Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-12-24
2001-07-10
Hunter, Daniel (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S269000, C455S575100
Reexamination Certificate
active
06259930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to antennas for portable telephones and, in particular, to a portable telephone antenna circuit having reduced susceptibility to the human body and a method for realizing the same.
2. Description of the Related Art
A portable telephone, such as a cellular telephone or a cordless telephone, generally employs a helical antenna, a &lgr;/4 antenna, a &lgr;/2 dipole antenna or a &lgr;/2 monopole antenna. However, the helical antenna is rarely employed in a portable telephone, since it has poor antenna characteristics. For example, a significant amount of power is converted to heat due to the high inductance of the helical antenna.
Moreover, the &lgr;/4 antenna, the &lgr;/2 dipole antenna and the &lgr;/2 monopole antenna, which are commonly employed in a portable telephone, are susceptible to current leakage through the human body, as shown in
FIGS. 1A
to
1
C.
FIGS. 1A
to
1
C are diagrams illustrating current leakage caused when the various antennas applicable to a portable telephone come into contact with the human body. The leakage current flows through the user's body, when the user holds the portable telephone to his/her ear to converse using the telephone. An increase in the leakage current brings about a reduction in the coverage area of the portable telephone. Referring to
FIGS. 1A
to
1
C, the &lgr;/4 antenna (see
FIG. 1A
) has the largest current leakage, the &lgr;/2 dipole antenna (see
FIG. 1C
) has the second largest current leakage, and the &lgr;/2 monopole antenna (see
FIG. 1B
) has the least largest current leakage. That is, among the antennas of
FIGS. 1A
to
1
C, the &lgr;/2 monopole antenna can offer the widest coverage area to the portable telephone. For this reason, the &lgr;/2 monopole antenna is widely employed in portable telephones.
Nevertheless, when the portable telephone employing the &lgr;/2 monopole antenna comes into close contact with the human body, the standing wave ratio (SWR) increases, thus deteriorating the antenna characteristics. The increase in the SWR results in a reduction in the coverage area of the portable telephone.
Of course, the antenna for a portable telephone can be designed in fill consideration of such antenna characteristics. In such a case, however, the antenna is relatively longer in length than the body of the portable telephone. For example, in the case when the &lgr;/2 monopole antenna is employed in a 900 Mhz cordless telephone, the antenna should be about 16 cm, which is much longer than the body of an ordinary cordless telephone.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a portable telephone antenna circuit with reduced susceptibility to the human body and a method for realizing the same.
It is another object of the present invention to provide a portable telephone antenna circuit for preventing an increase in a standing wave ratio when the portable telephone antenna comes in contact with the human body, and a method for realizing the same.
It is still another object of the present invention to provide an antenna circuit for increasing a coverage area of a portable telephone and a method for realizing the same.
It is further still another object of the present invention to provide an antenna circuit capable of contributing to a reduction in length of an antenna for a portable telephone, and a method for realizing the same.
In one aspect of the invention, there is provided an antenna circuit for a portable telephone. The antenna circuit includes: an RF (Radio Frequency) module having an impedance of about 50&OHgr;; an antenna having an impedance of about 450 to 500&OHgr;, for radiating an RF signal output from said RF module into the air and outputting an RF signal captured from the air to said RF module; and a matching circuit connected between said RF module and said antenna to match an impedance characteristic of said RF module with an impedance characteristic of said antenna, wherein said matching circuit includes an inductor having an inductance of about 24 mH connected between an output of said RF module and said antenna and a capacitor having a capacitance of about 1 pF connected between said antenna and a ground, said capacitor being coupled in parallel to said inductor.
In another aspect of the invention, there is provided a method for embodying an antenna circuit for a portable telephone including an RF module having a first impedance, an antenna having a second impedance and a matching circuit connected between the RF module and the antenna to match the first impedance with the second impedance. In the method, the Smith chart is searched for real resistance component values of the antenna and the RF module, so as to designate the real resistance component value of the antenna as a value of a first position and the real resistance component value of the RF module as a value of a second position. A parallel capacitance value and a serial inductance value for moving the first position to the second position are calculated by using an admittance chart and an impedance chart of the Smith chart, respectively. The inductor having the calculated inductance value is connected between an output of the RF module and the antenna, and the capacitor having the calculated capacitance value is connected between the antenna and a ground, the capacitor being coupled in parallel with the inductor. The first impedance is about 50&OHgr; and the second impedance is about 450 to 500&OHgr;. The inductor has an inductance of about 24 mH and the capacitor has a capacitance of about 1 pF. The antenna is a &lgr;/2 monopole antenna which is about 11 cm long.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.
REFERENCES:
patent: 4730195 (1988-03-01), Phillips et al.
patent: 4806944 (1989-02-01), Jacomb-Hood
patent: 4992752 (1991-02-01), Cioffi
patent: 5668560 (1997-09-01), Evans et al.
patent: 5778308 (1998-07-01), Sroka et al.
patent: 5784687 (1998-07-01), Itoh et al.
patent: 5936583 (1999-08-01), Sekine et al.
Dilworth & Barrese LLP
Hunter Daniel
Nguyen Thuan T.
Samsung Electronics Co,. Ltd.
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