Antenna, antenna unit, and communication device using them

An antenna has a base substrate, a coil formed from a conductor wound around the base substrate, and a plurality of terminals connected to the conductor. Uncovered base substrate portions where the conductor is absent are formed on the base substrate except the start and end of turns of the coil. The terminals are provided on respective sides of the coil parallel to a coil axis and on the uncovered base substrate portions.

BACKGROUND

1. Field of the Invention

The present invention relates to an RF-ID; namely, a radio communication medium processing device that establishes communication with a radio communication medium, like an IC card and an IC tag, or an antenna and an antenna unit used in the radio communication medium itself, as well as to a communication device using the antenna and the antenna unit.

2. Background Art

Portable terminals, such as portable phones, equipped with built-in RF-ID radio tags or a function of reading a non-contact IC card or an IC tag have recently become proliferated. Antenna units that each include a magnetic sheet affixed to an aperture area of a loop antenna (a coil axis of the loop antenna is perpendicular to the magnetic sheet) are frequently used.

In order to attach a related art antenna, it is necessary to secure a location, in a portable terminal, that is substantially equal in area to the antenna. This has become a factor for hindering a reduction in the size and thickness of the portable terminal.

SUMMARY

Accordingly, the present invention aims at providing an antenna and an antenna unit that enable realization of space saving and that exhibit superior communication performance.

The present invention provides an antenna comprising: a base substrate; a coil formed from a conductor wound around the base substrate; and a plurality of terminals connected to the conductor, wherein uncovered base substrate portions where the conductor is absent are formed on the base substrate except a start and end of turns of the coil; and the terminals are provided on respective faces of the coil parallel to a coil axis and on the uncovered base substrate portions.

The present invention makes it possible to provide an antenna and an antenna unit that enable realization of space saving and that exhibit superior antenna performance, as well as to provide a communication device using them.

DETAILED DESCRIPTION

According to the present invention, it is possible to provide an antenna including a base substrate; a coil formed from a conductor wound around the base substrate; and a plurality of terminals connected to the conductor. Uncovered base substrate portions where the conductor is absent are formed on the base substrate except the start and end of turns of the coil. The terminals are provided on the respective sides of the coil parallel to a coil axis and on the uncovered base substrate portions. It is thereby possible to provide an antenna and an antenna unit, which enable space saving and which exhibit superior communication performance, and a communication device using them.

Further, it is preferable that the number of turns of the coil of the antenna is larger than an integral multiple by substantially one-half of the turn, because the antenna can efficiently utilize the electric current flowing over the metallic element on which the antenna is to be mounted.

Moreover, the uncovered base substrate portion is formed on each end of the base substrate, whereby a magnetic field passing through an interior of the coil is made substantially parallel to the coil axis, so that an electric current can efficiently be guided.

The plurality of terminals connected to the coil are on the same uncovered base substrate portion. As a result, it is thereby possible to provide an antenna and an antenna unit, which enable space saving and which exhibit superior communication performance, and a communication device using them.

The terminals each are placed at substantial four corners of the coil. The conductor is connected to the terminals, among the four terminals, placed on both sides of the base substrate with its coil axis interposed therebetween. It is thereby possible to provide an antenna and an antenna unit, which enable space saving and which exhibit superior communication performance, and a communication device using them.

An imaginary straight line passing through the two terminals connected to the conductor is substantially parallel to the winding direction of the coil. The magnetic field passing through the interior of the coil can thereby be made substantially parallel to the coil axis, so that an electric current can efficiently be guided.

Moreover, the imaginary straight line passing through the two terminals connected to the conductor is substantially parallel to a diagonal line of the base substrate. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

The plurality of terminals connected to the conductor are placed on both sides of the base substrate with its coil axis interposed therebetween. The imaginary straight line passing through the two terminals connected to the conductor is substantially parallel to the winding direction of the coil. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

The plurality of terminals to which the conductor is to be connected are provided on both sides of the base substrate with the coil axis interposed therebetween. An imaginary straight line passing through the two terminals to which the conductor is to be connected is substantially parallel to a diagonal line of the base substrate. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

The antenna is mounted such that at least one of the uncovered base substrate portions provided on the antenna is situated outside of the outer periphery of the metallic element on which the antenna is mounted. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

It is preferable that the coil is arranged in such a way that the winding direction of the coil and the ends of the base substrate that is a metallic element become parallel to each other, because the electric current flowing over the metallic element on which the antenna is mounted can efficiently be utilized.

Furthermore, it is preferable that the coil is arranged such that the winding direction of the coil and the flow of the electric current flowing through the metallic element become parallel to each other, because the electric current flowing over the metallic element on which the antenna is mounted can efficiently be utilized.

The plurality of terminals each are placed at substantially four corners of the coil. Of the four terminals, two pairs of terminals, each of which consists of two terminals placed in the vicinity of the two corners situated along one side of the base substrate, each are joined together by means of the joints provided along the respective sides of the base substrate. It is thereby possible to acquire an antenna unit that does not require an excessive length for the coil and that is not limited in terms of directivity when mounted on the communication device.

The terminals act as fixing portions when the antenna unit is mounted, whereby the antenna unit can stably be placed in a communication device, or the like.

The joints extend substantially parallel to the coil axis of the base substrate. It is thereby possible to easily acquire an antenna unit that does not require an excessive length for the coil and that is not limited in terms of directivity when mounted on a communication device.

Embodiment

An embodiment of the present invention is hereunder described by reference to the drawings.

FIG. 1is an oblique perspective view of an antenna of an embodiment of the present invention.

An antenna1is configured in the following manner. Namely, a conductor4is wound around a base substrate3, thereby making up a coil30. The coil30is covered with a protective material2and is also provided with terminals5connected to the conductor4and fixing terminals6that are not connected to the conductor4and that are intended for enhancing vibration resistance and packing strength.

The terminals5are provided on respective surface sides of the coil30parallel to a coil axis A and within an uncovered base substrate portion31not provided with the coil30.

Detailed descriptions are provided for a layout of the terminals5. In the present embodiment, the terminals5are provided on the respective surface sides of the coil30parallel to the coil axis A. When viewed in a direction B perpendicular to the surfaces provided with the terminals5, at least one of the input/output terminals5is situated within a plane of the uncovered base substrate portion31. Namely, when viewed in the direction B, at least one of the terminals5overlaps a surface of the uncovered base substrate portion31.

All you have to do is to place the terminals5on the surface sides parallel to the coil axis A and in the vicinity of the uncovered base substrate portion31; namely, an area around the coil30or an area around the uncovered base substrate portion31exclusive of a surface perpendicular to the coil axis A. It is not necessary to place the terminals5in such a way that at least one of the terminals5overlaps the surface of the uncovered base substrate portion31when viewed in the direction B, as in the case with the present embodiment.

It is preferable to use a magnetic substance, such as ferrite, for the base substrate3, whereby a magnetic flux passing through the coil30increases, to thus enable enhancement of communication performance. However, the base substrate3is not limited to a magnetic substance and can also be formed from; for instance, ceramic, a resin, and the like.

It is preferable to use a wire such as a sheathed copper wire or tape-shaped or ribbon-shaped metal such as narrow copper foil for the conductor4. However, there may also be adopted a method for affixing metal to a surface of a magnetic core3by means of plating or evaporation so as to leave necessary areas intact, to thus form the coil30.

It is also preferable to form the terminals5by punching or bending an alloy formed from copper and iron, or the like. Further, it is also preferable to plate surfaces of the terminals5with metal, such as zinc, so that the surfaces can readily be soldered.

The fixing terminals6are also formed in the same manner as are the input/output terminals5. However, the fixing terminals6may be omitted according to the size and usage of the antenna1. Further, the fixing terminals6can also be provided in any numbers.

Further, a mold like an epoxy resin, a tape, and paint, and others, are used for the protective material2. The protective material2can be given objectives of preventing breaking of wire of the conductor4, breakage of the base substrate3, and forming a suction block for use in an automatic mounting machine, and others. Moreover, in order to prevent erroneous printing of a mark and a part number of an input/output pin on a top surface of the antenna1, the protective material2is preferable. Although the antenna has a configuration involving use of the protective material2in the present embodiment, the protective material2may also be omitted.

InFIG. 1, the coil30is wound about 7.5 turns; namely, the number of turns is larger than an integral multiple by about a one-half of turn. Therefore, input and output terminals are placed with the coil30sandwiched therebetween. This is preferable because, when a plurality of antennas are connected and when an antenna is inserted into a portion of a loop conductor, the terminals5are placed on both sides of the antenna1, which facilitates wiring.

InFIG. 1, the terminals5are situated on a lower side of the antenna1when the antenna1is connected to a board. Further, the number of turns of the conductor4is set to 7.5 turns. Hence, the number of turns of the conductor4wound around the upper surface of the base substrate3is greater than the number of turns of the conductor4wound around the lower surface of the same.

The reason for this is that, when the antenna1is mounted on a metallic element, the conductor4on the lower surface of the antenna1becomes close to the metallic element and is susceptible to a magnetic field developing from an eddy current of the metallic element in a direction of canceling a signal. The conductor4on the upper surface of the same, however, is less susceptible to the magnetic field. Hence, a characteristic of the coil30is improved when the number of turns of the conductor4on the upper surface less susceptible to the eddy current becomes greater.

FIG. 2is a plan view of the antenna of the embodiment of the present invention.

A characteristic of the present invention lies in that the terminals5connected to the conductor4are situated along the uncovered base substrate portion31. In the antenna shown inFIG. 2, the fixing terminals6are provided along another uncovered base substrate portion31as in the case with the terminals5. However, the locations of the fixing terminals6are not particularly limited.

The uncovered base substrate portion shown inFIG. 1designates an area on the base substrate3where the conductor4is not provided rather than the coil30where the conductor4is tightly wound around the base substrate.

In the present embodiment, the uncovered base substrate portions31are provided on the respective ends of the base substrate3. However, the arrangement is preferable because, for instance, when a magnetic field comes from the outside, it becomes possible to make the magnetic field passing through an interior of the coil30more parallel to the coil axis by means of such a layout, thereby increasing an electric current induced by the coil30. Further, the two terminals5are placed within a plane of the same uncovered base substrate portion31. It thereby becomes possible to achieve a layout exhibiting the highest performance when the antenna1is mounted on a metallic element. An overall geometry of the antenna is substantially square; however, the geometry is not limited to square.

FIG. 3is a plan view of another antenna of the embodiment of the present invention.

The antenna differs from the antenna shown inFIG. 2in terms of the positions of the terminals5. The terminals5are placed along a diagonal line. When such an antenna1is mounted on a metallic element, the antenna becomes slightly inferior in performance to the antenna shown inFIG. 1. However, since the inferiority does not exert any substantial influence, a terminal layout, such as that described in connection with the present embodiment, can be selected according to situations in which the antenna is used.

FIG. 24is a plan view of still another antenna of the embodiment of the present invention.

InFIG. 24, a start and end of a turn of the conductor4are oblique, and the conductor4is present in the uncovered base substrate portions31. Since the uncovered base substrate portions31of the present invention are defined as areas that are exclusive of the start and end of the turn and where the conductor4is not present. Therefore, the antenna shown inFIG. 24also falls within the scope of the present invention. The start and end of the turn is considered to be approximately one-half of turn.

When the antenna of the present invention is placed on the metallic element, the following advantages are yielded, as a result of the uncovered base substrate portions being provided, when the uncovered base substrate portions are placed in the interior of the metallic element and when the uncovered base substrate portions are placed at ends of the metallic element.

When the uncovered base substrate portions are placed in the interior of the metallic element in a case where a magnetic substance is used as the base substrate, a magnetic field developing in the interior of the coil becomes more parallel to a coil axis than a case where the uncovered base substrate portions are not provided. Therefore, transmission and receiving operations can efficiently be performed, so that an efficiency of the antenna can be enhanced.

Further, when the uncovered base substrate portions are placed on an exterior of the metallic element and when an antenna having terminals connected to both ends of the uncovered base substrate portions is used, the antenna can be made efficient by means of a minimum number of coil turns.

When the coil is wound up to both ends of the base substrate without use of the uncovered base substrate portions as in the case with the related art, the coil situated outside of the metallic element cannot capture the magnetic field on the metallic element induced by an electric current; hence, the coil does not contribute to the antenna characteristic or efficiency. When the base substrate does not protrude from the metallic element and when the coil is wound up to both ends of the base substrate, the magnetic field developing in the coil in the vicinity of the ends of the base substrate does not become parallel to the coil axis even when the base substrate is a magnetic substance, so that the antenna characteristic is deteriorated.

For these reasons, in the present embodiment, the uncovered base substrate portions are provided on both sides of the antenna in order to enhance the antenna characteristic.

FIG. 4is a schematic diagram of a first antenna unit using the antenna of the embodiment of the present invention, showing a configuration achieved when the antenna1shown inFIG. 2is mounted on a substrate7. Since ends of the substrate7are illustrated in an enlarged manner, right, left, and lower portions of the substrate7are not illustrated.

A ground pullout portion11not having a conductor is provided along an outer periphery of a conductor pattern8forming a ground, and input/output terminal lands9are provided along the outer periphery such that the uncovered base substrate portions31of the antenna1and the terminals5are situated.

A length of the uncovered base substrate portions achieved in the direction of the coil axis is substantially identical with a length of the ground pullout portion11.

The conductor pattern8is further provided with fixing terminal lands10for securing the fixing terminals6, and the fixing terminal lands are electrically connected to the conductor pattern8.

In view of performance, it is preferable that a ground electrode which is an interior layer of the substrate should not be present in the ground pullout portion11. However, when the substrate7is thick, or the like, there can also be adopted a configuration in which the ground pullout portion11is provided in only a layer in proximity to the antenna1.

A glass epoxy base material, or the like, is usually used for the substrate7, and copper is often used for the conductor pattern8. However, the substrate and the conductor pattern are not limited to these materials, and other materials can also be used. A surface of the substrate is usually provided with a solder resist, a silk screen print, and others. Further, the conductor pattern8is assumed to be a ground in the present embodiment, but a pattern raised from the ground may also be used. At this time, it is better for the conductor pattern to have a larger area. For example, when a magnetic field is exerted on the antenna from the outside, an eddy current developing in the conductor pattern becomes large, with the result that communication performance is improved.

AlthoughFIG. 4shows an embodiment in which the antenna1is mounted on the substrate7, a location where the antenna is to be mounted is not limited to the substrate. For instance, the antenna can also be mounted on a metallic element, such as a battery frame and a liquid crystal panel frame. As a result of adoption of the configuration such as that shown inFIG. 4, the coil30can utilize an area on the conductor pattern8where the highest current density appears, so that the performance of the antenna1can consequently be made best.

FIG. 5is a schematic diagram of an antenna unit using another antenna of the embodiment of the present invention, showing a configuration in which the antenna shown inFIG. 3is mounted on the substrate7. The ground pullout portion11not having a conductor is provided along the outer periphery of the conductor pattern8forming the ground. The input/output terminal land9and the fixing terminal land10are provided such that the uncovered base substrate portions31, the terminals5, and the fixing terminals6of the antenna1are situated in the ground pullout portion. The other input/output terminal land9and the other fixing terminal land10are provided in the conductor pattern8. By means of such a configuration, the coil30can utilize the area on the conductor pattern8where the highest current density appears. Hence, superior communication performance that is slightly inferior to that achieved by the configuration shown inFIG. 4can be obtained.

FIG. 6is a schematic diagram of a second antenna unit using the antenna of the embodiment of the present invention. Although having a similar layout, the antenna unit is different from the antenna unit shown inFIG. 4in terms of a shape of the ground pullout portion11, a shape of the input/output terminal land9, and a shape of the fixing terminal land10. It is preferable to round edges of the pattern as shown inFIG. 6, because occurrence of a loss, which would otherwise arise when the electric current flowing along a surrounding of the outer periphery of the conductor pattern8concentrates on the edges, can be avoided. Although the terminal layout achieved when the terminals are provided in the antenna shown inFIG. 2is illustrated, the terminal layout is not limited to the illustrated layout.

FIG. 7is a schematic diagram of a third antenna unit using the antenna of the embodiment of the present invention. The antenna unit differs from its counterparts shown inFIGS. 4 through 6in that the input/output terminal lands9are made such that one uncovered base substrate portion31is arranged outside of the outer periphery of the conductor pattern8rather than the ground pullout portion11being provided below one uncovered base substrate portion31. Even the configuration makes it possible for the coil31to utilize an area on the conductor pattern8where the highest current density develops, so that superior communication performance can be acquired. Although the terminal layout achieved when the terminals are provided in the antenna shown inFIG. 2is illustrated, the terminal layout is not limited to the illustrated layout. The similar layout can also be acquired even in the case of the antenna shown inFIG. 3.

Although a signal line to the input/output terminal lands9is not illustrated inFIGS. 4 through 7, it is preferable to route a line so as to run through an interior layer or a back side of the substrate7, because the line does not hinder the electric current flowing through the conductor pattern8. Moreover, the fixing terminal lands10may or may not be connected to the conductor pattern8.

When the antenna1is mounted on a metallic element that is not a substrate, difficulty is considered to be encountered in performing reflow mounting operation. In this case, the antenna1is fixed to a predetermined position by means of a double-sided table, or the like. Power can be fed to the terminals5by means of physical contact of a pin, soldering of a wire, or the like. Hence, an antenna unit exhibiting superior communication performance can be provided in the same manner as in the case where the antenna is mounted on the substrate.

Explanations are now given to a concept that the antenna1of the present invention provided on a metallic element through surface mounting acts as an antenna in a direction perpendicular to the plane of the metallic element.

FIG. 8is a conceptual rendering of the present invention. The drawing illustrates that the antenna1of the present invention is mounted on the substrate7such that uncovered base substrate portions are situated outside of a conductor pattern outer periphery12.

First, explanations are provided to a case where a signal is input to the antenna1. When a signal is input to the antenna1, an electric current flows into a coil of the antenna1, and the electric current induces a magnetic field in a direction of a coil axis of the coil. Specifically, if the antenna is continually held in this state, the antenna stays orthogonal to the magnetic field perpendicular to the substrate7, and hence the antenna cannot act as an antenna. The magnetic field induces, in the substrate7, an electric current14that generates a magnetic field13in a direction of cancelling the magnetic field of the antenna1. The electric current14flows along the conductor pattern outer periphery12and exhibits the highest current density at the outer periphery and a smaller current density with an increasing distance toward the interior of the substrate. Since the electric current14flowing along the conductor pattern outer periphery12forms a large loop path, a magnetic field thereby develops in a direction perpendicular to a principal plane of the substrate7. Therefore, it is seen that the antenna1becomes an antenna exhibiting superior performance in a direction perpendicular to the principal surface of the substrate7.

By reference toFIG. 8, explanations are now provided to a case where a magnetic field is exerted on, in a direction perpendicular to, the substrate7from the outside. When an external magnetic field perpendicular to the principal plane of the substrate7is exerted, the electric current (eddy current)14that induces a magnetic field in a direction of cancelling the external magnetic field develops in the substrate7. The magnetic field13caused by the electric current14induces an electric current in the antenna1, and the electric current is output as a signal. Consequently, the antenna1is understood to become an antenna that exhibits superior performance with respect to the external magnetic field in the direction perpendicular to the principal surface of the substrate7.

From above, the antenna1can be said to become an antenna that exhibits superior communication performance when mounted on a metallic element.FIG. 8shows a conceptual rendering of a case where the antenna1is mounted on the substrate7. However, a component where the antenna1is to be mounted is not limited to the substrate. The component can also be a metallic element, such as a battery frame, a liquid crystal panel frame, and a metallic enclosure.

Arrows provided inFIG. 8for designating directions are used for expressing directions achieved at a certain moment. In reality, the magnetic field and the signal remain oscillating at certain frequencies; therefore, their directions become opposite in another moment.

InFIG. 8, for the sake of explanation of the concept, lands for inputting or outputting a signal to or from the antenna1or fixing lands are not provided on the substrate7. In this state, there is no structure that hinders the electric current flowing over the plane of the substrate7. However, connections between the antenna unit1and other components must be embodied by means of aerial wiring, or the like, which undesirably hinders miniaturization, or the like, of an entire antenna unit. When automatic mounting is considered, lands must be provided in reality. There has been a necessity for contemplating a land layout whose structure least hinders the electric current flowing over the substrate7.

To this end, the land layout has been contemplated under the following conditions in the present embodiment.

In the antenna used for the test, rectangular parallelepiped ferrite measuring 5 mm×5 mm×0.4 mm was used for the base substrate3; a sheathed copper line having a diameter of 0.26 mm was used as the conductor4; and an antenna having 7.5 turns was used. At this time, the length of the coil30was set to 3 mm, and the uncovered base substrate portion31having a width of 1 mm was provided on either side of the coil.

An antenna, such as that illustrated by a plan view of an antenna implemented by an ordinary chip component structure shown inFIG. 9, is presumed as an ordinary conceivable structure, and the antenna is taken as a comparative example for the present embodiment. In order to give high priority to antenna sensitivity, terminals are considered not to be provided in an opening direction of the coil of the antenna. In a chip coil, or the like, that is not so large in normal times, input/output terminals105assume a structure in which there are provided terminals that each have a width close to a width of the chip, as shown inFIG. 9. Since only two terminals, which are a total of input and output terminals, are provided, two terminals are considered to be suffice. There is mentioned a conceivable reason that a greater terminal width is desirable in consideration of ease of mounting operation and soldering strength.

FIG. 10shows that an antenna101is mounted on the substrate7. Since the input/output terminals105are provided, ground pullout portions115for the input/output terminals105are formed in the conductor pattern outer periphery12.

For this reason, even when the substrate7receives a magnetic field from the outside and when the electric current has developed in the substrate7, flow of the electric current14flowing over the substrate7is blocked by the ground pullout portions115, to thus become meandered. A characteristic of the antenna is therefore assumed to be undesirable.

Specifically, when the conductor pattern is made as illustrated inFIG. 10and when the antenna is arranged, an electric current flowing in a direction perpendicular to the coil axis of the antenna is small, and the antenna cannot efficiently receive the electric current flowing over the substrate7. Therefore, the antenna characteristic is deteriorated.

This state was taken as Test1, and the ground pullout portions115were made so as to measure 4 mm high×2 mm wide. In the state shown inFIG. 10, the antenna was matched to 50Ω at 13.56 MHz. A sinusoidal wave signal that exhibited a sensitivity of 20 dBm at 13.56 MHz was input from a signal generator to the antenna, and magnetic field intensity was measured at a point elevated 30 mm from the principal plane of the substrate7. The magnetic field intensity measured at this time was taken as 100%, and Tests2to7provided below were compared.

FIG. 11is a descriptive view of Tests2and3. With a view toward preventing occurrence of the large meander of the electric current14seen in the explanatory view of Test1shown inFIG. 10, area C was made so as not to interrupt the conductor pattern outer periphery12. The area C is a partial area of the conductor pattern that has a width equivalent to a distance from the conductor pattern outer periphery12to a ground pullout portion15for use in arranging input/output terminal lands. The width of the area C from the conductor pattern outer periphery toward an interior is taken as C. Reference symbol D is a distance from the conductor pattern outer periphery12to an inner end of the substrate of the ground pullout portion15for use in arranging input/output terminal lands. While the distance D was set to 4 mm, measurement was likewise conducted in the same manner as in Test1on condition that the width C was 1 mm for Test2and that the width C was 3 mm for Test3. Test results show that the magnetic field intensity acquired in Test2came to 124% when compared with the magnetic field intensity acquired in Test1and that the magnetic field intensity acquired in Test3came to 131% when compared with the same. It is seen that the antenna characteristics becomes improved as the width C becomes greater.

FIG. 12is a descriptive view of Test4. Making a non-coil area of the antenna jut out the conductor pattern outer periphery12in order to increase the area C shown inFIG. 11was terminated, and the ground pullout portion11was provided instead. The width C could thereby be increased to 4 mm. Further, the distance D came to 5 mm at this time. Measurement similar to that described in connection with Test1was carried out on the assumption that the size of the ground pullout portion11measured 5 mm wide×1 mm high. Consequently, the magnetic field intensity came to 124% when compared with the magnetic field intensity acquired in Test1. A presumable reason for the measurement result being worse than that acquired in Test3is that a vertical edge of the ground pull out portion is close to the coil and that the electric current14thereby becomes partially parallel to the coil axis.

FIG. 13is a descriptive view of Test5. In response to a result of Test4, the edge of the ground pullout portion11was cut at an angle of 45° in order to locate the edge away from the coil. The path for the electric current14can thereby be made substantially perpendicular to the coil axis, so that the antenna characteristic can be presumed to be recovered. A result of measurement performed in the same manner as in the case with Test1shows that the magnetic field intensity was improved to 134% when compared with the magnetic field intensity acquired in Test1.

FIG. 14is a descriptive view of Test6. In order to make the state of Test5better, there is a necessity for obviating from the path for the electric current14the ground pullout portions15for arranging the input/output terminal lands9that hinder the electric current14. To this end, the ground pullout portion11was enlarged, and only halves of the input/output terminals placed in the path for the electric current14were moved to the interior of the ground pullout portion11. One input/output terminal land9was placed in the ground pullout portion11. Measurement similar to that described in connection with Test1was performed at this time while the ground pullout portion was still given a width of 9 mm and a height of 1 mm. A result of measurement shows that the magnetic field intensity was further improved to 138% when compared with the magnetic field intensity acquired in Test1.

FIG. 15is a descriptive view of Test7. Relocating the ground pullout portion15for arranging the input/output terminal lands9performed in Test6to the interior of the ground pullout portion11is effective. Therefore, the other ground pullout portion15for arranging the input/output terminal lands9was moved into the interior of the ground pullout portion11, and a total of two input/output terminal lands9were provided in the ground pullout portion11. Measurement similar to that described in connection with Test1was performed at this time while the ground pullout portion11was given a width of 11 mm and a height of 1 mm. A result of measurement shows that the magnetic field intensity was further improved to 145% when compared with the magnetic field intensity acquired in Test1.

As can be seen inFIG. 8, the magnetic field intensity achieved when no lands are provided on the substrate7was measured by connecting a matching circuit directly to the antenna terminal, whereby a magnetic field intensity of 134% could be measured.

FIG. 16shows a graph pertaining to the results of Tests1through7. A broken line provided at a level of 134% depicts magnetic field intensity achieved in an ideal state (FIG. 8) where no lands were provided on the substrate7. The result shows that all of the measures are effective for the antenna of the comparative example shown inFIG. 9and that a superior communication characteristic is exhibited.

Moreover, it is understood that Test5(FIG. 13), Test6(FIG. 14), and Test7(FIG. 15) exhibit communication characteristics better than the communication characteristic yielded by the configuration inFIG. 8that is an ideal state and that the communication characteristics become better than the original characteristic of the antenna1.

A presumable reason for this is that the electric current14is bent along the ground pullout portion11as a result of the ground pullout portion11being provided along the conductor pattern outer periphery12, so that the current density is increased at a position below the antenna1; especially, a position below the coil30. Therefore, provision of the ground pullout portion11and placing the uncovered base substrate portion of the antenna1in the ground pullout portion11can be said to be very effective. It is understood that the present invention is effective for providing an antenna and an antenna unit which exhibit superior communication performance.

For more comparison, similar tests were carried out by use of a sheet-like, loop antenna having a related art structure. A ferrite sheet measuring 25 mm×15 mm and having a thickness of 0.4 mm was affixed to the location of the antenna1shown inFIG. 8, and an antenna whose planes were provided with three turns of a sheathed copper line having a diameter of 0.26 mm and that had an exterior shape measuring 24 mm×14 mm was affixed to a position on the ferrite sheet. The magnetic field intensity of the related art antenna came to 137%. Therefore, the test shows that the antenna of the present invention can exhibit magnetic field intensity equal to or greater than the magnetic field intensity exhibited by the related art antenna by means of 7% of the area of the related art antenna (calculated in terms of the area of ferrite). Specifically, the present invention can be said to provide an antenna capable of greatly contributing to space saving.

A test conducted in relation to a winding number is now described.

FIG. 19shows a graph of a result of a winding number test. Winding numbers are plotted along a horizontal axis, and values acquired by normalization of magnetic field intensity induced by a 0.5 turn are plotted along a vertical axis. The antenna used in the test assumes a shape, such as that shown in an oblique perspective view of the antenna shown inFIG. 17. Ferrite measuring 21 mm×4 mm×0.2 mm was used for the base substrate3. The antennas were experimentally manufactured from a thin copper plate having a thickness of 0.1 mm while the width of the copper plate was changed from 1 mm to 0.6 mm according to the number of turns. As illustrated in the schematic diagram ofFIG. 18showing a winding number test, the antenna1was made close to the end of the substrate7, and the antenna was placed such that the uncovered base substrate portion was situated outside of the conductor pattern8. Lands were not made on the substrate7, and the pattern was connected directly to the terminals5. The antenna was matched to 50Ω at 13.56 MHz, and a sinusoidal wave signal that exhibited a sensitivity of 20 dBm at 13.56 MHz was input from the signal generator to the antenna, and magnetic field intensity was measured at a point elevated 30 mm from the principal plane of the metallic element. As shown inFIG. 19, the magnetic field intensity increases with an increase in winding number. An increase rate, however, shows that the magnetic field intensity greatly increases when the winding number is larger than an integral number by one-half of turn. The conductor of the coil situated on a side where the conductor does not face a metallic element6is less susceptible to the eddy current flowing over the surface of the metallic element6. However, an electric current develops, in a direction of being cancelled by the eddy current flowing over the surface of the metallic element6, in the conductor of the coil2situated on a side where the conductor faces the metallic element6. Therefore, an increase in magnetic field intensity can be presumed to be small when the winding number assumes an integral number. This is effective for efficiently designing antenna from a smaller amount of material.

Explanations are now given to a case where the antenna is built in a portable terminal.

FIG. 20is an exploded oblique perspective view of a portable terminal using the antenna of the embodiment of the present invention, andFIG. 21is an oblique perspective view of a back side of a substrate shown inFIG. 20. A portable terminal16includes a liquid crystal panel17, buttons18, a substrate19and a battery20that are enclosed within enclosures21and22, and others. The antenna1is attached to the substrate19. The antenna1is mounted on a surface of the substrate19opposite to its side where the liquid crystal panel17is provided. The ground pullout portion11is formed in the substrate19. Although unillustrated, components, such as ICs, an RF module, antennas for other frequencies, a speaker, and a camera unit, are assumed to be mounted on the substrate19.

FIG. 21is a view showing a back side of the substrate19, and two antennas1are provided on the substrate19. When the antenna is provided in numbers as mentioned above, the electric current flowing over the surface of the substrate can be used more efficiently than the case where one antenna is used. Therefore, use of two antennas is preferable. As a matter of course, the antennas1do not need to be arranged symmetrically in the horizontal direction as shown inFIG. 21, nor is the number of antennas limited to two. Best performance is exhibited when antennas are mounted at substantially center points on respective long sides of the substrate where the highest concentration of the electric current flowing over the substrate appears. However, the antennas perform their functions even when mounted at any locations, so long as they are around the substrate19. Therefore, it is possible to produce an antenna unit without concern for footprints of antennas by mounting the antennas in unoccupied space. Moreover, when the antenna1is smaller in height than other components to be mounted, the antenna1is mounted in space between the higher mounted components, whereby the thickness of the antenna1does not exert any influence on a design thickness of the portable terminal. Hence, an antenna unit can be produced without involvement of an increase in thickness of a portable phone, which would otherwise be induced by use of a related art sheet-like antenna. The antennas1are mounted on the substrate19inFIG. 20. However, an antenna unit can be produced by mounting the antennas1on a metallic element, such as a frame of the battery20and a frame of the liquid crystal panel17.

FIG. 22is a circuit diagram of the antenna circuit of the present invention.FIG. 22Ais a circuit diagram for a case where one antenna1is incorporated.FIG. 22Bis a circuit diagram for a case where two antennas are mounted.FIG. 22Cis a circuit diagram for a case where three antennas are used. The circuit includes the antenna(s)1, the terminals5, a resonance frequency control capacitor34, and matching circuit connection terminals33connected to a matching circuit, an IC, or the like. When a plurality of antennas are used, the antennas1are interconnected by means of an interconnection conductor(s)32, whereby the number of antennas can readily be increased. Therefore, it becomes possible to readily enhance the antenna characteristic. Capacitance of the resonance frequency control capacitor34is determined from inductance of the antennas1achieved when the antennas1are mounted at predetermined locations and from a frequency used.FIG. 22shows only one resonance frequency control capacitor34, fine control may also be enabled by use of a plurality of resonance frequency control capacitors. Moreover, the resonance frequency control capacitor34can also be provided in a matching circuit connected to the matching circuit connection terminals33.

FIG. 23is an exploded oblique perspective view of the portable terminal using the antenna of the embodiment of the present invention. The antenna1is provided on an interior surface of the enclosure22. The substrate19or an unillustrated component to be mounted on the substrate19is utilized as a metallic element for the antenna1. Even when the antenna1is not mounted directly on the metallic element, an antenna device exhibiting superior communication performance can be produced by adoption of the arrangement where a metallic element is located in the vicinity of the antenna1when the portable terminal is assembled. As above, in addition to being mounted on the metallic element, the antenna1can also be provided on the interior surface of the enclosure.

Detailed descriptions are now provided to a terminal structure.

The structure includes a magnetic substance made of a substantially rectangular parallelepiped; a coil around which the magnetic substance is wound and which has two ends; a first terminal that has first connection portions respectively provided in the vicinity of two corners located along one side of the magnetic substance and that has a joint for connecting the first connection portions provided along one side of the magnetic substance; and a second terminal that has second connection portions respectively provided in the vicinity of two corners located along a side of the magnetic substance opposing its one side and that has a joint for connecting the second connection portions and that is provided along the opposite side of the magnetic substance. One end of the coil is connected to any of the first connection portions, and the other end of the coil is connected to any of the second connection portions. It is thereby possible to produce an antenna unit whose coil does not require any excessive length and that is not limited in terms of directivity when mounted in a communication device.

The first connection portions and the second connection portions are arranged so as to act as fixing portions at the time of mounting of the antenna unit. The antenna unit can thereby be stably set in a communication device, or the like.

The structure also includes a magnetic substance made of a substantially rectangular parallelepiped; a coil around which the magnetic substance is wound and which has two ends; a first terminal that has first connection portions respectively provided in the vicinity of two corners located along one side of the magnetic substance and that has a joint for connecting the first connection portions provided along one side of the magnetic substance; and a second terminal that has second connection portions respectively provided in the vicinity of two corners located along a side of the magnetic substance opposing its one side and that has a joint for connecting the second connection portions and that is provided along the opposite side of the magnetic substance. One end of the coil is connected to one of the first connection portions, and the other end of the coil is connected to the other of the first connection portions. The first connection portions of the first terminal are disconnected. It is thereby possible to connect a line of the communication device, or the like, and a coil by use of any of the plurality of connection portions. In particular, it becomes possible to connect connection portions belonging to one terminal to a line of a communication device, or the like, whereby an antenna unit can be produced while directivity achieved when the antenna is mounted is further enhanced.

FIG. 25is a rough schematic view of the antenna unit of the embodiment of the present invention, showing a state of the antenna unit achieved before a coil is wound. Reference numeral101designates ferrite assuming the shape of a substantially rectangular parallelepiped. Reference numerals102aand102bdesignate terminal portions and connected to locations around four corners of the ferrite. The terminal portion102aestablishes an electrical connection between positions A and C, and the terminal portion102bestablishes an electrical connection between positions B and D. The terminal portion102aincludes a terminal103aprojecting outside from the ferrite101at the position A, a terminal103cprojecting outside from the ferrite101at the position C, and a rod-shaped joint104ainterconnecting the connection portions. The joint104ais provided along one side of the ferrite101. The terminal portion102balso assumes the same structure as that of the terminal portion102a. A joint104bprovided along another side of the ferrite101opposing the one side interconnects terminals103band103d. The respective terminals103ato103dalso exhibit functions of fixing the antenna unit to the communication device, or the like, when the antenna unit is mounted on the communication device, or the like.

FIGS. 26 and 27are rough schematic views of the antenna units of the embodiment of the present invention, showing that a coil is wound around the antenna unit shown inFIG. 25. InFIG. 26, one end of the coil105is connected to the terminal103asituated at the position A of the terminal portion102a, and the other end of the coil105is connected to the terminal103bsituated at the position B of the terminal portion102b. In the terminal portion102a, the terminal103aand the terminal103care joined together by means of the joint104a, and the terminal103cof the terminal portion102aand the terminal103bof the terminal portion102bare held in an electrically conducted state by way of the coil105. Accordingly, as shown inFIG. 26, even when the coil105is connected to the terminal103aand the terminal103b, respectively, the line of the communication device can be connected to the terminal103situated at the position C of the terminal portion102aand the terminal103bsituated at the position B of the terminal portion102b. In the case of the antenna unit shown inFIG. 26, one line of the communication device can be connected to the terminal103aa situated at the position A of the terminal portion102aor the terminal103csituated at the position C of the terminal portion102a. The other line can be connected to the terminal103blocated at the position B of the terminal portion102bor the terminal103dlocated at the position D of the terminal portion102b. As a consequence, a degree of directivity freedom achieved when the antenna unit is mounted on the communication device can be enhanced.

FIG. 27shows a case where the line of the communication device is connected solely to one terminal portion102a. The coil105is connected to both the terminal103alocated at the position A of the terminal portion102aand the terminal103clocated at the position C of the terminal portion102a. In the meantime, the line of the communication device is also connected to both the terminal103aand the terminal103cof the terminal portion102a. Provided that the terminal portion102aremains in the state shown inFIG. 26, the terminal103aand the terminal103care connected together, to thus be brought into electrical conduction. As mentioned above, when only a connection between the line of the communication device and only one terminal portion102ais desired, all you have to do is to disconnect the joint104aas shown inFIG. 27. So long as the joint104ais disconnected, one side of the antenna device can be connected to the line of the communication device. The degree of directivity freedom achieved when the antenna unit is mounted on the communication device can be enhanced as in the case of the antenna unit shown inFIG. 26.

When actually mounted in a communication device, the antenna unit is used while the ferrite101and the terminal portions102aand102bare coated with a resin, or the like. On this occasion, only extremities of the respective terminals103a,103b,103c, and103dare exposed through the resin, and the thus-exposed extremities are connected to a line of the communication device.

As mentioned above, the antenna unit includes the base substrate3; the coil30formed from the conductor4wound around the base substrate3; and the plurality of terminals5connected to the conductor4. The uncovered base substrate portions31where the conductor4is absent are formed on the base substrate3except the start and end of turns of the coil30. The terminals5are provided on the end face side of the coil30parallel to the coil axis and in the uncovered base substrate portions31. It is thereby possible to provide an antenna and an antenna unit, which enable space saving and which exhibit superior communication performance, and a communication device using them.

Further, it is preferable that the number of turns of the coil30of the antenna1is larger than an integral multiple by substantially one-half of turn, because the antenna can thereby efficiently utilize the electric current flowing over the metallic element on which the antenna is to be mounted.

Moreover, the uncovered base substrate portion31is formed on each end of the base substrate3, whereby a magnetic field passing through an interior of the coil is made substantially parallel to the coil axis, so that an electric current can efficiently be guided.

The plurality of terminals5connected to the coil30are on the single uncovered base substrate portion31. As a result, it is thereby possible to provide an antenna and an antenna unit, which enable space saving and which exhibit superior communication performance, and a communication device using them.

The terminals5each are placed at substantial four corners of the coil30. The conductor4is connected to the terminals5, among the four terminals5, placed on both sides of the base substrate3with its coil axis interposed therebetween. It is thereby possible to provide an antenna and an antenna unit, which enable space saving and which exhibit superior communication performance, and a communication device using them.

An imaginary straight line passing through the two terminals5connected to the conductor4is substantially parallel to the winding direction of the coil30. The magnetic field passing through the interior of the coil can thereby be made parallel to the coil axis, so that an electric current can efficiently be guided.

Moreover, the imaginary straight line passing through the two terminals5connected to the conductor4is substantially parallel to a diagonal line of the base substrate3. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

The plurality of terminals5connected to the conductor4are placed on both sides of the base substrate3with its coil axis interposed therebetween. The imaginary straight line passing through the two terminals5connected to the conductor4is substantially parallel to the winding direction of the coil30. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

Furthermore, the plurality of terminals5connected to the conductor4are arranged on both sides of the base substrate3with the coil axis interposed therebetween. The imaginary straight line passing through the two terminals5connected to the conductor4is substantially parallel to the diagonal line of the base substrate3. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

The antenna is mounted such that at least one of the uncovered base substrate portions provided on the antenna is situated outside of the outer periphery of the metallic element on which the antenna is mounted. As a result, it is thereby possible to acquire an antenna unit that enables efficient utilization of the electric current flowing over the metallic element and that exhibits superior communication performance.

It is also preferable that the coil30is arranged in such a way that the winding direction of the coil and the ends of the base substrate7that is a metallic element become parallel to each other, become the electric current flowing over the metallic element on which the antenna is mounted can thereby be efficiently utilized.

It is also preferable that the coil30is arranged in such a way that the winding direction of the coil and the flow of the electric current flowing through the metallic element become parallel to each other, because the electric current flowing over the metallic element on which the antenna is mounted can thereby be efficiently utilized.

The plurality of terminals5each are placed at substantially four corners of the coil30. Of the four terminals5, two pairs of terminals5, each of which consists of two terminals5placed in the vicinity of the two corners situated along one side of the base substrate3, each are joined together by means of the joints104provided along the respective sides of the base substrate3. It is thereby possible to acquire an antenna unit that does not require an excessive length for the coil and that is not limited in terms of directivity when mounted on the communication device.

The terminals5act as fixing portions when the antenna unit is mounted, whereby the antenna unit can stably be placed in a communication device, or the like.

The joints104extend substantially parallel to the coil axis of the base substrate3. It is thereby possible to easily acquire an antenna unit that does not require an excessive length for the coil and that is not limited in terms of directivity when mounted on a communication device.

According to the antenna and the antenna unit of the present invention, the antenna unit can be made by utilization of clearance between components in the enclosures. Therefore, space saving of the antenna unit becomes possible, which is useful for miniaturization of the enclosures. For instance, the antenna and the antenna unit can be utilized as; an RF-ID antenna (tag) of a portable phone.

The disclosure of Japanese Patent Application No. 2009-197844 filed Aug. 28, 2010, including specification, drawings and claims is incorporated herein by reference in its entirety.