Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-04-13
2002-11-05
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06476767
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a microstrip-line chip antenna element suitable for microwave wireless communications apparatuses such as portable wireless phones and wireless local area network LAN, and an antenna apparatus comprising such a chip antenna element and a communications apparatus comprising such an antenna apparatus.
PRIOR ART
In microwave wireless communications apparatuses, particularly portable communications apparatuses such as cellular phones, monopole antennas and microstrip-line antennas are generally used for achieving miniaturization and reduction in thickness. A microstrip-line antenna element put into practical use at present has, as described in Japanese Patent Laid-Open No. 10-209740, a radiation electrode formed on an upper surface of a dielectric, rectangular parallelepiped body, high-frequency electric signal being fed from below.
FIG. 36
schematically shows the structure of this microstrip-line antenna element. When operated as an antenna, the antenna element is mounted onto a printed circuit board having a ground conductor
96
, and a feeding line
94
is disposed on a lower surface of the printed circuit board. An electric line force F is generated between an open end
91
of a radiation electrode
90
and the ground conductor
96
, whereby a magnetic flux is generated in a perpendicular direction to the radiation electrode
90
, efficiently emitting electromagnetic wave to the space. The length D of the radiation electrode
90
is usually about ¼ of a wavelength, generating a magnetic flux in a perpendicular direction to the radiation electrode
90
at resonance, the direction of an electric line force F being in perpendicular to the magnetic flux emitted from the end surface
91
of the radiation electrode
90
. With respect to the shape of the radiation electrode
90
in a plan view, various shapes such as circle, pentagon, etc. are proposed in addition to rectangle, though vertically or horizontally symmetric shapes are mostly used.
Antennas used for portable communications apparatuses should be small, efficient in radiation and substantially omni-directional. For this purpose, a small antenna element has a structure in which a radiation electrode is disposed on an upper surface or inside of an insulating substrate, because the wavelength of electric current flowing through the radiation electrode is made shorter by influence of the insulating substrate. Because the same radiation effect can be kept even though the radiation electrode is made shorter, the antenna can be miniaturized. The necessary length d of the antenna is represented by the following equation (1):
d=c
/(2
f
0
∈r
) (1),
wherein ∈r is a specific dielectric constant of the insulating substrate, f
0
is a resonance frequency, and c is the velocity of light.
As is clear from the equation (1), the length d of an antenna element having a microstrip-line structure can be made shorter as the insulating substrate has a larger specific dielectric constant ∈r at a constant resonance frequency f
0
. In other words, with a substrate having a high specific dielectric constant ∈r, a small microstrip-line antenna element can be obtained with the same performance. Because a small antenna element is indispensable particularly for cellular phones, etc., the development of smaller, high-performance antenna elements has been desired.
There is an inverted F antenna as an antenna applicable to portable communications apparatuses other than the microstrip-line antenna. The inverted F antenna is constituted by an F-shaped antenna conductor comprising a bent portion at an end connected to a ground conductor plate, a center bent portion connected to a feeding line via a gap. Because the antenna conductor needs only to be as long as about ¼ of a wavelength, it may be regarded as an antenna having a shape obtained by laterally expanding the microstrip-line antenna element.
The conventional microstrip-line antenna element has the following disadvantages in miniaturization. That is, when the radiation electrode is made smaller by increasing the specific dielectric constant ∈r of an insulating substrate, a resonance bandwidth of the resonance frequency f
0
becomes narrower, whereby the antenna is operable only in a narrow frequency range.
This means the restriction of a frequency range available for communications, not preferable for antenna for cellular phones, etc. Accordingly, to develop a practically useful antenna, it should have wide bandwidth characteristics. Particularly in multi-frequency antennas using two or more frequencies, the phenomenon of narrowing a bandwidth is a serious problem, which cannot be controlled only by the properties of the insulating substrate.
A resonance bandwidth BW, a resonance frequency f
0
and a Q value representing the performance of an antenna at resonance meet the following relation:
BW=f
0
/Q
(2).
The height H a microstrip-line antenna element equal to the thickness of its insulating substrate and the Q value meet the following relation:
Q∝∈r/H
(3).
Known as a small microstrip-line antenna is an antenna having a radiation electrode divided to two parts at center, one end of the divided radiation electrode is electrically connected to a ground conductor plate (Hiroyuki Arai, “New Antenna Engineering,” Sogo-Densi Shuppan, pp. 109-112). Because the length of the radiation electrode is about ¼ of a wavelength at resonance frequency, this antenna is as small as about 50% of the conventional antenna.
Japanese Patent Laid-Open No. 11-251816 discloses a microstrip-line antenna element operable at an expanded bandwidth with a radiation electrode formed on an edge region (adjacent two surfaces) of the substrate. When this microstrip-line antenna element is assembled in a portable communications apparatus, however, a radio wave emitted mainly from the end of the radiation electrode induces electric current in a nearby casing or in conductors on the circuit board, making the current-induced conductors function as an apparent antenna. Thus, the characteristics of this antenna is variable depending on ambient environment, causing impedance mismatching at a feed point and the variation of radiation directivity.
Further, because electronic circuit parts mounted near the antenna element are affected by a high-frequency electromagnetic wave emitted from the end of the radiation electrode, there arise problems of deteriorating communications performance such as noises, errors, irregular oscillation, etc. Conventional means for coping with such problems was to fully separate nearby circuit parts from the antenna element, failing to increase the mounting density of parts near the antenna, thus largely hindering the miniaturization of communications apparatuses.
OBJECT OF THE INVENTION
Accordingly, an object of the present invention is to provide a small microstrip-line antenna element having a sufficient Q value with high gain and broad bandwidth.
Another object of the present invention is to provide an antenna apparatus comprising such an antenna element mounted onto a circuit board with improved mounting density without affecting nearby parts.
A further object of the present invention is to provide a communications apparatus such as a portable information terminal, etc. comprising such an antenna apparatus.
SUMMARY OF THE INVENTION
As a result of investigation by simulation to achieve the miniaturization and increase in bandwidth of an antenna element, it has been found: (1) the antenna element can equivalently be provided with a plurality of resonance circuits by properly designing the shapes of a radiation electrode go and grounding electrodes; (2) radiation directivity can be achieved with high gain and without unnecessary field emission by properly designing the arrangement of electrodes; and (3) an area occupied by the antenna can be reduced while providing good antenna characteristics by properly designing the mounting of an antenna onto a groun
Aoyama Hiroyuki
Kikuchi Keiko
Sugiyama Yuta
Tonomura Kenichi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hitachi Metals Ltd.
Le Hoang-anh
LandOfFree
Chip antenna element, antenna apparatus and communications... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Chip antenna element, antenna apparatus and communications..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chip antenna element, antenna apparatus and communications... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2945667