JP2006311152A - Broadband antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a broadband which is incorporated in an information terminal such as a personal computer, a mobile phone or a PDA and can make a transmission/reception at both of a WAN band and a wireless LAN band. <P>SOLUTION: A first slit S1 and a second slit S2 whose one end is respectively open are formed to the antenna comprising a high frequency side radiation element 1a and a multiple foldback shaped low frequency side element 1b, and the first and second slits S1, S2 are electromagnetically coupled so as to be resonated with each other. Further, a feeding point P1 is provided in the vicinity of a connection part between the high frequency side radiation element 1a and the multiple foldback shaped low frequency side element 1b, and moreover an earth point P2 is provided at an edge of an edge part 4a of a ground plate 4 opposed to the feeding point P1 with the first slit S1 inbetween, and a feeding coaxial cable 5 is connected to the feeding point P1, and the earth point P2. <P>COPYRIGHT: (C)2007,JPO&INPIT

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. More specifically, the present invention relates to an antenna that can cover a wide band from a WAN band used in a cellular phone to a wireless LAN band with one antenna.

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 multi-frequency 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 (S), and the inner conductor of the coaxial cable (5) is opened to the slit (S). By connecting the external conductor to the ground point (P2) at the feeding point (P1) located at the end and feeding power to the element part (1), the slit (S) resonates with the high-frequency radiation element (1a). It is devised to function as a slit antenna having a resonance point in the vicinity of the point. In addition, (1b) is a low frequency side radiation element.
However, even with this antenna, although moderate communication quality is ensured, it has been found that depending on the application or installation environment, a sensitivity failure due to insufficient bandwidth occurs. This failure is not only in the frequency bands (2 GHz and 5 GHz) used in wireless LAN and the like, but also in lower frequency bands, particularly in the WAN bands (824 MHz to 960 MHz and 1710 MHz to 2200 MHz) used in mobile phones and the like. It is easy to happen. Furthermore, when the operating frequency is low, the element length becomes long, so that the antenna shape and dimensions become large, and some devices cannot be incorporated.
Furthermore, recently, with the demand for higher frequency, the band used in wireless LAN etc. (2 GHz and 5 GHz) and the WAN band used in mobile phones (824 MHz to 960 MHz and 1710 MHz to 2200 MHz) with one antenna. There is also a growing demand for wider bandwidths that can handle both bands.

Therefore, an object of the present invention is to provide a broadband antenna that is small in size and does not have a fear of insufficient bandwidth.
Another object of the present invention is to provide a broadband antenna having excellent communication sensitivity in both the WAN band and the wireless LAN band.

  The present inventors have excellent communication sensitivity in a desired wide band by allowing two slits that resonate by electromagnetic coupling to coexist in an antenna including a high-frequency side radiating element and a multi-folded low-frequency side radiating element. It came to realize.

In the antenna of the present invention, the following remarkable effects can be expected.
(1) Due to the resonance between the two slits and the interaction between the two slits and the multi-folded low-frequency antenna that contributes to the reduction of the antenna size, the bandwidth in the vicinity of the resonance point of the high-frequency radiation element is reduced. As it spreads, the frequency characteristic (VSWR) can be improved, and the communication sensitivity is greatly improved.
(2) By making the element width of a part of the low frequency side element at least 4 mm and wider than the width of the high frequency side radiating element, transmission and reception in both the WAN band and the wireless LAN band can be performed with one antenna. Further improvement.
(3) It can be applied to various types of antennas such as a three-dimensional antenna and a planar antenna, and is expected to be applied for various purposes.

Hereinafter, an example of a broadband antenna in which the resonance point between two slits 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 a broadband antenna according to the present invention.
FIG. 2 is a perspective view when a feeding coaxial cable is attached to the broadband antenna of FIG.
FIG. 3 is a graph (graph) showing the frequency characteristics (VSWR characteristics) of the wideband antenna of the present invention.
FIG. 4 is a perspective view showing an example of a conventional antenna corresponding to two frequencies.
In FIGS. 1 and 2, (1) is an element portion, which is shown as a so-called dual type which is composed of a high-frequency side radiating element (1a) and a low-frequency side radiating element (1b). The latter low-frequency side radiating element (1b) is configured in a multiple folded (meander) shape from the end of the high-frequency side radiating element (1a) through the connecting portion (A). Here, (1b-1) is the first-stage element, (1b-2) is the second-stage element that is folded back from the first-stage element (1b-1) through the folding portion (B), and (1b-3) ) Is a third-stage element that is folded back from the second-stage element (1b-2) via the folded portion (C). (2a) and (2b) are respectively located near the connection (A) between the high-frequency side radiating element (1a) and the low-frequency side first stage element (1b-1), on the opposite side of these elements and It is a protrusion provided on the same line. (3) is a short-circuit portion that electrically connects the high-frequency radiation element (1a) and the ground plate (4). At that time, the high-frequency side radiating element (1a) and the low-frequency side radiating element (1b) are arranged in parallel with the ground plate (4) via the short-circuit portion (3). As a result, the projection (2a), the high-frequency side radiating element (1a), the short-circuit portion (3), and the edge (4a) of the ground plate (4) form a first slit (S1) that is open at one end. Further, a second slit (S2) whose one end is opened is formed by the projecting portion (2a), the projecting portion (2b), and the connecting portion (A).
Furthermore, (L) is the length of the high-frequency radiation element (1a), (L1) is the length of the slit (S1), (L2) is the width of the slit (S1), (L3) is the protrusion (2a), Each length of (2b), (L4) is the width of the protrusion (2a), (2b), (L5) is the length of the slit (S2), (L6) is the width of the slit (S2), (L7 ) Is the distance between the high frequency side element (1a) and the low frequency side element (1b-1), and (P1) is the internal conductor of the coaxial cable (5) (FIG. 2) for supplying power to the element part (1). It is located in the vicinity of the connecting portion (A) at the feeding point. (P2) is an earth point for connecting the outer conductor of the cable (5), and is provided at a position facing the feeding point (P1) at the edge (4a) of the ground plate (4) across the slit (S1). It is done.
What is characteristic of the present invention is that a slit antenna function is provided in a state in which the slits (S1) and (S2) are connected by electromagnetic coupling, and the slits and multiple folded low frequency side elements are provided. This is due to the use of the interaction. By doing so, not only the bandwidth in the high frequency band is greatly expanded, but also the communication sensitivity in both the WAN band and the wireless LAN band is improved.
This point will be described in detail below.
In the present invention, the slit resonance between the slits (S1) and (S2) is used to widen the bandwidth, but in this case, not the slit resonance over the entire length of the slits (S1) and (S2) but the slit ( Since a wide variety of resonance patterns are generated by slit resonance in part of S1) and (S2), the bandwidth is widened over a wide band.
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. Here, the length (L1) of the slit (S1) is preferably 40 mm to 60 mm, and the length (L5) of the slit (S2) is preferably 20 mm to 30 mm. Further, each of the protrusions (2a) and (2b) The length (L3) may be set to about 20% to 50% of the length of the high-frequency side radiating element (1a). Specifically, this (L3) may be 18 mm to 29 mm, preferably the same as the length (L5) of the slit (S2) or about (L5-2 mm). The widths (L4) of the protrusions (2a) and (2b) are 0.5 mm to 2.0 mm, preferably 1 mm to 1.5 mm. Usually, the corresponding radiating element portions (1a) and (1b-1) are used. ) Width. Further, in the present invention, the feeding point (P1) and the earth point (P2) are positioned in the vicinity of the connection part (A). Thereby, the slits (S1) and (S2) can be electromagnetically coupled to resonate more as a slit antenna, so that the bandwidth of the antenna is widened. On the other hand, if the distance (L2) between the high-frequency radiation element (1a) and the edge (4a) of the ground plate (4) is too wide, the electromagnetic field induced in the slit (S1) becomes weak and widens the band. The effect is lost, and on the contrary, if this interval is too narrow, an unstable state such as interference occurs. From this, it is preferable to adjust (L2) in the range of 0.5 mm to 2.0 mm. For the same reason, it is preferable to adjust the distance between the protrusions (2a)-(2b) (the width (L6) of the slit (S2)) in the range of 0.5 mm to 2.0 mm.

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. However, as will be described later, the low-frequency side radiating element (1b) may have a partial width of 4 mm or more and wider than the high-frequency side radiating element (1a). Further, there is no particular limitation on the thickness, but about 0.1 mm to 1 mm is sufficient. The distance between the high-frequency side radiating element (1a) and the low-frequency side radiating element (1b-1) is preferably 1 mm or more in order to ensure stable operation. If these intervals are less than 0.1 mm, unstable phenomena such as interference may occur. For the same reason, it is preferable that the distance between the low-frequency radiation elements (1b-1) and (1b-2) and the distance between (1b-2) and (1b-3) are also 1 mm or more. .
As a material of these radiating elements (1a) and (1b), conductive metals such as white (white copper), copper, iron and brass are preferable. In producing the high-frequency side radiating element (1a) and the multi-folded low-frequency side radiating element (1b), a single plate of these metals is punched out, and the projecting portions (2a) and (2b) and the short-circuited portion (3) The ground plate (4) may be integrally punched. 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 preferred. Therefore, if more stable antenna operation is desired, the area may be increased 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. In order to connect the end of the inner conductor of the cable (5) to the feed point (P1) and the outer conductor to the ground point (P2), soldering or ultrasonic connection may be used.
With the above configuration, in the bands (2 GHz and 5 GHz) used in a normal wireless LAN or the like, the above antenna can realize sufficient communication sensitivity, but the WAN band (824 MHz to 960 MHz and 1710 MHz to 2200 MHz), the communication sensitivity may be slightly inferior to the LAN band. Therefore, in order to further stabilize the communication in the WAN band, the element width of at least a part of the multi-folded low frequency side radiation element (1b) is 4 mm or more and wider than the width of the high frequency side radiation element (1a). Thus, it is effective to ensure sufficient electrolytic strength in the low band. In this case, it is preferable that the area of the element portion having a width of 4 mm or more occupies 20% or more with respect to the total surface area of the multi-folded low-frequency radiation element (1b). Incidentally, in FIG. 1 and FIG. 2, the width of the second stage element (1b-2) among the multiple folded low frequency side radiation elements (1b) is 4 mm or more, and the high frequency side radiation element (1a). The example which made it wider than the width of is shown. By doing so, a broadband antenna capable of covering both the WAN band and the LAN band as shown in FIG. 3 described later is obtained.
The above embodiment is an example in which the slit (S1) and the slit (S2) are resonated by electromagnetic coupling, and the resonance point is set to the maximum resonance frequency. The resonance point is set to an arbitrary and desired resonance frequency. May be. This embodiment is an example of a two-frequency antenna, but it goes without saying that it can be expanded to three or more frequencies according to the number of radiating elements. Furthermore, it goes without saying that the antenna itself can be developed into a three-dimensional antenna or a planar antenna depending on the situation of the antenna mounting space other than the above-described antenna made of sheet metal. It should be noted that the slit (S) and the projecting portion (2) can be set as separate third frequency elements, and in this case, it is possible to cope with three frequencies in the manner shown in FIG. deep.

In the following, an example in which the broadband antenna capable of covering from the WAN band to the LAN band shown in FIGS.
First, the following a. ~ D. In this manner, the radiating elements (1a) and (1b), the short-circuit portion (3), the connection portion (A), the protruding portions (2a) and (2b), and the ground plate (4) were prepared.
a. As the high-frequency radiation element (1a), an element having a length (L) of 20 mm and a width of 1.5 mm corresponding to a wavelength of 1800 MHz 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 1.5 mm (slit width (L2)). Was 1.5 mm long and 3 mm wide.
b. As the multiple folded low-frequency side radiating element (1b), an element having a total length of 94 mm corresponding to a wavelength of 894 MHz is multiplexed from the end of the high-frequency side radiating element (1a) through a connecting portion (A) having a width of 3 mm (3 Heavy) A folded low frequency side element (1b) was formed. At that time, the first stage element (1b-1) is 1.5 mm wide and 20 mm long, the second stage element (1b-2) is 5 mm wide and 50 mm long, and the third stage element (1b-3) is The width was 3 mm, the length was 20 mm, and the distance between each element was 2 mm.
c. Projections (2a) and (2b) are formed on the same line of each element on the opposite side of the connection (A) between the high-frequency radiation element (1a) and the first-stage element (1b-1) on the low-frequency side. . Each of these protrusions had a length (L3) of 27 mm and a width (L4) of 1.5 mm.
d. The dimensions of the ground plate (4) were 50 mm in height and 50 mm in width.
As a result, the high-frequency radiation element (1a) and the edge (4a), the protrusion (2a), and the short-circuit part (3) of the ground plate (4) have a length (L1) of 47 mm and a slit width (L2). A slit (S1) having an open end of 1.5 mm was formed. Further, a slit (S2) having a length (L3) of 27 mm, a slit width (L6) of 1.5 mm and an open end is formed by the protrusions (2a) and (2b) and the connecting portion (A). . These two slits (S1) and (S2) are slits that resonate at a wavelength near 1800 MHz when a part of the slits near the open end of each slit is electromagnetically coupled to each other.
In the punched product, the feeding point (P1) is provided in the vicinity of the connecting portion (A), while the position of the ground point (P2) faces the feeding point (P1) with the slit (S1) interposed therebetween. It was set as the position of the upper end of the edge (4a) of the ground plate (4). Finally, a fluororesin (PFA) -covered high-frequency coaxial cable (5) with an outer diameter of 1.13 mm and an inner conductor diameter of 0.24 mm straddles the open portion of the slit (S1), and the end portion of the inner conductor of the cable Is connected to the feeding point (P1) and the outer conductor of the cable is connected to the ground point (P2) by soldering to obtain a personal computer built-in antenna as shown in FIG.
When the bandwidth of this antenna was measured, as shown in FIG. 3, the VSWR in both the WAN band (824 MHz to 960 MHz and 1710 MHz to 2200 MHz) and the LAN band (2.5 GHz / 5 GHz) was 600 MHz or less. That was enough.
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 wideband antenna of this invention. It is a perspective view at the time of attaching the coaxial cable for electric power feeding to the broadband antenna of FIG. It is a figure (graph) which shows the frequency characteristic (VSWR) of the wideband antenna of this invention. It is a perspective view which shows an example of the conventional antenna corresponding to 2 frequencies.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Element part 1a High frequency side radiation element 1b Multiple folded low frequency side radiation element 1b-1 First stage element 1b-2 in low frequency side radiation element (1b) Two stages in low frequency side radiation element (1b) Eye element 1b-3 Third-stage element 2a, 2b in low-frequency radiation element (1b) Protruding part 3 Short-circuit part 4 Ground plate 4a Edge of ground plate (4)
5 Coaxial cable A for feeding A Connection portion B, C between the high-frequency side radiating element (1a) and the low-frequency side radiating element (1b) Folding portion S1 First slit S2 Second slit
L Length of high-frequency radiation element (1a) L1 Length of slit (S1) L2 Width of slit (S1) L3 Length of protrusions (2a) and (2b) L4 Projection (2a) and (2b) Each width L5 Length of slit (S2)
L6 Slit (S2) width
L7 Distance P1 between the high frequency side element (1a) and the low frequency side element (1b-1)
Feed point P2 Earth point

Claims (12)

In an antenna in which a radiating element portion to which a feeding point is provided and a ground plate to which an earth point is provided are connected in parallel via a short-circuit portion, the radiating element portion is a high-frequency side radiating element connected to the short-circuit portion And a multi-folded low frequency side radiating element connected to the end of the high frequency side radiating element; from the vicinity of the connecting portion between the high frequency side radiating element and the low frequency side radiating element, On the same side and on the same line of each element, a projecting portion is provided, so that one end of the projecting portion, the high-frequency side radiating element, the short-circuit portion, and the ground plate on the same line as the high-frequency side radiating element An open first slit is formed, and a second slit is formed at one end of the two projecting portions and the connecting portion;
The wideband antenna, wherein the first slit and the second slit resonate by electromagnetic coupling. The broadband antenna according to claim 1, wherein the feeding point is provided in the vicinity of a connection portion between the high-frequency side radiating element and the low-frequency side radiating element. The broadband antenna according to claim 1 or 2, wherein the high-frequency side radiating element has a width of 1 mm to 5 mm. The broadband antenna according to any one of claims 1 to 3, wherein a width of at least a part of the low-frequency side radiating element is 4 mm or more and wider than a width of the high-frequency side radiating element. The broadband antenna according to claim 4, wherein the area of the element portion of 4 mm or more occupies 20% or more of the total surface area of the low-frequency radiation element. The broadband antenna according to any one of claims 1 to 5, wherein a resonance point between the first slit and the second slit is at or near the maximum resonance frequency. The broadband antenna according to any one of claims 1 to 6, wherein a width of the first slit is 0.5 mm to 2.0 mm. The broadband antenna according to claim 1, wherein the first slit has a length of 40 mm to 60 mm. The broadband antenna according to any one of claims 1 to 8, wherein a width of the second slit is 0.5 mm to 2.0 mm. The broadband antenna according to claim 1, wherein a length of the second slit is 20 mm to 30 mm. The wide-band antenna according to any one of claims 1 to 10, wherein a length of the protruding portion is 18 mm to 29 mm. The wide-band antenna according to any one of claims 1 to 11, wherein the width of the protruding portion is 0.5 mm to 2.0 mm.

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