JP4066874B2 - Monopole antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a monopole antenna which is used for receiving UHF band television waves and which realizes a wide band and high gain characteristic in a small size.
[0002]
[Prior art]
A conventional monopole antenna is composed of an antenna element made of a metal rod or metal plate having a quarter wavelength to obtain a broadband high gain frequency characteristic, and a matching circuit for matching the connection terminal impedance. (For example, see Patent Document 1). FIG. 7 shows a conventional receiving device described in Patent Document 1. In FIG. In FIG. 7, the antenna element 1 has a metal linear shape, and the antenna connection terminal 3 is converted to an impedance necessary for high gain frequency characteristics via the matching circuit 2. The matching circuit uses a two-stage low-pass filter composed of an inductance L and a capacitor C, thereby realizing wideband frequency characteristics. In addition, the name of the unipole antenna found in general literature of antenna engineering is synonymous with the monopole antenna.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 6-252791 (page 4, FIG. 1)
[0004]
[Problems to be solved by the invention]
However, in the conventional configuration, when receiving a wideband UHF band TV wave transmitted from 470 MHz to 770 MHz, the antenna impedance of the antenna element cannot be matched to the wideband, and the antenna element length adjustment structure is provided. In order to obtain the gain, there is a problem that a length of ¼ wavelength close to the lower limit frequency is required. Further, in order to provide the matching circuit on the ground terminal side of the antenna element, a circuit board and a holding structure are necessary, and there are problems in ease of handling and manufacturing price.
[0005]
In recent years, along with miniaturization of mobile mobile radio devices, there has been a problem that antenna storage and detachability are poor and the device protrudes greatly from the device housing.
[0006]
The present invention solves the above-described conventional problems, and by realizing an antenna element with a simple structure, an antenna having a length shorter than a quarter wavelength of a lower limit frequency of a required frequency band is realized. An object of the present invention is to provide a small monopole antenna that does not require a matching circuit.
[0007]
[Means for Solving the Problems]
In order to solve the conventional problem, the monopole antenna of the present invention short-circuits one side of a coaxial antenna element composed of an outer conductor and a center conductor, and grounds the coaxial center conductor different from the short-circuited side, An antenna output terminal is provided on the outer conductor of the antenna, and the antenna is realized with a length shorter than a quarter wavelength of the frequency to be used.
[0008]
This configuration matches the antenna radiation impedance with an antenna element length shorter than ¼ wavelength of the lower limit frequency to be used to match the antenna output impedance to the required output impedance over a wide band by the action of the grounded central conductor. It radiates radio waves more efficiently than the outer conductor without the need for a circuit.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0010]
(Embodiment 1)
FIG. 1 is a configuration diagram of a monopole antenna according to Embodiment 1 of the present invention. In FIG. 1, the same components as those in FIG.
[0011]
In FIG. 1, the antenna element 1 has a coaxial structure with an outer conductor 6 and a center conductor 5, one end of the coaxial tip is electrically short-circuited, and the outer conductor end of the coaxial end that is not short-circuited is connected to the antenna output terminal 3. It consists of the structure. The dielectric 7 has a role of supporting the central conductor.
[0012]
The output impedance Za of the antenna element having such a configuration can be explained by a characteristic in which the antenna radiation impedance Zb by the external conductor and the coaxial impedance Zc whose terminal is short-circuited are connected in parallel as shown in FIG. The antenna impedance Zb of the outer conductor 6 is a characteristic in which the length L is a frequency of 1/4 wavelength and is approximately 23 ohms and is inductive when the frequency is high, and is capacitive when the frequency is low, and one end is short-circuited. The coaxial impedance Zc of length L is open when the electrical execution length is ¼ wavelength, and exhibits capacitance when the frequency is high, and exhibits inductivity when the frequency is low. FIG. 2B is a characteristic diagram of changes in the impedances Zb and Zc, and the frequency FL is a length in which the coaxial length L indicates a quarter wavelength. The Za required for the parallel connection of Zb and Zc having the characteristics shown in FIG. 2 <b> not only cancels the capacitive and inductive characteristics at a frequency lower than the frequency FL, but also has an effect of approaching the connection impedance of 75 ohms. The antenna impedance can be brought close to 75 ohms even at a frequency higher than the frequency FL. As shown in FIG. 3, this is due to the impedance conversion action of an inverse L circuit composed of reactance elements.
[0013]
FIG. 4 shows an example of the antenna output characteristic of the embodiment according to the present invention and a linear antenna characteristic example without a simple matching circuit in a Smith chart with a reference impedance of 75 ohms. How wide the frequency characteristic region near the center of the Smith chart indicates the good broadband frequency characteristics of the antenna.
[0014]
For example, if the UHF frequency is FL = 600 MHz, the antenna element length L can be calculated by the speed of light / frequency, and L = 12.5 cm. In an example in which the antenna element length L is 12.5 cm, television radio wave frequencies of 470 MHz to 770 MHz are contained in a circle within VSWR = 2, which indicates that the antenna element is small and has good frequency characteristics.
[0015]
In the conventional example of the L and C two-stage low-pass filter matching unit, the function of converting the impedance of 23 ohms to 75 ohms based on the principle of FIG. 3 was used, but the matching frequency bandwidth was limited. .
[0016]
In the linear antenna according to the conventional example, the antenna impedance is larger than 75 ohms if the frequency is lower than the frequency corresponding to ¼ wavelength. However, the monopole antenna according to the present embodiment approaches 75 ohms, and the antenna becomes small. it can.
[0017]
Although the dielectric 7 varies in bandwidth and center frequency due to the difference in dielectric constant, the required characteristics can be obtained by appropriately selecting the antenna element length L. Further, when the central conductor can be mechanically held, it is not indispensable for the present embodiment.
[0018]
Further, in the present embodiment, the outer conductor 6 may use a mesh-like braided wire made of a metal wire other than the metal pipe. In this case, the outer conductor 6 can be mechanically flexible.
[0019]
(Embodiment 2)
FIG. 5 is a configuration diagram of a monopole antenna according to Embodiment 2 of the present invention.
[0020]
In FIG. 5, the same components as those in FIGS. 1 and 7 are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 5, the output ring 8 has an outer conductor 6 and a sliding portion, guides the antenna element 1 to the antenna storage case 11 when the antenna is stored, and electrically connects the antenna output terminal 3 and the antenna element 1 when the antenna is operated. Play a role. When the outer case 10 is made of a metal conductor, it operates as an antenna grounding plate, and when the outer case 10 is non-conductive, the antenna storage case 11 becomes the ground 4. Both the outer case 10 and the antenna storage case 11 are connected to the central conductor 5 of the antenna element 1 by the ground connection plate 16.
[0021]
According to such a configuration, when a radio wave is not received by a mobile device such as a portable device, there is no unnecessary protrusion in the device and the device can be easily handled with reliability.
[0022]
In this embodiment, the antenna element 1 is provided with an antenna housing case inside the device. However, the antenna output terminal side may be separated from the device with a connector structure.
[0023]
(Embodiment 3)
FIG. 6 is a configuration diagram of a monopole antenna according to Embodiment 3 of the present invention.
[0024]
In FIG. 6, the same components as those in FIGS. 1 and 7 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 6, the outer conductor 6 in FIG. 1 is replaced with a conductive plate 12 having a recess in the length direction of the width W and the length L, and a coating comprising a central conductor 13 and an insulating dielectric 14 attached to the recess. The wire 15 is short-circuited to the conductive plate 12 at the end of each other. The covered wire 15 is connected to the ground 4 on a different side from the short-circuited connection portion, and has an antenna output terminal from one end different from the short-circuited connection portion with the covered wire of the conductive plate 12.
[0025]
Since the center conductor 13 of the covered wire 15 along the recess is sufficiently smaller than the width of the conductive plate 12 and has fallen into the recess, there is no electromagnetic radiation to the outside from the center conductor 13, and the conductivity viewed from the ground side. The frequency characteristics of the impedance of the plate 12 and the covered wire 15 are the same as those of the first embodiment. Although the outer conductor 6 and the conductive plate 12 have different external shapes, the same radio wave radiation characteristics can be obtained if the width W of the conductive plate is made slightly larger than the coaxial diameter.
[0026]
According to such a configuration, the outer conductor 6 and the central conductor 5 of the first embodiment are replaced with the conductive plate 12 and the covered wire 15, so that the antenna output impedance obtained by the conductive plate has the same effect as described in the first embodiment. In addition to obtaining high gain characteristics, a monopole antenna having a length L shorter than a quarter wavelength of the lower limit frequency to be used can be realized.
[0027]
【The invention's effect】
As described above, according to the monopole antenna of the present invention, the matching circuit provided between the antenna element and the antenna output terminal is not required, and it can be used at a wide frequency range. An antenna that is smaller than the length of / 4 wavelength and has good characteristics can be realized.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a monopole antenna according to a first embodiment of the present invention. FIG. 2 is a characteristic explanatory diagram of the first embodiment of the present invention. FIG. 3 is an output impedance explanatory diagram of a first embodiment of the present invention. 4 is a characteristic comparison diagram of a linear antenna according to Embodiment 1 of the present invention. FIG. 5 is a configuration diagram of a monopole antenna according to Embodiment 2 of the present invention. FIG. 6 is a monopole according to Embodiment 3 of the present invention. Configuration diagram of antenna [Fig. 7] Configuration diagram of conventional monopole antenna [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Antenna element 2 Matching circuit 3 Antenna output terminal 4 Grounding 5 Center conductor 6 Outer conductor 7 Dielectric 8 Output ring 9 Insulating ring 10 Exterior 11 Antenna storage case 12 Conductive plate 13 Central conductor 14 Insulating dielectric 15 Covered wire 16 Ground connection plate

Claims (2)

Electrically shorting one side of the more becomes the antenna element and the external conductor and the outer conductor substantially central conductors of the same length that emits radio waves, and grounding the center conductor from the side that is not short circuit the antenna element Connected in the vertical direction, equipped with an antenna output terminal at the outer conductor termination on the ground side,
The monopole antenna, wherein the outer conductor and the center conductor have a coaxial configuration with the center conductor as a center.   A conductive plate having a dent in a flat plate, a coated wire made of a central conductor and an insulating dielectric, and one end of the previous conductive plate is short-circuited to the coated wire attached to the dent of the flat plate; A monopole antenna with the other end of the antenna grounded and an antenna output terminal provided on the other end of the conductive plate.

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