JP2009055375A - Loop antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a loop antenna which is optimal for incorporating it into a mobile terminal. <P>SOLUTION: This antenna has a loop element in which a current flows and a ground plate. With this arrangement, the loop element is formed in a frame shape and is connected to a metal plate. The ground plate is disposed inside the loop element to be separated spatially, and a potential difference is imparted to between the loop element and the ground plate. When this antenna is connected to a signal source and is used as a transmission antenna, this antenna materializes a fine input impedance matching ranging over a wide band, while radiating an electromagnetic wave. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a loop antenna that is optimal for installation in a mobile terminal.

  The Ministry of Internal Affairs and Communications has announced that analog television broadcasting will be completed by July 24, 2011, and terrestrial digital television broadcasting will begin. Along with this, terrestrial digital television broadcast services are provided for mobile terminals. In Japanese digital terrestrial television broadcasting, radio waves in the UHF (Ultra High Frequency) band of 470 MHz to 770 MHz are used.

  In accordance with the digital terrestrial television broadcasting service, it is required to develop an optimum antenna for incorporation into a mobile terminal.

Some antennas have already been proposed for incorporation into mobile terminals (Patent Documents 1 to 5, etc.).
JP 2007-19882 A JP 2006-174207 A JP 2006-86739 A JP 2005-341542 A JP 2005-341541 A JP 2005-39762 A

  By the way, since a mobile terminal is carried by a user and used, downsizing is required so that the mobile terminal is convenient to carry.

  When the mobile terminal housing has a projection such as an antenna, it is uncomfortable when it is carried. Therefore, the surface of the terminal housing needs to have a planar structure as much as possible.

  The antenna disclosed in the above-mentioned patent document needs to be further improved when incorporated in the terminal casing.

  An object of the present invention is to provide a loop antenna having a structure suitable for a mobile terminal.

In order to achieve the above object, a loop antenna of the present invention has an antenna element through which a current flows, and a ground plane,
Spatially separating the antenna element and the ground plane;
The antenna element has a structure in which a potential difference is provided between the antenna element and the ground plane.

  According to the present invention, an optimal antenna for incorporation into a mobile terminal can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIGS. 1, 7, 12, and 14, the loop antenna according to the embodiment of the present invention is a loop antenna that transmits and receives electromagnetic waves, and includes a loop element 1 through which a current flows and a ground plane 2. Have.

  The loop element 1 and the ground plane 2 are spatially separated from each other, and a potential difference is provided between the loop element 1 and the ground plane 2.

  A specific structure in which the loop element 1 and the ground plane 2 are spatially separated will be described. When the three-axis directions in the figure are set as xyz, in the loop antenna shown in FIGS. 1 and 7, the ground plane 2 is positioned inside the frame-shaped loop element 1 on the xy plane, and the connecting piece 3 The metal plate 1a is coupled to the frame-shaped loop element 1 through the frame. The loop antenna shown in FIGS. 12 and 14 has a structure in which the ground plane 2 is arranged outside the frame-shaped loop element 1 in the xy plane.

In the case of the loop antenna shown in FIGS. 1 and 7, it is desirable that the outer peripheral length (L = 2L _x + 2L _y , or 2πr) of the metal plate 1 a is set to be substantially the same as the peripheral length of the loop element 1. Even in the case of the loop antenna shown in FIGS. 12 and 14, it is desirable to set the outer peripheral length L of the ground plane 2 to be substantially the same as the peripheral length of the loop element 1.

  The operation when the loop antenna according to the embodiment of the present invention shown in FIGS. 1, 7, 12, and 14 is used as a transmission antenna will be described.

  When power is supplied between the loop element 1 and the ground plane 2, a potential difference is generated between the loop element 1 and the ground plane 2. At that time, in the structure shown in FIG. 1 and FIG. 7, a current efficiently flows to the loop element 1 due to the synergistic effect of the ground plane 2 and the metal plate 1a. Further, in the structure shown in FIGS. 12 and 14, the current efficiently flows into the loop element 1 due to the effect of the ground plane 2.

  When the current flows through the loop element 1, an electromagnetic wave as a transmission wave is radiated from the loop element 1.

  Next, the operation when the loop antenna according to the embodiment of the present invention shown in FIGS. 1, 7, 12, and 14 is used as a receiving antenna will be described.

  When the received wave arrives at the loop element 1, a potential difference is generated between the loop element 1 and the ground plane 2 due to the received wave. When receiving, in the structure shown in FIG. 1 and FIG. 7, current efficiently flows to the loop element 1 due to the synergistic effect of the ground plane 2 and the metal plate 1 a. Further, in the structure shown in FIGS. 12 and 14, the current efficiently flows into the loop element 1 due to the effect of the ground plane 2.

  As described above, in the embodiment of the present invention, the loop element 1 and the ground plane 2 are spatially separated on the same plane. When the embodiment of the present invention is applied to a mobile terminal, it is optimal for use in an elongated state. In addition to this, it is also possible to configure and use a two-fold structure.

  Since the embodiment of the present invention is similar to the case structure of a mobile phone, the loop element and the ground plane can be easily incorporated into the case of the mobile phone.

  Furthermore, since the loop element 1 and the ground plane 2 are spatially separated, the circuit element can be easily incorporated on the ground plane 2 or on the metal plate 1a. Although the mobile phone has been described as an example of the mobile terminal, the mobile terminal is not limited to the mobile phone and can be similarly applied to a mobile terminal other than the mobile phone.

  In the embodiment of the present invention, since a potential difference is provided between the loop element and the ground plane, current can be passed through the loop element, electromagnetic waves can be reliably transmitted and received, and the original function of the antenna can be achieved. It can be demonstrated.

  According to the embodiment of the present invention, by arranging the ground plane 2 inside or outside the loop element 1, a combination of a loop element and a ground plane (including a metal plate) to be applied can be appropriately selected. . Furthermore, since the loop element is a frame-shaped element, the loop element can be easily processed. When the loop element and the ground plane (including the metal plate) are arranged in the same plane, a ground plate common to the mobile terminal device can be used as the loop element and the ground plane (including the metal plate).

In the embodiment of the present invention, the outer peripheral length of the metal plate 1a coupled to the loop element 1 via the connection piece 3 and the peripheral length of the loop element are set substantially the same, thereby matching the input impedance over a wide band. Is peeled off. When the metal plate 1a is not used, the input impedance is matched by setting the peripheral length of the loop element 1 and the outer peripheral length of the ground plate 2 to be substantially the same length.
(Embodiment 1)

  Next, an example in which the ground plane 2 is arranged inside the loop element 1 will be described as the first embodiment.

  As shown in FIGS. 1 and 2, the loop antenna according to Embodiment 1 of the present invention has a structure in which the loop element 1 is a frame-shaped element and the ground plane 2 is disposed inside the loop element 1. Further, a metal plate 1 a is coupled to the loop element 1 via a connection piece 3. The metal plate 1 a is disposed adjacent to the loop element 1, and the connection piece 3 electrically connects the metal plate 1 a and the loop element 1.

In the first embodiment, the peripheral length of the loop element 1 and the outer peripheral length (L = 2L _x + 2L _y ) of the metal plate 1a are set to be substantially the same.

  The three axis directions in FIGS. 1 and 2 are assumed to be xyz. As illustrated, the loop element 1 and the ground plane 2 are disposed in the xy plane, and the ground plane 2 is disposed inside the loop element 1. Further, the metal plate 1 a is disposed in the xy plane adjacent to the loop element 1. In addition, between the loop element 1 and the ground plane 2, the slit 4 is arrange | positioned, and the loop element 1 and the ground plane 2 are electrically disconnected.

  In the loop antenna according to the first embodiment, the positional relationship of the feeding point F when feeding power between the loop element 1 and the ground plane 2 is technically examined.

Since the frequency band of digital terrestrial television broadcasting is set in the range of 470 MHz to 770 MHz, the center frequency is set to 600 MHz for convenience (the wavelength λ at this time is 500 mm, which is called the center wavelength). To be precise, the center frequency is 620 MHz. And the VSWR value was measured over the range of 470 MHz-770 MHz. At this time, the position of the feeding point F was specified on the condition that the value was 5 or less (reference condition). Here, VSWR is an abbreviation for Voltage Standing Wave Ratio and means a voltage standing wave ratio. 3 (b), 4 (b), 5 (b), and 6 (b), the horizontal axis represents frequency, the vertical axis represents VSWR value, and the frequency band of 470 MHz to 770 MHz is indicated by a double-headed arrow f. _L, is shown by _{f H.}

1 and 2, the dimension of the vertical side Lx of the loop element 1 is 0.19λ (λ: center wavelength), the horizontal side Ly is 0.14λ, the peripheral length of the loop element 1 and the outer peripheral length of the metal plate 1a (L = 2L _x + 2L _y ) was set to 0.66λ. Then, the position of the feed point F was changed along the loop element 1 in the counterclockwise direction with the connection piece 3 as a reference.

  3A and 3B show an example in which the position of the feeding point F is separated from the connection piece 3 by a length of about 0.18λ (λ: center wavelength).

  In FIG. 3B, the condition that the frequency is about 470 MHz to 660 MHz and the VSWR value is 5 or less is satisfied. However, at 660 MHz or more, the VSWR value is 5 or more. That is, it is clear that the reference condition is not satisfied at the position of the feeding point F shown in FIG.

  Next, an example in which the position of the feeding point F is separated from the connection piece 3 by a length of about 0.33λ (λ: center wavelength) is shown in FIGS.

  In the case shown in FIG. 4A, as is clear from FIG. 4B, the condition that the VSWR value is 5 or less is satisfied in the frequency range of 470 MHz to 770 MHz. That is, it can be seen that the reference condition is satisfied.

  Next, an example in which the position of the feeding point F is separated from the connecting piece 3 by a length of about 0.38λ (λ: center wavelength) is shown in FIGS.

  In the case shown in FIG. 5A, as apparent from FIG. 5B, the condition that the VSWR value is 5 or less is satisfied in the frequency range of 470 MHz to 770 MHz. That is, it can be seen that the reference condition is satisfied.

  6A and 6B show an example in which the position of the feeding point F is separated from the connection piece 3 by a length of about 0.52λ (λ: center wavelength).

  In FIG. 6B, the condition that the VSWR value is 5 or less is satisfied in the frequency range of 500 MHz to 580 MHz, but the VSWR value becomes 5 or more at 580 MHz or more. It is clear that the reference condition is not satisfied at the position of the feeding point F shown in FIG.

  From the examination results of FIGS. 3 to 6, when the peripheral length of the loop element 1 is set to 0.66λ (λ: center wavelength), in order to obtain a good VSWR, the position of the feeding point F is set to the connection piece 3. On the other hand, it can be said that it is desirable to set 0.33λ and 0.38λ. At this time, the feeding position 0.33λ is ½ of the circumference length 0.66λ, and the feeding position 0.38λ is only slightly shifted by about 0.05λ with respect to the feeding position 0.33λ. .

  In other words, it can be said that the position of the feeding point F between the loop element 1 and the ground plane 2 should be set to about ½ of the circumference of the loop element 1. In this case, “near ½” means to include a range in the vicinity of ½.

  Next, the perimeter length of the loop element 1 to obtain a good VSWR by changing the perimeter of the loop element 1 was examined. At this time, the position of the feeding point F is always set to about ½ of the circumference of the loop element 1. As a result, it was concluded that the circumference of the loop element 1 should be set in the range of 0.6λ to 1.0λ (λ: center wavelength).

  From the above, as shown in FIGS. 1 and 2, in the structure in which the ground plane 2 is arranged inside the frame-shaped loop element 1, the peripheral length of the loop element 1 is 0.6λ to 1.0λ (λ: It was set to the range of (center wavelength), and the observation was made that the feeding point F should be set in the vicinity of ½ of the circumference of the loop element 1 with the connection piece 3 as a reference.

  According to Embodiment 1 of the present invention, not only can the effects of the basic configuration described above be obtained, but also, for example, by forming a slit in the conductive plate on the substrate, the loop element and the ground plane can be easily processed. Can do. Furthermore, positioning of the loop element and the ground plane can be easily performed.

According to the first embodiment of the present invention, the circumference of the loop element 1 is set in the range of 0.6λ to 1.0λ (λ: center wavelength), and the feeding point F is counterclockwise from the connection piece 3. By measuring and setting the position around ½ of the circumference of the loop element, broadcast signals can be received with high sensitivity over the frequency band of terrestrial digital television broadcasting.
(Embodiment 2)

  Next, an example in which the loop element 1, the base plate 2, and the metal plate 1a are formed in a circular shape instead of a rectangular shape will be described as a second embodiment.

  In the loop antenna according to the second embodiment of the present invention, as shown in FIGS. 7 and 8, the peripheral length of the circular loop element 1 and the outer peripheral length of the circular metal plate 1a (2πr, where r is the loop element 1 And the radius of the metal plate 1a) are set substantially the same. Further, the base plate 2 has a circular shape, and other configurations are the same as those in the first embodiment.

  In the second embodiment, the position of the feeding point F between the loop element 1 and the ground plane 2 is technically examined.

Since the frequency band of digital terrestrial television broadcasting is set in the range of 470 MHz to 770 MHz, the center frequency is set to 600 MHz for convenience (the wavelength λ at this time is 500 mm, which is called the center wavelength). To be precise, the center frequency is 620 MHz. And the VSWR value was measured over the range of 470 MHz-770 MHz. At this time, the position of the feeding point F was specified on the condition that the value was 5 or less (reference condition). In FIGS. 9B and 10B, the horizontal axis represents frequency, the vertical axis represents VSWR value, and the frequency band of 470 MHz to 770 MHz is indicated by double arrows f _L and f _H.

  7 and 8, the circumference of the loop element 1 is set to about 0.66λ (λ: center wavelength), and the position of the feeding point F is counterclockwise along the loop element 1 with the connection piece 3 as a reference. Was changed.

  FIGS. 9A and 9B show an example in which the position of the feeding point F is separated from the connection piece 3 by a length of 0.165λ (λ: center wavelength).

  In FIG. 9B, the VSWR value is 5 or less in the frequency range of about 470 MHz to about 580 MHz, but the VSWR value is 5 or more at about 580 MHz or more. It is clear that the above reference condition is not satisfied at the position of the feeding point F shown in FIG.

  Next, an example in which the position of the feeding point F is separated from the connection piece 3 by a length of 0.33λ (λ: center wavelength) is shown in FIGS. 10 (a) and 10 (b).

  In FIG. 10A, as is apparent from FIG. 10B, the VSWR value is 5 or less in the frequency range of 470 MHz to 770 MHz. That is, it can be seen that the reference condition is satisfied.

  As a result of the above examination, it was proved that the function as a loop antenna was sufficiently exhibited even when the frame-shaped loop element 1, the ground plane 2 and the metal plate 1a were circular.

  Similarly to the first embodiment, in the second embodiment as well, the circumference of the loop element 1 is set in the range of 0.6λ to 1.0λ (λ: center wavelength), and the feeding point F is defined with reference to the connection piece 3. It has been found that it should be set around ½ of the circumference of the loop element. Although not described in detail, it has also been found that similar results can be obtained even with an elliptical shape similar to a circular shape.

According to the second embodiment of the present invention, not only the effects of the first embodiment can be obtained, but also the function as a loop antenna can be sufficiently exerted even when a circular shape (including an elliptical shape) is used instead of a rectangular shape. It can correspond to the purpose of use or the built-in space in the housing of the mobile terminal.
(Embodiment 3)

  Next, an example in which the arrangement of the loop element 1 and the ground plane 2 is different will be described as a third embodiment.

  In the loop antenna according to Embodiment 3 of the present invention, as shown in FIGS. 11 and 12, the ground plane 2 is disposed outside the frame-shaped loop element 1. The ground plane 2 and the loop element 1 are adjacent to each other, and a feeding point F is set between them.

  11 and 12, the coordinate system is xyz, as shown in the figure. The ground plane 2 is positioned in the xy plane and arranged outside the frame-shaped loop element 1. The loop element 1 and the ground plane 2 are adjacent to each other in the x-axis direction.

  The feeding point F in the third embodiment may be set at any location in the y-axis direction as long as it is between the opposing sides of the loop element 1 and the ground plane 2 that are arranged adjacent to each other. In the figure, a case where the feeding point F is set to the right end position is shown.

  11 and 12, the peripheral length of the loop element 1 and the outer peripheral length (2Lx + 2Ly) of the ground plane 2 are set to be approximately equal.

13 and 14 are examples in which a wider band characteristic is realized as compared with the loop antennas shown in FIGS. 11 and 12. That is, since the loop antenna shown in FIGS. 13 and 14 is meandering the loop element 1 shown in FIGS. 11 and 12, the length measured along the center of the line (referred to as the loop center line length. Perimeter length). Is not longer than the center line length of the loop element 1 shown in FIGS. 11 and 12 (in this case, it is equal to the peripheral length). 13 and 14 also, the peripheral length (2L _x + 2L _y ) of the loop element 1 and the outer peripheral length (2L _x + 2L _y ) of the ground plane 2 are set to be approximately equal.

  11 and 12, the center line length (in this case, equal to the peripheral length) of the loop element 1 is set to about 0.64λ (λ: center wavelength), and the VSWR in this case is indicated by a broken line in FIG. . In this case, the reference condition is satisfied.

Further, an investigation was conducted to identify the range of the center line length (in this case, equal to the peripheral length) of the loop element 1 in FIGS. As a result, it was concluded that the center line length of the loop element 1 should be set in the range of 0.6λ to 1.0λ (λ: center wavelength).

  13 and 14, the VSWR value when the center line length of the meander loop element 1 is set to about 1.28λ (λ: center wavelength) is shown in FIG. The solid line in the figure is the survey result in this case. In this case, the reference condition is satisfied. It was found that the lower limit frequency was lower than that without the meander, so that it was operating over a wider band.

Next, an investigation was conducted to specify the range of the center line length of the meandered loop element 1, and a conclusion was reached that it should be set in the range of 1.2λ to 2.0λ (λ: center wavelength). .

  According to Embodiment 3 of the present invention, a broadcast signal can be received with high sensitivity in the frequency band of digital terrestrial television broadcasting even when the ground plane is arranged outside the frame-shaped loop element.

  Furthermore, according to the third embodiment, a mobile terminal device can be incorporated using an empty space existing inside the frame-shaped loop element. In other words, it can be said that the space existing inside the casing of the mobile terminal can be used effectively.

  Note that the radiation characteristics of the loop antennas according to the first to third embodiments of the present invention are similar to each other and are eight-shaped in the xz plane. It is omnidirectional in the yz plane.

So far, the connection piece 3 in FIGS. 1 and 7 has been described as being in the xy plane, but the connection piece 3 is not necessarily limited to be in this plane. For example, in a mobile terminal that can be folded, the connection piece 3 may have a structure that can rotate around the y-axis (for example, a hinge structure).

In the above description, the loop element 1 in FIGS. 1, 7, 11, and 13 has been described as being in the xy plane, but the loop element 1 is not necessarily limited to be in this plane. For example, a mobile terminal that can be folded may have a structure in which the loop element 1 can be rotated around the y-axis using a hinge or the like.

  According to the present invention, it is possible to provide an optimum loop antenna to be incorporated into a mobile terminal and to provide an antenna that can be used in a desired frequency band.

It is a perspective view which shows the loop antenna which concerns on Embodiment 1 of this invention. It is a top view which shows the loop antenna which concerns on Embodiment 1 of this invention. (A) is a top view which shows the case where the feed point F is changed in Embodiment 1, (b) is a characteristic view which shows the relationship between VSWR and a frequency. (A) is a top view which shows the case where the feed point F is changed in Embodiment 1, (b) is a characteristic view which shows the relationship between VSWR and a frequency. (A) is a top view which shows the case where the feed point F is changed in Embodiment 1, (b) is a characteristic view which shows the relationship between VSWR and a frequency. (A) is a top view which shows the case where the feed point F is changed in Embodiment 1, (b) is a characteristic view which shows the relationship between VSWR and a frequency. It is a perspective view which shows the loop antenna which concerns on Embodiment 2 of this invention. It is a top view which shows the loop antenna which concerns on Embodiment 2 of this invention. (A) is a top view which shows the case where the feed point F is changed in Embodiment 2, (b) is a characteristic view which shows the relationship between VSWR and a frequency. (A) is a top view which shows the case where the feed point F is changed in Embodiment 2, (b) is a characteristic view which shows the relationship between VSWR and a frequency. It is a top view which shows the example of a change of the loop antenna which concerns on Embodiment 3 of this invention. It is a perspective view which shows the example of a change of the loop antenna which concerns on Embodiment 3 of this invention. It is a top view which shows the example of a change of the loop antenna which concerns on Embodiment 3 of this invention. It is a perspective view which shows the example of a change of the loop antenna which concerns on Embodiment 3 of this invention. It is a characteristic view which shows the relationship between VSWR and frequency in Embodiment 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Loop element, meander loop element 1a Metal plate 2 Ground plate 3 Connection piece 4 Slit

Claims (9)

A loop element through which a current flows, and a ground plane;
Spatially separating the loop element and the ground plane;
A loop antenna having a structure in which a potential difference is provided between the loop element and the ground plane. The loop antenna according to claim 1, wherein the loop element is a frame-shaped element, and the ground plane is arranged inside the loop element. The loop antenna according to claim 2, wherein the loop element and the metal plate are coupled via a connection piece. The loop antenna according to claim 1, wherein the loop element is a frame-shaped element, and the ground plane is disposed outside the loop element. The loop antenna according to claim 3, wherein the circumference of the loop element and the outer circumference of the metal plate are set to be substantially the same. The loop antenna according to claim 4, wherein a peripheral length of the loop element and an outer peripheral length of the metal plate are set to be substantially the same. The peripheral length of the loop element is set in the range of 0.6λ to 1.0λ (λ: center wavelength),
4. The loop antenna according to claim 3, wherein a feeding point between the loop element and the ground plane is set in the vicinity of ½ of the circumference of the loop element with reference to the connection piece. The loop antenna according to claim 4, wherein a center line length of the loop element is set in a range of 0.6λ to 1.0λ (λ: center wavelength). The loop element is a meandered element,
The loop antenna according to claim 4, wherein a center line length of the loop element is set in a range of 1.2λ to 2.0λ (λ: center wavelength).

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