Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1999-06-30
2001-08-07
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S702000, C343S873000
Reexamination Certificate
active
06271803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chip antenna and to radio equipment including such a chip antenna. More particularly, this invention relates to a small-sized and broad-bandwidth chip antenna and the radio equipment including such a chip antenna.
2. Description of the Related Art
Up to now, in radio equipment such as a portable telephone terminal, a pager, etc., there have been used a wire antenna represented by a monopole antenna. When the radio equipment is made small-sized, the antenna is required to be of small size. However, in the case of a monopole antenna, as the length of a radiation conductor becomes &lgr;/4 (&lgr;: wavelength of the resonance frequency), for example, about 4 cm in the case of an antenna having 1.9 GHz as its resonance frequency, the antenna itself comes to be too large, which means a problem because the need for small size cannot be satisfied.
To overcome the above problem, the present applicant has proposed a chip antenna as shown in
FIG. 12
herein and in Japanese Unexamined Patent Publication No. 8-316725. The chip antenna
50
comprises a basic body
51
of a rectangular solid made up of dielectric ceramics containing barium oxide, aluminum oxide, and silica as its main components, a conductor
52
spirally arranged inside the basic body
51
, and a feeding terminal
53
for applying a voltage to the conductor
52
formed on the surface of the basic body
51
. One end of the conductor
52
is led out to the surface of the basic body
51
and connected to a feeding terminal
53
. Further, the other end of the conductor
52
is made a free end
54
inside the basic body
51
.
In the above construction, a small-sized chip antenna
50
has been realized by means of the spirally disposed conductor
52
.
Generally, the resonance frequency f and bandwidth BW of a chip antenna are expressed as in the following equations:
f=
1/(2&pgr;·(
L·C
)
½
) (1)
BW=k·
(
C/L
)
½
(2)
where L is the inductance of the conductor, C is the capacitance produced between the conductor and ground, and k is a constant.
FIG. 13
shows the frequency characteristic of the reflection loss of the chip antenna
50
of FIG.
12
. From this drawing, it is understood that the bandwidth of a chip antenna
50
giving two or more of VSWR (voltage standing wave ratio) is about 225 MHz around the center frequency of 1.95 GHz.
However, in the case of the above-mentioned chip antenna, as the conductor is spirally arranged in order to make the chip antenna small-sized, the inductance L of the conductor becomes large. As a result, as clearly understood from Equation (2) there is a problem that as the inductance L of the conductor increases the bandwidth BW is narrowed.
SUMMARY OF THE INVENTION
To overcome the above described problems, the present invention provides a chip antenna of small size and having a large bandwidth and radio equipment including such a chip antenna.
One preferred embodiment of the present invention provides a chip antenna comprising a basic body made of a ceramic material; a first conductor and a second conductor respectively disposed at least either inside or on the surface of the basic body so as to be close to each other; a feeding terminal for applying a voltage to the first conductor, disposed on the surface of the basic body, and connected to the first conductor; and a grounding terminal disposed on the surface of the basic body and connected to the second conductor.
According to the above structure and arrangement, because at least inside or on the surface of the basic body one end of the first conductor is connected to the feeding terminal and one end of the second conductor is connected to the grounding terminal and disposed so as to be close to each other, leakage current generated from the first conductor flows through the second conductor.
Consequently, as the first and second conductors resonate at the same time because of the leakage current, only the feed to the first conductor causes the chip antenna to have a plurality of resonance frequencies, which makes it possible for the chip antenna to be small-sized, of broad bandwidth, and of low power dissipation.
In the above described chip antenna, at least one of the first and second conductors may be connected to a free terminal, and the free terminal may be disposed on the surface of the basic body.
According to the above described structure and arrangement, because the free terminal to which the other end of at least one of the first and second conductors is connected is disposed on the surface of the basic body, the capacitance generated between the first and second conductors of the chip antenna and the ground of the radio equipment mounted with the chip antenna is able to be increased. Therefore, it becomes possible to lower resonance frequencies and broaden bandwidth.
In the above described chip antenna, the first and second conductors may be disposed so as to be parallel to each other.
According to the above described structure and arrangement, the first and second conductors may be enlarged and accordingly the line length of the first and second conductors is lengthened.
Therefore, because the inductance values of the first and second conductors may be made large, it becomes possible to lower the resonance frequencies and widen the bandwidth.
In the above described chip antenna, the first and second conductors may be disposed substantially spirally.
According to the above described structure and arrangement, because first and second conductors are spirally formed by adjustment of the pitch of the coil of the first conductor and the pitch of the coil of the second conductor, it is possible to easily adjust the inductance values of the first and second conductors. Therefore, it becomes possible to easily adjust the resonance frequencies and bandwidth.
In the above described chip antenna, the first and second conductors may be formed substantially in a meandering way.
According to the above described structure and arrangement, it is possible to lower the height of the basic body and accordingly it becomes possible to lower the height of the chip antenna.
Another preferred embodiment of the present invention provides radio equipment including any one of the above described chip antennas.
Because a small-sized and broad-bandwidth chip antenna is provided, radio equipment of small size and of broad bandwidth can be realized.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
REFERENCES:
patent: 5541616 (1996-07-01), Kawahata et al.
patent: 5668557 (1997-09-01), Kawahata
patent: 5870066 (1999-02-01), Asakura et al.
patent: 5903240 (1999-05-01), Kawahata et al.
patent: 6002366 (1999-12-01), Kawahata et al.
patent: 6023251 (2000-02-01), Koo et al.
Dakeya Yujiro
Kanba Seiji
Suesada Tsuyoshi
Tsuru Teruhisa
Watanabe Kunihiro
Le Hoang-anh
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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