JP4667310B2 - Multi-antenna with parasitic elements - Google Patents

Description

  The present invention relates to a multi-antenna, and more particularly to a multi-antenna for a mobile communication terminal including a plurality of feeding elements and parasitic elements.

  Conventionally, as a multi-antenna or array antenna for a mobile communication terminal, a diversity antenna is generally used, and an ideal antenna condition in which a half-wave dipole antenna is used and an antenna element interval is about 0.5 wavelength is assumed. It is said that. This is to obtain a high antenna gain without generating a grating lobe based on the array theory, and in order to avoid a decrease in gain due to the effect of coupling between elements, the antenna element spacing is set to about 0.5 wavelength. There are many things to do.

  A multi-antenna with a 0.5 wavelength interval composed of a half-wave dipole antenna can obtain a high antenna gain by beam forming and a correlation coefficient between antenna elements is reduced. Considering this, it was difficult to mount it on a portable terminal or the like that is particularly required to be downsized. In addition, previous studies on multi-antennas have not considered a realistic antenna configuration.

  Furthermore, as a multi-antenna for a terminal, there is a PDC portable terminal in which two antennas having a whip shape and an inverted F shape are arranged with an element interval of 0.5 wavelength or less as shown in FIG. However, this is merely an antenna arrangement for obtaining a diversity effect, and it has not been studied about an antenna configuration that is compatible with beam forming, diversity, and MIMO transmission, which are being considered for application to the next generation mobile communication system.

  For example, as a multi-antenna for a terminal that can be used in a mobile communication system that performs beam forming, diversity, or MIMO transmission, as shown in FIG. 18, a protrusion is formed at the end of a card-type wireless terminal mounted in an external expansion slot of a notebook computer A configuration in which a plurality of radiating elements are arranged is conceivable. This is composed of a circuit board 180, a feeding point 181, and a monopole feeding element 182. In the case of this multi-antenna configuration, the effect of mutual coupling between antennas is large, so that the radiation efficiency is lowered and it is difficult to obtain sufficient antenna performance. Therefore, a multi-antenna that can be applied to a mobile communication system that is less affected by mutual coupling has been desired.

Conventionally, the following patent documents are known for improving antenna characteristics by adding a parasitic element. However, all use a single feeding element, and use a multi-antenna having a plurality of feeding elements.
JP 2003-283238 A JP 2004-6431 A JP 2005-286895 A JP 2006-50496 A JP 2006-67234 A

A multi-antenna according to a feature of the present invention includes a circuit board having a plurality of feeding points; a plurality of feeding elements having one end opened and the other end connected to the feeding point; One or more parasitic elements connected to
The feeding element and the parasitic element have an element length of 0.2 to 0.3 wavelength in terms of the wavelength of the used frequency band; and the parasitic element is attached to the circuit board in the vicinity of the arbitrary feeding point. It is characterized by connecting.

  The feeding element or the parasitic element may have a bent structure.

  The feeding element and the parasitic element may have a branch structure.

  The parasitic element may be arranged on the surface or inside of a dielectric having an arbitrary dielectric constant.

  The feeding element can be arranged to be perpendicular and parallel to the circuit board, and the parasitic element can be connected to the circuit board in the vicinity of the feeding point of the feeding element arranged perpendicular to the circuit board.

  The parasitic elements may be arranged orthogonal to each other.

  The multi-antenna may be configured to perform beam forming for controlling directivity.

  The multi-antenna may be configured to perform diversity.

  The multi-antenna may be configured to perform MIMO transmission that increases transmission capacity by parallel transmission of spatial physical channels.

  The above multi-antenna may be configured to switch and use beamforming, diversity, or MIMO transmission according to the surrounding propagation environment for communication.

  According to the multi-antenna according to the embodiment of the present invention, it is possible to provide a multi-antenna that uses a plurality of antennas and has little performance deterioration due to mutual coupling.

  Hereinafter, embodiments of an antenna device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing a basic configuration of a multi-antenna 8 according to the first embodiment of the present invention. The multi-antenna 8 basically includes a circuit board 10, a plurality of feeding points 11 on the circuit board 10, and a plurality of feeding elements 12. Each feed element 12 has one end open and the other end connected to the corresponding feed point 11. The multi-antenna 8 further includes one or a plurality of parasitic elements 13 having one end opened and the other end connected to the circuit board 10. The feed element 12 and the parasitic element 13 have a length of 0.2 wavelength to 0.3 wavelength in terms of the wavelength of the used frequency band. The parasitic element 13 is connected to the circuit board 10 in the vicinity of an arbitrary feeding point 11.

  As an antenna for a portable terminal, a quarter-wave monopole antenna that can be miniaturized and built-in is often used. In this embodiment, a monopole antenna having an element length of about 1/4 wavelength is used. ing.

  Further, in the embodiment of FIG. 1, there are two feeding elements 12, which are arranged at the end of the circuit board 10 and are connected to the feeding point 11, respectively. One parasitic element 13 is connected to the vicinity of one of the feeding points at the end of the circuit board (not connected to the feeding point).

  The graph of FIG. 2 shows a comparison of characteristics between the terminal multi-antenna 8 according to the first embodiment and the terminal multi-antenna having the conventional configuration as shown in FIG. The values shown in FIG. 2 are values obtained as a result of calculating the mutual coupling amount and the radiation efficiency of the respective antennas constituting the multi-antenna using the numerical calculation by the moment method. The conventional multi-antenna for terminals does not include a parasitic element as shown in FIG.

From the graph of FIG. 2, it can be seen that in the case of a terminal multi-antenna having a conventional configuration, the mutual coupling amount is -10 dB or more, and the radiation efficiency is degraded by about 1 dB due to the strong mutual coupling. On the other hand, in the case of the multi-antenna of the first embodiment of the present invention, the mutual coupling amount is about −15 dB, and it is understood that the deterioration of the radiation efficiency is suppressed to about 0.1 dB.
[Length of parasitic element]
Here, the length of the parasitic element 13 will be described. In the graph of FIG. 3, the value which evaluated the mutual coupling amount with respect to the length of the parasitic element 13 of the multi antenna 8 for terminals according to 1st Example by numerical calculation is shown.

  In the graph of FIG. 4, the value which evaluated the radiation efficiency with respect to the length of the parasitic element 13 of the multi antenna 8 for terminals according to 1st Example by numerical calculation is shown.

  From FIG. 3, for example, in order to reduce the mutual coupling amount to −10 dB or less, it is necessary to convert the length of the parasitic element 13 to 0.2 wavelength to 0.3 wavelength in terms of the wavelength of the used frequency band. I understand. Also, from FIG. 4, for example, in order to make the degradation of radiation efficiency within 0.2 dB, the length of the parasitic element 13 is converted to the wavelength of the used frequency band to be 0.2 wavelength to 0.3 wavelength. I understand that it is necessary. That is, the present inventors set the length of the parasitic element 13 to about ¼ wavelength similarly to the feeder element 12, and positively generate current not only in the feeder element 12 but also in the parasitic element 13. It was confirmed that the radiation efficiency can be improved by reducing the coupling between the antennas.

  FIG. 5 is a schematic diagram showing a basic configuration of a terminal antenna 58 according to the first embodiment of the present invention, which is provided with three feeding elements. Of the three feeding elements 52, one parasitic element 53 is arranged for each two.

  The graph of FIG. 6 shows a comparison of the characteristics of the terminal multi-antenna 58 according to the first embodiment of the present invention and the conventional terminal multi-antenna, as in FIG. When three feed elements are used, the amount of mutual coupling is about −5 dB in the case of a terminal multi-antenna having a conventional configuration, and the radiation efficiency is deteriorated by 2 dB or more due to the mutual coupling. You can see that On the other hand, in the case of the multi-antenna 58 of the first embodiment of the present invention, the mutual coupling amount is about −10 dB, and it can be seen that the deterioration of the radiation efficiency is suppressed within 1 dB.

In a multi-antenna in which a plurality of antennas are mounted on a portable terminal having a limited antenna volume, a sufficient distance between the antennas cannot be ensured, so that radiation efficiency is likely to deteriorate due to the influence of mutual coupling between antennas. In response to such a problem, in the first embodiment of the present invention, one parasitic element having a length of 0.2 to 0.3 wavelength in terms of the wavelength of the used frequency band is provided in the vicinity of an arbitrary feeding point. By connecting to the circuit board one by one, current can be generated not only on the feed element but also on the parasitic element, coupling between antennas can be reduced, and radiation efficiency can be improved.
In the present embodiment, an example in which at most one parasitic element is arranged at each feeding point is shown, but the effect is not changed even if two or more parasitic elements are arranged at each feeding point. One parasitic element at each feeding point is sufficient.

  FIG. 7 is a schematic diagram showing a basic configuration of a multi-antenna 78 according to the second embodiment of the present invention. This embodiment has the same configuration as that of the first embodiment, except that the feeding element 72 or the parasitic element 73 of the multi-antenna 78 has a bent structure. For the feed element 72 or the parasitic element 73 having a bent structure, the element length is converted to a wavelength of 0.2 to 0.3 wavelengths by converting the wavelength of the frequency band, and the parasitic element 73 is set near any feed point. By connecting to the circuit board one by one, a current is generated not only on the feed element 72 but also on the parasitic element 73, and the same effect as in the first embodiment can be obtained.

  By making the feeding element 72 or the parasitic element 73 into a bent structure, the antenna can be lowered in posture and can be built in a portable terminal housing of an arbitrary shape, and both antenna performance and design can be achieved.

  FIG. 8 is a schematic diagram showing a basic configuration of a multi-antenna 88 according to the third embodiment of the present invention. This embodiment has the same configuration as that of the first embodiment, except that the feeding element 82 and the parasitic element 83 of the multi-antenna 88 have a branch structure. For the feeding element 82 or the parasitic element 83 having a branch structure, the length from the feeding point to the open end via the branching point is converted into the wavelength of the used frequency band by 0.2 wavelength to 0.3 wavelength. By connecting the parasitic elements to the circuit board one by one near the arbitrary feeding point, current is generated not only on the feeding element 82 but also on the parasitic element 83, and the same effect as in the first embodiment is obtained. Can be obtained.

  By using the feed element 82 or the parasitic element 83 as a branch structure, a multiband applicable to a plurality of frequency bands can be realized while using the same antenna configuration, and mutual coupling in a plurality of frequency bands can be reduced. The effect and the improvement effect of radiation efficiency can be acquired.

  FIG. 9 is a schematic diagram showing a basic configuration of a multi-antenna 98 according to the fourth embodiment of the present invention. This embodiment has the same configuration as that of the first embodiment, but is different in that the parasitic element 93 of the multi-antenna 98 is arranged on the surface or inside of the dielectric 94 having an arbitrary dielectric constant. The parasitic element 93 disposed on the surface of or inside the dielectric 94 having an arbitrary dielectric constant is also converted to a wavelength that takes into account the dielectric constant of the operating frequency band and has a wavelength of 0.2 to 0.3. By setting the wavelength and connecting each parasitic element 93 to the circuit board one by one in the vicinity of an arbitrary feeding point, a current is generated not only on the feeding element 92 but also on the parasitic element 93, as in the first embodiment. Effects can be obtained.

  By disposing the parasitic element 93 on the surface of or inside the dielectric 94 having an arbitrary dielectric constant, the volume required for mounting the parasitic element 93 can be reduced, and the antenna can be downsized. Can do. For example, in the basic configuration of the multi-antenna 98 according to the fourth embodiment of the present invention shown in FIG. 9, when a dielectric having a relative dielectric constant of 3 is used, the mutual coupling reduction effect and the radiation efficiency improvement effect are maintained. The physical element length of the parasitic element can be shortened by the wavelength shortening effect due to the arrangement of the dielectric, and the antenna volume can be reduced to about ½.

  FIG. 10 is a schematic diagram showing a basic configuration of the multi-antenna 108 according to the fifth embodiment of the present invention. This embodiment has the same configuration as that of the first embodiment, but is different in that each feeding element 102 of the multi-antenna 108 is arranged vertically and parallel to the circuit board 100, respectively. The parasitic element 103 is connected to the circuit board in the vicinity of the feeding point of the radiating element 102 arranged perpendicular to the circuit board 100. Also for the feed element 102 arranged perpendicularly and parallel to the circuit board, the element length is converted to a wavelength of 0.2 to 0.3 wavelength in terms of the frequency band, and the parasitic element 103 is as shown in the figure. By connecting to the circuit board 100, a current is generated not only on the feed element 102 but also on the parasitic element 103, and the same effect as in the first embodiment can be obtained.

  By arranging the feed elements 102 vertically and in parallel, mutual coupling between the antennas can be reduced. Further, by arranging the parasitic element 103 in the vicinity of the feeding point of the feeder element 102 arranged vertically, the ground function of the feeder element 102 arranged vertically is strengthened, and the radiation of the feeder element 102 arranged vertically is radiated. The vertical polarization component increases for the pattern.

  For example, when the multi-antenna 108 according to the present embodiment is mounted on a mobile terminal and used, the vertical polarization component is dominant in the incoming waves around the terminal, so that the radiation characteristics of the terminal and the consistency of the incoming waves are The effective gain in the portable terminal is improved.

  FIG. 11 is a schematic diagram showing a basic configuration of a multi-antenna 118 according to the sixth embodiment of the present invention. This embodiment has the same configuration as that of the first embodiment, but is different in that the parasitic elements 113 of the multi-antenna 118 are arranged orthogonal to each other. In the case of the embodiment shown in FIG. 11, one parasitic element 113 is arranged in the vicinity of all the feeding points 111 to which the three feeding elements 112 are connected, and the parasitic element 113. Are arranged orthogonal to each other. Even when parasitic elements 113 that are orthogonal to each other are arranged, the element length is converted to a wavelength that takes into account the dielectric constant of the operating frequency band to be 0.2 to 0.3 wavelengths, and the parasitic element 113 is arbitrarily set. By connecting each one to the circuit board 110 in the vicinity of the feeding point, a current is generated not only on the feeding element 112 but also on the parasitic element 113, and the same effect as in the first embodiment can be obtained. By disposing the parasitic elements 113 so as to be orthogonal to each other, it is possible to reduce the influence of mutual coupling between the parasitic elements, and it is possible to reduce the mutual coupling between antennas and improve the radiation efficiency.

  In the present embodiment, an example in which the orthogonal parasitic elements are configured in the same plane as the circuit board is disposed, but in the case where each parasitic element is disposed in a plane that is not the same, The same effect can be obtained.

  FIG. 12 is a schematic diagram showing a basic configuration of a multi-antenna 128 according to the seventh embodiment of the present invention. This embodiment is an example in which the multi-antenna according to the present invention is applied to beam forming in which a gain increasing effect is obtained by directivity synthesis. This embodiment is configured using the multi-antenna of any one of the first to fifth embodiments, and includes a beam forming circuit 124 that performs directivity synthesis. Since the multi-antenna apparatus 128 in the present embodiment uses the multi-antenna described in the first to fifth embodiments as an antenna, the influence of mutual coupling between the antennas is small, and high radiation efficiency can be obtained. Accordingly, a high gain increasing effect can be obtained even in beam forming in which directivity synthesis is performed.

FIG. 13 is a schematic diagram showing a basic configuration of a multi-antenna 138 according to the eighth embodiment of the present invention. This embodiment is an example in which the multi-antenna according to the present invention is applied to diversity in which a gain increasing effect can be obtained by combining signals.
This embodiment is configured using the multi-antenna of any of the first to fifth embodiments, and includes a diversity circuit 134 that combines signals. Since the multi-antenna apparatus 138 in the present embodiment uses the multi-antenna described in the first to fifth embodiments as an antenna, the influence of mutual coupling between the antennas is small, and high radiation efficiency can be obtained. As the mutual coupling between antennas is reduced, the correlation between antennas, which is closely related to the diversity gain, is also suppressed to a sufficiently low level. Therefore, a high gain increase effect can be obtained even in diversity in which signals are combined.

  FIG. 14 shows an example in which the multi-antenna according to the present invention is applied to polarization diversity in which a gain increasing effect can be obtained by combining signals between different polarizations. In this example, the multi-antenna of the fifth embodiment is used, and a diversity circuit 144 that combines signals is provided. Since the multi-antenna apparatus 148 in the present embodiment uses the multi-antenna described in the fifth embodiment as an antenna, the influence of mutual coupling between the antennas is small, and high radiation efficiency can be obtained. Further, since the parasitic element 143 is arranged in the vicinity of the feeding point of the vertically arranged feeding element 142, the vertically arranged feeding element 142 has a vertical polarization component and is arranged in parallel. 142 has a horizontal polarization component. As a result, since each antenna constituting the multi-antenna 148 has vertical and horizontal independent polarization characteristics, the inter-antenna correlation closely related to the diversity gain can be suppressed sufficiently low. Therefore, a high gain increasing effect can be obtained in polarization diversity in which signals between different polarizations are combined.

  In addition, when the parasitic element which is the prior art is not arranged, even when the feeding element is arranged perpendicular to the circuit board, a vertical polarization component cannot be obtained due to the influence of the current generated in the circuit board. Polarization diversity could not be realized.

  FIG. 15 is a schematic diagram showing a basic configuration of a multi-antenna 158 according to the ninth embodiment of the present invention. This embodiment is an example in which the multi-antenna according to the present invention is applied to MIMO transmission in which transmission capacity is increased by parallel transmission of spatial physical channels. This embodiment is configured using the multi-antenna of any of the first to fifth embodiments, and includes a MIMO transmission circuit 154 that performs signal processing related to MIMO transmission. Since the multi-antenna apparatus 158 in the present embodiment uses the multi-antenna described in the first to fifth embodiments as an antenna, the influence of mutual coupling between the antennas is small, and high radiation efficiency can be obtained. Moreover, the correlation between antennas can be kept low. Therefore, even in MIMO transmission in which the transmission capacity is increased by parallel transmission of spatial physical channels, the effect of increasing the high transmission capacity can be obtained.

  FIG. 16 is a schematic diagram showing a basic configuration of a multi-antenna 168 according to the tenth embodiment of the present invention. This embodiment is an example in which the multi-antenna according to the present invention is applied to a system that switches between beamforming, diversity, and MIMO transmission. This embodiment is configured using the multi-antenna of any of the first to fifth embodiments, and includes a beamforming diversity MIMO transmission circuit 164 that performs signal processing relating to beamforming, diversity, and MIMO transmission. . Since the multi-antenna apparatus 168 in the present embodiment uses the multi-antenna described in the first to fifth embodiments as an antenna, the influence of mutual coupling between the antennas is small, and high radiation efficiency can be obtained. Moreover, the correlation between antennas can be kept low. Therefore, even in MIMO transmission that increases transmission capacity by beamforming for combining directivity, diversity for combining signals, and parallel transmission of spatial physical channels, it has the effect of increasing high gain and increasing transmission capacity. Obtainable. Furthermore, by switching between the above three types according to the surrounding propagation environment in which communication is performed, optimum signal transmission independent of the environment can always be performed, and the system capacity can be increased.

It is the schematic which shows the basic composition of the multi-antenna according to 1st Example of this invention. It is a figure which shows the mutual coupling amount and radiation efficiency of the multi-antenna according to 1st Example of this invention. It is a figure which shows the mutual coupling amount with respect to the length of the parasitic element of the multi-antenna according to 1st Example of this invention. It is a figure which shows the radiation efficiency with respect to the length of the parasitic element of the multi-antenna according to 1st Example of this invention. It is the schematic which shows the basic composition at the time of setting the feed element of the multi-antenna according to 1st Example of this invention to three. FIG. 6 is a diagram showing the amount of mutual coupling and radiation efficiency when there are three feeding elements of the multi-antenna shown in FIG. 5 according to the first embodiment of the present invention. It is the schematic which shows the basic composition of the multi-antenna according to 2nd Example of this invention. It is the schematic which shows the basic composition of the multi-antenna according to 3rd Example of this invention. It is the schematic which shows the basic composition of the multi-antenna according to 4th Example of this invention. It is the schematic which shows the basic composition of the multi-antenna according to 5th Example of this invention. It is the schematic which shows the basic composition of the multi-antenna according to 6th Example of this invention. It is the schematic which shows the basic composition of the multi-antenna according to 7th Example of this invention. It is the schematic which shows the basic composition of the multi-antenna according to 8th Example of this invention. It is the schematic which shows the basic composition at the time of applying the multi-antenna according to the 8th Example of this invention to polarization diversity. It is the schematic which shows the basic composition of the multi-antenna according to 9th Example of this invention. It is the schematic which shows the basic composition of the multi-antenna according to 10th Example of this invention. It is the schematic which shows the basic composition of the diversity antenna for the conventional terminal. It is the schematic which shows the basic composition of the conventional multi-antenna for terminals.

Explanation of symbols

8 Multi-antenna 10 Circuit board 11 Feed point 12 Feed element 13 Parasitic element

Claims (10)

Circuit board with multiple feed points;
A plurality of feed elements having one end open and the other end connected to the feed point; and one or more parasitic elements having one end open and the other end connected to the circuit board;
A multi-antenna with:
The feed element and the parasitic element have an element length of 0.2 to 0.3 wavelength in terms of a wavelength in a use frequency band; and the parasitic element is located near any feed point A multi-antenna characterized by being connected to a circuit board. The multi-antenna according to claim 1, wherein the feeding element or the parasitic element has a bent structure. The multi-antenna according to claim 1, wherein the feeding element and the parasitic element have a branched structure. The multi-antenna according to claim 1, wherein the parasitic element is disposed on or inside a dielectric having an arbitrary dielectric constant. The feeder element is arranged perpendicularly and parallel to the circuit board, and the parasitic element is connected to the circuit board in the vicinity of a feeding point of the feeder element arranged perpendicular to the circuit board. The multi-antenna according to 1. The multi-antenna according to claim 1, wherein the parasitic elements are arranged orthogonal to each other. 6. The multi-antenna according to claim 1, wherein beam forming for controlling directivity is performed. 6. The multi-antenna according to claim 1, wherein diversity is performed. The multi-antenna according to any one of claims 1 to 5, wherein MIMO transmission is performed to increase transmission capacity by parallel transmission of spatial physical channels. The multi-antenna according to any one of claims 1 to 5, wherein beamforming, diversity, or MIMO transmission is switched and used in accordance with a surrounding propagation environment in which communication is performed.

Images