Antenna element and antenna device

An antenna element (10) includes: a feeding point (16); a connector (15) in which an external antenna is detachably engaged; a first partial element (11) connecting the feeding point (16) and the connector (15); and a second partial element (12) branching from the first partial element (11) and having an open end (12a) at a different position from the connector (15).

TECHNICAL FIELD

The present invention relates to an antenna technology, and more specifically to an antenna technology using a detachable external antenna.

BACKGROUND ART

Patent Literature 1 discloses one of antenna technologies using a detachable external antenna. An antenna device disclosed in Patent Literature 1 uses an earphone cable as an external antenna.

CITATION LIST

Patent Literature

Patent Literature 1

SUMMARY OF INVENTION

Technical Problem

The antenna device disclosed in Patent Literature 1 can secure excellent antenna characteristics in a state where the earphone cable is engaged, but cannot receive a radio signal in a state where the earphone cable is not engaged, that is, in the absence of an antenna element.

The present invention is attained in view of the above problem. It is a main object of the present invention to provide a technology for securing excellent antenna characteristics even in a case where an external antenna is not engaged.

Solution to Problem

In order to solve the above problem, an antenna element in accordance with an aspect of the present invention includes: a feeding point; a connector in which an external antenna is detachably engaged; a first partial element connecting the feeding point and the connector; and a second partial element branching from the first partial element and having an open end at a different position from the connector.

Advantageous Effects of Invention

According to an aspect of the present invention, while the external antenna is not engaged, an electric current dominantly flows between the feeding point and the open end via the second partial element. Thus, it is possible to secure excellent antenna characteristics even in a case the external antenna is not engaged.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below with reference to the drawings. Note that members having the same function in the embodiments are given the same reference numerals.

FIG. 1is a view illustrating overviews of antenna elements10in accordance with Embodiments 1 through 3 of the present invention. (a) ofFIG. 1illustrates the overview of the antenna element10in accordance with Embodiment 1, (b) ofFIG. 1illustrates the overview of the antenna element10in accordance with Embodiment 2, and (c) ofFIG. 1illustrates the overview of the antenna element10in accordance with Embodiment 3. Note thatFIG. 1illustrates the antenna element10being incorporated into an antenna device30and being connected to a circuit section20which is provided in the antenna device30.

The antenna device30is not limited to any specific device, provided that it performs at least one of (i) transmission of radio signals and (ii) reception of radio signals via the antenna element10. For example, the antenna device30can be applied to not only terminals such as mobile phone terminals (including smart phones), mobile information terminals (including tablet terminals) but also radio devices in general, such as image display devices capable of radio transmission and/or radio reception and audio output devices capable of radio transmission and/or radio reception.

The circuit section20includes a radio circuit section21and a matching circuit section22, and transmits and receives a radio signal by feeding the antenna element10. Note that the matching circuit section22can be provided as necessary or can be omitted. Further, the matching circuit section22is adjusted so as to have an optimum matching constant in a state in which any external antenna is not engaged. However, the arrangement of the matching circuit section22is not limited to such an arrangement. For example, the matching circuit section22can be arranged such that it detects engagement of the external antenna and then switches the matching so that the matching has the optimum matching constant in a state in which the external antenna is engaged, when the external antenna is engaged.

The antenna element10is constructed by a feeding point16, a connector15, and a plurality of partial elements (11through14). The antenna element10is placed in a fully off-ground area. Note that, the fully off-ground area does not mean a transmission line having characteristic impedance of, for example, 50Ω or 75Ω, but means an area where the antenna element10is placed at a distance, from the ground, enough to operate as a so-called radiating element.

The feeding point16is a part that is fed by the circuit section20, and the feeding point16can be, for example, a junction of a feeding line extending from the circuit section20. A method for connecting the feeding point16and the feeding line extending from the circuit section20is not limited to any specific method, provided that the feeding point16and the feeding line extending from the circuit section20are connected directly to each other or connected to each other in a high-frequency manner. For example, the connection may be made by, for example, pressing or soldering a plate spring, a gasket, or the like provided at the end of the feeding line to the feeding point16. Alternatively, conductors may be faced in close proximity to each other and connected by a capacitor.

The connector15is configured such that the external antenna is detachably engaged in the connector15. As described later, the connector15can be constructed as an earphone jack in a case where the external antenna is an earphone cable. Note, however, that the external antenna is not limited to the earphone cable, provided that the external antenna is an attachable/detachable antenna and that the connector15is connected directly to the external antenna or connected to the external antenna in a high-frequency manner.

The partial elements (11through14) are parts that constitute an antenna element and are not limited to any specific ones, provided that the partial elements are conductors constructed to be capable of emitting radio waves. The partial elements can be each, for example, a conductive pattern formed on a substrate, a conductive pattern formed on a flexible printed circuit board, a conductive pattern formed on a dielectric such as a resin by LDS (Laser Direct Structuring) method, an MID (Molded Interconnect Device), a DPA (Direct Printed Antenna), or the like. Alternatively, the partial elements may be a combination of any of the exemplified ones (For example, the conductive pattern formed on the substrate is provided in an area close to a feeding end, while the pattern formed by the LDS method is provided in the other area).

In each of the embodiments, the antenna element10includes: a first partial element11connecting the feeding point16and the connector15; and a second partial element12branching at a branch point11afrom the first element11and having an open end12aat a different position from the connector15. Note that no switch is provided at the branch point11a, and the first partial element11and the second partial element12are connected to the feeding point16regardless of an engagement state of the external antenna.

In Embodiment 1, the branch point11is provided at about a midpoint position of the first partial element11(see (a) ofFIG. 1). The first partial element11constructs (i) a path from the branch point11ato the connector15and (ii) a path from the branch point11ato the feeding point16. The second partial element12constructs a path from the branch point11ato the open end12a. Note that the path from the branch point11ato the feeding point16can be referred to as a third partial element14, and the path from the feeding point16to the open end12a(in other words, a path formed by a combination of the second element12and the third element14) can be referred to as a fourth partial element13.

According to Embodiment 1, while the external antenna is engaged, an electric current dominantly flows through the external antenna and the first partial element11, and it is therefore possible to secure antenna characteristics. While the external antenna is not engaged, an electric current dominantly flows through the second partial element12and the third partial element14(i.e. the fourth partial element13), and it is therefore possible to secure antenna characteristics.

On the other hand, in a case where the second partial element12is absent, antenna characteristics can be degraded while the external antenna is not engaged. That is, in the absence of the second partial element12, an electric current dominantly flows through the first partial element11which has an open end corresponding to the connector15, while the external antenna is not engaged. In this case, the connector15can be located at a position that is unfavorable in serving as the open end of the antenna element (e.g. at a position around which a metallic component is present) because the connector15can be provided in a limited location in the antenna device in order to allow the external antenna to be detachably engaged in the connector15. Particularly, in a case where the connector15is an earphone jack, a signal wire for audio signals approaches the open end of the first partial element11. This causes degradation in antenna characteristics of the first partial element11.

In contrast, according to Embodiment 1, the open end12ais located at a different position from the connector15, and the open end12ais provided at a distance from the metallic component which is present around the connector15. This facilitates an electric current flowing through the second partial element12. Accordingly, while the external antenna is not engaged, an electric current dominantly flows between the feeding point16and the open end12avia the second partial element12. This allows the path connecting the feeding point16and the opening end12a(i.e. the fourth partial element13) to operate as a monopole antenna, and therefore makes it possible to prevent degradation in antenna characteristics. In particular, the open end12a, unlike the connector15, has a high degree of placement flexibility. Therefore, as compared to the connector15, the open end12acan be provided under conditions advantageous to an antenna, including a secure distance from a peripheral metallic component, and length, thickness, and the like appropriate for emission of radio waves. Accordingly, it is possible to attain more excellent antenna characteristics.

In Embodiment 2, the branch point11ais provided at a connection part of the first partial element11at which part the first partial element11is connected to the connector15(see (b) ofFIG. 1). The first partial element11constructs a path from the branch point11ato the feeding point16, and the second partial element12constructs a path from the branch point11ato the open end12a. Note that the path from the feeding point16to the branch point11a(i.e. the first partial element11) can be referred to as the third partial element14, and the path from the feeding point16to the open end12a(i.e. the path formed by a combination of the second partial element12and the first partial element11) can be referred to as the fourth partial element13.

According to Embodiment 2, as in Embodiment 1, while the external antenna is engaged, an electric current dominantly flows through the external antenna and the first partial element11, and it is therefore possible to secure antenna characteristics. Further, as in Embodiment 1, the open end12ais located at a different position from the connector15, and the open end12ais provided at a distance from the metallic component which is present around the connector15. This facilitates an electric current flowing through the second partial element12. Accordingly, while the external antenna is not engaged, an electric current dominantly flows through the second partial element12and the first partial element11(i.e. the fourth partial element13), and it is therefore possible to secure antenna characteristics. Further, as in Embodiment 1, the opening end12ahas a high degree of placement flexibility, Therefore, the open end12acan be provided under conditions advantageous to an antenna, including a secure distance from a peripheral metallic component, and length, thickness, and the like appropriate for emission of radio waves. Accordingly, it is possible to attain more excellent antenna characteristics.

In Embodiment 3, the first partial element11and the second partial element12are branched at the feeding point16(see (c) ofFIG. 1). The first partial element11constructs a path from the feeding point16to the connector15, and the second partial element12constructs a path from the feeding point16to the open end12a. Note that the path from the feeding point16to the open end12acan be referred to as the fourth partial element13.

According to Embodiment 3, as in Embodiment 1, while the external antenna is engaged, an electric current dominantly flows through the external antenna and the first partial element11, and it is therefore possible to secure antenna characteristics. Further, as in Embodiment 1, the open end12ais located at a different position from the connector15, and the open end12ais provided at a distance from the metallic component which is present around the connector15. This facilitates an electric current flowing through the second partial element12. Accordingly, while the external antenna is not engaged, an electric current dominantly flows through the second partial element12(the fourth partial element13), and it is therefore possible to secure antenna characteristics. Further, as in Embodiment 1, the opening end12ahas a high degree of placement flexibility, Therefore, the open end12acan be provided under conditions advantageous to an antenna, including a secure distance from a peripheral metallic component, and length, thickness, and the like appropriate for radiation of radio waves. Accordingly, it is possible to attain more excellent antenna characteristics.

(Suitable Electrical Lengths of the Partial Elements]

In each of the embodiments, the partial elements are preferably arranged such that an electrical length of the fourth partial element13(a sum of a second electrical length L2, an electrical length of the second partial element12, and an electrical length of the third partial element14) is closer to a ¼ wavelength of an applied frequency of the antenna element10than to an electrical length of the first partial element11(first electrical length L1).

According to the arrangement as described above, while the external antenna is not engaged, an electrical length of the path from the open end12ato the feeding point16(second electrical length L2) is closer to the ¼ wavelength of the applied frequency of the antenna element10than to an electrical length of the path from the connector15to the feeding point16(first electrical length L1). This generates a greater resonance in the path from the open end12aand the feeding point16(fourth partial element13) and allows a larger amount of electric current to flow over the path from the open end12ato the feeding point16(fourth partial element13). This makes it possible to further improve antenna characteristics.

Especially, the electrical length of the fourth partial element13(second electrical length L2) is preferably not less than a ⅛ wavelength of the applied frequency of the antenna element10but not more than a ⅜ wavelength of the applied frequency of the antenna element10, and is further preferably approximately a ¼ wavelength of the applied frequency of the antenna element10. With such an arrangement, the fourth partial element13suitably operates as a monopole antenna.

Further, the partial elements are preferably arranged such that an electrical length of the third partial element14(third electrical length L3) is longer than one fourth of the second electrical length L2, or that the electrical length of the third partial element14(third electrical length L3) is longer than whichever shorter one of (i) one fourth of the second electrical length L2or (ii) a 1/16 wavelength of the applied frequency of the antenna element10(In other words, the third electrical length L3is preferably longer than whichever shorter one of (i) one fourth of the second electrical length L2or (ii) the 1/16 wavelength of the applied frequency of the antenna element10.).

With such an arrangement, while the external antenna is engaged, an electric current is hard to flow through the second partial element12(resonance is hard to occur in the second partial element12), and a larger amount of electric current flows through the external antenna. This makes it possible to further improve antenna characteristics.

More specifically, an electrical length of the second partial element12(fourth electrical length L4) is determined by subtracting the electrical length of the third partial element14(third electrical length L3) from the electrical length of the fourth partial element13(second electrical length L2). With an arrangement in which the second electrical length L2is closer to the ¼ wavelength of the applied frequency of the antenna element10, and the third electrical length L3is longer than one fourth of the second electrical length L2or longer than the 1/16 wavelength of the applied frequency of the antenna element10, the electrical length of the second partial element12(fourth electrical length L4) becomes sufficiently shorter than the ¼ wavelength of the applied frequency of the antenna element10(for example, in a case where the second electrical length L2is the ¼ wavelength of the applied frequency of the antenna element10, the fourth electrical length L4becomes not more than a 3/16 wavelength of the applied frequency). Therefore, resonance in the second partial element12occurs at a frequency falling outside a band of the applied frequency (at a frequency higher than the applied frequency). With this arrangement, while the external antenna is engaged, an electric current is hard to flow through the second partial element12, and a larger amount of electric current flows through the external antenna. This makes it possible to further improve antenna characteristics.

Note that the above-described conditions are not satisfied in Embodiment 3. This is because, in Embodiment, the third partial element14is absent, and the third electrical length L3is therefore taken as 0.

[Embodiment in which the Connector15Serves as an Earphone Jack]

Next, more detailed embodiments will be described below. In Embodiments 4 through 6, the antenna devices30in Embodiments 1 through 3 respectively are arranged such that each of the antenna devices30is a mobile phone terminal having a function of receiving a digital television broadcast (one-segment broadcast or full-segment broadcast), and that each of the connectors15is an earphone jack for allowing an external antenna (earphone cable)40detachably engaged therein. The other arrangements in Embodiment 4, 5, and 6 are similar to those in Embodiment 1, 2, and 3, respectively.

In the above arrangement, the earphone cable is used as the external antenna40, and the earphone jack is used as the connector15. This arrangement eliminates the need to separately provide another connector15for allowing the external antenna to be engaged in that connector15. Further, any earphone can be used as the external antenna40.

Further, in Embodiments 4 through 6, the antenna element10is an antenna for receiving a digital television broadcast. It is considered that a user often views a digital television broadcast with the external antenna (earphone cable)40engaged in the connector15. Therefore, by using the external antenna (the earphone cable)40as an antenna for receiving a digital television broadcast, it is possible to suitably receive a digital television broadcast in order for the user to view the digital television broadcast.

FIG. 2is a view illustrating an appearance of a front side of the antenna device (mobile phone terminal)30in accordance with Embodiments 4 through 6.FIG. 2illustrates a state where the external antenna (earphone cable)40is not engaged. As illustrated inFIG. 2, the connector (earphone jack)15is provided on a right end of a top end part of the antenna device30when viewed from the front. Further, a liquid crystal panel31is provided in a central part of the antenna device30. Further, an operation button32is arranged in the lower end part of the antenna device30.

FIG. 3is views each illustrating an appearance of a back side of the antenna device (mobile phone terminal)30in accordance with Embodiments 4 through 6. (a) ofFIG. 3illustrates an appearance of a back side of the antenna device30in accordance with Embodiment 4, (b) ofFIG. 3illustrates an appearance of a back side of the antenna device30in accordance with Embodiment 5, and (c) ofFIG. 3illustrates an appearance of a back side of the antenna device30in accordance with Embodiment 6.FIG. 3illustrates a state where the external antenna (earphone cable)40is not engaged.FIG. 3also illustrates a state where a battery cover (not shown) to be placed on the rearmost back face of the antenna device30(mobile phone terminal)30is removed so that the antenna element10is exposed to view.

As illustrated inFIG. 3, in Embodiments 4 through 6, the antenna element10is provided on a back-side surface of a housing of the antenna device (mobile phone terminal)30. Further, a part where the feeding point16of the antenna element10is provided passes through the housing. The antenna element10is fed by the circuit section20via a spring, a gasket or the like, inside the housing.

In Embodiment 4, the open end12ais provided at a different position from the connector15. In other words, the open end12ais provided apart from, for example, a signal wire for audio signals which signal wire is provided in the connector15. With this arrangement, an electric current dominantly flows over a path connecting the feeding point16and the open end12a, via the second partial element12and a part of the first partial element11(see (a) ofFIG. 3). Similarly, in Embodiment 5, the open end12ais provided at a different position from the connector15, so that an electric current dominantly flows over the path connecting the feeding point16and the open end12a, via the first partial element11and the second partial element12(see (b) ofFIG. 3). In Embodiment 6, the open end12ais provided at a different position from the connector15, and an electric current dominantly flows over the path connecting the feeding point16and the open end12a, via the second partial element12(see (c) ofFIG. 3).

Accordingly, as illustrated inFIG. 4, it is possible to obtain a suitable return loss at an applied frequency. Note that,FIG. 4is a graph showing an example return loss of the antenna element10in a case where the external antenna (earphone cable)40is not engaged, in Embodiments 4 through 6.

FIG. 5is a view illustrating an appearance of a back side of the antenna device (mobile phone terminal)30in accordance with Embodiments 4 through 6.FIG. 5illustrates a state where the external antenna (earphone cable)40is engaged (a state where an earphone plug41is inserted into the connector (earphone jack)15). Further, similarly toFIG. 3,FIG. 5illustrates a state where the battery cover (not shown) to be placed in the rearmost back face of the antenna device (mobile phone terminal)30is removed so that the antenna element10is exposed to view.

In Embodiment 4, as shown in (a) ofFIG. 5, the external antenna (earphone cable)40is connected to the feeding point16via the earphone plug41, the connector (earphone jack)15, and the first partial element11. In this arrangement, the external antenna (earphone cable)40is provided apart from a metallic component of the antenna device (mobile phone terminal)30. This facilitates an electric current to flow through the external antenna (earphone cable)40. Accordingly, an electric current hardly flows through the second partial element12, but dominantly flows through the external antenna (earphone cable)40. Similarly, in Embodiment 5, the external antenna (earphone cable)40is connected to the feeding point16via the earphone plug41, the connector (earphone jack)15, and the first partial element11, so that an electric current dominantly flows through the external antenna (earphone cable)40(see (b) ofFIG. 5). Similarly, in Embodiment 6, the external antenna (the earphone cable)40is connected to the feeding point16via the earphone plug41, the connector (earphone jack)15, and the first partial element11, so that an electric current dominantly flows through the external antenna (earphone cable)40(see (c) ofFIG. 5).

Accordingly, as illustrated inFIG. 6, it is possible to obtain a highly suitable return loss at an applied frequency. Note that,FIG. 6is a graph showing an example of return loss of the antenna element10in Embodiments 4 through 6, in a case where the external antenna (earphone cable)40is engaged.

Note that, the external antenna (earphone cable)40is not limited to any specific antenna and can be any antenna irrespective of, for example, length and type. From one viewpoint, however, the electrical length of the external antenna (earphone cable)40is more preferably such that the electrical length of the external antenna40is sufficiently longer than the fourth partial element13. In addition, the electrical length of the external antenna (earphone cable)40is further preferably not less than a ⅜ wavelength of an applied frequency of the antenna element10, and particularly preferably not less than a ½ wavelength of the applied frequency. Using the external antenna (the earphone cable)40sufficiently longer in electrical length than the fourth partial element13generates no resonance of a ¼ wavelength system. This makes it possible to reduce an effect caused while the external antenna (earphone cable)40is attached to a human body (ears).

FIG. 7is a view illustrating an example main configuration of the connector (earphone jack)15in Embodiments 4 through 6. With reference toFIG. 7, the description below deals with an arrangement in which an external conductor (ground wire) of the earphone cable is used as an antenna. The present invention, however, is not limited to such an arrangement. Alternatively, a signal wire for audio signals or the like of the earphone cable can be used as an antenna.

As shown inFIG. 7, the connector (earphone jack)15includes: a signal wire15aconnecting to a signal wire for sound, microphone input, and the like of the external antenna (earphone cable)40; and a ground terminal15bfor connecting to the external conductor (ground wire).

The ground terminal15bhas branches. One branch of the ground terminal15bis connected to the ground of the antenna device (mobile phone terminal)30, and the other branch is connected to the first partial element11via a connecting part15dsuch as a gasket. A filter15cis provided between the ground terminal15band the ground and between the connecting part15dand the ground.

When the earphone plug41is inserted into the connector (earphone jack)15, the external conductor (ground wire) of the external antenna (earphone cable)40is connected to the first partial element11via the ground terminal15band the connecting part15d, so that the external conductor (ground wire) of the external antenna (earphone cable)40can be used as an antenna.

Note that the filter15cis constructed by, for example, a choke coil and is arranged to interrupt (release) an electric current of an applied frequency of the antenna element10in a high-frequency manner. Accordingly, it is possible to interrupt (release) between the ground of the antenna device (mobile phone terminal)30and the first partial element11in a high-frequency manner. Therefore, it is possible (i) to avoid a high-frequency connection between the feeding point16and the ground of the antenna device (mobile phone terminal)30, and (ii) to successfully use the external conductor (ground wire) of the external antenna (earphone cable) as an antenna.

Similarly, in a case where a signal wire of the external antenna (earphone cable)40, such as a signal wire for audio signals, is to be used as an antenna, the connecting part15dconnecting to the first partial element11is electrically connected to any one of the signal wires15awhich one is intended to be used as the antenna, and the filter15c, which is arranged so as to interrupt (release) an electric current of the applied frequency of the antenna element10in a high-frequency manner, is placed at a position closer to the circuit than to the connecting point between the signal wire15aand the connecting part15d(at a position opposite the connector15). Such an arrangement allows an existing signal wire, a ground wire, or the like to be used as an antenna, while eliminating a dedicated antenna wire.

In the above-described arrangement, a ground wire, a signal wire for audio signals or the like signal which signals are used in the external antenna (earphone cable)40are individually used as an antenna. The present invention is not limited to such an arrangement. Alternatively, a ground wire and a signal wire for audio signals or the like signals can be tied in a bundle to be used as an antenna. Further alternatively, only a plurality of signal wires for audio signals or the like signals can be tied in a bundle to be used as an antenna.

(Comparison with Another Configuration]

Another antenna device configured differently from the antenna device of the present invention will be described below in comparison with the antenna device30in accordance with the foregoing embodiments.FIG. 8is a view illustrating an antenna device configured differently from the antenna device of the present invention.

In an antenna device90illustrated in (a) ofFIG. 8, connection between the feeding point16and the connector15is made without any intermediate antenna element, as in the technique disclosed in Patent Literature 1.

Such an arrangement brings about excellent antenna characteristics in a case where the external antenna40is engaged. However, in a case where the external antenna40is not engaged, anything that can operate as an antenna does not exist. This disables transmission and reception.

In an antenna device91illustrated in (b) ofFIG. 8, the feeding point16and the connector15are connected to each other via an element92. Further, the feeding point16and the connector15are connected to both ends of the element92.

Such an arrangement brings about excellent antenna characteristics in a case where the external antenna40is engaged. However, in a case where the external antenna40is not engaged, the open end of the element92corresponds to the connector15. Therefore, the open end approaches a metallic component, such as a signal wire for audio signals, provided in the connector15. Thus, it is difficult to secure excellent antenna characteristics.

In contrast, the antenna device30in accordance with the foregoing embodiment can secure excellent antenna characteristics even in a case where the external antenna40is not engaged.

An antenna element10in accordance with Aspect 1 of the present invention includes: a feeding point16; a connector15in which an external antenna40is detachably engaged; a first partial element11connecting the feeding point16and the connector15; and a second partial element12branching from the first partial element11and having an open end12aat a different position from the connector15.

According to the above arrangement, while the external antenna40is not engaged, an electric current dominantly flows between the feeding point16and the open end12avia the second partial element12. This makes it possible to secure antenna characteristics.

On the other hand, in a case where the second partial element12is absent, antenna characteristics can be degraded while the external antenna40is not engaged. That is, in the absence of the second partial element12, an electric current dominantly flows through the first partial element11whose open end corresponds to the connector15, while the external antenna is not engaged. In this case, the connector15can be located at a position that is unfavorable in serving as the open end of the antenna element (e.g. at a position around which a metallic component is present) because an available location of the connector15can be provided in a limited location in the antenna device in order to allow the external antenna to be engaged in the connector15detachably. Particularly in a case where the connector15is an earphone jack, a signal wire for audio signals approaches the open end of the first partial element11. This causes degradation in antenna characteristics of the first partial element11.

In contrast, according to the above arrangement, the open end12ais located at a different position from the connector15, and the open end12ais provided at a distance from the metallic component which is present around the connector15. This facilitates an electric current flowing through the second partial element12. Accordingly, while the external antenna40is not engaged, an electric current dominantly flows between the feeding point16and the open end12avia the second partial element12. This allows the path connecting the feeding point16and the open end12ato operate as a monopole antenna, and therefore makes it possible to prevent degradation in antenna characteristics.

As described above, the above arrangement makes it possible to secure excellent antenna characteristics even in a case where the external antenna40is not engaged.

The antenna element10in accordance with Aspect 2 of the present invention is preferably arranged in Aspect 1 such that a second electrical length L2from the feeding point16to the open end12ais closer to a ¼ wavelength of an applied frequency of the antenna element10than a first electrical length L1from the feeding point16to the connector15is.

According to the above arrangement, a greater resonance is generated over the path from the open end12ato the feeding point16via the second partial element12, and a larger amount of electric current flows over the path from the open end12ato the feeding point16. Therefore, it is possible to further improve antenna characteristics.

The antenna element10in accordance with Aspect 3 of the present invention is preferably arranged in Aspect 2 such that a third electrical length L3from the feeding point16to a branch point11aat which and the second partial element12is branched from the first partial element11is longer than whichever shorter one of (i) one fourth of the second electrical length L2or (ii) a 1/16 wavelength of the applied frequency of the antenna element10.

According to the above arrangement, the electrical length of the second partial element12is sufficiently shorter than the ¼ wavelength of the applied frequency of the antenna element10. This causes the second partial element12to resonate at a frequency falling outside a band of the applied frequency (at a frequency higher than the applied frequency). With this arrangement, while the external antenna is engaged, an electrical current is hard to flow through the second partial element12, and a larger amount of electric current flows through the external antenna. This makes it possible to further improve antenna characteristics.

The antenna element10in accordance with Aspect 4 of the present invention can be arranged in Aspects 1 through 3 such that the external antenna40is an earphone cable while the connector15is an earphone jack.

According to the above arrangement, the earphone cable is used as the external antenna40, while the earphone jack is used as the connector15. This arrangement eliminates the need to separately provide another connector15for allowing the external antenna to be engaged in that connector15.

The antenna device30in accordance with Aspect 5 of the present invention is provided with the antenna element10of Embodiments 1 through 4 described earlier.

According to the above arrangement, the antenna device30can secure excellent antenna characteristics even in a case where the external antenna40is not engaged.

The antenna device30in accordance with Aspect 6 of the present invention may be arranged in Aspect 5 such that the antenna device30includes a metallic component (such as signal wires15a), wherein the open end12ais provided farther from the metallic component than the connector15is.

According to the above arrangement, it is possible to secure more excellent antenna characteristics in a case where the external antenna40is not engaged.

The present invention is not limited to the descriptions of the embodiments, but can be altered by a person skilled in the art within the scope of the claims. An embodiment derived from a proper combination of technical means disclosed in different embodiments is also encompassed in the technical scope of the present invention. Moreover, a novel technical feature can be created by a combination of technical means disclosed in these embodiments.

INDUSTRIAL APPLICABILITY

The present invention is applicable to radio devices in general.

REFERENCE SIGNS LIST