Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1999-09-28
2001-07-03
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000, C343S846000
Reexamination Certificate
active
06255994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inverted-F antenna and a radio communication system equipped with the antenna and more particularly, to an inverted-F antenna capable of operation in separate frequency bands or a wide frequency band formed by overlapping separate frequency bands, and a radio communication system necessitating the switching of its operating frequency band, such as a digital portable or mobile telephone.
2. Description of the Prior Art
In general, mobile radio communication systems such as cellular phones exchange communications or messages by using one of assigned frequency bands.
In recent years, as the popularity of cellular phones has explosively grown, the exchange of communications or messages has become difficult to be performed by using a single specified frequency band. To cope with this situation, cellular phones tend to be equipped with a function enabling the communication/message exchange using separate frequency bands or a single wider frequency band.
Conventionally, an inverted-F antenna has been widely used as a receiving antenna of a cellular phone, because it can be formed compact. However, an inverted-F antenna has a disadvantage that the operable frequency band is comparatively narrow. Therefore, various techniques have been developed to make it possible for an inverted-F antenna to cover separate frequency bands or a wider frequency band.
For example, the Japanese Non-Examined Patent Publication No. 10-65437 published in March 1998 discloses an improvement of an inverted-F antenna, which was invented by the inventor of the present invention, T, Saito. This improved antenna is shown in
FIGS. 1
to
3
.
As shown in
FIG. 1
, the prior-art inverted-F antenna
110
is comprised of a rectangular conductor plate
100
serving as a radiating element, a circuit board
106
serving as a ground conductor, and a dielectric spacer
107
placed between the plate
100
and the board
106
. The spacer
107
serves to fix the distance between the conductor plate
100
and the circuit board
106
at a specific value, thereby stabilizing the radiating characteristics of the antenna
110
. The long-side length of the conductor plate
100
is La and the short-side length thereof is Lb.
The conductor plate or radiating element
100
has a feeding terminal
102
for feeding a Radio-Frequency (RF) electric signal to the element
100
or receiving a RF electric signal therefrom, a grounding terminal
103
for grounding he element
100
to the board or ground conductor
106
, and a switching terminal
104
for switching the resonant frequency of the antenna
110
. The radiating element
100
and the terminals
102
,
103
, and
104
are formed by a conductor plate. The terminals
102
,
103
, and
104
are L-shaped and connected to a short-side of the rectangular radiating element
100
. The pitch between the terminals
102
and
103
is Lc. The pitch between the terminals
103
and
104
is Ld.
The lower part of the feeding terminal
102
, which is bent to be parallel to the circuit board
106
, is separated from the board
106
by a rectangular hole
106
a
penetrating the board
106
. Therefore, the feeding terminal
102
is not electrically connected to the board
106
. The lower part of the terminal
102
is electrically connected to a receiver circuit
108
in a radio section
120
of a cellular phone, as shown in FIG.
2
.
The lower part of the grounding terminal
103
, which is bent to be parallel to the circuit board
106
, is contacted with and electrically connected to the board
106
. The lower part is fixed to the board
106
by soldering. Thus, the terminal
103
is electrically connected to the ground.
The lower end of the switching terminal
104
, which is bent to be parallel to the circuit board
106
, is separated from the circuit board
106
by a rectangular hole
106
b
penetrating the board
106
. The lower end of the terminal
104
is electrically connected to one terminal of a switch
105
located in the hole
106
b
. The other terminal of the switch
105
is electrically connected to the board
106
.
The switch
105
is controlled by a controller circuit
109
in the radio section
120
of the cellular phone, as shown in FIG.
2
. If the switch
105
is turned off, the switching terminal
104
is electrically disconnected from the circuit board
106
, in which only the grounding terminal
103
is electrically connected to the board
106
. If the switch
105
is turned on, the switching terminal
104
is electrically connected to the circuit board
106
, in which not only the grounding terminal
103
but also the switching terminal
104
are electrically connected to the board
106
.
When the switch
105
is in the OFF state, the perimeter L of the rectangular radiating element
100
is given as
L=(2La+2Lb).
In this case, as shown in
FIG. 3
, the VSWR (Voltage Standing-Wave Ratio) is minimized at a frequency f
1
. In other words, the resonant frequency of the antenna
110
is f
1
.
On the other hand, when the switch
105
is in the ON state, the equivalent electric length L′ of the rectangular radiating element
100
is given as
L′≈(2La+2Lb−Ld).
In this case, as shown in
FIG. 3
, the VSWR is minimized at a frequency f
2
higher than f
1
. In other words, the resonant frequency of the antenna
110
is switched from f
1
to f
2
.
Thus, the resonant frequency of the prior-art antenna
110
can be changed between f
1
and f
2
and accordingly, the cellular phone having the antenna
110
is capable of covering two separate frequency bands or a wide frequency band formed by overlapping the two separate frequency bands.
Although not shown here, the Japanese Non-Examined Patent Publication No. 62-188504 published in August 1987 discloses a patch antenna comprising two relatively-movable radiating elements in addition to a ground plate. An RF signal is fed to the ground plate by a coaxial feeding line. The two radiating elements can be overlapped and contacted with each other, thereby changing the total volume or dimension of the radiating elements. Thus, the resonant frequency of the prior-art patch antenna disclosed in the Japanese Non-Examined Patent Publication No. 62-188504 can be changed, thereby covering two separate frequency bands or a wide frequency band formed by overlapping the two separate frequency bands.
Recently, there arises a problem that the available frequencies assigned to cellular phones tend to be short due to the increased traffic. To solve this problem, a consideration that new frequency bands are assigned to cell phones in addition to the conventional assigned frequency bands has been made, thereby relaxing or decreasing the congestion.
To cope with this consideration, the above-described prior-art antennas have the following problems.
With the prior-art antenna disclosed in the Japanese Non-Examined Patent Publication No. 10-65437, the resonant frequency is changed by connecting or disconnecting electrically the switching terminal
104
to or from the circuit board
106
. Therefore, to cope with a newly-assigned frequency band, another switching terminal needs to be provided to the radiating element
100
. However, the addition of the switching terminal is not always possible.
For example, if a newly-assigned frequency band (e.g., 830 MHz-band or near) is located between the two conventionally-available frequency bands (e.g., 820 MHz- and 880 MHz-bands) and near one of these two frequency bands, a newly-added switching terminal needs to be provided between the grounding terminal
103
and the switching terminal
104
and at the same time, it needs to be located near one of the terminals
103
and
104
. However, some specific limit exists in fabricating actually the prior-art antenna
110
with the detachable ground terminals. As a result, the prior-art antenna
110
is difficult to cope with the addition of a newly-assigned frequency band.
Also, in recent years, cellular phones have been becoming more compact and more lightweig
Chen Shih-Chao
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wong Don
LandOfFree
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