JP2009159291A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiband antenna device that can be easily designed and fabricated and appropriately mounted on a cellular phone, or the like. <P>SOLUTION: This multiband antenna device 100 includes a substrate 30 comprising a feeding point and a short circuit point, a UWB (Ultra Wide Band) antenna 10 connected to the feeding point, and a non-feeding element 20 having a short circuit end connected to the short circuit point and an open end being the other end of the short circuit end. The UWB antenna 10 and the non-feeding element 20 include a proximal portion that is closer to the open end than the short circuit end of the non-feeding element 20, and the non-feeding element 20 is operated by electromagnetic coupling to the UWB antenna 10 in the proximal portion. In the antenna device 100, a low VSWR characteristic can be obtained in a relatively high frequency band by the action of the UWB antenna 10, and a low VSWR characteristic can be obtained in a low frequency band by the action of the non-feeding element 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antenna device, and more particularly to a small multiband antenna device used for a mobile phone.

  In the field of mobile communication, multiband antennas are being promoted in order to cope with the problem of frequency depletion of mobile phones and the increase in communication speed. Wireless communication systems such as WLAN (Wireless Local Area Network), WMAN (Wireless Metropolitan Area Network), and WPAN (Wireless Personal Area Network) are also in progress.

  In such a situation, the conventional multiband antenna apparatus directly feeds each antenna element having a length corresponding to each of different frequencies, uses a parasitic element, It has been composed by combining these methods.

  FIG. 14 shows a list of wireless communication systems used (or will be used in the future) by mobile phones, and includes a plurality of types of networks. Here, referring to the frequency range of each system, it is considered that a close frequency band can be realized by one antenna element. Therefore, for example, an antenna device as shown in FIG. 15 has been developed.

  The antenna 104 of FIG. 15 has three branches: a first branch corresponding to GSM1900 and UMTS, a second branch corresponding to GSM1800, GSM1900 and UMTS, and a third branch corresponding to GSM900 and GSM1800. It is composed of elements. In this way, when a branch branched from the middle of a certain antenna element is counted as one antenna element, if the adjacent frequency bands shown in the table of FIG. 14 are each realized by one element, the GSM system (GSM850, GSM900, The antennas corresponding to the four frequency bands of GSM1800 and GSM1900, the frequency band of UMTS, and the frequency band of UMTS can be realized with about two to three antenna elements.

  However, the number of antenna elements must be increased in order to make the antenna additionally compatible with a frequency band such as Mobile-Wimax, for example. Since mutual interference occurs between the antenna elements, an increase in the number of antenna elements results in a drastic increase in the difficulty of designing the antenna device.

  On the other hand, in order to make the antenna device compatible with multiple bands, it is conceivable to use a UWB (Ultra Wide Band) antenna in addition to a method of increasing the number of antenna element branches. As a typical small UWB antenna, there is a disk monopole antenna as shown in FIGS. As shown in the schematic side view of 16 (b), the disk monopole antenna is configured by arranging the disk 10 perpendicular to the ground plane 30.

  At this time, the VSWR characteristic of the disk monopole antenna is smaller than 2 in a frequency band higher than the frequency at which the disc diameter D is substantially equal to λ / 4. Therefore, for example, when the diameter D of the disc is 25 mm, a VSWR characteristic smaller than 2 is obtained in a band of 3 GHz to 20 GHz or more.

  However, when such a disk monopole antenna is simply enlarged to form a multiband mobile phone antenna that can be used from GSM850 (824 to 894 MHz), the diameter D of the disk becomes about 90 mm and is mounted on the mobile phone. The size is inappropriate.

Regarding the downsizing of the disk monopole antenna, for example, it is also described in Patent Document 1, but the applicant should devise the shape of the antenna element, the arrangement method on the ground plane, the material of the dielectric, etc. independently. Therefore, we have developed a small UWB antenna that can be used in a size of about λ / 10 to λ / 12. However, even when a multiband mobile phone antenna that can be used from GSM850 (824 to 894 MHz) is configured using this technology, the antenna has a height of 30 mm or more and is still suitable for mounting on a mobile phone. It cannot be said.
JP 2004-328062 A

Thus, the need for miniaturization in multiband antenna devices is increasing. In addition, it is desirable that such an antenna device has a simpler structure and is easier to design and manufacture than a multiband antenna composed of approximately the same number of antenna elements as has been conventionally seen.
In view of these problems, an object of the present invention is to provide a multiband antenna device having a small and simple structure capable of obtaining good antenna characteristics in a wide band.

In order to achieve this object, a multiband antenna device according to the present invention includes a substrate having a feed point and a short-circuit point, a UWB antenna connected to the feed point, a short-circuit end connected to the short-circuit point, and the other end of the short-circuit end. The UWB antenna and the parasitic element have a proximity portion in a region closer to the open end than the short-circuited end of the parasitic element, and the parasitic element is a proximity portion. It operates by electromagnetic coupling with the UWB antenna.
In this multiband antenna device, a plurality of parasitic elements having the same electrical length may be provided. The multiband antenna device may include a plurality of parasitic elements having different electrical lengths.

  The multiband antenna device according to the present invention has a small and simple configuration having a smaller number of elements than a conventional multiband antenna device. Therefore, design and manufacture can be facilitated, and it can be suitably mounted on a mobile phone or the like.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a configuration of a multiband antenna device according to an embodiment of the present invention. As shown in the figure, the antenna device 100 includes a UWB antenna 10 and an inverted L antenna 20 installed on a ground plane 30. Among these, the UWB antenna 10 is a feeding element connected to a feeding point, and the inverted L antenna 20 is a parasitic element.

  As is well known, the UWB antenna and the inverted L antenna are originally used individually as shown in FIGS. 2 (a) and 2 (b). The UWB antenna 10 in FIG. 2A corresponds to a frequency of DCS (1800 MHz band) or higher, and the inverted L antenna 21 in FIG. 2B corresponds to the frequencies of GSM850 and GSM900 (824 to 894 MHz, 890 to 960 MHz). If it is assumed, the VSWR characteristics when each is used alone are as shown in FIG. Here, the VSWR characteristic of the UWB antenna is represented by a solid line, and the VSWR characteristic of the inverted L antenna is represented by a broken line.

  When the UWB antenna 10 and the inverted L antenna 21 are combined to operate as the antenna device 100, two configurations are possible in which one is a feeding element and the other is a parasitic element. The first configuration is an antenna apparatus 100 that feeds power to the UWB antenna 10 and leaves no power to the inverted L antenna 20 as shown in FIG. This is the same as that shown in FIG. 1 as the configuration of the present invention. The second configuration is an antenna device 101 that supplies no power to the UWB antenna 12 and supplies power to the inverted L antenna 21. FIG. 3C shows the VSWR characteristics of the antenna devices 100 and 101 with a solid line and a broken line. In the figure, (F) indicates Feed, that is, power is supplied, and (P) indicates Parasitic, that is, power is not supplied.

  In general, when an antenna device is configured with a feed element and a parasitic element, the main characteristics of the antenna device are determined by the feed element, and the parasitic element plays a role in causing changes in the characteristics. Therefore, in FIG. 3C, the VSWR characteristic obtained by the first configuration using the UWB antenna as a feed element is mostly similar to the VSWR characteristic of the UWB antenna shown in FIG. Further, the VSWR characteristic of the inverted L antenna shown in FIG. 2C is reflected in the low band where the low VSWR characteristic cannot be obtained with the UWB antenna. Accordingly, the antenna device 100 according to the first configuration exhibits a VSWR characteristic lower than 2 over a wide band.

On the other hand, the VSWR characteristic obtained by the second configuration using the inverted L antenna as the feeding element is mostly the same as the VSWR characteristic of the inverted L antenna shown in FIG. Only low values can be obtained.
Therefore, the object of the present invention is not suitable for the antenna device 102 using an inverted L antenna as a feed element, but an inverted L antenna using a UWB antenna as a feed element, which can obtain good VSWR characteristics over a wider band. The antenna device 100 is a parasitic element.

  Here, in constructing the antenna device from the UWB antenna and the inverted L antenna, a device is required for the arrangement of both elements. That is, the antenna device of the present invention is intended to add the characteristics of an inverted L antenna that is a parasitic element without greatly affecting the characteristics of the UWB antenna that is a feeding element. In order to achieve this, it is necessary to increase the distance between the power feeding part of the power feeding element and the short-circuited part of the parasitic element as long as the operation of the parasitic element can be ensured.

  In the antenna device 100, the feeding element 10 is used as a feeding probe for the parasitic element 20, and the parasitic element 20 operates by electromagnetic coupling by the feeding element 10. The location of the electromagnetic coupling is a region where the feeding element 10 and the parasitic element 20 are close to each other, that is, an A part in FIG. 4A close to the open end of the parasitic element 20 or a B part near the short-circuited end of the parasitic element 20. Can be roughly divided into two locations. Of these, the portion A near the open end is dominant in coupling to the base resonance (λ / 4) of the parasitic element, and the portion B near the short-circuited end is dominant in coupling to the higher order resonance. It is preferable to bond with.

FIG. 4B shows an example of the calculation result of the VSWR characteristic when the distance d between the feeding element 10 and the parasitic element 20 in the B part is changed between 0.5 mm and 22.5 mm. From the figure, it can be seen that the best VSWR characteristics can be obtained when the distance d is 22.5 mm. In other words, it can be seen that when the distance d is increased to reduce the coupling amount of the portion B, the UWB antenna, which is a feeding element, can easily secure the original broadband characteristics.
If it is desirable to reduce the size even at the expense of the characteristics of the feed element, that is, the UWB antenna, the UWB antenna and the inverted L antenna may be arranged closer to each other.

Next, the miniaturization of the antenna device 100 will be examined.
As already described, the antenna device 100 includes the feeding element 10 and the parasitic element 20. Referring again to FIG. 1, the height h of the antenna device 100 is about 44 mm (λ (1 .71 GHz) / 4). This is too big to be mounted on a mobile phone.

  Therefore, for example, the antenna device 100 can be reduced in size by using generally-used methods for reducing the size of the antenna device, such as three-dimensional antenna element shape and optimization of the antenna mounting position.

  Among these, regarding the three-dimensional shape, for example, the antenna length can be shortened by increasing the thickness of the antenna. As for the optimization of the antenna mounting position, it is conceivable to mount the antenna in a place where the ground plane is easily excited. This point will be described assuming that the antenna device 100 is mounted on a finite ground plane such as a mobile phone.

  5A to 5C show the arrangement position and the VSWR characteristic when the UWB antenna 10 having a disk element having a diameter of 20 mm is arranged on the ground plane 30 having a size of 100 mm × 50 mm. Here, when the UWB antenna 10 is arranged on one relatively short side of the ground plane 30, the case where it is arranged at the end as shown in FIG. 5A and the case where it is arranged at the center as shown in FIG. Then, different VSWR characteristics can be obtained. FIG. 5C shows the VSWR characteristics of the end arrangement and the center arrangement, and the value of the VSWR is obtained from the lower frequency band when the UWB antenna 10 is arranged at the end rather than the center of one side of the ground plane 30. It turns out that becomes low.

  On the other hand, also when the monopole antenna 22 having a size of 20 mm × 2 mm of the ground plane 30 having the size of 100 mm × 50 mm is arranged, the VSWR characteristics change depending on the arrangement position of the monopole antenna 22. As shown in FIG. 6 (c), when placed at the end of one relatively short side of the ground plane 30 as shown in FIG. 6 (a) and when placed in the center as shown in FIG. 6 (b). Different VSWR characteristics are obtained. That is, as with the UWB antenna 10, the value of the VSWR becomes lower from a lower frequency band when arranged at the end. Since the inverted L antenna 20 used in the antenna device 100 of the present invention is a kind of monopole antenna, it can be considered that the same result can be obtained.

  As described above, the UWB antenna 10 and the feed point, which are feed elements, and the parasitic element 20 and the short-circuit point are all arranged near the end of the ground plane, thereby contributing to high performance or downsizing of the antenna device. can do. Therefore, the arrangement shown in FIG. 7A is preferable. Also, if the configuration of the antenna device 100 becomes difficult if the feeding point and the short-circuiting point are simultaneously arranged at both ends of the ground plane because the ground plane is wide, the high-frequency band that the UWB antenna 10 serving as the feeding element is in charge of The arrangement can be changed depending on which of the low-frequency bands that the parasitic element 20 is in charge of and which performance and downsizing are prioritized. For example, the antenna device 100 may be disposed at the position shown in FIG. 7B when priority is given to the high frequency band, and at the position shown in FIG. 7C when priority is given to the low frequency band.

  By the way, in the implementation of the antenna device of the present invention, the UWB antenna which is a feeding element is not limited to the disk shape as described above, and may be an ellipse, a semicircle, a polygon as long as it is a monopole UWB antenna. The same effect can be obtained even with other shapes. Therefore, in combination with the antenna mounting position as described above, as another embodiment of the present invention, for example, an antenna device as shown in FIGS. 8 and 10 can be manufactured.

  An antenna device 100a shown in FIGS. 8A and 8B is installed at an end portion of a ground plate 30 of 80 mm × 45 mm, and includes a feeding element 10 and a parasitic element 20. As shown in the development view of FIG. 8B, the feeding element 10 has a feeding point at the contact point with the ground plane 30, and the parasitic element 20 has a short-circuit point at the contact point with the ground plane 30. The parasitic element 20 is electromagnetically coupled to the feed element 10 at a location surrounded by a circle C adjacent to the feed element 10. Further, the electromagnetic coupling can be optimized by adjusting the distance between the feeding element 10 and the parasitic element 20 at this point.

FIG. 9 shows the VSWR characteristics of the antenna device 100a. Considering VSWR <3 as a practical value, generally good characteristics are obtained over a wide band.
Similarly, the antenna device 100b shown in FIGS. 10A and 10B is also installed at the end portion of the ground plate 30 of 80 mm × 45 mm, and is composed of the feeding element 10 and the parasitic element 20. 10B shows that the feeding element 10 has a feeding point at the contact point with the ground plane 30 and the parasitic element 20 has a short-circuiting point at the contact point with the ground plane 30. FIG. The parasitic element 20 can be optimized by electromagnetically coupling to the feeder element 10 at a location surrounded by a circle D adjacent to the feeder element 10 and adjusting the distance between the feeder element 10 and the parasitic element 20. It is.

  FIG. 11 shows the VSWR characteristics of the antenna device 100b. Although the characteristics in the vicinity of 4 GHz are deteriorated in the figure, there is no problem in the function of the antenna device 100b on the assumption that this band is not used.

  Thus, the antenna device of the present invention exhibits different VSWR characteristics by variously changing the shapes of the UWB antenna and the parasitic element. In these antenna devices 100a and 100b, the feeding element 10 and the parasitic element 20 may be formed by patterning on the surface of the prism 40 having a cross section of 10 mm square.

  Here, in the case where the prism 40 is formed of a dielectric, and the size is reduced by using this, the dielectric loss generally increases gradually as the frequency increases due to the characteristics of the dielectric, and the radiation efficiency increases. descend. On the other hand, if the prism 40 is made of a magnetic material and is to be miniaturized, a sudden increase in loss is expected outside the applicable band. This is because at present, there is no magnetic material having good characteristics in a high-frequency wide band, and the magnetic material is developed and designed specifically for the applicable frequency. For this reason, at present, it is necessary to use a configuration in which the effect of downsizing the magnetic material is utilized only with the magnetic material application frequency, rather than downsizing the entire antenna device with the magnetic material.

  In the configuration of the antenna device 100 of the present invention, the inverted L antenna, which is a parasitic element, is limited in charge of radiation in the low frequency region. Therefore, as shown briefly in FIG. 12, by using a dielectric for the portion where the feed element is disposed and using a magnetic material only for the portion where the parasitic element is disposed, the size can be reduced and UWB can be achieved at the same time. The antenna device can be realized without reducing the radiation efficiency of the high-frequency wideband portion that the element is in charge of.

By such a device, the height h of the antenna device 100 can be suppressed to about 10 to 15 mm (λ (1.71 GHz) / 12).
In implementing the multiband antenna device according to the present invention, the number of parasitic elements is not limited to one. For example, as shown in FIG. 13 (a), the antenna device is widened by using a plurality of parasitic elements having substantially the same electrical length, and the low bands (824 to 960 MHz, 1710 to 2170 MHz) are parasitic elements. It is possible to realize the antenna device 102 that is in charge of 20 and 23 and that is in charge of the high frequency band (2.3 GHz and above).

  Alternatively, as shown in FIG. 13B, the antenna device can be multibanded by using a plurality of parasitic elements having different electrical lengths, and a low band (824 to 960 MHz, 1710 to 2170 MHz) can be set to the parasitic element 20. It is also possible to realize the antenna device 103 in which the parasitic element 24 is responsible for the higher band (2305 to 2690 MHz) and the feeder element 11 for the higher band (3.1 GHz and higher).

  With the above configuration, according to the present invention, for example, a multi-band that can be used in all of 5 bands of WMAN, 3 bands of WMAN, 3 bands of WLAN, 2 bands of WPAN, and IMT-Advanced band. A band antenna device can be provided. Further, based on the basic configuration shown in FIG. 1, for example, by enlarging the UWB antenna portion, it is possible to provide an antenna device that is compatible with Japan PDC and GPS.

  Note that the multiband antenna device according to the present invention does not necessarily correspond to all of the communication methods shown in the table of FIG. 14, and takes into consideration various circumstances such as a region where a mobile phone equipped with the antenna device is used. It is possible to select a desired characteristic and perform a more effective design.

  As mentioned above, although the Example of the antenna device by this invention was described, this invention is not limited to these but can be implemented variously.

Schematic which shows the structure of the multiband antenna apparatus by one Example of this invention. (A) is the schematic of a UWB antenna, (b) is the schematic of an inverted L antenna, (c) is a figure which shows the VSWR characteristic of each antenna. (A), (b) is a figure which shows the structural example of the combination of a UWB antenna and a reverse L antenna, (c) is a figure which shows the VSWR characteristic of each structural example. (A) is a figure which shows the coupling | bond part in the multiband antenna apparatus by one Example of this invention, (b) is a figure which shows the change of the VSWR characteristic according to the distance between a feed element and a parasitic element. (A) And (b) is a figure which shows the arrangement position of a UWB antenna, (c) is a figure which shows the VSWR characteristic according to an arrangement position. (A) And (b) is a figure which shows the arrangement position of a monopole antenna, (c) is a figure which shows the VSWR characteristic according to an arrangement position. (A), (b), (c) is a figure which shows the arrangement position of the antenna apparatus by this invention. (A) is a perspective view of the multiband antenna device by another Example of this invention, (b) is an expanded view. The figure which shows the VSWR characteristic of the multiband antenna apparatus by the Example shown in FIG. (A) is a perspective view of the multiband antenna device by another Example of this invention, (b) is an expanded view. The figure which shows the VSWR characteristic of the multiband antenna apparatus by the Example shown in FIG. The figure explaining utilization of the dielectric material and magnetic body in size reduction of the antenna apparatus of this invention. (A) And (b) is the schematic of the multiband antenna device by another Example of this invention. 1 is a diagram showing a representative mobile phone-mounted wireless communication system. The figure which shows an example of a structure of the conventional multiband antenna apparatus. (A) And (b) is a figure which shows a general disc monopole antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Antenna apparatus 10 Feeding element 20 Parasitic element 30 Ground plane h Antenna height

Claims (3)

A substrate with a feed point and a short-circuit point;
A UWB (Ultra Wide Band) antenna connected to the feed point;
A parasitic element having a short-circuit end connected to the short-circuit point and an open end that is the other end of the short-circuit end,
With
The UWB antenna and the parasitic element have a proximity portion in a region closer to the open end than the short-circuited end of the parasitic element,
The parasitic element operates by electromagnetic coupling with the UWB antenna in the proximity portion. The multiband antenna device according to claim 1,
A multiband antenna device comprising a plurality of the parasitic elements having the same electrical length. The multiband antenna device according to claim 1,
A multiband antenna device comprising a plurality of parasitic elements having different electrical lengths.

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