JP2004165942A - Two-frequency common antenna system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-frequency common antenna system which has an excellent and stable return loss characteristic and a high gain in a high frequency band and can share frequencies of a mobile communication system even with an ordinary whip antenna. <P>SOLUTION: This antenna system 10 is a dipole 12 composed of dipole elements 12a and 12b of metal foils which have arbitrary widths on a dielectric substrate 11 to share two frequency bands, and characterized in that a position shifting from the geometric center point CO between both ends of the dipole elements by a certain length along the length of the dipole elements is regarded as the feed center point C of the dipole 12. The dipole 12 is made to resonate at a frequency fed from common feeders 15a and 15b through the feed center point C, the dipole element 12a which is shorter between the dipole elements is fed from the feeders through the feed center point C to make its dipole element length resonate at a frequency f2 (f2>f1), and the operation mode is set to a whip antenna. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mobile station antenna device in, for example, a mobile communication system, and more particularly to a dual frequency antenna device including a dipole antenna and a whip antenna, which is required to have shared characteristics in two frequency bands.
[0002]
[Prior art]
Conventionally, as this type of dual-frequency antenna device, there is, for example, a whip antenna type as shown in FIG.
In FIG. 6, the dual-frequency antenna device 1 includes a trap circuit 3 including a coil and the like, which is inserted in series in the middle of the antenna element 2, and a dual-frequency dual-use antenna at a feed point of the antenna device 1. And a power supply matching circuit 4. 5 is a feed line.
[0003]
The feed matching circuit 4 includes a loading coil L1 and a capacitor C1 of the matching circuit. In this case, the structure of the feeding point includes a loading coil L1, and in order to perform impedance matching at two frequencies, the coil C1 is used to reduce the inductance of the loading coil L1 in a desired high frequency band. Are arranged in parallel in the middle of the process and resonate at two frequencies.
[0004]
When the frequency of the loading coil L1 is low, the impedance can be matched without much need for the coil L1 and its manufacturing accuracy. However, when the frequency becomes 1 GHz or more, in order to realize dual frequency sharing, In addition, the joining accuracy of the coil L1 and the capacitor C1, the loss of the coil L1, and the like cannot be ignored.
[0005]
[Problems to be solved by the invention]
In mobile communication systems in recent years, mobile communication terminals capable of receiving a plurality of frequencies within the same area have become widespread. This is a system in which when a certain frequency band is crowded, it is assigned to a different frequency band.
Along with this, the existence of a place where a small antenna that shares two frequencies is required as an auxiliary antenna of the mobile terminal has been expected or long-awaited.
[0006]
In addition, since the frequency band of a mobile phone is higher than that of an on-board antenna of the 500 MHz band or less, it is difficult to share the frequency with a normal whip antenna, and even if it is realized, the cost is increased and it is not realistic. There was a problem. Therefore, there is a need for an antenna that has good and stable return loss characteristics in a high frequency band and is inexpensive.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-mentioned problems, to provide a good and stable return loss characteristic in a high frequency band, a high gain, and a mobile communication system even with a normal whip antenna. It is an object of the present invention to provide an inexpensive dual-frequency antenna device that can share the same frequency.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the configuration of the dual-frequency antenna device of the present invention is a metal foil having an arbitrary width on a dielectric substrate, or a metal flat plate having an arbitrary width, in order to share two frequency bands. A dipole consisting of a dipole element is formed, and a position shifted by a length in the length direction of the dipole element from a geometric center between both ends of the dipole element is set as a feeding center point of the dipole, and the dipole is used as the feeding center. A dipole antenna that resonates at a first frequency f1 that is fed from a common feed line via a center point, and is fed from the feed line via the feed center, and the shorter one of the dipole elements A dual-frequency antenna device that resonates at a second frequency f2 (f2> f1) with a dipole element length and operates in a whip antenna mode. That.
[0009]
In the dual frequency antenna device, the certain length may be a length from the geometric center to an end of the shorter dipole element and a position at a quarter of the wavelength of the second frequency f2.
[0010]
This is a dual-frequency antenna device in which a plurality of pairs of dipole elements of the dipole antenna are formed on the same dielectric substrate and operated as a diversity antenna.
[0011]
The dual-frequency antenna device, wherein the feed line is constituted by a balanced circuit, a balanced-unbalanced conversion circuit, a microstrip line of an unbalanced circuit, or a balun.
[0012]
Since the dual-frequency antenna device of the present invention is configured as described above to share two frequency bands, it resonates and operates as a dipole antenna at a low first frequency f1, and operates at the respective lengths. Of the two dipole elements different from each other, resonance is performed at a high second frequency f2 (f2> f1) mainly at the shorter dipole element length, and the dipole element is operated as a whip antenna.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be illustratively described in detail with reference to the drawings. 1 and 2 are views showing one embodiment of a dual-frequency antenna device according to the present invention. FIG. 1 is a front view showing the configuration of the dual-frequency antenna device, and FIG. FIG. 7 is a diagram showing a current distribution with dotted lines when resonance occurs at a low first frequency f1 and a high second frequency f2 of the two frequencies, respectively.
[0014]
In FIG. 1, the dual-frequency antenna device 1 is made of a metal foil having an arbitrary width formed on one surface of a dielectric substrate 11 and has a first frequency f1 in a 0.8 GHz band (its wavelength is λ1), the case where the second frequency f2 is an antenna shared by two frequencies used in the 1.5 GHz band (its wavelength is λ2), and two linearly formed two dipoles constituting the first dipole 12 are shown. The length between both ends of the dipole elements 12a and 12b is formed to be approximately (λ1) / 2 so as to resonate at the frequency f1.
[0015]
One of the dipole elements 12a, 12b extends from the geometric center point C0 of the length between both ends of the dipole elements 12a, 12b at about (λ1) / 2 of the frequency f1 in the length direction of the dipole elements 12a, 12b. A position shifted from the end of the antenna f to a point at about (λ2) / 4 of the frequency f2 is defined as a feeding center point C of the antenna device 10, and the shorter one of the dipole elements 12a and 12b has a length of about (λ2). ) / 4 of the dipole element 12a is resonated at the frequency f2.
[0016]
From the feeding center point C of the antenna device 10, on both sides of a slit 19 having a length L provided on a center line C1 in a direction perpendicular to the dipole elements 12a and 12b (downward vertical direction in FIG. 1). A U-shaped dipole U-shaped balun portion 13a made of a metal foil having a width is formed, and respective ends 13b and 13c are formed so as to be connected to respective ends of the dipole elements 12a and 12b. .
[0017]
Accordingly, the second dipole 13 is formed of the dipole elements 12a and 12b and the dipole U-shaped balun portion 13a, and resonates the dipole element 12a at the frequency f2.
The total length of the dipole elements 12a and 12b and the dipole U-shaped balun portion 13a forming the second dipole 13 is about 1.5 times the wavelength λ2 of the frequency f2 as shown in FIG. The length L of the slit 19 is about (λ2) / 4 or more of the frequency f2 and is determined by impedance matching with the later-described balun 14 or the wavelength of the frequency f2 from the central feeding point 20 described later. It is about 1/4 of λ2.
[0018]
A feed line for feeding power to the first and second dipoles 12 and 13 includes a feed line 15a formed on the other surface side of the dielectric substrate 11 and a U-shaped bottom of the dipole U-shaped balun portion 13a. Form the feed line 15b.
[0019]
A feed line 15a formed on the other surface (the back side in FIG. 1) of the dielectric substrate 11 has one end on one side (the left side in FIG. 1) of the slit 19 provided on the center line C1. Along the other side of the slit 19, a balun 14 is formed along the other side (the right side in FIG. 1) of the slit 19. The other end is connected to a feeding end at the lower end of the dielectric substrate 11.
[0020]
The balun 14 is formed so that its length is approximately (λ2) / 4 of the second frequency f2 from the central feeding point 20 and is matched. The dipole elements 12a, 12b; 12a, 12b, 13a as radiating elements of the first and second dipoles 12, 13, respectively, are provided from the feed lines 15a, 15b via the central feed point 20. Thus, the power of the predetermined frequency is supplied.
[0021]
Thus, the structure of the balun 14 is an open structure. In addition, a portion surrounding the balun 14 including the power supply lines 15a and 15b as a power supply balun portion 17 by a chain line in FIG. 1 is illustrated.
[0022]
The dipole element 12a operates as a whip antenna. In this case, the whip antenna using the dipole element 12a of the antenna device 10 is an antenna that does not require a ground such as a ground plate.
As shown in FIG. 2, the whip antenna whose current distribution at the second frequency f2 extends over a length of 3/2 of the wavelength λ2 does not require a ground such as a ground plate below the antenna. Still, the antenna can radiate in the horizontal direction with the directivity of the vertical plane.
[0023]
The antenna device 10 is a deformed dipole antenna device that is asymmetric when viewed from the center feeding point 20.
Further, the antenna device 10 can operate as a diversity antenna shared by two frequencies by forming a plurality of pairs of the dipole elements 12a, 12b, 13a on the same dielectric substrate 11 in the vertical direction.
[0024]
In the present embodiment, an example in which the first and second dipoles 12 and 13 are formed on one surface of the dielectric substrate 11 with a metal foil has been described. You may let it.
Further, in the present embodiment, one frequency f1 used is in the 0.8 GHz band and the other frequency f2 is in the 1.5 GHz band. However, the present invention is not limited to this, and other frequencies f1 may be used in other frequencies. Of course, preferably, the frequency f2 is about twice the frequency f1.
[0025]
The frequency versus return loss characteristics of each of the frequency bands, that is, the first frequency f1 = 0.8 GHz band and the second frequency f2 = 1.5 GHz band, of the dual-band antenna device 10 are as follows. As shown in FIG. 3, broadband characteristics are obtained.
[0026]
Further, with respect to the dual-frequency antenna device 10, when the dipole element 12a is operated as a whip antenna, a directional characteristic diagram in a horizontal plane shows a first frequency f1 = 0.8 GHz band, a second frequency f2 = 1. FIGS. 4A and 4B show the in-plane directional characteristics of the magnetic field in the 5 GHz band.
Similarly, in the vertical plane directional characteristics, the electric field in-plane directional characteristics at the first frequency f1 = 0.8 GHz band and the second frequency f2 = 1.5 GHz band are shown in FIGS. It is shown in b).
[0027]
The dual-frequency antenna device 10 can be configured by connecting a balanced circuit, a balanced-unbalanced conversion circuit, a microslip line of an unbalanced circuit, or a balun to the feed lines 15a and 15b, respectively.
[0028]
Note that the technology of the present invention is not limited to the technology in the above-described embodiment, and may be implemented by means of another embodiment that performs the same function. Addition is possible.
[0029]
【The invention's effect】
As is apparent from the above description, according to the dual-frequency antenna device of the present invention, a dipole is formed on a dielectric substrate in order to share two frequency bands, and a geometrical configuration between both ends of the dipole element is formed. A position shifted from the center by a length in the length direction of the dipole element is set as a feeding center point of the dipole, and the dipole is resonated at a first frequency f1 fed from a common feeding line through the feeding center point. A dipole antenna, and feeds power from the feed line via the feed center point, and resonates at a second frequency f2 (f2> f1) with the shorter dipole element length of the dipole elements; and Operation mode is set to whip antenna, so return loss characteristics in high frequency band are good and stable, high gain, and can move with normal whip antenna With frequency can be shared Shin method of inexpensive it can be downsized, an excellent effect that dualband dipole antenna device is obtained.
[0030]
According to the present invention, a dielectric substrate is used without using a matching element or the like at the trap circuit and the feeding point, that is, without using an inductance part (the coil) and a capacitance part as compared with the conventional one. Since the dipole element can be formed thereon, the manufacturing accuracy is high and it is very efficient for mass production. Since there is no loss or the like in the coil, there is an effect that a high gain can be stably obtained.
[Brief description of the drawings]
FIG. 1 is a view showing one embodiment of a dual-frequency antenna device according to the present invention, and is a front view showing the configuration of the dual-frequency antenna device.
FIG. 2 is a diagram showing a current distribution by a dotted line when the dipole of the antenna device of FIG. 1 resonates at a low first frequency f1 and a high second frequency f2 among two frequencies.
FIG. 3 is a diagram illustrating frequency versus return loss characteristics of the dual frequency antenna device of FIG. 1;
4A and 4B are directional characteristics diagrams in a horizontal plane of the dual-frequency antenna device of FIG. 1; FIG. 4A is a directional characteristics diagram in a magnetic field plane at a first frequency f1 = 0.8 GHz; FIG. FIG. 9 is a diagram showing a directivity characteristic in a magnetic field plane at a second frequency f2 = 1.5 GHz.
5A is a directional characteristic diagram in a vertical plane of the dual-frequency antenna device of FIG. 1, and FIG. 5A is a directional characteristic diagram in an electric field plane at a first frequency f1 = 0.8 GHz; FIG. FIG. 5 is a diagram showing the in-plane directional characteristics at the second frequency f2 = 1.5 GHz.
FIG. 6 is an explanatory view showing a configuration of a whip antenna type antenna device as an example of a conventional dual frequency antenna device.
[Explanation of symbols]
Reference Signs List 10 dual frequency antenna device 11 dielectric substrate 12 first dipole 12a, 12b dipole element 13 second dipole 13a dipole U-shaped balun portion 13b, 13c end 14 balun 15, 15a, 15b feed line 17 feed balun portion 19 slit 20 Central feeding point C Feeding center point C0 Geometric center point C1 Center lines f1, f2 Frequency

Claims (4)

In order to share the two frequency bands, a dipole composed of a dipole element made of a metal foil having an arbitrary width or a metal flat plate having an arbitrary width is formed on a dielectric substrate, and a geometry between both ends of the dipole element is formed. A position shifted by a distance in the length direction of the dipole element from the target center is defined as a feeding center point of the dipole, and the dipole resonates at a first frequency f1 at which the dipole feeds from a common feeding line via the feeding center point. A dipole antenna, and feeds power from the feed line via the feed center point, and resonates at a second frequency f2 (f2> f1) with the shorter dipole element length of the dipole elements. A dual-frequency antenna device wherein the operation mode is a whip antenna. 2. The device according to claim 1, wherein the certain length is a length from the geometric center to a position corresponding to a quarter of a wavelength of the second frequency f <b> 2 from an end of the shorter dipole element. 3. 2. The dual-frequency antenna device according to item 1. 3. The dual-frequency antenna device according to claim 1, wherein a plurality of pairs of the dipole elements of the dipole antenna are formed on the same dielectric substrate to operate as a diversity antenna. 4. 3. The dual-frequency antenna device according to claim 1, wherein the feed line includes a balanced circuit, a balanced-unbalanced conversion circuit, a microstrip line of an unbalanced circuit, or a balun. 4.

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