3and a secondary side circuit including a coil element L4, and the coil element L3and the coil element L4are electromagnetically coupled to each other. A reactance element16is inserted between the coil element L4and the third radiating element13.

The coil element L1is connected between the first radiating element11and the coupling element19, and the coil element L2is connected between the second radiating element12and the coupling element19.

The first radiating element11, the second radiating element12, and the third radiating element13cover a predetermined frequency band, respectively. For example, the first radiating element11covers a low band, and the second radiating element12and the third radiating element13cover a high band. The bandwidth of the high band can be defined by a length of the second radiating element12, a length of the third radiating element13, a reactance of the reactance element16, an inductance of the coil element L2, and a degree of coupling of the coupling element19.

With the above configuration, two or more plurality of radiating elements may be connected to the primary side circuit or the secondary side circuit of the coupling degree adjustment circuit.

Eighth Preferred Embodiment

FIG. 17is a circuit diagram of an antenna device108according to an eighth preferred embodiment of the present invention. According to the eighth preferred embodiment of the present invention, three radiating elements11,12, and13are provided. A coupling degree adjustment circuit26C is connected between a feeding portion of these radiating elements11,12, and13, and a feeding circuit30.

The coupling degree adjustment circuit26C includes a coupling element19and coil elements L1, L2and L3. The coupling element19includes a primary side circuit including a coil element L5and a secondary side circuit including a coil element L4, and the coil element L5and the coil element L4are electromagnetically coupled to each other. A reactance element16is inserted between the coil element L4and the third radiating element13.

The coil elements L1and L3are connected between the first radiating element11and the coupling element19, and the coil elements L2and L3are connected between the second radiating element12and the coupling element19. The coil elements L1, L2, and L3function both as a branch circuit and a matching circuit.

The first radiating element11, the second radiating element12, and the third radiating element13cover a predetermined frequency band, respectively. For example, the first radiating element11covers a low band, and the second radiating element12and the third radiating element13cover a high band. The bandwidth of the high band can be defined by a length of the second radiating element12, a length of the third radiating element13, a reactance of the reactance elements16, an inductance of the coil elements L2and L3, and a degree of coupling of the coupling element19.

In this way, a matching circuit may be provided on a side of the radiating element of the primary side circuit of the coupling degree adjustment circuit.

Ninth Preferred Embodiment

FIG. 18is a circuit diagram of an antenna device109A according to a ninth preferred embodiment of the present invention. According to the ninth preferred embodiment of the present invention, three radiating elements11,12, and13are provided. A coupling degree adjustment circuit26D is connected between the feeding portion of these radiating elements11,12, and13, and a feeding circuit30.

The coupling degree adjustment circuit26D includes a coupling element22A and coil elements L1, L2and L3. The coupling element22A includes a primary side circuit including coil elements L5and L6and a secondary side circuit including a coil element L4, and the coil element L6and the coil element L4are electromagnetically coupled to each other. A reactance element16is inserted between the coil element L4and the third radiating element13.

The coil elements L1and L3are connected between the first radiating element11and the coupling element22A, and the coil elements L2and L3are connected between the second radiating element12and the coupling element22A. The coil elements L1, L2, and L3function both as a branching circuit and a matching circuit.

Of the three coil elements L4, L5, and L6that define the coupling element22A, mutual induction M46between the coil elements L6-L4, mutual induction M56between the coil elements L6-L5, and mutual induction M45between the coil elements L5-L4are generated. An impedance of the primary side circuit, an impedance of the secondary side circuit, and a degree of coupling can be defined by the three coil elements L4, L5, and L6and the mutual induction M46, M56, and M45.

The first radiating element11, the second radiating element12, and the third radiating element13cover a predetermined frequency band, respectively. For example, the first radiating element11covers a low band, and the second radiating element12and the third radiating element13cover a high band. The bandwidth of the high band can be defined by a length of the second radiating element12, a length of the third radiating element13, a reactance of the reactance elements16, an inductance of the coil elements L2and L3, and a degree of coupling of the coupling element22A.

In this way, a coupling element may be defined by three or more coil elements.

FIG. 19is a circuit diagram of an antenna device109B equipped with a coupling element22B of which the configuration differs from the configuration of the coupling element22A. The coil elements L6a, L6b, and L5are provided in the primary side circuit. In other words, the coil element L6illustrated inFIG. 18is divided into coil elements L6aand L6b, and the coil element L6aand the coil element L5are coupled to each other and the coil element L6band the coil element L4are coupled to each other. As described above, a coupling amount and an inductance may be configured to be set up individually.

Tenth Preferred Embodiment

FIG. 20is a block diagram illustrating a configuration of a communication terminal apparatus of a tenth preferred embodiment of the present invention. This communication terminal apparatus is a mobile phone terminal, for example, and is equipped with an antenna device101, a high frequency circuit module7, a transmitting circuit6, a receiving circuit8, and a baseband circuit5. The antenna device101includes a coupling degree adjustment circuit21, and a first radiating element11and a second radiating element12. The high frequency circuit module7is equipped with a high frequency switch that switches transmitting signals in a low band and a high band and received signals in a low band and a high band and a demultiplexing/multiplexing circuit. The transmitting circuit6includes a transmitting circuit for a low band, and a transmitting circuit for a high band. In addition, the receiving circuit8includes a receiving circuit for a low band, and a receiving circuit for a high band.

While the coupling degree adjustment circuit21preferably is the coupling degree adjustment circuit21disclosed in the first preferred embodiment or the second preferred embodiment of the present invention, the coupling degree adjustment circuits described in the third to the ninth preferred embodiments of the present invention, other than this circuit, may also be used. It should be noted that the coupling degree adjustment circuit21embedded in the high frequency circuit module7may define one module.