Antenna structure and wireless communication device having the same

An antenna element has a dielectric base, at least a portion of which is arranged in a non-ground region of a substrate. A feeding radiation electrode has an intermediate path that is connected to a feeding portion and that is arranged to extend in a perimeter direction of the dielectric base on a side surface of the dielectric base adjacent to the non-ground region and spaced away from a ground region. The feeding radiation electrode has an open end side path that is arranged to extend along a loop path from the termination of the intermediate path and an open end of the extended distal end is arranged parallel or substantially parallel to and spaced apart from the intermediate path. A dielectric material having a high dielectric constant, which increases the capacitance between the intermediate path and the open end, is located in a region including the spaced region between the intermediate path and parallel or substantially parallel open end.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antenna structure provided for a wireless communication device, such as a cellular phone, and a wireless communication device having the antenna structure.

2. Description of the Related Art

FIG. 9is a schematic perspective view of an example of an antenna structure (for example, see Japanese Unexamined Patent Application Publication No. 2006-203446). The antenna structure40has an antenna element41. The antenna element41is defined by a dielectric base42and a feeding radiation electrode43. The feeding radiation electrode43is provided on the dielectric base42and operates as an antenna. The feeding radiation electrode43has a slit S. Due to the slit S, the feeding radiation electrode43has a long electrical length extending from a feeding portion Q, which defines one end of a current path of the feeding radiation electrode43, to an open end K, which defines the other end, as compared to the case in which no slit S is provided. Thus, by elongating the electrical length, the size of the feeding radiation electrode43is reduced, while the feeding radiation electrode43may have an electrical length with which the feeding radiation electrode43resonates at a predetermined wireless communication frequency band.

The antenna element41is, for example, mounted in a non-ground region Zp of a circuit board44of a wireless communication device. The circuit board44has a ground region Zg in which a ground electrode45is provided and the non-ground region Zp in which no ground electrode45is provided. The antenna element41is mounted on the non-ground region Zp. When the antenna element41is mounted at a predetermined position in the non-ground region Zp, the feeding portion Q of the feeding radiation electrode43is electrically connected to a wireless communication circuit47through a feeding line46provided on the circuit board44.

In the antenna structure40, for example, when a wireless transmission signal is supplied from the wireless communication circuit47to the feeding radiation electrode43, the feeding radiation electrode43resonates and then the wireless transmission signal is wirelessly transmitted. In addition, when a signal arrives and the feeding radiation electrode43resonates to receive the signal, the received signal is transferred from the feeding radiation electrode43to the wireless communication circuit47.

Incidentally, in recent years, miniaturization has been required, particularly, for a wireless communication device, such as a portable mobile terminal with wireless communication function (for example, cellular phone). Because of this requirement, miniaturization is also required for the antenna structure. To miniaturize the antenna element41, the feeding radiation electrode43also needs to be miniaturized. However, when the feeding radiation electrode43is miniaturized, the electrical length becomes insufficient and, therefore, the resonant frequency of the feeding radiation electrode43cannot be decreased to a desired frequency. As a result, the feeding radiation electrode43is not able to wirelessly communicate in a predetermined wireless communication frequency band. Thus, to miniaturize the feeding radiation electrode43, it is necessary to take some measures to elongate the electrical length.

As an example of such measures, as shown inFIG. 9, the feeding radiation electrode43has a meandering shape, or other suitable shape, to elongate the physical length from the feeding portion Q to the open end K, thus elongating the electrical length. When these measures are used, the shape of the feeding radiation electrode43is complex and, in addition, the path width of the feeding radiation electrode43is relatively narrow. A narrow path width problematically causes an increase in conduction loss and, as a result, the efficiency of the antenna deteriorates. In addition, with a complex shape, a problem arises in that it is difficult to adjust the resonant frequency of the feeding radiation electrode43.

In addition, with the configuration of the antenna structure40shown inFIG. 9, in addition to the problems related to miniaturization, the following problems also exist. That is, the antenna element41is mounted on the circuit board44, such that the antenna element41is arranged adjacent to the ground electrode45that is required for the circuit board44. Then, the electric field of the feeding radiation electrode43is attracted toward the ground electrode45to increase the Q value. For this reason, there is a problem in that it is difficult to provide a wide frequency band for wireless communication.

In addition, for example, a hand that is holding or operating a wireless communication device (for example, cellular phone) may be located near the feeding radiation electrode43. The hand functions as a ground and, therefore, a stray capacitance is formed between the feeding radiation electrode43and the hand. Due to the stray capacitance, there is a problem in that the antenna characteristic fluctuates or degrades to reduce the reliability to wireless communication.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention are provided.

An antenna structure according to a preferred embodiment of the present invention includes an antenna element including a feeding radiation electrode, which operates as an antenna, that is provided on a dielectric base, and a substrate including a ground region in which a ground electrode is provided and a non-ground region in which no ground electrode is provided, wherein the antenna element is supported by the substrate so that at least portion of the antenna element is arranged in the non-ground region, wherein the feeding radiation electrode includes an intermediate path that is connected to a feeding portion of the feeding radiation electrode for electrical conduction and that is arranged to extend in a perimeter direction on a side surface of the dielectric base adjacent to the non-ground region, and an open end side path that is arranged to extend along a loop path that extends from the termination of the intermediate path in a direction so as to separate from the intermediate path on a surface of the dielectric base and then return toward the intermediate path, wherein an open end of the extended distal end is parallel or substantially parallel to and spaced apart from the intermediate path, wherein the dielectric base includes a plurality of base portions including a base portion having a portion disposed in a spaced region between the parallel or substantially parallel open end and intermediate path of the feeding radiation electrode, and wherein the base portion having the portion disposed in the spaced region between the parallel or substantially parallel open end and intermediate path is made of a dielectric material having a dielectric constant greater than dielectric constants of the other base portions.

An antenna structure according to another preferred embodiment of the present invention includes an antenna element including a feeding radiation electrode, which operates as an antenna, that is provided on a dielectric base, and a substrate including a ground region in which a ground electrode is provided and a non-ground region in which no ground electrode is provided, wherein the antenna element is supported by the substrate so that at least portion of the antenna element is arranged in the non-ground region, wherein the feeding radiation electrode includes an intermediate path that is connected to a feeding portion of the feeding radiation electrode for electrical conduction and that is arranged to extend in a perimeter direction on a side surface of the dielectric base adjacent to the non-ground region, and an open end side path that is arranged to extend along a loop path that extends from the termination of the intermediate path in a direction so as to separate from the intermediate path on a surface of the dielectric base and then return toward the intermediate path, wherein an open end of the extended distal end is parallel or substantially parallel to and spaced apart from the intermediate path, and wherein a dielectric material having a dielectric constant greater than the dielectric base is disposed in the spaced region between the parallel or substantially parallel open end and intermediate path of the feeding radiation electrode.

A wireless communication device according to another preferred embodiment of the present invention includes an antenna according to a preferred embodiment of the present invention.

In various preferred embodiments of the present invention, the open end of the feeding radiation electrode is preferably arranged parallel or substantially parallel to and spaced apart from the intermediate path, and a capacitance is generated and present between the open end and the intermediate path. The open end is a portion having the strongest electric field within the feeding radiation electrode. Thus, by forming the capacitance between the open end and the intermediate path, it is possible to effectively increase the capacitance component of the feeding radiation electrode to thereby elongate the electrical length. By so doing, preferred embodiments of the present invention greatly decrease the resonant frequency of the feeding radiation electrode.

In addition, a preferred embodiment of the present invention preferably includes any one of the following configurations. That is, preferred embodiments of the present invention provide a configuration in which a dielectric base portion having a portion disposed in the spaced region between the parallel or substantially parallel open end and intermediate path is made of a dielectric material having a dielectric constant greater than the other dielectric base portion. In addition, another preferred embodiment of the present invention provides a configuration in which a dielectric material having a dielectric constant greater than the dielectric base is disposed in the spaced region. With these configurations, preferred embodiments of the present invention are able to further increase the capacitance between the open end and the intermediate path to elongate the electrical length and, therefore, it is possible to decrease the resonant frequency of the feeding radiation electrode. Thus, preferred embodiments of the present invention are able to overcome the problem that the electrical length is insufficient and, therefore, it is easy to miniaturize the feeding radiation electrode.

In preferred embodiments of the present invention, the feeding radiation electrode preferably has a plurality of resonant frequencies. Then, among these plurality of resonant frequencies, by utilizing a basic mode which is a resonant operation at a basic resonant frequency, which is the lowest frequency, and a higher mode which is a resonant operation at a higher resonant frequency that is greater than the basic resonant frequency, wireless communication may be performed at a plurality of frequencies with one feeding radiation electrode.

Between the higher resonant frequency and the basic resonant frequency, the higher resonant frequency is substantially an integral multiple of the basic resonant frequency. With the above relationship, as the basic resonant frequency is decreased, the higher resonant frequency is also decreased. In addition, the resonant frequency of the feeding radiation electrode is preferably adjusted by changing the inductance component of the feeding radiation electrode or changing the capacitance component, and the rate of change in the higher resonant frequency with respect to a change in inductance component of the feeding radiation electrode is greater than the rate of change in the basic resonant frequency.

Thus, for example, in order to eliminate an insufficient electrical length due to miniaturization, when the resonant frequency is adjusted by changing the inductance component of the feeding radiation electrode, the following problem arises. That is, when the basic resonant frequency is decreased to a desired frequency by increasing the inductance component of the feeding radiation electrode to elongate the electrical length, a problem of top loading occurs. The top loading problem means that the higher resonant frequency excessively decreases beyond the allowable range of variations in frequency.

In contrast, according to preferred embodiments of the present invention by increasing the capacitance between the open end and the intermediate path, the capacitance component of the feeding radiation electrode is increased and, therefore, it is possible to easily decrease the resonant frequency. That is, preferred embodiments of the present invention prevent the top loading problem by adjusting the capacitance component of the feeding radiation electrode to thereby adjust the resonant frequency.

In addition, with preferred embodiments of the present invention, it is easy to adjust the dielectric constant of the spaced region between the parallel or substantially parallel open end and intermediate path. Thus, it is easy to adjust the resonant frequency of the feeding radiation electrode by adjusting the capacitance between the open end and the intermediate path. Furthermore, preferred embodiments of the present invention are able to decrease the resonant frequency of the feeding radiation electrode by increasing the capacitance between the open end and the intermediate path. Thus, preferred embodiments of the present invention do not require the feeding radiation electrode to have a complex shape, such as a meandering shape, for example, as is required in the prior art. That is, preferred embodiments of the present invention do not require a reduction in the path width of the feeding radiation electrode. Thus, it is possible to prevent a conduction loss by preventing the concentration of electric current and, therefore, it is possible to improve the efficiency of the antenna.

Furthermore, in preferred embodiments of the present invention, the one end, at which the electric field is strongest within the feeding radiation electrode, is provided on the side surface of the dielectric base adjacent to the non-ground region spaced away from the ground region (or in a region at an end of the dielectric film adjacent to the non-ground region spaced away from the ground region). Moreover, preferred embodiments of the present invention form a capacitance between the open end and the intermediate path. Thus, preferred embodiments of the present invention are able to greatly reduce the electric field attracted to the ground electrode from the feeding radiation electrode. Thus, in preferred embodiments of the present invention, because the Q value is decreased to widen the frequency band, it is possible to improve the efficiency of the antenna.

Furthermore, preferred embodiments of the present invention have a configuration in which the open end, at which the electric field is strongest within the feeding radiation electrode, forms a capacitance with the intermediate path. Thus, for example, even when the hand of a person who operates the wireless communication device is located adjacent to the feeding radiation electrode, it is possible to prevent the stray capacitance between the feeding radiation electrode and the hand. By so doing, preferred embodiments of the present invention prevent variations and degradation of the antenna characteristic due to the hand of a person, and the like, and, therefore, it is possible to improve the reliability of wireless communication.

Furthermore, when the dielectric base is preferably made of resin, for example, when the feeding radiation electrode is defined by a conductor plate, the feeding radiation electrode may be integrally molded with the dielectric base by insert molding, for example. Thus, it is easy to manufacture the antenna element, and it is possible to thermally weld the feeding radiation electrode with the dielectric base or adhesively bond the feeding radiation electrode with the dielectric base, for example.

When the feeding radiation electrode is preferably formed by plating, the dielectric base made of resin needs to be configured so that a portion defining the feeding radiation electrode is made of a resin having good plating adhesion. Thus, the entire dielectric base may preferably be made of a resin having good plating adhesion, for example. However, a resin having good plating adhesion typically has a low dielectric constant and, therefore, it is impossible to satisfactorily increase the capacitance between the open end of the feeding radiation electrode and the intermediate path.

Thus, in a preferred embodiment of the present invention in which the feeding radiation electrode is formed by plating, the dielectric base surface portion on which the feeding radiation electrode is formed, is preferably made of a resin having a low dielectric constant (for example, relative dielectric constant less than about 6) and having good plating adhesion, and the majority of the remaining dielectric base portion is preferably made of a resin having a high dielectric constant (for example, relative dielectric constant greater than or equal to about 6) and having poor plating adhesion. In this manner, by configuring the dielectric base to have a combination of the resin having good plating adhesion and the resin having poor plating adhesion, it is possible to obtain a configuration in which a dielectric material having a high dielectric constant that increases the capacitance between the open end and the intermediate path is provided in the spaced region between the open end and the intermediate path.

In addition, in another preferred embodiment of the present invention, the dielectric base surface portion, on which the feeding radiation electrode is disposed, is preferably made of a resin having a low dielectric constant and good plating adhesion, the spaced region between the open end and the intermediate path is preferably made of a resin having a dielectric constant, which is greater than the resin having the low dielectric constant and good plating adhesion, and poor plating adhesion, and the majority of the remaining dielectric base portion is preferably made of a resin having a low dielectric constant and poor plating adhesion. A dielectric material having a high dielectric constant, which increases the capacitance between the open end and the intermediate path, is preferably provided in the spaced region between the open end and the intermediate path. With this configuration, it is possible to form the feeding radiation electrode on the dielectric base made of resin by plating, for example. Furthermore, with this configuration, it is possible to arrange a dielectric material that increases the capacitance between the open end and the intermediate path in the spaced region between the open end of the feeding radiation electrode and the intermediate path. Furthermore, with this configuration, because the other portion is made of a resin having a low dielectric constant, it is possible to reduce the electric field caught by a ground.

Furthermore, when the non-feeding radiation electrode is provided on the dielectric base in addition to the feeding radiation electrode, it is possible to widen the frequency band of wireless communication using multiple resonations of the feeding radiation electrode and non-feeding radiation electrode and, therefore, it is possible to improve the antenna characteristic.

In addition, with a configuration in which a dielectric material having a dielectric constant, by which the electromagnetic coupling state between the feeding radiation electrode and the non-feeding radiation electrode is adjusted, is provided in the spaced region between the feeding radiation electrode and the non-feeding radiation electrode in the dielectric base, the following advantages are obtained. That is, with the above-described configuration, it is possible to easily adjust the electromagnetic coupling state between the feeding radiation electrode and the non-feeding radiation electrode to thereby make it possible to easily adjust the input impedance of the antenna element. Thus, it is easy to match the impedance of the antenna element with the impedance of the wireless communication circuit side that is electrically connected to the antenna element and, therefore, it is easy to improve the efficiency of the antenna. Therefore, preferred embodiments of the present invention having the above configuration obtain further improved antenna characteristics.

Furthermore, preferred embodiments of the present invention provide a configuration in which the antenna element is fixedly supported on the inner wall surface of the housing in which the substrate is accommodated and arranged instead of being fixed to the substrate, such that it is possible to increase the area of the substrate for mounting components by not arranging the antenna element on the substrate. In addition, because the housing easily ensures an installation space for the antenna element as compared to the substrate, it is possible to decrease the restrictions on the size of the antenna element. Furthermore, with the configuration that the feeding radiation electrode is provided on the dielectric film, it is possible to reduce the thickness of the antenna element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments according to the present invention will be described with reference to the accompanying drawings.

FIG. 1Ashows a schematic perspective view of an antenna structure according to a first preferred embodiment. FIG.1B shows a schematic perspective view of the antenna structure as viewed from the rear side ofFIG. 1A.FIG. 1Cis a schematic exploded view of the antenna structure ofFIG. 1A. The antenna structure1of the first preferred embodiment includes an antenna element2and a substrate3. The substrate3is preferably a circuit board of a wireless communication device, such as a cellular phone, for example. The substrate3includes a ground region Zg in which a ground electrode4is provided and a non-ground region Zp in which no ground electrode4is provided. In the first preferred embodiment, the non-ground region Zp is disposed at one end of the substrate3. In addition, a wireless communication circuit (high-frequency circuit)5is provided on the substrate3(seeFIG. 1B).

The antenna element2is preferably mounted (surface mounted) in the non-ground region Zp of the substrate3. The antenna element2preferably includes a dielectric base6and a feeding radiation electrode7. The dielectric base6preferably has a rectangular parallelepiped shape, for example. A dielectric material8having a high dielectric constant is provided at a surface portion of a region A shown inFIG. 1con the dielectric base6. In other words, in the first preferred embodiment, the dielectric base6preferably includes a base portion that defines the surface portion of the region A and a base portion other than the base portion. The region A is arranged in accordance with a specific portion of the feeding radiation electrode7, and the specific portion will be described later.

In the first preferred embodiment, the dielectric material that defines the dielectric base6is preferably a resin having a relative dielectric constant less than about 6, for example. An example of the dielectric material is an LCP (liquid crystal polyester resin) or SPS (syndiotactic polystyrene resin) preferably having a relative dielectric constant less than about 6, for example. In addition, the dielectric material8having a high dielectric constant, provided on the surface portion of the region A of the dielectric base6, is preferably a composite resin having a relative dielectric constant greater than or equal to about 6, for example. An example of the dielectric material having a high dielectric constant is an LCP or an SPS having a relative dielectric constant greater than or equal to about 6, mixed with a ceramic powder. The dielectric material8having a high dielectric constant is preferably embedded in the surface portion of the dielectric base6. The thickness of the dielectric material8having a high dielectric constant is, for example, about 1 mm, and is preferably thinner than the thickness of the dielectric base6.

The feeding radiation electrode7is defined by a conductor plate. The feeding radiation electrode7is integrally bonded on the surface of the dielectric base6preferably using an insert molding technique, thermal welding method, adhesive bonding method, or other suitable method. The feeding radiation electrode7has a portion disposed on a front surface6fof the dielectric base6, a portion disposed on a top surface6tof the dielectric base6, and a portion extending from the portion disposed on the top surface6t, to a rear surface6b. An extended distal end portion of the feeding radiation electrode7, extended to the rear surface6b, defines a feeding portion Q, and the feeding portion Q is electrically connected to the wireless communication circuit5. The feeding radiation electrode7preferably has a slit S to regulate a current path. Based on the current path, the feeding radiation electrode7is divided into a feeding portion side path10, an intermediate path11and an open end side path12.

The feeding portion side path10is a feeding radiation electrode portion that extends from the feeding portion Q through the rear surface6band top surface6tof the dielectric base6to the front surface6f. Note that the front surface6fis a side surface on the side adjacent to the non-ground region Zp and away from the ground region Zg. The intermediate path11is a feeding radiation electrode portion that extends from the termination of the feeding portion side path10on the front surface6fof the dielectric base6in a perimeter direction (in other words, in a direction along the lower side of the front surface6f). The open end side path12is a feeding radiation electrode portion that extends along a loop path that extends from the termination of the intermediate path11in a direction to separate from the intermediate path11on the surface of the dielectric base6and then returns toward the intermediate path11. The extended distal end defines an open end K of the feeding radiation electrode7, and the open end K is parallel or substantially parallel to and spaced apart from the intermediate path11.

The above-described region A of the dielectric base6is a spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7. As described above, the region A is preferably made of the dielectric material having a dielectric constant greater than the dielectric base portion other than the region A. Thus, the first preferred embodiment is capable of increasing the capacitance formed between the open end K and the intermediate path11as compared to a configuration in which the region A has the same dielectric constant as that of the other dielectric base portion.

Note that in the first preferred embodiment, the dielectric material having a high dielectric constant, provided in the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7, is embedded in the surface portion of the dielectric base6to define a portion of the dielectric base6(a portion that defines the dielectric base6). Instead of providing the portion of the dielectric base6, for example, the dielectric material having a high dielectric constant may be configured as follows. That is, the dielectric material having a high dielectric constant may be a sheet-like member (high dielectric constant sheet)13as shown inFIG. 2. The high dielectric constant sheet13is preferably bonded by, for example, an adhesive agent, to the surface of the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7. In this case, the high dielectric constant sheet13is capable of increasing the capacitance between the open end K of the feeding radiation electrode7and the intermediate path11.

In addition, in the first preferred embodiment, the feeding radiation electrode7is preferably made of a conductor plate. Instead, the feeding radiation electrode7may be, for example, made of a conductor film on a film made of resin to define a film antenna, and the film antenna may be adhesively bonded to the dielectric base6.

Hereinafter, a second preferred embodiment of the present invention will be described. Note that in the description of the second preferred embodiment, like reference numerals denote like components to those of the first preferred embodiment, and repetitive description of the same components is omitted.

In the second preferred embodiment, the feeding radiation electrode7is preferably formed by plating, for example.FIG. 3Aschematically shows the dielectric base6in the second preferred embodiment as viewed from the front side.FIG. 3Bschematically shows the dielectric base6ofFIG. 3Aas viewed from the rear side. As shown inFIGS. 3A and 3B, the dielectric base6preferably includes a base portion made of a resin14having a high dielectric constant and poor plating adhesion and a base portion made of a resin15having a low dielectric constant and good plating adhesion. The resin15having a low dielectric constant and good plating adhesion defines a surface portion of a feeding radiation electrode forming region. The resin14having a high dielectric constant and poor plating adhesion preferably defines the majority of the dielectric base portion other than the base portion made of the resin15. The resin14having a high dielectric constant and poor plating adhesion is preferably a dielectric material having, for example, a relative dielectric constant greater than or equal to about 6 and that is poorly adhesive to a plated conductor film. The resin having poor plating adhesion may be, for example, polyester, polyphenylene sulfide, polyether ether ketone, polyether imide, polysulfone, polyether sulfone, SPS, or other suitable resin. By adding the above resin with, for example, ceramic powder, or other suitable resin, for increasing the dielectric constant, it is possible to increase the relative dielectric constant to, for example, about 6 or greater. In addition, the resin15having a low dielectric constant and good plating adhesion is preferably a dielectric material having, for example, a relative dielectric constant less than about 6 and that has good adhesion to a plated conductor film. The resin having good plating adhesion preferably may be, for example, a resin that is obtained by mixing the above described resin having poor plating adhesion with an electroless plating catalyst so as to have a property of good plating adhesion.

Because the dielectric base6is configured as described above, the second preferred embodiment has the following features. That is, when the dielectric base6is immersed in a plating liquid, a plated conductor film is provided only on the surface of a portion of the dielectric base6, at which the resin15having good plating adhesion is provided, to thereby form the feeding radiation electrode7. Here, because the region in which the slit S of the feeding radiation electrode7is provided is made of the resin14having poor plating adhesion, no conductor film is formed and, as a result, the slit S is formed. Then, the resin14having poor plating adhesion is a dielectric material having a high dielectric constant, so the following configuration similar to that of the first preferred embodiment is formed in the second preferred embodiment. That is, the dielectric material having a dielectric constant greater than the resin14having good plating adhesion, located at the dielectric base portion at which the open end K and the intermediate path11are provided, is arranged in the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7.

The configuration other than the above in the antenna structure1of the second preferred embodiment is similar to that of the first preferred embodiment.

Hereinafter, a third preferred embodiment of the present invention will be described. Note that in the description of the third preferred embodiment, like reference numerals denote like components to those of the first and second preferred embodiments, and repetitive description of the same components is omitted.

In the third preferred embodiment, the feeding radiation electrode7is formed by plating, for example. In addition,FIG. 4Aschematically shows a state of the dielectric base6in the third preferred embodiment as viewed from the front side.FIG. 4Bschematically shows a state of the dielectric base6ofFIG. 4Aas viewed from the rear side. As shown inFIGS. 4A and 4B, the dielectric base6includes a base portion made of a resin14having a high dielectric constant and poor plating adhesion, a base portion made of a resin15having a low dielectric constant and good plating adhesion, and a base portion made of a resin16having a low dielectric constant and poor plating adhesion. Note that, the resin having a high dielectric constant is preferably, for example, a resin having a relative dielectric constant greater than or equal to about 6, and the resin having a low dielectric constant is preferably, for example, a resin having a relative dielectric constant less than about 6. The resin14having a high dielectric constant and poor plating adhesion preferably defines a surface portion of a spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7. The resin15having a low dielectric constant and good plating adhesion preferably defines a surface portion of a feeding radiation electrode forming region. The resin16having a low dielectric constant and poor plating adhesion preferably defines the majority of the dielectric base portion other than those portions described above.

In the third preferred embodiment, the resin provided at the surface portion of the feeding radiation electrode forming region of the dielectric base6is a resin having good plating adhesion. For this reason, the third preferred embodiment, as well as the second preferred embodiment, is capable of easily forming the feeding radiation electrode7in the feeding radiation electrode forming region of the dielectric base6by plating, for example. Note that in the third preferred embodiment, the resin16having poor plating adhesion, which primarily defines the dielectric base6, is preferably a dielectric material having a low dielectric constant. Therefore, in the third preferred embodiment, if the resin15having good plating adhesion is provided only at the surface portion of the feeding radiation electrode forming region in the resin16having poor plating adhesion, the following problem occurs. That is, the dielectric material provided in the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7is the resin16having a low dielectric constant and poor plating adhesion, which is the same as that of the other regions in which the slit S is provided. Then, in order to increase the dielectric constant of the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7, in the third preferred embodiment, the surface portion of the dielectric base is made of the resin14having a high dielectric constant and poor plating adhesion as described above. Thus, the dielectric constant of the spaced region between the parallel or substantially parallel open end K and intermediate path11increases to thereby make it possible to increase the capacitance.

The configuration other than the above in the antenna structure1of the third preferred embodiment is similar to that of the first or second preferred embodiment.

Hereinafter, a fourth preferred embodiment of the present invention will be described. Note that in the description of the fourth preferred embodiment, like reference numerals denote like components to those of the first to third preferred embodiments, and repetitive description of the same components is omitted.

FIG. 5Ashows a schematic perspective view of an antenna structure according to the fourth preferred embodiment.FIG. 5Bshows a schematic perspective view of the antenna structure as viewed from the rear side ofFIG. 5A. The antenna structure1of the fourth preferred embodiment includes a non-feeding radiation electrode18on the dielectric base6of the antenna element2in addition to the configurations of the first to third preferred embodiments. The non-feeding radiation electrode18is preferably arranged adjacent to the feeding radiation electrode7at an interval D, and is preferably electromagnetically coupled to the feeding radiation electrode7to generate multiple resonances. The non-feeding radiation electrode18, as well as the feeding radiation electrode7, is preferably defined by a conductor plate, a conductor film that defines a film antenna, or a plated conductor film. In the fourth preferred embodiment, the non-feeding radiation electrode18preferably has a slit S, and a current path of the non-feeding radiation electrode18has a loop shape. In addition, one end of the non-feeding radiation electrode18defines a ground end G, and the other end defines an open end K. The non-feeding radiation electrode18has a ground end side path20, an intermediate path21, and an open end side path22.

The ground end side path20is preferably a non-feeding radiation electrode portion that is arranged to extend from the ground end G through the top surface6tof the dielectric base6toward the side surface (front surface)6fof the dielectric base6adjacent to the non-ground region Zp and away from the ground region Zg. The intermediate path21is preferably a non-feeding radiation electrode portion that is arranged to extend from the termination of the ground end side path20on the front surface6fof the dielectric base6in a perimeter direction of the dielectric base6. The open end side path22is preferably a non-feeding radiation electrode portion that is arranged to extend along a loop path that extends from the termination of the intermediate path21in a direction to separate from the intermediate path21on the front surface6fand top surface6tof the dielectric base6and then returns toward the intermediate path21. The extended distal end of the open end side path22defines an open end K, and the open end K is preferably parallel or substantially parallel to and spaced apart from the intermediate path21.

The dielectric base6of the fourth preferred embodiment may have any one of the configurations of the dielectric bases6described above in the first to third preferred embodiments. For example, when the feeding radiation electrode7is made of a conductor plate, the dielectric base6preferably has a configuration similar to the first preferred embodiment. When the feeding radiation electrode7is formed by plating, the dielectric base6preferably has a configuration similar to the second or third preferred embodiment. In the dielectric base6of the fourth preferred embodiment, as described in the first to third preferred embodiments, the dielectric material (not shown inFIGS. 5A and 5Bbut shown as a dielectric material8inFIG. 1A, a high dielectric constant sheet13inFIG. 2, and a resin14inFIGS. 3A and 4A) having a high dielectric constant is provided in the spaced region between the parallel open end K and intermediate path11of the feeding radiation electrode7. In addition, when further improved antenna characteristics are required, in the dielectric base6, a dielectric material having a high dielectric constant is provided in the spaced region between the parallel or substantially parallel open end K and intermediate path21of the non-feeding radiation electrode18. The dielectric material having a high dielectric constant provided in the spaced region between the parallel or substantially parallel open end K and intermediate path21may be the same as or may be different from the dielectric material having a high dielectric constant formed in the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7.

Furthermore, in the dielectric base6, a dielectric material24is preferably provided in a spaced region D between the feeding radiation electrode7and the non-feeding radiation electrode18. The dielectric material24preferably has a dielectric constant by which the electromagnetic coupling state between the feeding radiation electrode7and the non-feeding radiation electrode18is adjusted to a predetermined state. As the electromagnetic coupling state between the feeding radiation electrode7and the non-feeding radiation electrode18is changed, the input impedance of the feeding radiation electrode7varies. Thus, the dielectric constant between the feeding radiation electrode7and the non-feeding radiation electrode18is set so that the electromagnetic coupling state between the feeding radiation electrode7and the non-feeding radiation electrode18matches the impedance of the antenna element2(feeding radiation electrode7) with the impedance of the wireless communication circuit5. In accordance with this setting, the dielectric material24is determined. The dielectric material24may have a dielectric constant greater than the dielectric constant of the dielectric base6or may have a dielectric constant less than the dielectric constant of the dielectric base6.

Hereinafter, a fifth preferred embodiment of the present invention will be described. Note that in the description of the fifth preferred embodiment, like reference numerals denote like components to those of the first to fourth preferred embodiments, and repetitive description of the same components is omitted.

FIG. 6Aschematically shows the antenna structure1according to the fifth preferred embodiment of the present invention as viewed from the lower side. In the fifth preferred embodiment, the antenna element2is fixedly supported on an inner wall surface of a housing26in which the substrate3is accommodated and arranged by, for example, an antenna support member (not shown) instead of being fixedly supported by the substrate3. In the fifth preferred embodiment, the antenna element2is preferably arranged at a portion spaced apart from a region in which the substrate3is arranged. In addition, the housing26is preferably made of an insulating material, such as resin, for example, and the entire housing is preferably a non-ground region. Thus, the entire antenna element2is arranged in the non-ground region.

FIG. 6Bschematically shows one preferred embodiment of a structure in which the antenna element2is electrically connected to the substrate3. In the example shown inFIG. 6A, connecting elastic conductor pieces27qand27gare electrically connected respectively to the feeding portion Q of the feeding radiation electrode7of the antenna element2and the ground end G of the non-feeding radiation electrode18of the antenna element2. As the elastic conductor pieces27qand27grespectively press and contact the surface of the substrate3by elastic force, the elastic conductor piece27qis electrically connected to the wireless communication circuit5of the substrate3, and the elastic conductor piece27gis grounded to the ground electrode4of the substrate3.

Note that the structure in which the antenna element2is electrically connected to the substrate3is not limited to the preferred embodiment shown inFIG. 6Band another connecting structure may be used. In addition, in the example shown inFIG. 6A, the dielectric base6of the antenna element2has a shape having a front surface wall portion6f, a top surface wall portion6t, a right end surface wall portion6r, and a left end surface wall portion61. However, the dielectric base6may have another shape, such as a rectangular parallelepiped shape, for example. Furthermore, in the example shown inFIG. 6B, the feeding radiation electrode7and the non-feeding radiation electrode18are provided on the dielectric base6. However, as in the case of the first to third preferred embodiments, only the feeding radiation electrode7may be provided on the dielectric base6.

The configuration other than the above in the antenna structure1of the fifth preferred embodiment is similar to that of the first to fourth preferred embodiments. The dielectric material (not shown inFIGS. 6A and 6Bbut shown as a dielectric material8inFIG. 1A, a high dielectric constant sheet13inFIG. 2, and a resin14inFIGS. 3A and 4A) having a high dielectric constant is preferably provided in the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7. In addition, when the non-feeding radiation electrode18is provided, a dielectric material having a high dielectric constant may be provided in a spaced region between the parallel or substantially parallel open end K and intermediate path (not shown inFIGS. 6A and 6Bbut shown as an intermediate path21inFIG. 5A) of the non-feeding radiation electrode18.

Hereinafter, a sixth preferred embodiment of the present invention will be described. Note that in the description of the sixth preferred embodiment, like reference numerals denote like components to those of the first to fifth preferred embodiments, and repetitive description of the same components is omitted.

In the sixth preferred embodiment, the antenna element2has a dielectric film28as shown inFIG. 7Ainstead of the dielectric base6. The dielectric film28is preferably made of a dielectric material having a low dielectric constant (for example, a relative dielectric constant less than about 6). The feeding radiation electrode7and the non-feeding radiation electrode18, which are defined by conductor films, are arranged on the surface of the dielectric film28by, for example, sputtering, vapor deposition, or other suitable method. In addition, a high dielectric constant sheet30preferably made of a dielectric material having a dielectric constant greater than the dielectric film28(for example, relative dielectric constant greater than or equal to about 6) is provided on the back surface side of the dielectric film28. The high dielectric constant sheet30is provided in the spaced region between the parallel or substantially parallel open end K and intermediate path (not shown inFIGS. 6A and 6Bbut shown as an intermediate path11inFIG. 5A) of the feeding radiation electrode7and, where necessary, in the spaced region between the parallel or substantially parallel open end K and intermediate path21of the non-feeding radiation electrode18. Note that in the example shown inFIG. 7A, the high dielectric constant sheet30is preferably provided on the back surface side of the dielectric film28. However, the high dielectric constant sheet30may be arranged on the surface of the feeding radiation electrode7or non-feeding radiation electrode18provided on the front surface side of the dielectric film28.

In the sixth preferred embodiment, a resin film, for example, is preferably provided on the surfaces of the feeding radiation electrode7and non-feeding radiation electrode18to protect the feeding radiation electrode7and the non-feeding radiation electrode18. In addition, as shown in the schematic cross-sectional view ofFIG. 7B, the dielectric film28is preferably fixedly bonded to the inner wall surface of the housing26by an adhesive agent31, for example. Furthermore, the feeding radiation electrode7provided on the dielectric film28is preferably electrically connected to the wireless communication circuit5of the circuit board3through a connecting member32A shown inFIG. 7A. In addition, the non-feeding radiation electrode18provided on the dielectric film28is preferably electrically connected to the ground electrode4of the circuit board3through a connecting member32B shown inFIG. 7A.

The configuration other than the above in the antenna structure1of the sixth preferred embodiment is similar to that of the first to fifth preferred embodiments. Note that in the example shown inFIG. 7A, the non-feeding radiation electrode18is preferably provided. However, for example, when the antenna characteristic required by the specifications may be obtained only by the feeding radiation electrode7, the non-feeding radiation electrode18may be omitted. In addition, the dielectric film28, on which the feeding radiation electrode7and the non-feeding radiation electrode18are provided, is preferably fixedly supported by the housing26. However, the dielectric film28may be fixedly supported by the substrate3by, for example, a support member, or other suitable member. Furthermore, the dielectric film28is preferably configured in a shape such that it is bent along the inner wall surface of the housing26. However, the dielectric film28may, for example, have a substantially planar shape that is not bent depending on a location of arrangement.

Hereinafter, a seventh preferred embodiment of the present invention will be described. The seventh preferred embodiment relates to a wireless communication device. The wireless communication device of the seventh preferred embodiment is provided with any one of the antenna structures1described in the first to sixth preferred embodiments. In addition, various structures of the wireless communication device, other than the antenna structure, may be used. Here, the configuration of the wireless communication device, other than the antenna structure, may have any configuration, and the description thereof is omitted.

Note that the present invention is not limited to the first to seventh preferred embodiments, and various preferred embodiments may be used. For example, in the first to seventh preferred embodiments, the entire dielectric base6or the entire dielectric film28is preferably arranged in the non-ground region Zp. However, a portion of the dielectric base6or the dielectric film28may be arranged in the ground region Zg. In this case, the spaced region between the parallel or substantially parallel open end K and intermediate path11of the feeding radiation electrode7and the spaced region between the parallel or substantially parallel open end K and intermediate path21of the non-feeding radiation electrode18are arranged on the side surface of the dielectric base6or a portion of the dielectric film28in the non-ground region Zp, which is spaced away from the ground region Zg.

In addition, in the example shown inFIGS. 6A and 6BorFIGS. 7A and 7B, the dielectric base6or the dielectric film28is arranged outside the substrate3. However, a portion of or the entire the dielectric base6or the dielectric film28may be arranged on the surface of the substrate3.

Furthermore, in the first to seventh preferred embodiments, the feeding portion Q of the feeding radiation electrode7is set at the lower portion of the side surface (rear surface)6b, adjacent to the ground region Zg, of the dielectric base6. In addition, the feeding portion side path10of the feeding radiation electrode7is arranged to extend in a path from the feeding portion Q through the top surface6tof the dielectric base6toward the side surface8(front surface)6fin the non-ground region Zp away from the ground region Zg. However, the position of the feeding portion Q is not limited to the rear surface6bof the dielectric base6; and instead, for example, the position of the feeding portion Q may be the bottom surface of the dielectric base6.

In addition, in the first to seventh preferred embodiments, the feeding portion side path10extends from the feeding portion Q through the top surface6tof the dielectric base6toward the intermediate path11on the front surface6faway from the ground region Zg. The extending path of the feeding portion side path10is not limited; and instead, for example, the feeding portion side path10may be arranged to extend from the feeding portion Q through the bottom surface of the dielectric base6toward the intermediate path11formed on the front surface6f. Furthermore, when the feeding portion Q is provided at the lower side of the front surface6fof the dielectric base6, the feeding portion side path10may be omitted. In addition, the feeding portion side path10may be extremely short.

Furthermore, in the first to fifth preferred embodiments, the open end side path12of the feeding radiation electrode7extends over two surfaces, that is, the front surface6fand top surface6t, of the dielectric base6. Instead, the open end side path12may be, for example, provided only on the front surface6fof the dielectric base6as shown inFIG. 8Aor may extend over three or more surfaces from among the front surface6f, top surface6t, rear surface6b, and right end surface of the dielectric base6, including the front surface6f. In this case, the open end side path12is arranged to extend along a loop path that extends from the termination of the intermediate path11in a direction to separate from the intermediate path11on the surface of the dielectric base6and then returns toward the intermediate path11, and the open end K of the extended distal end is arranged parallel or substantially parallel to and spaced apart from the intermediate path11. Note that the same applies to the non-feeding radiation electrode18.

Furthermore, the dielectric base6is not limited to the configurations described in the first to fifth preferred embodiments. For example, as shown inFIG. 8B, the dielectric base6may include a base portion6F, which defines the front surface6fand is made of a dielectric material having a high dielectric constant (for example, relative dielectric constant greater than or equal to about 6), and a base portion6M, which defines the dielectric base portion other than the base portion6F and is made of a dielectric material having a low dielectric constant (for example, relative dielectric constant less than about 6).

Furthermore, in the fourth preferred embodiment, the dielectric material24for adjusting the electromagnetic coupling state between the feeding radiation electrode7and the non-feeding radiation electrode18is provided in the spaced region D between the feeding radiation electrode7and the non-feeding radiation electrode18. However, in some cases, such a dielectric material24for adjusting the electromagnetic coupling state need not be provided. This is the case in which the electromagnetic coupling state between the feeding radiation electrode7and the non-feeding radiation electrode18is set in a predetermined state.

The antenna structure according to preferred embodiments of the present invention and the wireless communication device including the same are capable of elongating the electrical length of the feeding radiation electrode with a simple configuration and easily achieving miniaturization. In addition, preferred embodiments of the present invention are capable of improving the reliability in a wide frequency band and in a wireless communication. Thus, the antenna structure according to preferred embodiments of the present invention and the wireless communication device having the same is effectively applied to a wireless communication device that must, for example, be miniaturized and used to communicate in a wide frequency band, such as a cellular phone.