JP4636949B2 - Multi-frequency antenna - Google Patents

Description

  The present invention relates to a small multi-frequency antenna incorporated in an information terminal device such as a personal computer, PDA (portable information device), mobile phone, or VICS.

In recent years, PDAs and the like mounted on a wireless LAN or Bluetooth (short-range wireless data communication system) are increasingly required to be miniaturized as antennas have multiple frequencies.
Therefore, the present applicant has previously proposed a dual type small antenna as shown in FIG. 4 (Japanese Patent Application No. 2004-101374). In this antenna, the high-frequency radiation element (1a), the ground plate (4), and the short-circuit portion (3) form a slit (S1) ("first slit" to be described later) and a coaxial cable (5). The inner conductor is connected to the feeding point (P1) located at the open end of the slit (S1), the outer conductor is connected to the ground point (P2), and the element part (1) is fed to thereby form the slit (S1). It is devised to function as a slit antenna having a resonance point in the vicinity of the resonance point of the high-frequency side radiating element (1a). In addition, (1b) is a low frequency side radiation element, and (A) is a connection part of a high frequency side radiation element (1a) and a low frequency side radiation element (1b).
However, in such an antenna, although moderate communication quality is ensured, it has been found that the size of the element portion becomes a problem when the installation space is severe. Furthermore, in this case, it has also been found that impedance matching becomes difficult because the surrounding conductive parts and the element part electromagnetically interfere with each other.
Therefore, if a multi-frequency antenna having a smaller and simple structure and easy impedance matching is realized, its significance is great.

Accordingly, an object of the present invention is to provide a multi-frequency antenna having excellent communication sensitivity by having a small and simple structure and sufficient bandwidth.
Another object of the present invention is to provide a multi-frequency antenna with easy impedance matching.

The present inventors bent the tip part into an L-shape on the left side (upper left part of the drawing) of the low-frequency side radiating element of the multi-frequency antenna shown in FIG. We focused on the structure to be confronted. As a result, as shown by the hatched portion in FIG. 1, an L-shaped second slit having one end opened at the high-frequency side radiating element, the low-frequency side radiating element, and the short-circuited portion is additionally formed. The element part is further reduced in size. In addition, since the first slit functions as a slit antenna having a resonance point in the vicinity of the resonance point of the high frequency radiation element, desired communication sensitivity is also realized.
Furthermore, according to the present invention, it has been determined that impedance matching is facilitated by providing a notch at the end facing the first slit (FIG. 4).

The antenna of the present invention has the following remarkable effects as compared with the conventional antenna.
(1) The radiating element portion is reduced in size by arranging the tip of the low-frequency side radiating element in an L shape.
(2) Since the first slit functions as a slit antenna having a resonance point in the vicinity of the resonance point of the high-frequency side radiating element, communication sensitivity is improved.
(3) Impedance adjustment is facilitated by providing a notch at the end of the radiating element facing the first slit.
(4) By increasing the number of the radiating elements described above, it is possible to easily cope with multi-frequency antennas having three or more frequencies.
(5) Not only a planar antenna but also various types of antennas such as a three-dimensional antenna can be handled, and it is expected to be applied for various purposes.

Hereinafter, the case of an antenna for two frequencies in which the resonance point by the first slit is set to the maximum resonance frequency will be described with reference to the accompanying drawings.
FIG. 1 is a front view showing an example of the dual-frequency antenna of the present invention.
FIG. 2 is a perspective view when a feeding coaxial cable is attached to the antenna of FIG.
FIG. 3 is a graph (graph) showing the frequency characteristic (VSWR) of the antenna of the present invention corresponding to two frequencies.
FIG. 4 is a perspective view showing an example of the antenna of the prior invention corresponding to two frequencies.
1 and 2, (1), (1a), (1b), (3), (4), (5) (FIG. 2), (A), (S1), (P1) and (P2) Is the same as in FIG. On the other hand, (2) is a notch part, and (B) is a front-end | tip part of the low frequency side radiation | emission element (1b). Furthermore, (L) is the length of the high-frequency side radiating element (1a), (L1) is the length of the slit (S1), and (L2) is the edge of the high-frequency side radiating element (1a) and the ground plate (4) ( 4a) (slit width), (L3) is the width of the notch (2), and (L4) is the depth of the notch (2).
In such an antenna, the high-frequency side radiating element (1a) is formed in parallel with the ground plate (4) via the short-circuit portion (3), and further, from the terminal portion of the element (1a) to the connecting portion (A). The low-frequency side radiating element (1b) is formed in parallel with the ground plate (4) so as to be folded in an L shape. And the linear 1st slit (S1) by which one end was open | released by the high frequency side radiation | emission element (1a), a short circuit part (3), and the edge part (4a) of a ground board (4) is formed. Furthermore, the terminal portion (B) of the low-frequency side radiating element (1b) is arranged to be orthogonal to the ground plate (4) in an L-shaped form, and therefore the terminal portion thereof is connected to the ground plate (4). Opposite. As a result, as indicated by the hatched lines in FIG. 1, one end of the high-frequency side radiating element (1a), the low-frequency side radiating element (1b), the short-circuit portion (3), and the edge (4a) of the ground plate (4) An open L-shaped second slit (S2) is formed.
The first characteristic of the present invention is that, in addition to the first slit (S1), a second L-shaped slit (S2) having an open end is additionally formed. By doing so, the lateral width is shortened as compared with the low-frequency side radiating element (1b) of FIG. 4, so that the space can be used effectively. As a result, the size and shape of the low frequency side radiating element portion can be reduced.
Furthermore, in a preferred aspect of the present invention, when the relationship between the length (L) of the high-frequency radiation element (1a) and the length (L1) of the slit (S1) satisfies (L)> (L1), Due to the interaction with the feeding point (P1) and the ground point (P2) located in the vicinity of the open part of the slit (S1), the function of the slit antenna is given to this slit (S1). As a result, the effect of expanding the bandwidth of the antenna is significantly improved, and an antenna with excellent sensitivity can be realized.
This point will be described in detail below.
In the present invention, in order to improve the communication sensitivity by expanding the bandwidth in the vicinity of the resonance point on the high frequency side of the two frequencies, the resonance frequency in the slit portion (S1) is set in the vicinity of the resonance frequency of the high frequency radiation element (1a). Is important. Thereby, since the slit (S1) resonates at a resonance frequency in the vicinity of the resonance frequency of the high-frequency radiation element (1a), the bandwidth of the antenna can be widened. The length (L1) of the slit (S1) may be a length in the vicinity of the length (L) of the high-frequency radiation element (1a). Specifically, it may be set to either (L)> (L1) or (L) <(L1). In this case, in order to further reduce the width of the element portion (1) and the ground plate (4), it is particularly preferable that (L)> (L1) as shown in FIG. As a result, the slit (S1) resonates at a maximum resonance frequency higher than that of the high frequency side radiating element (1a), so that the bandwidth of the antenna can be widened.
More specifically, the length (L1) of the slit portion (S1) is adjusted according to the resonance frequency of the high-frequency side radiating element (1a) so that a bandwidth of 100 MHz (megahertz) to 2 GHz (gigahertz) can be secured. The resonance frequency may be set. As a result, sufficient communication sensitivity is realized.
Furthermore, what is important in the present invention is the positions of the feeding point (P1) and the ground point (P2). That is, it is important that the positions of the feeding point (P1) and the ground point (P2) are located near the open part of the slit (S1). This is because, when the position of the feeding point (P1) is in such a position, it is possible to resonate as a slit antenna having the maximum resonance frequency, and the bandwidth of the antenna can be widened. Furthermore, the positions of the feeding point (P1) and the ground point (P2) are preferably as close as possible to the slit (S1). This is because the feeding distance from the coaxial cable (5) to the slit (S1) is shortened and feeding loss is reduced, so that the electric field strength induced in the slit (S1) is increased and the sensitivity is improved.
Further, the distance between the high-frequency radiation element (1a) and the edge (4a) of the ground plate (4), that is, the slit width (L2) is also important. This is because if the distance (L2) is too wide, the electromagnetic field induced in the slit (S1) becomes weak and the effect of expanding the band is lost. On the other hand, if this distance is too small, instability such as interference occurs. It becomes a state. From this, it is preferable to adjust (L2) in the range of 0.5 mm to 3.0 mm.
With the above configuration, sufficient communication sensitivity is imparted to the antenna of the present invention. However, in order to make impedance matching easier, as shown in FIG. 1, the high-frequency side radiating element (1a) and the low-frequency side It is effective to provide a notch (2) facing the slit (S1) on the high-frequency side radiating element (1a) in the vicinity of the connection point (A) with the radiating element (1b). ) And a synergistic effect of the two effects of the impedance matching effect by the cut portion (2), an antenna having excellent sensitivity and easy impedance adjustment can be realized. The width (L3) of the cut portion (2) is 0.1 mm to 5 mm, more preferably 0.5 mm to 3 mm, and the depth (L4) is 0.5 mm to 3 mm, preferably 1 mm to 2 mm. Furthermore, the shape of the cut portion (2) may be any shape such as a triangle, a square, or an arc.

Next, the remaining configuration of the present invention will be described.
In the present invention, the length of each radiating element (1a), (1b) of the element part (1) is set to approximately 1/4 of the wavelength to be adopted, while its width is 1 mm to 5 mm. Adopted from the scope of. Further, there is no particular limitation on the thickness, but about 0.1 mm to 1 mm is sufficient. Further, the interval between the high-frequency side radiating element (1a) and the low-frequency side radiating element (1b) constituting the slit (S2) is preferably 1 mm or more in order to ensure stable operation. If these intervals are less than 1 mm, there is a concern that unstable phenomena such as interference occur.
As a material of these radiating elements (1a) and (1b), conductive metals such as white (white copper), copper, iron and brass are desirable. In making the high-frequency side radiating element (1a) and the low-frequency side radiating element (1b), a single plate of these metals is punched out, and a cut portion (2), a short-circuit portion (3), a ground plate (4), An integrally punched body may be used. Alternatively, it is also useful to obtain a desired antenna shape by etching the metal film in a state where a metal thin film such as a copper foil is attached to the flat insulating substrate.
As for the ground plate (4), in order to obtain stable antenna operation, the required minimum area (mm2) of the ground plate (4) satisfies λ / 4 * λ / 4 (λ is a wavelength) or more. Is desirable. Therefore, when more stable antenna operation is desired, it is preferable to increase the area as long as space permits. About the short circuit part (3), as long as the function which connects an element part (1) and a ground board (4) is exhibited, the shape is arbitrary.
As the feeding coaxial cable (5), a known high-frequency coaxial cable such as a fluororesin coating is employed. The end of the inner conductor of the cable (5) is connected to the feeding point (P1) in the vicinity of the open portion of the slit (S1), that is, the cable (5) straddles the open end, and the outer conductor is connected to the ground plate ( 4) Connect to the ground point (P2) provided above. In order to connect the coaxial cable (5) to the feeding point (P1) and the earth point (P2), soldering or ultrasonic connection may be used.
In the above description, the example in which the resonance point of the slit is set to the maximum resonance frequency has been described. However, the present invention is not limited to this and can be set to other resonance frequencies. Needless to say, the antenna itself can be developed into a three-dimensional antenna or a substrate antenna according to the situation of the antenna mounting space other than the above-described planar antenna made of sheet metal.
Moreover, although the example of 2 frequencies was shown in said description, it cannot be overemphasized that it can expand | deploy to the multi-frequency of 3 frequencies or more according to the structure number of a radiation element.
Further, in the present invention, the resonance point of the slit portion is set near the maximum resonance frequency and the band near the two frequencies is widened. Instead, if the slit portion is set as another third frequency element, FIG. It is added that it is possible to cope with three frequencies in the manner described above.

Hereinafter, an example in which the antenna for two frequencies shown in FIGS.
"Example 1"
1.
Creation of Radiation Elements (1a), (1b), and Ground Plate (4) First, as the high frequency side radiation element (1a), a length (L) corresponding to a wavelength of 4.5 GHz is 18 mm, a width is 1.0 mm, An element having a thickness of 0.4 mm is formed. At that time, the high-frequency radiation element (1a) and the edge (4a) of the ground plate (4) were arranged in parallel with an interval of 1.0 mm (width (L2) of the slit (S1)). Further, the length (4a) of the edge (4a) of the ground plate (4) (corresponding to the length (L1) of the slit (S1)) is higher than the resonance frequency 4.5 GHz of the high-frequency radiation element (1a). It was set to 16 mm corresponding to a wavelength of 5.5 GHz. Moreover, the short circuit part (3) was 1 mm in length, 2 mm in width, and 0.4 mm in thickness.
Thereby, the high frequency side radiation element (1a), the edge (4a) and the short circuit part (3) of the ground plate (4) have a length (L1) of 16 mm, a width (L2) of 1.0 mm, and a resonance frequency. A 5.5 GHz slit (S1) was formed.
Next, an element having a width of 1.5 mm, a length of 28 mm, and a thickness of 0.4 mm corresponding to a wavelength of 2.4 GHz is used as the low frequency side radiating element (1b) from the high frequency side radiating element (1a). It was formed to point in the opposite direction. At this time, the low-frequency side radiating element (1b) was arranged in parallel with the high-frequency side radiating element (1a) at a distance of 2 mm. Furthermore, the front-end | tip part (B) of the low frequency side radiation | emission element (1b) was bent at right angle by the length of 3 mm toward the edge part (4a) of the ground plate (4). Accordingly, the high-frequency side radiating element (1a), the low-frequency side radiating element (1b), the edge (4a) of the ground plate (4), and the short-circuited portion (3) have a width of 3 mm as shown in FIG. The L-shaped slit part (S2) having a length of 19 mm was formed.
At this time, the material of the element portion was white (bronze), while the ground plate (4) was white having a height of 32 mm, a width of 25 mm, and a thickness of 0.4 mm.
The feeding point (P1) is provided in the vicinity of the open portion of the slit (S1), that is, in the vicinity of the right end corner of the high-frequency radiation element (1a) facing the open portion of the slit (S1) toward FIG. On the other hand, the position of the earth point (P2) is also near the open portion of the slit (S1), that is, toward the feeding point (P1 on the edge (4a) of the ground plate (4) facing the slit (S1) toward FIG. ).
2. At the end of the antenna, a high-frequency coaxial cable coated with fluororesin (PFA) with an outer diameter of 1.13 mm and an inner conductor diameter of 0.24 mm is prepared as a feeding coaxial cable (5). The conductor was exposed. Then, by connecting the terminal portion of the inner conductor to the feeding point (P1) and the outer conductor to the ground point (P2) by soldering in such a manner that the cable straddles the open portion of the slit (S1), An antenna (1) for incorporating a personal computer was obtained.
When the bandwidth of this antenna was measured, as shown in FIG. 3, a band with a VSWR of 2 or less was sufficiently secured at 1500 MHz, and sufficient communication characteristics were obtained.
"Example 2"
In Example 1, an antenna was produced in the same manner as Example 1 except that the cut portion (2) was provided on the high-frequency radiation element (1a) facing the slit (S1). At that time, the notch part (2) was formed with a width (L3) of 1.2 mm and a depth (L4) of 1.5 mm at the center 1.5 mm from the right end of the high-frequency radiation element (1a). .
As a result of adjusting the impedance of this antenna, it was confirmed that it could be easily adjusted to the desired impedance.
The present invention has been described above with an example of an antenna built in a personal computer, but it goes without saying that various applications are possible within the scope of the idea of the present invention.

Since the antenna of the present invention is compact and has stable communication characteristics, in addition to personal computers, various information terminal devices such as PDAs, mobile phones, or VICS, information home appliances having communication functions, and It can be used for automobile related equipment as well.

It is a front view which shows an example of the antenna of this invention corresponding to 2 frequencies. It is a perspective view at the time of attaching the coaxial cable for electric power feeding to the antenna of FIG. It is a figure (graph) which shows the frequency characteristic (VSWR characteristic) of the antenna of this invention corresponding to 2 frequencies. It is a perspective view which shows an example of the antenna of the prior application corresponding to 2 frequencies.

Explanation of symbols

1 Element part
DESCRIPTION OF SYMBOLS 1a High frequency side radiation | emission element 1b Low frequency side radiation | emission element 2 Notch part 3 Short circuit part 4 Ground board 4a Edge of ground board (4)
5 Coaxial cable A for feeding High frequency side radiating element (1a) and low frequency side radiating element (1b)
Connection portion B Tip portion S1 of the low-frequency radiation element (1b) First slit S2 Second slit L Length L1 of the high-frequency radiation element (1) Length L2 of the slit (S1) Slit (S1) Width L3 width L4 of notch (2) depth P1 of notch (2)
Feed point P2 Earth point

Claims (7)

An element portion to which a feeding point is provided and a ground plate to which an earth point is provided are connected via a short-circuit portion; and the high-frequency side radiation element in which the element portion is connected to the short-circuit portion; It extends in a folded shape from the end of the element, and its tip is oriented in the direction opposite to the high-frequency radiation element, and further, the end of the tip is oriented in the direction facing the ground plate. A first slit whose one end is opened by the high-frequency side radiating element portion, the ground plate, and the short-circuit portion; and the high-frequency side radiating element and the low-frequency side radiating element; An L-shaped second slit whose one end is opened is formed by the frequency side radiation element and the short-circuit portion; and a feeding point and a ground point are provided in the vicinity of the open portion of the first slit. More, multi-frequency antenna, wherein the said first slits so as to function as a slit antenna having a resonance point in the vicinity of the resonance point of the high-frequency side radiation element. The multi-frequency antenna according to claim 1, wherein the high-frequency side radiating element is longer than the first slit. The multi-frequency antenna according to claim 1 or 2, wherein a cut portion is provided at an end portion of the high-frequency radiation element facing the first slit. The multifrequency antenna according to claim 3, wherein the cut portion has a width of 0.1 mm to 5.0 mm. The multi-frequency antenna according to claim 3 or 4, wherein the cut portion has a depth of 0.5 mm to 3.0 mm. The multi-frequency antenna according to claim 1, wherein a resonance point of the first slit is at or near a maximum resonance frequency. The multi-frequency antenna according to claim 1, wherein the width of the first slit is 0.5 mm to 3.0 mm.

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