Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-04-10
2003-06-17
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S846000, C343S702000
Reexamination Certificate
active
06580396
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates to a dual-band antenna, and more particularly, to a dual-band antenna with three resonators.
2. Description of the Prior Art
Radiotelephones generally refer to communications terminals that provide a wireless communications link to one or more other communications terminals. Radiotelephones are utilized in variety of different applications, including cellular phones, satellite communications systems, and so forth. Radiotelephones typically have an antenna for transmitting and/or receiving wireless communications signals.
Radiotelephones and other wireless communications device are undergoing constant miniaturization. Thus, there is an increased demand in small antennas that can be used as internally mounted antennas for radiotelephones. In addition, it is becoming desirable for radiotelephones to be able to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile communication) is a digital mobile telephone system that typically operates at a low frequency band, such as between 880 MHz and 960 MHz. DCS (Digital Communications system) is a digital mobile telephone system that typically operates at a high frequency band, such as between 1710 MHz and 1880 MHz. Since there are two different frequency bands, radiotelephone service subscribers who travel over service areas employing different frequency bands may need two separate antennas unless a dual-band antenna is used. Additionally, as the amount of data being sent through wireless communications signals increases, the bandwidth of the frequency band at which the antenna operates is required to increase as well.
Please refer to FIG.
1
.
FIG. 1
is a perspective view of a prior art antenna
10
disclosed in U.S. Pat. No. 5,926,139. The prior art antenna
10
comprises a conductive ground plate
14
, a conductive first plate
12
set above the ground plate
14
, a conductive connector
18
having two opposite ends connected to the ground plate
14
and the first plate
12
, and a signal feeder
19
having two terminals. One terminal of the signal feeder
19
is a grounded terminal electrically connected to the ground plate
14
, and the other terminal is a signal terminal
16
electrically connected to the first plate
12
. Data signals, which are transmitted from the antenna
10
or received by the antenna
10
are fed through the signal feeder
19
. The connector
18
is a short pin for connecting the first plate
12
and the ground plate
14
. For operating within two frequency bands, the first plate
12
of the prior art antenna
10
has two resonating regions
17
A,
17
B, each corresponding to one frequency band at which the antenna
10
operates. In addition, European Pat. No.EP0997974A1 discloses an antenna that is similar to the antenna
10
having the first plate
12
on which two resonating regions are disposed.
Please refer to FIG.
2
.
FIG. 2
is a correlation diagram between reflection and frequency of the prior art antenna
10
. The horizontal axis represents the frequency, and the vertical axis represents the absolute value of reflection. The reflection of an antenna can be used to evaluate a bandwidth of a frequency band at which the antenna operates. Generally, a frequency range under reflection of −10 decibel (dB) is used to be the frequency band at which the antenna operates. As shown in
FIG. 2
, the two resonating regions
17
A,
17
B of the antenna
10
(shown in
FIG. 1
) respectively correspond to two frequency bands A1, A2 of the antenna
10
distributed around frequencies fa, fb so that the antenna
10
can operate within the two frequency bands A1, A2.
Since the prior art antenna
10
is planar, it is very suitable for embedding into portable wireless communications devices, such as a cellular phone, so as to rid the device of protruding antennas. However, the prior art antenna
10
has a disadvantage of narrow bandwidth, especially a narrow bandwidth at a higher frequency. For example, the specification of a frequency band distributed around 1800 MHz must have a bandwidth of 170 MHz. However, the antenna
10
with regular dimensions does not have enough bandwidth to meet the requirements of a digital mobile phone system that operates at a frequency band of 1800 MHz. Thus, in order to increase the bandwidth of the antenna
10
, the dimensions of its corresponding resonating region are required to be enlarged. Unfortunately, enlarging the dimension of the resonating region will expand the physical area and the physical volume of the antenna
10
. Expanding the size in this way will adversely affect the ability to miniaturize a cellular phone.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to provide a dual-band antenna with three resonators to solve the above-mentioned problem.
According to the claimed invention, the antenna comprises a conductive ground plate, a conductive first plate, a conductive connector, and a signal feeder. The conductive first plate is set above the ground plate, and a fixed distance separates the first plate and the ground plate. The first plate comprises first, second, and third resonance regions with respective dimensions corresponding to wavelengths of first, second, and third frequencies at which the antenna operates. The first plate also comprises a connection region connected to the first, the second, and the third resonance regions. The conductive connector has two opposite ends respectively connected to the ground plate and the connection region. The signal feeder has two terminals respectively electrically connected to the ground plate and the first plate. The first, the second, and the third frequencies are different and respectively correspond to first, second, and third frequency bands of the antenna. The second frequency is close to the third frequency such that the second frequency band and the third frequency band are partially overlapped to cause the second frequency band and the third frequency band to merge.
It is an advantage of the claimed invention that the dual-band antenna with three resonators is capable of substantially broadening the bandwidth to overcome the prior art shortcomings.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
REFERENCES:
patent: 6366243 (2002-04-01), Isohatala et al.
patent: 6473044 (2002-10-01), Manteuffel et al.
patent: 199 83 824 (2000-06-01), None
patent: 1 026 774 (2000-08-01), None
patent: 1 079 463 (2001-02-01), None
patent: 1 168 491 (2002-01-01), None
patent: 1 202 386 (2002-05-01), None
Chi Mei Communication Systems, Inc.
Hsu Winston
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