Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-01-31
2004-03-16
Nguyen, Hoang V. (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000, C343S873000, C343S895000
Reexamination Certificate
active
06707427
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a chip antenna and an antenna unit including the same, and more particularly to a mono-pole antenna having a reduced size.
Herein, a mono-pole antenna is an antenna grounded at such a portion that a dipole antenna has a maximum current amplitude at a middle, and forming electric images by grounding portions of the dipole other than the middle. A dipole antenna has a radiation pattern having polarities at opposite ends which polarities are opposite to each other, and having a peak in a direction perpendicular to the dipole antenna.
2. Description of the Related Art
Though a lot of electronic devices have been reduced in both size and weight, an antenna is not yet remarkably reduced in size. This is because that an antenna would have a high gain if it had a wide area, whereas an antenna would have a small gain if it was reduced in size, and accordingly, had a small area. If reduced in size, an antenna would have a deteriorated impedance characteristic, and in particular, would have a reduced input resistance. As a result, there is caused a problem that power fed from a communication device is reflected at an input of an antenna, and resultingly, power radiated as electromagnetic waves is reduced.
With rapid popularization of a personal computer and a cellular phone, an antenna is requested to be fabricated in a smaller size and have higher performance in order to satisfy a need of communication between perso computers or communication between personal areas through bluetooth.
As an antenna which can be reduced in size with a length thereof being kept in a certain length, there is known an antenna having a mianda line or a helical line, that is, a mianda-shaped antenna (also referred to as “meander-shaped” in the art) or a helically shaped antenna.
For instance, Japanese Unexamined Patent Publication No. 9-55618 has suggested a chip antenna having a mianda line. The suggested chip antenna is illustrated in FIG.
1
.
The chip antenna
100
is comprised of a rectangular-parallelopiped substrate
101
comprised of a multi-layered dielectric layers, and an electrical conductor
104
formed on a surface
107
of the substrate
101
.
The electrical conductor
104
has an end
102
through which power is fed to the chip antenna
100
, and an open end
103
, and has a mianda-structure having 10 corners. The electrical conductor
104
is formed on the surface
107
of the substrate
101
by printing, evaporation, adhering or plating. The mianda-shaped electrical conductor
104
extends from a first edge
101
a
to a second edge
101
b
extending in parallel with the first edge
101
a.
The substrate
101
has a first side surface
108
and a second side surface
109
oppositely facing the first side surface
108
. A power-feeding terminal
105
is formed on the first side surface
108
, and a fixation terminal
106
is formed on the second side surface
109
. The electrical conductor
104
is electrically connected to the power-feeding terminal
105
through the end
102
, and the substrate
101
is fixed onto a circuit board (not illustrated) on which external circuits are fabricated, through the fixation terminals
106
.
It is necessary to apply an intensive current to an antenna for radiating electromagnetic waves therefrom. A current is generally applied to an antenna at a power-feeding point. In addition, it is necessary for the power-feeding point to have such a length that a radiation resistance is equal to 50 ohms, in order to match the antenna to a power-feeder. The rest of the antenna other than the power-feeding point is necessary only for generating an intensive current at predetermined frequency by resonating the rest of the antenna.
From the above-mentioned standpoint, Japanese Unexamined Patent Publication No. 2000-188506 has suggested an antenna which attempts to shorten a length of the antenna by replacing the rest of the antenna other than a power-feeding point with a reactance device. The antenna suggested in the Publication is illustrated in FIG.
2
.
As illustrated in
FIG. 2
, a linear electrical conductor pattern
112
is electrically connected at one end to a power-feeding point
113
, and at the other end to a reactance device
114
. The reactance device
114
is comprised of an electrical conductor having a first length in a length-wise direction which first length is longer than a second length perpendicular to the first length, such as a mianda-shaped electrical conductor. The reactance device
114
is mounted on an upper surface of a printed substrate
110
in an area where a ground pattern
111
is not formed in both upper and lower surfaces of the printed substrate
110
. The reactance device
114
and the linear electrical conductor
112
extend perpendicularly to each other, and forms reverse-L-shaped configuration.
However, the above-mentioned Japanese Unexamined Patent Publication No. 9-55618 is accompanied with the following problems.
In the Publication, the chip antenna
100
is resonated by introducing electromagnetic waves into the electrical conductor
104
having a length equal to a quarter of a wavelength of the electromagnetic waves. To this end, the electrical conductor
104
has to be reciprocated many times. This results in an increase in a length of the electrical conductor
104
, causing a bar in fabricating the chip antenna
100
in a small size.
In addition, the electrical conductor
104
has to be bent a lot of time in order to accommodate a longer electrical conductor
104
into a smaller space, resulting in a smaller space between adjacent electrical conductors
104
. Thus, electromagnetic coupling between adjacent electrical conductors
104
is strengthened, causing an increase in both radio-frequency loss and dielectric loss in the electrical conductor
104
and a current running on a surface of the electrical conductor
104
. As a result, both a radiation efficiency and a gain of the chip antenna
100
would be reduced.
Since a mono-pole antenna is located in an open space, the mono-pole antenna is likely to be electromagnetically coupled to a metal located therearound, and hence, the antenna characteristic is likely to change in dependence on surroundings. Accordingly, it is necessary for a mono-pole antenna to be designed to have a wide band width taking misregistration in mounting a mono-pole antenna into consideration.
However, since the chip antenna
100
is intended to be reduced in size by shortening a space between adjacent electrical conductors
104
in the above-mentioned Japanese Unexamined Patent Publication No. 9-55618, electromagnetic energy to be generated between electrical conductors
104
would be increased. The thus increased electromagnetic energy would cause a band width narrower, resulting in that the antenna characteristic is readily varied by surrounding metal parts existing around the chip antenna
100
.
The antenna suggested in the above-mentioned Japanese Unexamined Patent Publication No. 2000-188506 is accompanied with the following problems.
The antenna includes the reactance device. However, since the reactance device is a separate part, the use of the reactance device would increase a total cost of fabricating the antenna.
In addition, it would be quite difficult to accurately analyze an operation of the antenna, if the antenna is comprised of two different parts. This may result in that the antenna would not operate in a designed manner.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems in the conventional antennas, it is the first object of the present invention to provide a chip antenna and an antenna unit both of which have a wide band width though they are small in size, are hardly influenced by surrounding parts, and can be readily mounted on a substrate.
The second object of the present invention is to provide a chip antenna and an antenna unit both of which presents high radiation efficiency and high gain with a small loss.
The third object of the present invention is to provide a chip antenna and an a
Konishi Takayoshi
Tsukiji Takehiko
McGinn & Gibb PLLC
NEC Microwave Tube, Ltd.
Nguyen Hoang V.
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