JP2004328365A - Dipole antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dipole antenna which has a simple configuration, needs neither an impedance converter nor a matching circuit, and matches a cable impedance over a broadband frequency. <P>SOLUTION: The dipole antenna for covering a broadband frequency is realized by short-circuiting both ends of a coaxial antenna element 4 with a length of 1/2 wavelength comprising an outer conductor 8 and a center conductor 7, dividing the outer conductor of the coaxial antenna element 4 into two in the middle of the element 4, and providing antenna output terminals 3 for extracting a received radio wave output to the center ends of the outer conductor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dipole antenna used for receiving television waves in the UHF band and realizing a wide band and high gain characteristics in a small size.
[0002]
[Prior art]
As a conventional dipole antenna, a folded dipole antenna having a length of a half wavelength has been widely used with wideband characteristics (for example, see Non-Patent Document 1).
[0003]
FIG. 6 shows a conventional general folded dipole antenna 1 formed by folding a conductor having a radius r of about one wavelength so as to maintain a width W, and includes an impedance converter 2 for matching a normally used cable impedance of 75 ohms. It is a thing.
[0004]
The folded dipole antenna 1 can be analyzed as a circuit combination of a 波長 wavelength dipole antenna and a 波長 wavelength line whose tip is short-circuited, and has a wideband frequency characteristic with an output impedance near 300 ohms. In order to convert the output impedance from 300 ohms to 75 ohms, a radio wave received from an antenna is efficiently transmitted to an antenna output terminal 3 via an impedance converter 2 usually composed of a 4: 1 balun transformer.
[0005]
Further, as a conventional example of miniaturization of a dipole antenna, there is a dipole antenna including a loading coil and a matching circuit at the center of the dipole antenna for use in a wide frequency band (for example, see Patent Document 1). FIG. 7 shows a dipole antenna described in the above patent document. In FIG. 7, a loading coil 5 is connected to the center of a dipole antenna composed of an antenna element 4, and a matching circuit 6 composed of an inductor, a matching capacitor, and a variable capacitance diode is provided. Further, in order to obtain the required frequency band characteristic of the antenna output impedance, the capacitance of the varicap diode is changed so as to match the cable impedance by controlling the voltage applied to the varicap diode. FIG. 7 does not show a DC circuit applied to the varicap diode, but employs a configuration in which the applied voltage is changed according to the frequency used.
[0006]
[Non-patent document 1]
Yasuhito Mushi: "Antenna / radio wave propagation", Corona Co., Showa 46, PP. 43-45
[Patent Document 1]
JP-A-9-130132 (page 6, FIG. 1)
[0007]
[Problems to be solved by the invention]
However, in the configuration of the conventional folded dipole antenna, when the folded portion has the same diameter r, the output impedance is four times the output impedance of a simple dipole, and to match a 75 ohm cable used for transmitting a television signal, One impedance converter was required. In addition, a circuit board and a holding structure are required to provide a required impedance converter at the center of the antenna.
[0008]
Furthermore, in recent years, there has been a problem in terms of ease of handling related to the strength of the folded portion and manufacturing cost in order to attach it to a mobile wireless device of a mobile body.
[0009]
In the case of the dipole antenna having no folded portion disclosed in Patent Document 1, a complicated matching circuit including a loading coil, a capacitor, and an inductor is required to obtain a broadband frequency characteristic. A circuit board and a holding structure were required to have the antenna at the center.
[0010]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and realizes a dipole antenna with a simple structure, thereby eliminating the need for an impedance converter or a matching circuit and matching the cable impedance over a wide band of frequencies. The purpose is to provide.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned conventional problems, a dipole antenna according to the present invention is configured such that both ends of a coaxial half-wavelength antenna element composed of an outer conductor and a center conductor are short-circuited, The antenna has an antenna output terminal for extracting a received radio wave output from a center end of the outer conductor, thereby realizing a wide-band frequency dipole antenna.
[0012]
With this configuration, it is possible to match the antenna element with 75 ohms, which is the impedance of the connection cable, without bending the antenna element and without an impedance converter. Furthermore, a dipole antenna with a wide band frequency characteristic is realized with a simple coaxial structure and without a loading coil or a complicated matching circuit.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
(Embodiment 1)
FIG. 1 is a configuration diagram of a dipole antenna according to Embodiment 1 of the present invention.
[0015]
1, the same components as those in FIGS. 6 and 7 are denoted by the same reference numerals, and description thereof is omitted.
[0016]
In FIG. 1, an antenna element 4 having a coaxial structure with a diameter r by an outer conductor 8 and a center conductor 7 has a short-circuit portion 10 that is electrically short-circuited at both ends of the coaxial shaft. The antenna has an antenna output terminal 3 for extracting a received radio wave output from the center of the outer conductor 8. The dielectric 9 has a role of supporting the center conductor 7, and the length L of the antenna element 4 is selected to be approximately １ ／ wavelength of the used frequency.
[0017]
The output impedance Za of the antenna element 4 having such a configuration is, as shown in FIG. 2 (a), an antenna radiation impedance Zb having a simple dipole configuration with an external conductor and a coaxial impedance having a 1/4 wavelength length with the terminal short-circuited. It is determined by the characteristic that Zc, which is twice as large as Zd, is connected in parallel.
[0018]
The antenna impedance Zb composed of the outer conductor 8 having a diameter r is a characteristic in which the length L is about a half wavelength and is about 70 ohms, and when the frequency is high, inductive is shown, and when the frequency is low, capacitive is shown. The coaxial impedance Zd of length L / 2, one of which is short-circuited at one end, is Zd = Zod · tan (kL / ε), and the electrical execution length has an open characteristic at a frequency of ４ wavelength, and the frequency is high. When the frequency is low, the characteristic becomes inductive. Here, Zod is the characteristic impedance of the coaxial line, and k is 2π / λ. Further, Zc is Zc = 2Zd, assuming that coaxial cables whose ends are short-circuited are connected in series.
[0019]
FIG. 2B is a change characteristic diagram of the impedances Zb and Zc obtained in this manner, and the frequency FL is a length in which the coaxial length L indicates a half wavelength. Za obtained from the parallel connection of Zb and Zc having the characteristic shown in FIG. 2 <b> has an effect that at a frequency lower than the frequency FL, not only the capacitance and inductiveness are canceled but also the connection impedance approaches 75 ohms. Even if the frequency is farther than the frequency FL, there is an effect that the antenna impedance approaches 75 ohms.
[0020]
For example, since the frequency of a television wave is broadcast at 470 MHz to 770 MHz, when the center frequency FL is set to 600 MHz, the antenna element length L can be calculated by the speed of light / frequency ÷ 2, and L = 25 cm.
[0021]
FIG. 3 shows an output characteristic example of a dipole antenna having a diameter of 8 mm and a length of 25 cm according to the first embodiment of the present invention, and a simple dipole antenna characteristic example having the same size without a folded portion, centered on 75 ohms. This is shown in the Smith chart. The extent to which the frequency characteristic region near the center of the Smith chart is wide indicates the goodness of the broadband frequency characteristic. In the example of the dipole antenna according to the present invention, 470 MHz to 770 MHz, which are TV radio wave frequencies, fall within the circle of VSWR = 2, which indicates that the frequency characteristics are good.
[0022]
In the folded dipole antenna according to the related art, the output impedance at the feed unit 12 shown in FIG. In the dipole according to the present invention, the effect of condensing the output impedance of the center conductor 7 corresponding to the folded portion to 75 ohms is used. This is because the electromagnetic field radiated from the folded element affects the side element part close to the power supply part to increase the impedance, and the characteristic that the center conductor 7 of the present invention does not contribute to the electromagnetic field radiation action is different from the characteristic. Is caused.
[0023]
Although the bandwidth and the center frequency of the dielectric 9 change due to the difference in the dielectric constant, necessary characteristics can be obtained by appropriately selecting the antenna element length L. If the center conductor can be held mechanically, it is not indispensable to the present embodiment, and even if the dielectric 9 is partially or entirely missing, it is included in the embodiment of the present invention.
[0024]
Further, in the present embodiment, the outer conductor 8 may be other than a circular pipe, and when a mesh-shaped knitted wire made of a metal wire is used, it is possible to provide mechanical flexibility.
[0025]
(Embodiment 2)
FIG. 4 is a configuration diagram of a dipole antenna according to Embodiment 2 of the present invention.
[0026]
In FIG. 4, the same components as those in FIGS. 1 and 7 are denoted by the same reference numerals, and description thereof will be omitted.
[0027]
In FIG. 4, the outer conductor 6 in FIG. 1 is replaced by two conductive plates 12 having a recess in the length direction of the width W and the length L, and a conductive wire 13 and an insulating dielectric 14 attached to the recess. Both ends of the covered wire 15 are connected to an end of the conductive plate 12 by a short-circuit connection portion 16. The two conductive plates 12 are fixed at positions symmetrical to each other by a support 17 and a screw 18, and have a structure in which an antenna output terminal 3 is provided at the center end of the conductive plate 12 near the center of symmetry.
[0028]
The diameter of the conductive wire 13 of the covered wire 15 along the dent is sufficiently smaller than the width of the conductive plate, and since it falls into the dent, the high-frequency current flowing through the conductive wire 13 is not electromagnetically radiated to the outside. It is the same as the coaxial of the first embodiment having an impedance Zd determined by the plate 12 and the covered wire 15. Although the outer conductor 8 and the conductive plate 12 have different outer shapes, if the width W of the conductive plate 12 is slightly larger than the coaxial diameter r, the same radiation characteristics of radio waves can be obtained, and the length L of the 波長 wavelength used can be obtained. Thus, it plays a similar role as an antenna element that emits an electromagnetic field.
[0029]
According to such a configuration, by replacing the outer conductor 6 and the center conductor of the first embodiment with the conductive plate 12 and the covered wire 15, the antenna output impedance obtained by the conductive plate has the same effect as described in the first embodiment, A dipole antenna that can be used in a wide band frequency can be realized.
[0030]
In addition, a matching circuit is not required, the device is small, and there are no unnecessary projections on the device, thereby improving reliability and facilitating handling.
[0031]
In this embodiment, the support may be provided with an operating portion to provide a folding function and a storing function, or a structure including a covered wire may be used to separate and remove the device from the device.
[0032]
(Embodiment 3)
FIG. 5 is a configuration diagram of a dipole antenna according to Embodiment 3 of the present invention.
[0033]
5, the same components as those in FIGS. 1 and 7 are denoted by the same reference numerals, and description thereof will be omitted.
[0034]
In FIG. 5, an antenna element 19 of a coaxial structure having a short-circuit portion 10 at the end of a quarter wavelength of the frequency to be used, and an antenna element 20 of a pole or a plate-like conductor having the same length. The antenna element 4 is formed by arranging substantially in a straight line and connecting the coaxial center conductor 7 to the conductor 20 made of the conductor at the center of the whole.
[0035]
According to this configuration, an intermediate performance between the dipole antenna made of a simple conductor and the antenna according to the first embodiment of the present invention is obtained, and the performance with improved frequency characteristics of the antenna output impedance as compared with the simple dipole antenna is obtained. Is obtained.
[0036]
In addition, if the length L of the antenna element in FIG. 5 is made shorter than 波長 wavelength of the used frequency and the dielectric constant ε of the dielectric 9 is increased (for example, ε = 2.7 or more), By adding the inductor 21, the entire antenna size can be reduced in size. This is because the electrical execution length is increased by the effect of increasing the dielectric constant of the dielectric 9 due to the shortened coaxial length, and the capacitance component accompanying the shortening of the dipole antenna is reduced by one element of the inductor 21. Due to cancellation.
[0037]
With this configuration, a dipole antenna that is small and has a simple structure and wideband characteristics is realized.
[0038]
【The invention's effect】
As described above, according to the dipole antenna of the present invention, it is possible to match the impedance of the connecting cable to 75 ohms without bending the antenna element and without using an impedance converter. Furthermore, a dipole antenna having a wide band frequency characteristic can be realized with a simple coaxial structure without a loading coil or a complicated matching circuit.
[Brief description of the drawings]
1 is a configuration diagram of a dipole antenna according to a first embodiment of the present invention; FIG. 2 is a diagram illustrating characteristics of the first embodiment of the present invention; FIG. 3 is a diagram illustrating output impedance of the first embodiment of the present invention; 4 is a configuration diagram of a dipole antenna according to a second embodiment of the present invention. FIG. 5 is a configuration diagram of a dipole antenna according to a third embodiment of the present invention. FIG. 6 is a configuration diagram of a conventional dipole antenna having a folded structure. Configuration diagram of conventional dipole antenna using matching circuit
REFERENCE SIGNS LIST 1 folded dipole antenna 2 impedance converter 3 antenna output terminal 4 antenna element 5 loading coil 6 matching circuit 7 center conductor 8 outer conductor 9 dielectric 10 short-circuit portion 12 conductive plate 13 conductive wire 14 insulating dielectric 15 covered wire 16 short-circuit connection Part 17 Support 18 Screw 19 Coaxial antenna element 20 Antenna element 21 made of a conductor Inductor

Claims (3)

An outer conductor for radiating radio waves and a center conductor are arranged coaxially, and both ends of the center conductor constitute an antenna element having short-circuit portions at both ends of the outer conductor. A dipole antenna with an antenna output terminal in the section. Two conductive plates with a dent in a flat plate are arranged in a straight line, and a covered wire made of a conductive wire and an insulating dielectric is attached to the dent of the flat plate. 2. The dipole antenna according to claim 1, wherein the dipole antenna has a structure in which an antenna output terminal is provided at an end of a central portion of the two conductive plates connected and arranged in a straight line. The dipole antenna according to claim 1, wherein the antenna element on one side connected to the antenna output terminal is formed of only a conductor, and a center conductor is connected to the conductor.

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