JPH04183101A - Antenna circuit - Google Patents

Abstract

PURPOSE:To miniaturize an antenna circuit so as to be easily produced and to obtain a wide band characteristic by folding toward the ground surface and a feeder section one end of a conductor surface that is used as the antenna element and connecting the tip of the conductor surface to the other section of the conductor surface so as to form a loop. CONSTITUTION:Ene ond (d) of antenna element 11 is folded to the metallic case, to a feeder section, and further folded inside twice so that the tip of the antenna element 11 connects the antenna element at a position farther from the feeder section for antenna element 11 to form an antenna loop. The upper surface (e) of the metallic case 3 acts as the ground surface. GaP D2 between the folded section (d) of antenna element 11 and the upper surface (e) of metallic case 3 generates a capacity, and if the folded section (d) and the upper surface (e) have the same resonance frequency, the area of the capacity is reduced. Further, since the area that generates the capacity is wide, the gap may be made large and the dimension precision becomes moderate. Furthermore, since a loop is added to the tip of the antenna element, the change in reactance relative to the resonance frequency becomes moderate and the band characteristic spreads over a wider band.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to reduce the size of antenna circuits built into mobile communication equipment, etc. so that they are easy to manufacture and have broadband characteristics, and one end of the conductor surface is connected to the ground plane. The conductor surface is folded back toward the power feeding section, and the tip of the folded section is connected to a part of the conductor surface.

[Field of Industrial Application] The present invention relates to an antenna circuit built into a mobile communication device or the like.

In recent years, in the field of mobile communications, there has been active development of terminal equipment that people carry around, such as cordless telephones, pagers, and mobile phones. Since these devices are meant to be carried by humans, making them smaller and lighter is an important issue.

[Conventional technology]

There is a whip antenna that has been used for a long time as an antenna circuit used in these portable devices. However, this type of antenna has the disadvantage that it is a rod-shaped antenna or protrudes from the main body, so it is easily damaged when the device is dropped or hits something, and it also gets in the way. Many types of antennas are also used.

Figure 3 shows one of the built-in antennas known as "inverted F antennas" that have been used in the past. FIG. 3(a) is a perspective view, and FIG. 3(b) is a side view seen in the direction of the arrow in FIG. 3(a).

In FIG. 3, the antenna element 1 is provided in parallel at a predetermined height from the top surface of the metal case 3, which is the ground plane, and is connected to one side of the metal case 3, and near this connection point. It is connected to an internal electric circuit (not shown) via a power supply line provided in the main body.

Generally, this type of antenna is considered to be a modification of a slot antenna, and its resonant frequency is determined by the total circumference length, and is the frequency at which the length ranges from λ to λ/2.

For example, if this type of antenna is manufactured in the 900 MHz band, an antenna element with an outer circumference (2X(I!+w)) or about 170 am is required. Further, the height h of the antenna element 1 from the top surface of the metal case 3 is required to be about 10 mm due to restrictions on its gain and bandwidth. If the above-mentioned whip antenna is used with a length of λ/2, the same performance can be achieved with a total length of 170 mm and a diameter of about 1 to 3 mm, so it cannot be said that the antenna in Figure 3 is smaller. hard.

One possible method for downsizing the antenna circuit shown in FIG. 3 is to provide a capacitance between a part of the antenna element 1 and the ground to lower the resonant frequency without changing the height h.

Figure 4 shows a conventional antenna circuit using such a method, in which the end of the antenna element 1 is bent downward at a right angle, and the antenna element is placed on the side opposite to the side connected to the antenna element on the top surface of the metal case 3. A protruding portion parallel to the bent portion a is provided to provide a capacitance due to the gap D1.

FIG. 5 shows another conventional antenna circuit which has been miniaturized. In this conventional example, a notch C is made in the antenna element l to increase the circumferential length of the antenna element and lower the resonant frequency. In other words, the same resonant frequency can be obtained with smaller antenna elements.

[Problem to be solved by the invention]

If the antenna circuit of FIG. 4 is to be significantly miniaturized (for example, by 1/3), the value of the capacitance provided locally will be a considerably large value, and the resonant frequency will be determined almost entirely by this capacitance value. Then, in order to increase the capacity, gap D
, becomes considerably small, and its dimensional accuracy becomes strict, making manufacturing difficult. Furthermore, the band characteristics of the antenna are narrow band characteristics because the area of the antenna element is reduced.

In the antenna circuit shown in Figure 5, there is no manufacturing problem because the resonant frequency is lowered without adding any capacitance, but the band characteristics are narrow because the area of the antenna element l is reduced. be.

An object of the present invention is to miniaturize the device so that it is easy to manufacture and has a wide band characteristic.

[Means to solve the problem]

In the present invention, one end of the conductor surface that becomes the antenna element is folded back toward the ground plane side toward the power feeding section. Furthermore, the tip of the conductor surface is connected to another part of the conductor surface to form a loop. [Operation] Capacitance is generated by the gap between the folded part and the ground plane, and if the resonant frequency is the same, the area will decrease.

Since the area of the part that generates the capacitance is wide, the gap can be large, and the dimensional accuracy becomes loose.

Also, since a loop is added to the tip of the antenna element,
Changes in reactance with respect to frequency become more gradual, and the band characteristics become wider.

〔Example〕

FIG. 1 is a diagram showing an antenna circuit according to an embodiment of the present invention.

In FIG. 1(a), one end d of the antenna element 11 is folded back toward the power feeding part on the side of the metal case, and further folded back inward, and the tip is connected at a position far from the power feeding part of the antenna element 11, and the loop is formed. is formed. The upper surface e of the metal case 3 acts as a ground plane. A capacitance is generated by the gap D2 between the folded portion d of the antenna element 11 and the upper surface e of the metal case 3, and the area decreases if the resonance frequency is the same.

FIG. 2 is a graph showing the relationship between the gap (Dl, D2) and the resonant frequency in the conventional circuit shown in FIG. 4 and the embodiment of the present invention shown in FIG. 1(a). Approximately 250M in the conventional circuit shown in Figure 4
Was there a fluctuation in Hz/mm (slope of the straight line on the graph)?
In the embodiment of the present invention shown in FIG. 1(a), the frequency was improved to about 55 MHz/mm.

FIG. 1(b) shows another embodiment.

In this embodiment, the antenna element 11 is folded back only once and is easier to manufacture than the antenna circuit of FIG. 1(a). However, the size shown in FIG. 1(a) can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an antenna circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the gap and the resonant frequency, and FIGS. 3 to 5 are diagrams showing the conventional antenna circuits 1 to 3. 1.11...Antenna element 2...Feeding line 3...Metal case Antenna circuit according to an embodiment of the present invention Relationship between gap and resonant frequency Figure 1
Figure 2 1al fb
) 1st conventional antenna circuit 3rd factor

Claims (2)

[Claims] (1) A part of the conductor surface (11) that is provided parallel to the ground plane and becomes the antenna element is connected to the ground plane, and a high frequency signal is fed to the other part of the conductor plane (11). In the antenna circuit, one end of the conductor surface (11) is folded back toward the ground plane side toward the power feeding section, and the tip of the folded portion is folded back toward the conductor surface (11).
) is connected to a part of the antenna circuit. (2) The antenna circuit according to claim 2, wherein the tip of the folded portion is further folded back in a direction opposite to the feeding portion.