JP2000188510A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily provide a desired radiation pattern by fitting a half-wave dipole antenna close to the surface of a metallic casing incorporating a radio machine, connecting the antenna and the radio machine by means of a feeder and connecting the feeder and the metallic casing by means of a reactance element. SOLUTION: A dipole antenna 101 is arranged so that it becomes parallel to one side of a casing 102. The casing is a conductor and is the shield of a radio circuit. A feeder 103 is arranged close to the surface of the casing 102 from the feeding point of the dipole antenna 101. A reactance element is arranged between the feeder 103 and the casing 102 by connecting them. The reactance element is constituted of a capacitor, an inductance and a variable capacitor. The antenna device returns a radiation pattern changed by the feeder 103 to the original one and is made into the desired radiation pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a built-in dipole antenna for a portable radio.

[0002]

2. Description of the Related Art In recent years, a radio and an antenna are often integrated. These wireless devices include portable wireless devices such as PHS and portable wireless devices, and small wireless base stations.
The antennas of these wireless devices are required to have characteristics close to non-directionality. Further, in the case of a portable wireless device, a built-in antenna is required in order to withstand damage when dropped, and in the case of a base station, damage caused by wind and rain.

[0003] However, in the case of such an antenna integrated with a wireless device, since the electromagnetic wave is radiated from the wireless device housing, the radiation from the antenna changes due to the influence of the radiation. It is known. The cause will be briefly described. These wireless device housings are made of a conductor and serve as a ground and a shield for a built-in wireless circuit. Since the housing is also grounded for the antenna, the high-frequency current supplied to the antenna flows into the housing, and radiation is also generated from the housing as described above. Especially for the built-in antenna, the radiation from the antenna is small,
It will be strongly affected by the radio housing.

[0004] In order to reduce these effects, proposals have been made to use a dipole antenna. (Japanese Unexamined Patent Publication No. 61-2005004) That is, the dipole antenna
This is because the antenna does not require a ground, so that the antenna does not need to be directly connected to the housing, which is the ground, so that the leakage of the high-frequency current to the housing can be expected. However, even in the case of this antenna, practically, there remains a problem in practical use. Because, as described below, also in this antenna, when the dipole antenna is arranged close to the housing, the radiation field of the antenna greatly changes depending on the length of the feed line.

FIG. 7 shows the result of a calculation made by the inventors regarding the above-mentioned change. Hereinafter, the data described in this specification are the results of performing an electromagnetic field simulation using a simple model simulating a wireless device having an operating frequency of 2500 MHz. FIG. 7 shows an antenna model in the case of the conventional antenna arrangement used this time. In the model, the wireless device housing was simplified to use only a metal plate, and the short side of the substrate was set to two-thirds wavelength and the long side to three-half wavelengths. FIG. 7 shows a pattern when the wireless device is viewed from above. As can be seen from the pattern, it is shown that the radiation pattern greatly changes as the length of the feed line changes.

[0006] Conventional inventions and technical reports have never considered the occurrence of such a large change.
The qualitative explanation alone states that the use of a dipole antenna can reduce the effects of the housing. That is,
Ignoring the secondary and serious problems that actually occurred that became apparent for the first time this time, there were problems that remain to be put to practical use.

Here, the reason why a large change occurs in the radiation pattern as described above will be briefly described.

The antenna (a) has two radiation modes (b) and (c) as shown in FIG. Each of these two radiation modes has a structure having two wave sources. The radiation patterns emitted from these will be described below. Note that the radiation modes (b) and (c) are actually
Although they exist in an overlapped and fused form, they are hereinafter treated as being separable for convenience.

The main radiation sources in the radiation mode (b) are a portion surrounded by a broken line in the drawing, that is, a dipole antenna 101 which is the wave source 1 and a side of the housing 102 to which the dipole antenna 101 is close. Wave sources 2 are two wave sources. Here, the side on the housing 102 is a secondary wave source excited by the radiation of the antenna 101. These two
The radiation pattern of the radio waves radiated by the two wave sources has directivity, for example, as shown in FIG.

On the other hand, in the case of the radiation mode (c), one of the elements 101A of the dipole antenna 101, the wave source 1 constituted by a current leaking on the feed line 103, and the wave source 1 are transmitted through the feed line 103. Radiation is generated from the two wave sources of the wave source 2 due to the current leaking on the side near the dipole antenna 101 on the housing 102. In this radiation mode (c), the phase and amplitude of the current of the wave source 2 change depending on the length of the feed line. Thus, in the radiation mode (c), the radiation pattern changes depending on the length of the feed line. FIG. 6 shows a radiation pattern that changes depending on the length of the feed line. As is clear from the figure, a very large change in the radiation pattern occurs with a change in the length of the feed line.

By changing the length of the feed line in this way, the radiation mode (c) changes as shown in FIG. 7, and this radiation pattern is different from the radiation pattern created by the radiation mode (b). Is different, the radiation pattern created by the combination of (c) and (b) is changed as a result depending on the length of the feed line.

If the radiation pattern is determined by the length of the feed line as described above, it is considered that the length of the feed line should always be optimized as a countermeasure. However, in general, the length of the power supply line is not always guaranteed to be flexible. Actually, a wireless device includes an information processing circuit, a power supply circuit, and an interface unit with the outside in addition to the wireless circuit. Considering the overall optimum layout, the length of the feed line connecting the antenna and the wireless unit is not necessarily required. In some cases, it cannot be given priority.

As described above, it is very difficult to obtain a desired radiation pattern with an antenna that is integrated with a wireless device and is further incorporated.

[0014]

As described above,
In the prior art, it has been very difficult to obtain a desired radiation pattern with an antenna integrated with a radio and further integrated. There was also a method of using a dipole antenna to reduce the influence of unnecessary radiation from the housing.However, when the antenna is close to the housing, the unnecessary radiation from the feeder and the housing increases, and the desired There is a problem that a radiation pattern cannot be obtained.

[0015]

According to the antenna device of the present invention, a metal housing, a radio device built in the metal housing, a half-wave dipole antenna mounted close to the surface of the housing, and the antenna and the radio device are connected. And a reactance element connecting between the power supply line and the metal case.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the structure of an antenna device according to one embodiment of the present invention.

In the figure, 101 is a dipole antenna, 102
Is a metal housing, 103 is a coaxial feeder, and 104 is a wireless circuit. The dipole antenna 101 includes a housing 102
Are arranged so as to be parallel to one side of. The housing is a conductor and serves as a shield for the radio circuit. The feed line 103 is connected to the housing 1 from the feed point of the dipole antenna 101.
02, and a reactance element 105 is disposed between the power supply line and the housing 102 so as to connect them. This reactance element 1
05 is composed of, for example, a capacitor, an inductance, and a variable capacitor.

FIG. 2 is a graph showing the result of calculating a pattern using the radio antenna model constructed based on FIG. The length of the feed line 103 is 0.4
At two wavelengths, the reactance element 105 is mounted at a position of 0.33 wavelength. The graph shows the radiation pattern on the same plane as FIG. As is apparent from this figure, the radiation pattern changes by changing the value of the reactance element 105, and the radiation pattern can be changed to a desired radiation pattern. For example, when the value of reactance element 105 is -j100Ω, feed line 1
This is a pattern having almost the same shape as the pattern without 03 (FIG. 5). Further, the directivity of the radiation pattern is directed to the positive direction and the negative direction on the y-axis (−j2
00Ω and j25Ω). In other words, the antenna device of the present proposal can restore the radiation pattern changed by the feeder line 103 to a desired radiation pattern.

The principle of the present proposal will be briefly described with reference to FIG. In the description of the prior art in this specification, it is described that the radiation from the radiation mode (c) in FIG. 4 changes depending on the length of the feeder line 103, thereby changing the radiation from the entire antenna device. Was. In the proposed invention,
The reactance element 105 is connected to the power supply line 10 as shown in FIG.
2 and the metal casing 103. The equivalent circuit of (a) can be expressed as (b) of FIG. That is, a)
In the state of (1), an image current corresponding to the current flowing through the surface of the power supply line 102 is generated on the surface of the metal housing near the power supply line 102.
With 03, it can be considered that two parallel lines are formed. Further, since the portion surrounded by the broken line in (b) functions as a distributed constant circuit, it can be equivalently expressed as a reactance element as in (c). The value of the reactance in this portion is determined by the arrangement position of reactance element 105. To summarize the above, FIG. 3A can be equivalently expressed as two reactance elements connected in parallel as in FIG. Therefore, by adjusting both the arrangement position of the reactance element 105 and the value of the reactance element 105, the radiation pattern in the state shown in FIG. 4C is changed. You can get it.

FIG. 8 shows another embodiment of the present invention. This figure shows a simple configuration of the reactance element 105. In the figure, 220 is a coaxial line covered with a dielectric,
225 is a clasp of the cable, and 226 is a metal screw for fixing the clasp to the metal housing 102. FIG. 9 is an enlarged view of the coaxial wire 220 covered with a dielectric material, and shows the internal structure in an easy-to-understand manner. 224 is a dielectric covering the outer conductor 223.

FIG. 10 is a diagram showing the clasp 225 and its specification state. FIG. 10A is an enlarged view of the clasp 225. The clasp 225 is wound around the coaxial wire 220 as shown in FIG.
Stopped by the metal casing 102.

Here, the reason why the clasp works as a reactance element will be described. FIG. 10C is a sectional view when FIG. 10B) is cut off by the clasp 226. Feeding line 2
The outer conductor 223 of the 20
5 and insulated. Further, FIG. 10D) is an enlarged view of the outer edge portion, and the outer conductor 223 and the clasp 2 are insulated.
25 act as electrodes with each other, whereby the outer conductor 223, the clasp 225 and the dielectric 223
A capacitor will be formed. That is, this part equivalently functions as a reactance element. Further, by adjusting the width of the clasp, the capacitance of the capacitor can be changed, and the value of the reactance can be adjusted. FIG.
Are increased, and the value of the capacitance is increased.

[0024]

As described above, in the dipole antenna arranged close to the housing of the radio device, the radiation pattern is changed by the unnecessary current on the housing and the feed line, and the desired pattern is obtained. There was a problem that a pattern could not be obtained. However, as proposed in the present invention, by connecting a reactance element between the feeder line and the metal housing, and adjusting the value of this element, the radiation pattern radiated from the feeder line portion can be changed to be desired. A radiation pattern can be formed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of an antenna of the present invention.

FIG. 2 is a graph showing characteristics of the antenna of the present proposal.

FIG. 3 is a diagram for explaining the operation of the proposed antenna.

FIG. 4 is a schematic diagram showing a radiation mode of a conventional antenna.

FIG. 5 is a graph showing a radiation pattern when there is no feed line;

FIG. 6 is a graph showing a radiation pattern when a feed line is mainly used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Dipole antenna 102 Case 103 Feeding line 104 Radio circuit 105 Reactance element 220 Coated wire 226 Metal screw 225 Clasp 221 Inner conductor 222 Dielectric 223 Outer conductor 224 Dielectric

Claims (1)

[Claims] 1. A metal housing, a radio device built in the metal housing, a half-wavelength dipole antenna mounted close to a surface of the metal housing, and a power supply line connecting the antenna and the radio device. An antenna device including a reactance element that connects between the power supply line and the metal housing.