Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-02-02
2002-09-17
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000, C343S873000, C343S895000
Reexamination Certificate
active
06452548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface mount antenna capable of transmitting and receiving signals (radio waves) in different frequency bands and also to a communication device such as a portable telephone including such an antenna.
2. Description of the Related Art
In recent years, it is needed to commercially provide a single terminal having a multi-band capability for use in plural applications such as GSM (Global System for Mobile communication systems), DCS (Digital Cellular System), PDC (Personal Digital Cellular telecommunication system), and PHS (Personal Handyphone System). To meet the above requirement, Japanese Unexamined Patent Application Publication No. 11-214917 discloses a multiple frequency antenna of the surface mount type capable of transmitting and receiving signals in different frequency bands.
In this antenna, as shown in
FIG. 22A
, a dielectric member
105
is disposed on a ground plate
101
, and a conductive plate
102
having a cut-out
106
is disposed on the upper surface of the dielectric member
105
. When a signal is supplied via a feeding line
104
, a current in a fundamental mode flows through the conductive plate
102
, along a path L
1
from the side of a short-circuiting plate
103
toward the opposite side, and a current in a high-order mode (third-order mode in this specific example) flows along a path L
3
. Thus, this antenna has a frequency characteristic such as that shown in FIG.
22
B and is capable of transmitting and receiving signals at two different frequencies: a resonance frequency f
1
in the fundamental mode; and a resonance frequency f
3
in the high-order mode.
Note that in the present description, the fundamental mode refers to a resonance mode having the lowest resonance frequency of those in various resonance modes, and the high-order modes refer to resonance modes having resonance frequencies higher than the resonance frequency in the fundamental mode. When it is necessary to distinguish the respective high-order modes from each other, they are denoted by a second-order mode, a third-order mode, and so on in the order of increasing resonance frequencies.
In the case where currents in the fundamental mode and a high-order mode are passed through the same conductive plate
102
from its one end to the opposite end as in the conventional antenna described above, the difference between the resonance frequencies in the respective modes is determined by the difference between the lengths of the current paths. In general, the distance from one end to the opposite end of the conductive plate
102
is determined on the basis of the fundamental mode such that it becomes substantially equal to one-quarter the effective wavelength
1
in the fundamental mode (in other words, the resonance frequency in the fundamental mode is determined by the above-described distance). In order to set the resonance frequency in a high-order mode to a desired value, it is required that the length of the current path in the high-order mode should be different by a corresponding amount from the length of the current path in the fundamental mode. In the conventional technique described above, a difference in current path length is created by forming the cut-out
106
at a location where the current in the high-order mode becomes maximum thereby changing the current path L
3
in the high-order mode so as to have a greater length required to set the resonance frequency f
3
in the high-order mode to the desired value.
In the conventional technique described above, because the same conductive plate
102
is used for resonance in both the fundamental mode and the high-order mode, the size of the antenna can be reduced compared with the size of an antenna in which resonance in the fundamental mode and resonance in the high-order mode are achieved using different conductive plates. However, in the conventional technique described above, it is required that the cut-out
106
should be formed in the conductive plate
102
, and thus the conductive plate
102
should be large enough to form the cut-out
106
. This makes it difficult to achieve a further reduction in the size of the antenna.
Furthermore, in the conventional technique described above, the current path in the high-order mode is curved by the cut-out
106
thereby increasing the length thereof. Therefore, the change in the length of the current path is limited within a small range determined by the change in the perimeter of the cut-out
106
(that is, the change in the shape of the cut-out
106
). Thus, it is difficult to set the difference between the resonance frequency in the fundamental mode and the resonance frequency in the high-order mode over a large range.
Furthermore, it is difficult to precisely control the resonance frequency in the high-order mode by adjusting the perimeter (shape) of the cut-out
106
, and thus it is difficult to efficiently produce and provide an antenna having high performance and high reliability.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to efficiently and economically provide a high-performance, high-reliability, small-sized surface mount antenna having features that the difference between the resonance frequencies in the fundamental mode and the high-order mode can be adjusted and set over a wide range, and both the resonance frequencies in the fundamental mode and the high-order mode can be precisely set to desired values, and also to provide a communication device including such an excellent antenna.
According to an aspect of the present invention, to achieve the above object, there is provided a surface mount antenna comprising: a dielectric substrate; and a radiating electrode formed on the dielectric substrate, one end of the radiating electrode being an open end, a feeding electrode or a ground terminal being formed on the opposite end of the radiating electrode, wherein the radiating electrode includes a first part having a small electrical length per unit physical length and a second part having a greater electrical length than the small electrical length, the first part and the second part being arranged in series along a current path between the one end and the opposite end.
According to another aspect of the present invention, there is provided a surface mount antenna comprising: a dielectric substrate; and a radiating electrode formed on the dielectric substrate, one end of the radiating electrode being an open end, a feeding electrode or a ground terminal being formed on the opposite end of the radiating electrode, wherein the radiating electrode includes a first part in which a resonance current in a fundamental mode becomes maximum and a second part in which a resonance current in a high-order mode becomes maximum, the first part and the second part being arranged in series along a current path between the one end and the opposite end; and at least one of the first and second parts includes an inductance component disposed in series in the current path.
Preferably, the inductance component is formed by a meander electrode pattern.
Alternatively, the inductance component may be formed by a capacitance component connected in parallel to the first part or the second part.
The radiating electrode may be formed by a helical electrode pattern, and the inductance component may be formed by reducing the distance between adjacent electrodes of the helical electrode pattern.
The inductance component may also be formed by a member having a high dielectric constant, the member being disposed in the first part or the second part.
The surface mount antenna may further comprise a non-feeding radiation electrode formed adjacent the radiating electrode, the resonance mode associated with the non-feeding radiation electrode forms multiple resonance in conjunction with at least one of the fundamental mode and the high-order mode associated with the externally-connected electrode.
The non-feeding radiation electrode may include a part having a small electrical le
Ishihara Takashi
Kawahata Kazunari
Nagumo Shoji
Onaka Kengo
Tsubaki Nobuhito
Chen Shih-Chao
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Wong Don
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