JP2015073239A - Antenna device and radio communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact antenna device and radio communication equipment capable of suppressing a current proceeding to the external conductor of a coaxial cable if the coaxial cable is short, with maintained flexibility of the coaxial cable.SOLUTION: The antenna device includes an antenna part 2 and a coaxial cable 3 for feeding power to the antenna part 2. The antenna device further includes a branch conductor balun 12, disposed at the tip of the coaxial cable 3 apart therefrom, including a conductor wire 13 having one end electrically connected to an internal conductor 4 of the coaxial cable 3 and another end electrically connected to an external conductor 6 of the coaxial cable 3. The conductor wire 13 is wound around the periphery of the coaxial cable 3.

Description

  The present invention relates to an antenna device and a wireless communication device.

  In many cases, a high-frequency circuit of a wireless communication device includes an electrically unbalanced circuit including a coaxial cable for feeding. When an electrically unbalanced coaxial cable is used to feed power to an antenna part such as an electrically balanced dipole antenna, part of the fed high-frequency signal travels on the surface of the outer conductor of the feeding coaxial cable. Electromagnetic radiation is also generated from the surface of the outer conductor of the coaxial cable. As a result, there is a problem that electromagnetic waves are radiated from both the antenna element and the outer conductor surface of the coaxial cable, and it is difficult to obtain desired radiation characteristics (radiation pattern) due to interference between the electromagnetic waves.

  When a planar antenna such as an inverted F antenna in which the ground part and the element part are connected via the power feeding part is used as the antenna part, the height of the ground part (the length in the arrangement direction of the ground part and the element part in order to reduce the size). When the height is reduced, the overall pattern shape approaches the symmetry with respect to the power feeding portion, and the antenna portion approaches electrical equilibrium. Then, while the coaxial cable to be fed is electrically unbalanced, the antenna portion approaches electrical balance, and the amount of current traveling on the outer conductor of the coaxial cable increases. As a result, there is a problem that the radiation amount of the electromagnetic wave from the outer conductor of the coaxial cable increases and a desired radiation characteristic cannot be obtained due to interference with the electromagnetic wave radiated from the antenna unit.

  As a method of solving this problem, there is a method of attaching a balun as a balanced / unbalanced converter to a coaxial cable for feeding. As a balun, a Suppel top balun is generally used. The Suppel top balun is a cylindrical conductor, and its length is about 1/4 times the wavelength with respect to the center frequency of the operating frequency band (hereinafter simply referred to as λ / 4).

  A branch conductor balun is known as a balun other than the Suppel top balun. In the branch conductor balun, conductor wires having an electrical length of about λ / 4 are arranged in parallel along the coaxial cable, and one end of the conductor wire is electrically connected to the inner conductor of the coaxial cable (the connection portion between the inner conductor and the element portion). And the other end is electrically connected to the outer conductor of the coaxial cable.

  Using a Suppel top balun or branch conductor balun increases the impedance of the coaxial cable when viewed from the antenna side, reduces the progression of high-frequency signals to the outer conductor surface of the coaxial cable, and It becomes possible to reduce electromagnetic waves radiated from the conductor surface.

  In addition, there exists patent document 1 as prior art document information relevant to invention of this application.

Japanese Patent No. 3830358

  By the way, in a small antenna device built in a wireless communication device, an inner conductor and an outer conductor are composed of a plurality of strands in order to increase the degree of freedom of arrangement location in the device and suppress the enlargement of the entire device. It is desirable to supply power using a flexible coaxial cable.

  However, when the Suppel top balun is attached to the coaxial cable, the flexibility is lost at the portion where the Suppel top balun is attached, and there is a problem that the degree of freedom in routing is greatly reduced. The length of the Suppel top balun is approximately λ / 4. The length of λ / 4 is, for example, 0.075 m for a 1 GHz signal and 0.015 mm for a 5 GHz signal. In addition, since it is necessary to secure a space for accommodating the Suppel top balun having this length, the overall size of the device is increased. Furthermore, when the length of the coaxial cable is shorter than λ / 4, there is a problem that the Suppel top balun cannot be attached in the first place.

  When the branch conductor balun is used, the flexibility of the coaxial cable can be maintained as compared with the case where the Suppel top balun is used, but when the length of the coaxial cable is shorter than λ / 4, the conductor wire is attached. There is a problem that is difficult.

  Therefore, the object of the present invention is to solve the above-mentioned problems, and even when the coaxial cable is short, the current traveling to the outer conductor of the coaxial cable can be suppressed, and the flexibility of the coaxial cable can be maintained. The object is to provide a small antenna device and a wireless communication device.

  The present invention has been devised to achieve the above object, and is an antenna device including an antenna section and a coaxial cable that feeds power to the antenna section, and the coaxial cable is provided at the tip of the coaxial cable. And a branch conductor balun having a conductor wire having one end electrically connected to the inner conductor of the coaxial cable and the other end electrically connected to the outer conductor of the coaxial cable. An antenna device that is wound around a cable.

  The antenna portion is formed in a rectangular shape in plan view that is electrically connected to the outer conductor of the coaxial cable, and is separated from the ground portion so as to be along one side of the ground portion. You may consist of a planar antenna provided with the element part electrically connected with the said internal conductor of a cable.

  A fixing member may be provided so as to cover a front end portion of the coaxial cable and the conductor wire, and fix the conductor wire in close contact with the periphery of the coaxial cable.

  A plurality of the conductor wires having different lengths may be provided, and each of the plurality of conductor wires may be wound around the coaxial cable to constitute the branch conductor balun.

  You may use the insulated wire which provided the insulator around the conductor which consists of a several strand as said conductor wire.

  As the conductor wire, a second coaxial cable in which a second insulator and a second outer conductor made of a braid are provided around a second inner conductor made of a plurality of strands, and one end of the second inner conductor is attached The other end may be electrically connected to the inner conductor of the coaxial cable and the outer conductor of the coaxial cable.

  The present invention is also a wireless communication device equipped with the antenna device.

  According to the present invention, even when the coaxial cable is short, a small antenna device and a wireless communication device that can suppress the current that travels to the outer conductor of the coaxial cable and that can maintain the flexibility of the coaxial cable. Can provide.

It is a top view of the antenna device concerning one embodiment of the present invention. (A) is an enlarged view of the front-end | tip part of the coaxial cable in the antenna apparatus of FIG. 1, (b) is a cross-sectional view of a coaxial cable, (c) is a cross-sectional view of a conductor wire. (A) is a figure which shows the dimension of each part of the antenna apparatus of FIG. 1, (b) is a figure explaining the arrangement | positioning of the antenna apparatus at the time of measuring | S11 | and a gain, and the definition of a polarized wave. (A) is a figure which shows the measurement result of | S11 |, (b) is a figure which shows the measurement result of a gain. It is a schematic block diagram of the antenna device which concerns on one modification of this invention.

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

  FIG. 1 is a plan view of the antenna device according to the present embodiment. 2A is an enlarged view of the front end portion of the coaxial cable, FIG. 2B is a transverse sectional view of the coaxial cable, and FIG. 2C is a transverse sectional view of the conductor wire.

  As shown in FIGS. 1 and 2, the antenna device 1 includes an antenna unit 2 and a coaxial cable 3 that feeds power to the antenna unit 2.

  The coaxial cable 3 is formed by sequentially providing an insulator 5, an outer conductor 6, and a sheath 7 on the outer periphery of the inner conductor 4. As the coaxial cable 3, it is preferable to use a highly flexible cable in which the inner conductor 4 and the outer conductor 6 are formed by a plurality of strands. The inner conductor 4 may be one in which a plurality of strands are twisted, or may be a bundle of a plurality of strands without being twisted. As the outer conductor 6, a braided shield in which a plurality of strands are knitted may be used. In the present embodiment, the coaxial cable 3 in which the outer diameter of the outer conductor 6 is 0.9 mm and the outer diameter of the sheath 7 is 1.1 mm is used.

  The antenna unit 2 is preferably configured so that the maximum dimension of the conductor portion thereof is 3/8 times or less the wavelength corresponding to the center frequency of the operating frequency band in order to facilitate incorporation into the device.

  In the present embodiment, the antenna portion 2 is separated from the ground portion 8 so as to be along a rectangular ground portion 8 and one side of the ground portion 8 in a plan view electrically connected to the outer conductor 6 of the coaxial cable 3. And a planar antenna having an element portion 9 electrically connected to the inner conductor 4 of the coaxial cable 3. By configuring the antenna unit 2 with a planar antenna, it is easy to arrange in the device.

  The ground part 8 and the element part 9 are comprised from conductor plates, such as copper, white, and stainless steel. Here, the thickness of the conductor plate used for the ground part 8 and the element part 9 was 1 mm. In addition, the ground part 8 and the element part 9 are not restricted to a conductor plate, but may be composed of a conductor foil (conductor pattern) formed on the surface of a substrate such as glass epoxy.

  In the present embodiment, a short-circuit portion 10 that connects the ground portion 8 and the element portion 9 is formed at the right end of the ground portion 8 and the element portion 9 in the drawing, and a coaxial cable is provided on the left side of the short-circuit portion 10 in the drawing. 3 is formed, and the antenna unit 2 is configured by a so-called inverted F antenna.

  The short-circuit unit 10 is for facilitating adjustment of the input impedance of the antenna unit 2 and may be configured by a lumped constant element such as an inductor or a capacitor or a conductor pattern having frequency characteristics equivalent to those elements.

  The shape of the antenna unit 2 is not limited to that shown in the figure. For example, in FIG. 1, the tip end portion (left end portion in the drawing) of the element portion 9 is bent perpendicularly to the ground portion 8 side, but if the width of the antenna portion 2 (length in the left-right direction in the drawing) can be increased, a straight line is formed. It is good also as a shape. Further, the short-circuit unit 10 may be omitted, and the antenna unit 2 may be configured with a so-called inverted L antenna.

In the antenna unit 2, the height of the ground portion 8 (the length of the vertical direction in the drawing) the height of h ₁ and the element portion 9 (shown vertical length) are equal form h _2, relatively, electrical The structure is close to equilibrium.

  Now, the antenna device 1 according to the present embodiment further includes a branch conductor balun 12 attached to the distal end portion of the coaxial cable 3.

  The branch conductor balun 12 is configured by disposing a conductor wire 13 at a distal end portion of the coaxial cable 3 so as to be separated from the coaxial cable 3. One end of the conductor wire 13 is electrically connected to the inner conductor 4 of the coaxial cable 3 (more specifically, the connection portion between the inner conductor 4 and the element portion 9), and the other end is connected to the outer conductor 6 of the coaxial cable 3. Electrically connected. The conductor wire 13 is configured such that its electrical length is about 1/4 times the wavelength corresponding to the center frequency of the operating frequency band.

  In this embodiment, the insulated wire 16 in which the insulator 15 is provided around the conductor 14 composed of a plurality of strands is used as the conductor wire 13 of the branch conductor balun 12. By using the insulated wire 16 in which the conductor 14 is composed of a plurality of strands as the conductor wire 13, the flexibility of the coaxial cable 3 can be maintained while maintaining the flexibility of the coaxial cable 3 even at the position where the conductor wire 13 is attached. It can suppress that it falls. Here, a conductor wire 13 having an outer diameter of the conductor 14 of 0.5 mm and an outer diameter of the insulator 15 of 1 mm was used.

  In the antenna device 1 according to the present embodiment, the conductor wire 13 is wound around the coaxial cable 3. Here, the conductor wire 13 is spirally wound around the sheath 7 of the coaxial cable 3, but the method of winding the conductor wire 13 is not limited to the spiral shape. For example, the conductor wire 13 is wound so as to reverse the winding direction in the middle. It doesn't matter. That is, in the antenna device 1, the length of the coaxial cable 3 and the length of the conductor wire 13 intersect with each other, and the distance between the coaxial cable 3 and the conductor wire 13 is substantially constant. A conductor wire 13 is wound around the periphery. Here, since the outer diameter of the coaxial cable 3 is 1.1 mm and the outer diameter of the conductor wire 13 is 1 mm, the entire outer diameter when the conductor wire 13 is wound around the coaxial cable 3 is 3.1 mm.

  In the present embodiment, the winding pitch d when the conductor wire 13 is wound in a spiral shape, that is, when the conductor wire 13 makes one round around the coaxial cable 3 from the reference position in the circumferential direction and reaches the reference position again. The distance moved along the longitudinal direction of the cable 3 was 2 mm. If the winding pitch d is too small, the conductor 14 of the conductor wire 13 arranged for each winding pitch d along the longitudinal direction of the coaxial cable 3 operates as if it were one body, and the branch conductor balun 12 is operated. Therefore, the winding pitch d needs to be increased to such an extent that the operation as the branch conductor balun 12 can be obtained.

  A conductor 14 is extended from one end of the conductor wire 13, and the extended conductor 14 is fixed to a connection portion between the internal conductor 4 and the element portion 9 by solder or the like and is electrically connected. Further, a conductor 14 extends from the other end of the conductor wire 13, and the extended conductor 14 is fixed to the exposed external conductor 6 by removing a part of the sheath 7 with solder or the like, Electrically connected.

  In addition, about the connection of the conductor 14 and the outer conductor 6, it is also possible to crimp and fix using the ring-shaped metal component (caulking ring) which has a slit. By using the caulking ring, the connection work between the conductor 14 and the outer conductor 6 is facilitated.

  If the distance between the coaxial cable 3 and the conductor wire 13 changes, the effect of reducing the current traveling on the outer conductor 6 of the coaxial cable 3 also changes, so the conductor wire 13 is fixed around the coaxial cable 3. It is desirable. That is, the antenna device 1 includes a fixing member (not shown) that is provided so as to cover the distal end portion of the coaxial cable 3 and the conductor wire 13 and fixes the conductor wire 13 in close contact with the periphery of the coaxial cable 3. Is desirable.

  As the fixing member, an insulating member may be used, and examples thereof include a shrinkable tube and an adhesive tape. When using a shrinkable tube as the fixing member, the distal end portion of the coaxial cable 3 and the conductor wire 13 are disposed in the hollow portion of the shrinkable tube, and then the shrinkable tube is heated and contracted to place the conductor wire 13 around the coaxial cable 3. Fix in close contact. When an adhesive tape is used as the fixing member, the adhesive tape is wound around the conductor wire 13 and the conductor wire 13 is brought into close contact with the periphery of the coaxial cable 3 and fixed.

  By providing the fixing member, the distance between the outer conductor 6 of the coaxial cable 3 and the conductor wire 13 can be kept constant, and the effect of reducing the current traveling on the outer conductor 6 of the coaxial cable 3 can be kept constant. It is possible to reduce variations in antenna characteristics.

  Furthermore, by using a metal tape or the like for the fixing member or providing a shielding function by providing a metal layer around the fixing member, for example, a conductive object exists in the vicinity of the conductor wire 13. Also, it is possible to suppress the change in impedance and to stabilize the operation of the branch conductor balun 12.

  The antenna device 1 having the dimensions shown in FIG. 3A is manufactured, and as shown in FIG. 3B, the coaxial cable 3 is arranged along the normal direction of the antenna unit 2 and is an S parameter. S11 | and gain were measured. FIG. 4A shows the measurement result of | S11 |, and FIG. 4B shows the measurement result of the gain. As for the gain, the radiation pattern of a plane parallel to the surface of the antenna unit 2 is measured, and Gφ that is polarized parallel to the surface of the antenna unit 2 and the longitudinal direction of the coaxial cable 3 orthogonal to Gφ Measurement was performed for Gθ which is a parallel polarization. Table 1 shows the measured average values of Gφ and Gθ.

  For comparison, | S11 | and the gain were measured using the antenna device in which the branch conductor balun 12 was omitted, as in the antenna device 1 according to the present embodiment. The measurement results are shown in FIGS. 4 (a) and 4 (b) and Table 1.

  As shown in FIG. 4 (a), both the antenna device 1 (with balun) and the antenna device (without balun) without the branch conductor balun 12 have a small | S11 | near 920 MHz and good matching at the frequency. It was confirmed that.

  Further, as shown in FIG. 4B and Table 1, there is almost no difference in Gφ which is the main polarized wave radiated from the antenna unit 2 with or without the branch conductor balun 12, and the difference in average value is 0.2 dB. Was the same value.

  On the other hand, with respect to Gθ radiated from the coaxial cable 3, the antenna device 1 (with balun) is smaller than the antenna device (without balun) in which the branch conductor balun 12 is omitted, and the difference between the average values. Was 1.9 dB. The reason for this is considered to be that radiation of electromagnetic waves from the coaxial cable 3 is reduced by providing the branch conductor balun 12.

  That is, it can be seen that in the antenna device 1, the current traveling to the outer conductor 6 of the coaxial cable 3 is suppressed, and the radiation of the electromagnetic wave from the outer conductor 6 of the coaxial cable 3 parallel to Gθ is reduced.

  As described above, in the antenna device 1 according to the present embodiment, the coaxial cable 3 is disposed at the distal end portion away from the coaxial cable 3, one end being the inner conductor 4 of the coaxial cable 3 and the other end being the coaxial cable 3. A branch conductor balun 12 having a conductor wire 13 electrically connected to the outer conductor 6 is provided, and the conductor wire 13 is wound around the coaxial cable 3.

  By providing the branch conductor balun 12, it is possible to reduce the current traveling to the outer conductor 6 of the coaxial cable 3 while maintaining the flexibility of the coaxial cable 3. Furthermore, by winding the conductor wire 13 around the coaxial cable 3, the entire length of the branch conductor balun 12 can be shortened, and the present invention can be applied to the short coaxial cable 3.

  That is, according to the present invention, even when the coaxial cable 3 is short, the antenna device that can suppress the current traveling to the outer conductor 6 of the coaxial cable 3 and can maintain the flexibility of the coaxial cable 3. 1 can be realized.

As a result, even when a planar antenna in which the height h ₁ of the ground portion 8 is reduced is used as the antenna portion 2, the radiation amount from the outer conductor 6 of the coaxial cable 3 is suppressed, and the directivity shift, etc. This makes it possible to obtain a desired radiation characteristic and to realize a small antenna device 1 suitable for being incorporated in a device.

  The wireless communication device according to the present embodiment is equipped with the antenna device 1, and includes, for example, a sensor unit that measures temperature, humidity, power usage, luminous intensity, and the like, and measurement data wirelessly via the antenna device 1. Is a wireless sensor terminal or a mobile terminal such as a notebook computer. Since the antenna device 1 is small and the coaxial cable 3 is highly flexible and has a high degree of freedom in routing, a wireless communication device that is small and easy to assemble can be realized.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

  For example, in the above embodiment, the case where a planar antenna is used as the antenna unit 2 has been described. However, the antenna unit 2 is not limited to a planar antenna, and may be a dipole antenna, for example.

  Moreover, in the said embodiment, although the case where the insulated wire 16 was used as the conductor wire 13 was demonstrated, it is not restricted to this, For example, around the 2nd internal conductor which consists of a some strand as the conductor wire 13, 2nd Using a second coaxial cable provided with an insulator and a second outer conductor made of braid, one end of the second inner conductor is electrically connected to the inner conductor 4 of the coaxial cable 3, and the other end is electrically connected to the outer conductor 6 of the coaxial cable 3. You may comprise so that it may connect to.

  By using the second inner conductor of the second coaxial cable as the conductor of the conductor wire 13, for example, even when a conductive object is present in the vicinity of the conductor wire 13, a change in impedance is suppressed, and the branch conductor balun 12. It becomes possible to stabilize the operation. It should be noted that the second outer conductor of the second coaxial cable can naturally be used as the conductor of the conductor wire 13 although an effect such as suppression of a change in impedance cannot be obtained.

  Furthermore, although the case where there is one operating frequency band has been described in the above embodiment, the present invention is also applicable to a case where a plurality of operating frequency bands are provided.

  In this case, since there are a plurality of frequency bands of the current traveling to the outer conductor 6 of the coaxial cable 3, a plurality of conductor wires having different lengths corresponding to each frequency band as in the antenna device 51 shown in FIG. The branch conductor balun 12 may be configured by winding the plurality of conductor wires 13 around the coaxial cable 3. With this configuration, it is possible to simultaneously reduce the progression of currents in a plurality of frequency bands to the outer conductor 6. Although FIG. 5 shows the case where two conductor wires 13 are used, three or more conductor wires may be used.

DESCRIPTION OF SYMBOLS 1 Antenna apparatus 2 Antenna part 3 Coaxial cable 4 Inner conductor 6 Outer conductor 12 Branch conductor balun 13 Conductor wire

Claims (7)

An antenna device comprising an antenna unit and a coaxial cable that feeds power to the antenna unit,
A branched conductor balun having a conductor wire disposed at a distal end portion of the coaxial cable and spaced from the coaxial cable, one end electrically connected to the inner conductor of the coaxial cable and the other end electrically connected to the outer conductor of the coaxial cable. With
The antenna device, wherein the conductor wire is wound around the coaxial cable. The antenna portion is formed in a rectangular shape in plan view that is electrically connected to the outer conductor of the coaxial cable, and is separated from the ground portion so as to be along one side of the ground portion. The antenna device according to claim 1, comprising: a planar antenna including an element portion electrically connected to the inner conductor of the cable. The antenna device according to claim 1, further comprising: a fixing member that is provided so as to cover a front end portion of the coaxial cable and the conductor wire and that fixes the conductor wire in close contact with the periphery of the coaxial cable. The antenna device according to any one of claims 1 to 3, comprising a plurality of the conductor wires having different lengths, and each of the plurality of conductor wires being wound around the coaxial cable to constitute the branch conductor balun. The antenna device according to any one of claims 1 to 4, wherein an insulated wire provided with an insulator around a conductor composed of a plurality of strands is used as the conductor wire. As the conductor wire, a second coaxial cable in which a second insulator and a second outer conductor made of a braid are provided around a second inner conductor made of a plurality of strands, and one end of the second inner conductor is attached The antenna device according to claim 1, wherein the other end of the coaxial cable is electrically connected to the inner conductor of the coaxial cable and the outer conductor of the coaxial cable. A wireless communication device comprising the antenna device according to claim 1.