Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-10-17
2004-08-31
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06784843
ABSTRACT:
TECHNICAL FIELD
The present invention relates to multi-resonance antennas, and more particularly, relates to a broadband multi-resonance antenna suitable for a portable information terminal.
BACKGROUND ART
Recently, there has been a demand for linking information terminals such as cellular phones, portable mobile terminals, and stationary terminals having communication functions with one another by wireless communication using the high frequency 1 to 5 GHz band. One example of such a communication method uses a center frequency of 2.45 GHz and a bandwidth of approximately 100 MHz. The method wirelessly links nearby information terminals. Data signals, audio signals, and video signals can be transmitted and received in bulk.
Wireless transceivers incorporated into or added to these information terminals are required to be miniaturized as much as possible. Concerning antennas mounted on the wireless transceivers, so-called miniature surface-mounted antennas which are miniaturized as much as possible are required.
The electrical length of an antenna is determined by the frequency of the operating electromagnetic waves. In order to ensure satisfactory antenna characteristics using a small antenna, it is necessary to form a radiation electrode on a dielectric base member with a high relative dielectric constant. The size of the antenna is generally determined by the relative dielectric constant and the volume of the base member. In an antenna using a dielectric base member with a high relative dielectric constant, the radiation electrode can be shortened relative to the operating frequency. Accordingly, the electrical Q factor is improved, whereas the effective frequency band is narrowed.
In order to broaden the frequency band, there is a broad-band linear antenna described in Japanese Unexamined Patent Application Publication No. 6-69715.
As shown in
FIG. 12
, the antenna contains a feeding element
3
on the top surface of a circuit board
1
formed of polyimide. The feeding element
3
is a radiation electrode strip with a power feeder
2
. The antenna also contains a parasitic element
5
which differs in length from the feeding element
3
. The parasitic element
5
is a radiation electrode strip with a ground
4
at one end thereof. The feeding element
3
and the parasitic element
5
are arranged side-by-side in parallel to each other. In the antenna, electric-field coupling is established between the feeding element
3
and the parasitic element
5
, and the feeding element
3
feeds power to the parasitic element
5
, thus causing the feeding element
3
and the parasitic element
5
to resonate at multiple frequencies. As a result, a broad frequency band is achieved.
Regarding the foregoing antenna arranged as described above, the length of the radiation electrode of the feeding element
3
is limited to approximately 410 mm, and the length of the radiation electrode of the parasitic element
5
is limited to approximately 360 mm. It is thus difficult to configure a portable and miniature antenna. The antenna is not configured to adjust multi-resonance matching between the feeding element
3
and the parasitic element
5
.
In other words, in the foregoing antenna, it is difficult to form a plurality of radiation electrodes on the surface of a dielectric base member with a small volume so as to satisfy the conditions for optimal multi-resonance matching. Specifically, when the radiation electrode of the feeding element and the radiation electrode of the parasitic element are arranged on the same principal surface of the dielectric base member, the distance between the feeding element and the parasitic element becomes narrow. Thus, excessive electric-field coupling occurs. As shown in
FIG. 13
, a resonance frequency f
1
of the feeding element and a resonance frequency f
2
of the parasitic element are separated from each other, and hence the feeding element and the parasitic element do not resonate at multiple frequencies. When the radiation electrodes are shortened to force multi-resonance to occur, as shown in
FIG. 14
, satisfactory matching cannot be achieved in resonance at one side. Thus, the antenna is in a single resonance state at the resonance frequency f
1
, and the optimal multi-resonance matching cannot be achieved.
In order to achieve multi-resonance matching, the electric-field coupling between the feeding element and the parasitic element is required to be weakened. When the principal surface of the dielectric base member is widened, the size of the base member itself is increased. It is thus impossible to obtain a miniaturized surface-mounted antenna. When the width of each radiation electrode is reduced too much, inductance components vary widely, and the resonance characteristics become unstable. It is thus difficult to mass-produce the antenna. Alternatively, the radiation electrode of the feeding element and the radiation electrode of the parasitic element can be arranged on the principal surface and an end surface of the dielectric base member, respectively. When the distance between the feeding element and the parasitic element becomes too large, satisfactory electric-field coupling cannot be achieved. When screen-printing the radiation electrodes, it is necessary to print two sides, namely, the principal surface and the end surface. Thus, the number of printing steps is increased, and the manufacturing cost is increased.
DISCLOSURE OF INVENTION
In order to solve the foregoing problems, it is an object of the present invention to provide a multi-resonance between a feeding element and a parasitic element by suppressing excessive electric-field coupling between the feeding element and the parasitic element.
In order to achieve the foregoing object, the present invention solves the problems using the following arrangement. Specifically, a multi-resonance antenna of the present invention includes a feeding element including a first radiation electrode and a feeding electrode for feeding power to the first radiation electrode; a parasitic element including a second radiation electrode arranged next to the first radiation electrode; a ground electrode arranged opposite to an open end of each of at least one of the first radiation electrode and the second radiation electrode with a predetermined gap therebetween; and an electric-field deflector for suppressing electric-field coupling between the feeding element and the parasitic element, the electric-field deflector being formed in a portion where each open end and each ground electrode are opposed to each other.
According to the present invention, the electric-field deflector (s) is provided in one or both of portions where each open end of the feeding element and the parasitic element and each ground electrode are opposed to each other. Thus, the electric field is concentrated at the opposing portion between the open end and the ground electrode, and the electric-field coupling between the open end and the ground electrode is strengthened. In contrast, the electric-field coupling in the vicinity of the open ends of the feeding element and the parasitic element is weakened. Thus, the electric-field coupling between the feeding element and the parasitic element can be optimally adjusted, and satisfactory multi-resonance of the feeding element and the parasitic element can be caused to occur.
In other words, the electric field leaking from the vicinity of the open ends of the feeding element and the parasitic element where the electric field becomes the strongest is reduced, thus weakening the electric-field coupling between the feeding element and the parasitic element. As a result, the feeding element and the parasitic element can be caused to satisfactorily resonate at multiple frequencies.
In the multi-resonance antenna of the present invention, the first radiation electrode and the second radiation electrode may be radiation electrode strips which are arranged approximately parallel to each other. Preferably, the electric-field deflector substantially encloses the electric field generated between t
Ishihara Takashi
Kawahata Kazunari
Miyata Akira
Nagumo Shoji
Onaka Kengo
Keating & Bennett LLP
Le Hoang-anh
Murata Manufacturing Co. Ltd.
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