JP4762965B2 - Antenna device, portable wireless device, and portable television - Google Patents

Description

  The present invention relates to a small and inexpensive antenna device suitable for incorporation into a portable wireless device, a portable wireless device and a portable television equipped with the antenna device.

  An antenna device incorporated in a portable wireless device such as a cellular phone, a portable television (a portable television), or a wireless LAN terminal is required to be small and have a high gain. However, when the radiating conductor as the antenna body is downsized, it cannot be denied that the antenna gain decreases accordingly. That is, in order to increase the antenna gain, the length of the radiation conductor may be about ½ wavelength, but it cannot be denied that the radiation conductor itself is increased in size. On the other hand, when the length of the radiation conductor is shortened to about ¼ wavelength and the size is reduced, the impedance at the feeding point is increased. Therefore, the impedance between the feeding portion of the radiation conductor and the antenna driving circuit is increased. It is necessary to provide a matching circuit.

Incidentally, the impedance matching circuit is usually configured using a capacitor (capacitor component) and a coil (inductance component) (see, for example, Patent Document 1).
JP-A-11-145726

  By the way, even if the impedance matching circuit described above is made compact by using chip components such as a chip capacitor, a dedicated space for incorporating a printed circuit board on which the impedance matching circuit is mounted is required, and the overall shape of the antenna device is required. Cannot be denied. In addition, since the impedance matching circuit is required, the number of parts increases, and the manufacturing and assembly costs increase. Therefore, in order to reduce the size and price of the antenna device, it is desirable to omit an impedance matching circuit constructed using chip parts or the like.

  The present invention has been made in consideration of such circumstances, and its purpose is to match the impedance of the radiating conductor feeder and the antenna drive circuit without using chip components such as a chip capacitor, and to reduce its size. It is an object of the present invention to provide an inexpensive antenna device suitable for incorporation into a portable wireless device and the like, and further to a portable wireless device and a portable television equipped with this antenna device.

  In order to achieve the above-described object, the antenna device according to the present invention is such that a transmission line such as a coaxial cable or a microstrip line having a line length shorter than a quarter wavelength with respect to the resonance frequency is in an open state. Focuses on functioning as a capacitor (capacitor component) in the case of, and functioning as a coil (inductance component) in a short-circuited state at the tip, and preferably by integrating this transmission line into the radiating conductor. It is characterized by its miniaturization and cost reduction.

That is, the antenna device according to one aspect of the present invention is
(1) a radiation conductor having a length of approximately ¼ wavelength with respect to the resonance frequency;
(2) A counter conductor having a length shorter than a quarter wavelength with respect to the resonance frequency and disposed opposite to the radiation conductor and connected to a feeder line.

  Further, the opposing conductor disposed opposite the radiation conductor is connected to the feeder short-circuited one having the end portion not connected to the feeder line electrically connected to the radiation conductor, or to the feeder line. The open end type is such that the end on the non-side is electrically insulated from the radiation conductor. That is, this antenna device is characterized in that the radiation conductor and one conductor of a parallel line functioning as an inductance component or a capacitance component are integrated to reduce the size and the number of components. The radiating conductor and the opposing conductor are preferably realized as microstrip lines formed on both surfaces of a plate-like dielectric.

In addition, about the said radiation | emission conductor, it implement | achieves as what has a width | variety shape rather than an opposing conductor, and it is preferable to aim at the broadband-ization by this.
It is another object of the present invention to provide a portable wireless device using these antenna devices, particularly a portable television.

  As described above, according to the present invention, an antenna device that has a simple structure and can be easily reduced in size can be realized, and the manufacturing cost can be sufficiently reduced. Therefore, it is possible to provide a broadband antenna device suitable for incorporation into various portable wireless devices.

Hereinafter, an antenna device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a first embodiment, wherein 1 is a rod-shaped radiation conductor having a length of about ¼ wavelength with respect to the resonance frequency, and 2 is about ¼ wavelength with respect to the resonance frequency. It is a coaxial cable as a parallel conductor having a pair of line conductors having a shorter line length and arranged opposite to each other in parallel. One end of the outer conductor 2a of the coaxial cable 2 is connected to the radiating conductor 1, and one end of the inner conductor (core wire) 2b of the coaxial cable 2 is led from an antenna drive circuit (not shown). Connected to the feeder line 3.

  The coaxial cable 2 is of a short-circuited end type in which the outer conductor 2a and the inner conductor (core wire) 2b are electrically connected at the other end on the side not connected to the feeder line 3, or the outer conductor 2a. And the inner conductor (core wire) 2b are separated from each other and insulated from each other. The short-circuited coaxial cable 2 having a short end shorter than ¼ wavelength functions as a coil (inductance component) L with respect to the radiation conductor 1 as shown in FIG. The open coaxial cable 2 functions as a capacitor (capacitor component) C with respect to the radiation conductor 1 as shown in FIG.

  That is, the reactance of a parallel conductor such as the coaxial cable 2 varies depending on the line length. In particular, the reactance of the short-circuited short-circuit line has an inductance component as a coil when the line length is shorter than ¼ wavelength as shown in FIG. When it gets longer with the wavelength, it has a capacitor component as a capacitor. Conversely, the reactance of the open-ended line has a capacitor component as a capacitor when the line length is shorter than ¼ wavelength as shown in FIG. / When it becomes long over 2 wavelengths, it has an inductance component as a coil.

  Accordingly, if the line length of the coaxial cable (parallel line) 2 is adjusted in a range shorter than ¼ wavelength, and the other end is selected to be short-circuited or opened, the length of approximately ¼ wavelength is obtained. The coaxial cable 2 having a predetermined reactance (inductance component or capacitor component) is used by using the coaxial cable 2 shorter than the radiation conductor 1 set to be able to match the radiation conductor 1.

  FIG. 4 shows the experimental results of examining changes in the resonance frequency and the ratio band when the line length of the open-ended coaxial cable 2 connected to the feeding portion of the radiating conductor 1 is varied. In this experiment, a radiating conductor 1 in which a conductor having a size of 20 mm × 80 mm is formed on a PPE (polyphenylene ether resin) substrate having a relative dielectric constant ε of [3.5] and a thickness of 1.6 mm is used. I went. Then, the frequency range where the VSWR (standing wave ratio) is [3] or less is determined as the band, and the ratio of the resonance frequency (MHz) and the band to the resonance frequency is determined as the ratio band (%). The line length of the coaxial cable 2 is shown as a ratio to the wavelength when the resonance frequency is considered to be 750 MHz.

  In the experimental results shown in FIG. 4, it was confirmed that the resonance frequency gradually decreased from 900 MHz as the line length of the coaxial cable (parallel line) 2 was increased, and decreased to 650 MHz at approximately ¼ wavelength. At the same time, the ratio band gradually increases as the line length of the coaxial cable (parallel line) 2 becomes approximately 1/16 wavelength or more, and is increased to approximately 35% at approximately 1/8 wavelength. Further, when the line length of the coaxial cable (parallel line) 2 was further increased, it was confirmed that the specific band became about 50% at about ½ wavelength after the specific band was once increased.

  On the other hand, when the change of the resonance frequency and the ratio band when the line length of the short-circuited coaxial cable 2 was varied was examined, an experimental result as shown in FIG. 5 was obtained. In this experiment, as the line length of the coaxial cable (parallel line) 2 is increased, the resonance frequency gradually decreases from 700 MHz to 450 MHz, and the ratio band gradually decreases from 40% to 5%. confirmed.

  From these experimental results, it is clear that the band can be expanded by providing the radiating conductor 1 with the coaxial cable 2 that functions as an open-ended capacitor component of ¼ wavelength or less. In general, when the capacitor is attached to the radiating conductor (antenna) 1, the band is widened, and when the coil is attached, the resonance frequency is lowered, and as described above, the line length is reduced from a quarter wavelength. Further, it was confirmed that the same effect as in the case of using a capacitor or a coil can be exhibited by using the coaxial cable 2 set to be short.

  Thus, according to the antenna device configured as described above, the coaxial cable 2 is connected to the feeding portion of the radiating conductor 1 and the feeding line 3 is connected to the inner conductor (core wire) 2b of the coaxial cable 2 as described above. Therefore, it is possible to easily increase the bandwidth. Moreover, it is only necessary to use the coaxial cable 2 that can be disposed along the radiation conductor 1 without using a chip component such as a capacitor or a coil. Therefore, it is possible to easily reduce the size and simplify the structure itself. Can be planned. Further, since the conventional impedance matching circuit is not required, the number of components can be reduced, and the installation space for the printed circuit board on which the impedance matching circuit is mounted becomes unnecessary. As a result, secondarily, it becomes possible to facilitate the manufacture of the antenna device and reduce the manufacturing cost.

  Note that, as shown in FIG. 6A, a second embodiment of the antenna device according to the present invention, the radiating conductor 1 is configured as a tubular (tubular) shape, and this tubular (tubular) radiating conductor 1 is formed. The above-described coaxial cable 2 may be provided inside. As shown in the third embodiment in FIG. 6B, the tubular radiation conductor 1 and one conductor of a parallel line functioning as an inductance component or a capacitance component (corresponding to the outer conductor 2a of the coaxial cable) are integrated. By doing so, the other conductor of the parallel line (corresponding to the inner conductor 2b of the coaxial cable) may be arranged as the inner conductor 5 inside the tubular radiation conductor 1 in order to reduce the size and the number of parts.

  In this way, the inner conductor 5 arranged inside the tubular radiation conductor 1 is also short-circuited at the end that is not connected to the feeder 3 and is electrically connected to the tubular radiation conductor 1. What is necessary is just to implement | achieve as a thing of the open end type which electrically insulated the end part on the side which is not connected to the said feeder wire from the said tubular radiation | emission conductor 1 as a thing of a thing.

  Further, as shown in the fourth embodiment in FIG. 7, a microstrip line 4 can be used instead of the coaxial cable 2. The microstrip line 4 includes a pair of line conductors 4b and 4c made of a conductive film arranged in parallel on both surfaces of a predetermined dielectric substrate 4a, and a wide line conductor 4b forming a ground line (ground line). Is connected to the radiating conductor 1, and the feeder 3 is connected to one end of a narrow line conductor 4 c forming a strip line. In particular, the line conductor (strip line) 4c connected to the feeder line 3 has a structure in which the line length is shorter than ¼ wavelength. The microstrip line 4 having a structure in which the length of the dielectric substrate 4a is shorter than ¼ wavelength and a pair of line conductors 4b and 4c having the same length as the dielectric substrate 4a are provided in parallel on both surfaces thereof. Of course, it can be used.

  Even when such a microstrip line 4 is used, the line conductor 4b functions as the ground line (ground line) on the opposite side of the other end of the line conductor (strip line) 4c connected to the feeder line 3. Can be used as a short-circuited parallel line. Also, if the other ends of these line conductors 4b and 4c are kept disconnected (insulated state), they can be used as open-ended parallel line conductors, so that the coaxial cable 2 described above is used. Similar effects can be achieved.

  Incidentally, the radiation conductor 1 may be shared with the ground line (ground line) of the microstrip line 4 as shown in FIG. Specifically, the antenna device may be realized as a structure in which the radiation conductor 1 is provided on one surface of the dielectric substrate 4a and the line conductor (strip line) 4c that functions as a capacitor component is provided on the other surface of the dielectric substrate 4a. it can. Accordingly, in this case, the radiation conductor 1 also functions as an installation line facing the line conductor (strip line) 4c.

  Incidentally, when the other end of the line conductor (strip line) 4c is electrically connected to the radiation conductor 1 (the path conductor 4b forming the ground line) to realize a short-circuited parallel conductor, for example, a line conductor (strip line) ) A through hole is provided in the dielectric substrate 4a at the other end of 4c, and the line conductor 4c and the radiation conductor 1 may be electrically connected through the through hole. In the present embodiment, the radiation conductor 1 and the line conductor (strip line) 4c, which is the opposite conductor, are integrally configured via the dielectric 4a. However, these conductors may be configured separately. good.

  Further, when realizing the antenna device having the above-described structure, it is effective to widen the width of the radiating conductor 1 having a substantially ¼ wavelength so as to widen the band. Incidentally, when the width of the radiation conductor 1 is increased, the ratio band can be increased from 30% to about 55% as the width of the radiation conductor 1 is increased as shown in the experimental data in FIG. This experiment was conducted on a PPE (polyphenylene ether resin) substrate having a relative dielectric constant ε of [3.5], a thickness of 1.6 mm, and a size of 100 mm × 50 mm. A plurality of antenna devices having a structure as shown in FIG. 8 in which the radiation conductors 1 changed from 2 mm to 30 mm are respectively prepared, and the resonance frequency and the ratio band of each of these antenna devices are respectively examined. It is.

  When such a wide plate-like radiation conductor 1 was used, it was confirmed that as the width was increased, the resonance frequency decreased and a small antenna device could be realized. At the same time, as the width of the plate-like radiation conductor 1 was increased, the ratio band could be expanded, and it was confirmed that a wider band could be achieved. Therefore, in the case of the antenna device having such a structure, it is possible to facilitate the manufacture thereof and to greatly reduce the manufacturing cost.

  Thus, according to the antenna device having such a structure, the radiation conductor 1 and the microstrip line 4 (line conductor 4c) can be integrally formed on both surfaces of the dielectric substrate 4a. Simplification can be achieved. In particular, since the broadening by the wide radiation conductor 1 and the broadening by the microstrip line 4 (line conductor 4c) functioning as a capacitor act synergistically, the frequency band can be made sufficiently wide. In particular, such an antenna device can be compactly incorporated into a portable wireless device such as a portable television, and is suitable for reducing the size of the portable wireless device.

  In addition, this invention is not limited to each embodiment mentioned above. For example, the size (antenna length) of the radiating conductor 1 may be set to approximately ¼ of the wavelength according to the required resonance frequency. Further, it is sufficient to set the line length of the parallel conductor made up of the coaxial cable 2 and the microstrip line 4 to ¼ wavelength or less so that a required frequency band can be secured. Whether the parallel line has an open-ended structure or a short-circuited structure may be determined according to the antenna specifications. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

1 is a schematic configuration diagram of an antenna device according to a first embodiment of the present invention. The figure which shows equivalently the function of the coaxial cable in the antenna apparatus shown in FIG. The figure which shows the change characteristic of the reactance component with respect to the line length of the coaxial cable in the antenna apparatus shown in FIG. The figure which shows the change characteristic of the resonant period number and a specific band when changing the line | wire length of the coaxial cable of an open end type | mold in the antenna apparatus shown in FIG. The figure which shows the change characteristic of the number of resonance periods and a ratio band when changing the line length of the coaxial cable of a short-circuited tip type in the antenna apparatus shown in FIG. The schematic block diagram of the antenna apparatus which concerns on the 2nd and 3rd embodiment of this invention. The schematic block diagram of the antenna device which concerns on the 4th Embodiment of this invention. The schematic block diagram of the antenna device which concerns on the 5th Embodiment of this invention. The figure which shows the change characteristic of the resonant period number and a ratio band when changing the width | variety of the radiation conductor in the antenna apparatus shown in FIG.

Explanation of symbols

1 Radiation conductor (antenna element)
2 Coaxial cable (parallel conductor)
3 Feeding line 4 Microstrip line (parallel conductor)
5 Inner conductor

Claims (5)

A non-grounded radiation conductor having a length of approximately ¼ wavelength with respect to the resonance frequency;
A counter conductor having a length shorter than a quarter wavelength with respect to the resonance frequency, disposed opposite to the radiation conductor and connected to a feeder line;
And the opposing conductor is a short-circuited tip that is electrically connected to the radiation conductor at an end that is not connected to the feeder, or an end that is not connected to the feeder An antenna device comprising an open-ended type electrically insulated from the radiation conductor.   The antenna device according to claim 1, wherein the radiation conductor and the counter conductor are formed of microstrip lines formed on both surfaces of a plate-like dielectric. The radiation conductor, the antenna device according to claim 1 or 2 having a wider shape than the opposing conductor.   A portable wireless device equipped with the antenna device according to claim 1.   A portable television equipped with the antenna device according to claim 1.

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