JP2004343193A - Antenna system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a downsized antenna system for preventing a leakage current from flowing through a coaxial feeder. <P>SOLUTION: Radiation elements 10, 11 and a passive element 12 in parallel with them are deposited in a V shape. Then the interval between the radiation elements 10, 11 and the passive element 12 is selected to be nearly less than 1/4 wavelength of the wavelength equivalent to the operating center frequency. Thus, the antenna system 1 can be downsized. Consequently, it is prevented that the leakage current flows through an outer conductor of a coaxial cable 13 by connecting the passive element 12 to a shield part 13d of the coaxial cable 13 apart from the connecting position of the radiation elements 10, 11 by 1/4 wavelength. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an antenna device that includes at least a radiating element and a parasitic element, and that can directly connect an unbalanced coaxial feed line to an electrically balanced radiating element.
[0002]
[Prior art]
Conventionally, a Yagi-Uda antenna is generally used as a communication antenna having directivity. The Yagi-Uda antenna includes a radiating element, and a reflecting element and a waveguide element arranged before and after the radiating element. The distance between the radiating element and the reflecting element is approximately λ / 4, where λ is the wavelength at the used center frequency, and the distance between the radiating element and the waveguide element is also approximately λ / 4. The length of the radiating element that performs an electrically balanced operation is approximately λ / 2, the length of the reflecting element is slightly longer than λ / 2 so as to be inductive reactance, and the length of the waveguide element is , Which is slightly shorter than λ / 2 to provide capacity reactance.
[0003]
In the Yagi-Uda antenna having such a configuration, power is supplied by connecting the core wire and the outer conductor of the coaxial feeder to the radiating element of the dipole, respectively. Then, although the radiating element of the dipole operates in a balanced manner, the leakage current flows through the outer conductor of the coaxial feed line because the coaxial feed line is an unbalanced feed line. This leakage current is generated as a standing wave on the coaxial feed line, and has a minimum amplitude at a point λ / 4 from the feed point. When a leakage current flows in the outer conductor of the coaxial feed line, the current flowing in the radiating element of the dipole becomes unbalanced, and the front-to-back ratio (FB ratio) of the beam of the Yagi-Uda antenna deteriorates, and the voltage standing wave ratio ( VSWR). Therefore, in order to match the radiating element of the balanced operation with the coaxial feed line which is an unbalanced feed line, a balanced-unbalanced conversion device (balun) is conventionally provided. Alternatively, a blocking sleeve (super top) for blocking a leakage current has been provided. However, both the method using the spar top and the method using the balun have the problems that the structure of the power supply unit becomes complicated, the number of work steps for maintaining mechanical strength increases, and the cost increases. .
[0004]
Therefore, there has been proposed a Yagi-Uda antenna in which antenna characteristics are not deteriorated even when a coaxial feed line is directly connected to a balanced radiating element without using a balun or a supertop (for example, see Patent Document 1). In this Yagi-Uda antenna, a reflecting element or a waveguide element is arranged at a distance of about 1/4 wavelength from the radiating element and about 1/4 wavelength of the center frequency used, and the reflection is made to the outer conductor at a position about 1/4 wavelength from the feeding point of the coaxial cable. By connecting the element or the waveguide element, the reflection element or the waveguide element functions as a stub to prevent leakage current from flowing to the outer conductor of the coaxial feeder.
[0005]
[Patent Document 1] Japanese Patent No. 3165653
[Problems to be solved by the invention]
However, such a structure of the conventional Yagi-Uda antenna has a problem that the horizontal and vertical sizes of the Yagi-Uda antenna are limited to the wavelength of the operating frequency, which makes it difficult to miniaturize the antenna device. In this case, it is conceivable to reduce the wavelength by installing a high dielectric constant material around the element to reduce the size of the antenna device. However, radiation loss due to the high dielectric material occurs and the antenna gain is reduced. become. Furthermore, the shortening of the wavelength makes the dimensional tolerance of the physical length of the antenna stricter, which causes a large variation in electrical characteristics during mass production.
[0007]
Accordingly, it is an object of the present invention to provide an antenna device capable of preventing a leakage current from flowing through an outer conductor of a coaxial feed line without decreasing the antenna gain.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an antenna device according to the present invention is an antenna device including a radiating element of a V-shaped dipole, and a V-shaped parasitic element arranged substantially parallel to the radiating element. The V-shaped radiating element and the parasitic element are disposed substantially in parallel with an interval of less than approximately 波長 wavelength of the center frequency used, and are coaxial to feed the radiating element. The parasitic element is connected to the outer conductor at a position approximately one-quarter wavelength of the used center frequency wavelength from the feeding point of the cable, so that the parasitic element also functions as a stub for preventing leakage current. I have.
[0009]
In the antenna device of the present invention, a plurality of the parasitic elements may be arranged at substantially equal intervals before and / or after the radiating element.
Further, in the antenna device of the present invention, the radiating element and the parasitic element may be formed on a dielectric substrate.
[0010]
According to the present invention, the radiating element and the parasitic element are V-shaped, and the interval between the radiating element and the parasitic element is set to be less than approximately ４ wavelength of the used center frequency wavelength. The size can be reduced, and even if the size is reduced, a decrease in antenna gain can be prevented. In addition, since the parasitic element is connected to the outer conductor at a position approximately one-quarter wavelength of the used center frequency wavelength from the feeding point of the coaxial cable feeding the radiating element, a leakage current flows through the outer conductor of the coaxial feeding line. Can be prevented.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 show the configuration of an antenna device according to an embodiment of the present invention. However, FIG. 1 is a plan view of the antenna device of the present invention, and FIG. 2 is a side view thereof.
As shown in these drawings, the antenna device 1 according to the present invention includes a dipole radiating element including a radiating element 10 and a radiating element 11, and the radiating element 10 and the radiating element 11 are arranged in a V-shape. It is formed on an insulating substrate 20. A V-shaped parasitic element 12 is formed on an insulating substrate 20 substantially in parallel with the radiating element 10 and the radiating element 11. In this case, the radiating element 10, the radiating element 11, and the parasitic element 12 are formed as thin films made of metal and deposited or adhered on an insulating substrate 20.
[0012]
The distance between the radiating element 10 and the radiating element 11 and the parasitic element 12 is less than λ / 4, for example, approximately λ / 8, where λ is the wavelength at the used center frequency. As described above, the distance between the radiating element 10, the radiating element 11, and the parasitic element 12 is shortened so as to be less than λ / 4, and the radiating element 10, the radiating element 11, and the parasitic element 12 are V-shaped. Since the antenna device 1 is arranged in a bent shape, the antenna device 1 can be reduced in size. The V-shaped angle between the radiating element 10, the radiating element 11, and the parasitic element 12 is about 90 °. Further, the entire length of the dipole antenna including the radiating element 10 and the radiating element 11 that operate electrically balanced is approximately λ / 2, and the entire length of the parasitic element 12 functions as a reflective element as an inductive reactance. When it is made to function as a waveguide element as capacity reactance, it is made slightly longer than λ / 2.
[0013]
The dipole antenna including the radiating element 10 and the radiating element 11 is supplied with power from a coaxial cable 13. That is, as shown in FIG. 1, the outer sheath at the end of the coaxial cable 13 is removed to expose the shield portion 13a as an external conductor, and this shield portion 13a is electrically connected to one end of the radiating element 11 by soldering or the like. are doing. Further, the shield part at the end of the coaxial cable 13 and the insulating part therein are removed to expose the core wire 13c, and this core wire 13c is electrically connected to one end of the radiating element 10 by soldering or the like. In this case, the dipole antenna including the radiating element 10 and the radiating element 11 performs an electrically balanced operation, but the coaxial cable 13 is an unbalanced cable. Therefore, the outer skin of a portion having a length of approximately λ / 4 from the feeding point to the radiating element 10 and the radiating element 11 of the coaxial cable 13 is removed to expose the shield portion 13d. Then, the shield portion 13d is electrically connected to the center of the parasitic element 12 by soldering or the like.
[0014]
As a result, the parasitic element 12 has a length of about λ / 4 from the shield portion 13d, and functions as a λ / 4 stub whose tip is open. Then, the impedance when the parasitic element 12 is viewed from the shield part 13d becomes almost infinite. For this reason, even if the radiating element 10 and the radiating element 11 performing the balanced operation are directly supplied with power from the unbalanced coaxial cable 13 and a leakage current flows through the coaxial cable 13, the radiating element 10 and the radiating element 11 are exposed after the exposed shield portion 13 d of the coaxial cable 13. In this case, the leakage current flowing through the shield portion is prevented. In this way, the parasitic element 12 can prevent the leakage current from flowing through the outer conductor of the coaxial cable 13. The length from the feeding point of the coaxial cable 13 to the radiating element 10 and the radiating element 11 to the shield part 13d is approximately λ / 4, but the distance between the radiating element 10 and the radiating element 11 and the parasitic element 12 is Since it is smaller than λ / 4, for example, approximately λ / 8, the coaxial cable 13 therebetween is wound to form a winding portion 13b.
[0015]
Next, FIG. 3 is a plan view showing a configuration of a modification of the antenna device 1 according to the embodiment of the present invention. The antenna device 2 shown in FIG. 3 has the matching element 14 in the antenna device 1 shown in FIG. In general, the characteristic impedance of the coaxial cable 13 is set to 50Ω or 75Ω. However, the radiating element 10 and the radiating element 11 are bent in a V-shape, and the V-shaped Since the feed element 12 is arranged in parallel with the radiating element 10 and the radiating element 11, it is difficult to match with the coaxial cable 13. Therefore, in the antenna device 2 shown in FIG. 3, a matching element 14 for matching is provided to match the dipole antenna including the radiating elements 10 and 11 with the coaxial cable 13. One end of the matching element 14 is electrically connected to the shield part 13 a by soldering or the like, and the other end is connected to the middle of the radiating element 11.
[0016]
Other configurations of the antenna device 2 illustrated in FIG. 3 are the same as those of the antenna device 1 illustrated in FIG. 1, and thus description thereof will be omitted, but the antenna device 2 can be downsized. Further, also in the antenna device 2, it is possible to prevent a leakage current from flowing through the outer conductor of the coaxial cable 13.
In the antenna devices 1 and 2 described above, the size of the substrate 20 is about 240 × 220 mm, the length of the radiating element 10 and the radiating element 11 is about 127 mm, and a parasitic element functioning as a reflecting element. By setting the length of the radiating element 12 to about 165 mm and the distance between the radiating elements 10 and 11 and the parasitic element 12 to about 80 mm, the resonance frequency can be about 500 MHz. Thus, the antenna device according to the present invention can be downsized. The substrate 20 is a glass epoxy resin substrate, and has a relative dielectric constant 率 s of about 3.4.
[0017]
Next, FIG. 4 is a side view showing the configuration of another modification of the antenna device 1 according to the embodiment of the present invention, and FIG. 5 is an exploded view thereof. In the antenna device 3 shown in these figures, the winding portion 13b of the coaxial cable 13 is fixed to the substrate 20 in the antenna device 1 shown in FIG. That is, the fixing part 22 is inserted into the winding part 13b, and the screw 21 inserted into the fixing part 22 is screwed to the nut 23 arranged on the back side of the substrate 20 to fix the winding part 13b to the substrate 20. I have to. In this case, as shown in FIG. 5, the fixing tool 22 includes a flange portion 22a that comes into contact with the winding portion 13b, and a cylindrical portion 22b that extends from the flange portion 22a, and is made of synthetic resin or metal. . The fixing tool 22 has a through hole through which the screw 21 can be inserted.
[0018]
FIGS. 6A, 6B, and 6C show other examples of the configuration of the fixing tool 22. FIG. In the fixing tool 32 shown in FIG. 6A, a screw portion 32c integrated with a flange portion 32a instead of the screw 21 is extended from the lower surface. The screw portion 32c is inserted into a through hole formed in the cylindrical portion 32b, and the fixing tool 32 is inserted into the winding portion 13b. Next, the winding portion 13b can be fixed to the substrate 20 by screwing the screw portion 32c to the nut 23.
Further, in the fixing tool 42 shown in FIG. 6B, a screw portion 42c integrated with the fixing tool 42 instead of the screw 21 is extended from the lower surface of the cylindrical portion 42b. By inserting the fixing member 42 into the winding portion 13b and screwing the screw portion 42c thereof to the nut 23, the winding portion 13b can be fixed to the substrate 20.
Further, the fixing tool 52 shown in FIG. 6C has a female screw formed in a hole formed in the cylindrical portion 52b in the axial direction. The nut 23 is replaced by a screw 53 instead of the screw 21. The fixing part 52 is inserted into the winding part 13b, and a screw 53 is screwed into the female screw formed on the cylindrical part 52b of the fixing part 52 from the back side of the substrate 20, so that the winding part 13b is attached to the substrate 20. Can be fixed.
[0019]
Next, FIG. 7 shows the frequency characteristics of the voltage standing wave ratio (VSWR) of the antenna device 2 shown in FIG. 4, and FIG. 8 shows the directivity in the horizontal plane. In this case, the antenna device 2 has the above dimensions, the resonance frequency thereof is about 500 MHz, and the length of the matching element 14 is about 56 mm. Referring to FIG. 7, a good VSWR of about 1.2 is obtained at 500 MHz. Referring to FIG. 8, the maximum gain in the horizontal plane is about +3 dBd, the half value angle is about 80 °, and the front / back ratio (F / B ratio) is about 11 dB. The reason why such a large half-value angle is obtained is that the distance between the radiating element 10 and the radiating element 11 and the parasitic element 12 is set to about λ / 8 and less than λ / 4.
[0020]
In the above-described antenna device of the present invention, the number of parasitic elements is not limited to one, but two or more elements may be provided, or two or more parasitic elements may be arranged before and after the radiating element. In addition, the element length may be set to another length regardless of the quarter wavelength on one side. The V-shaped bending angle of the radiating element and the parasitic element may be an angle other than 90 °. Further, the matching means in the antenna device is not limited to Γ matching, and may be Ω matching or Q matching. Furthermore, matching may be performed by a lumped constant circuit using chip components.
Furthermore, in the antenna device of the present invention, instead of forming the radiating element and the parasitic element on the substrate, the radiating element and the parasitic element may be made of a metal rod. Furthermore, instead of winding the coaxial cable in the antenna device of the present invention, the antenna device may be bent.
[0021]
【The invention's effect】
As described above, according to the present invention, the radiating element and the parasitic element are V-shaped, and the interval between the radiating element and the parasitic element is set to be less than about １ ／ wavelength of the center frequency wavelength used. The size can be reduced, and even if the size is reduced, a decrease in antenna gain can be prevented. In addition, since the parasitic element is connected to the outer conductor at a position approximately one-quarter wavelength of the used center frequency wavelength from the feeding point of the coaxial cable for feeding the radiating element, a leakage current flows through the outer conductor of the coaxial feeding line. Can be prevented.
[Brief description of the drawings]
FIG. 1 is a plan view showing a configuration of an antenna device according to an embodiment of the present invention.
FIG. 2 is a side view showing the configuration of the antenna device according to the embodiment of the present invention.
FIG. 3 is a plan view showing a configuration of a modified example of the antenna device according to the embodiment of the present invention.
FIG. 4 is a side view showing a configuration of another modification of the antenna device according to the embodiment of the present invention.
FIG. 5 is an exploded view showing the configuration of another modification of the antenna device according to the embodiment of the present invention.
FIG. 6 is a diagram showing a configuration example of a fixing tool in a configuration of another modification of the antenna device according to the embodiment of the present invention.
FIG. 7 is a diagram illustrating a frequency characteristic of a VSWR of the antenna device according to the embodiment of the present invention.
FIG. 8 is a diagram illustrating a directional characteristic in a horizontal plane of the antenna device according to the embodiment of the present invention;
FIG. 9 is a diagram showing a configuration of a conventional antenna device.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 antenna device, 2 antenna device, 3 antenna device, 10 radiating element, 11 radiating element, 12 parasitic element, 13 coaxial cable, 13 a shield part, 13 b winding part, 13 c core wire, 13 d shield part, 14 matching element, 20 Substrate, 21 screw, 22 fixing tool, 22a flange, 22b cylinder, 23 nut, 32 fixing tool, 32a flange, 32b cylinder, 32c screw, 42 fixing, 42a flange, 42b cylinder, 42c screw Part, 52 fixing tool, 52a flange part, 52b cylindrical part, 53 screw

Claims (3)

An antenna device comprising: a radiating element of a V-shaped dipole; and a V-shaped parasitic element arranged substantially parallel to the radiating element,
The V-shaped radiating element and the parasitic element are arranged substantially in parallel with an interval of less than approximately 波長 wavelength of a used center frequency wavelength, and a coaxial cable for feeding the radiating element The parasitic element is connected to an outer conductor at a position approximately one-quarter wavelength of the used center frequency wavelength from the feeding point of the above, so that the parasitic element also functions as a stub for preventing leakage current. An antenna device characterized by the above-mentioned. 2. The antenna device according to claim 1, wherein a plurality of the parasitic elements are arranged at substantially equal intervals before and / or after the radiating element. The antenna device according to claim 1, wherein the radiating element and the parasitic element are formed on a dielectric substrate.

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