Communications: radio wave antennas – Antennas – With lumped reactance filter in active antenna
Reexamination Certificate
1999-12-15
2001-10-09
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With lumped reactance filter in active antenna
C343S802000
Reexamination Certificate
active
06300913
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an antenna, and in particular an antenna having two resonant frequencies.
Wireless portable communication devices typically have small antennas to allow ease of use of the communication devices. However, the size of the antenna typically results in the antenna having a narrow operational frequency band.
Some communication devices, however, are required to operate over different frequency ranges which differ significantly from one another. For example, a dual mode radiotelephone may be required to operate over more than one cellular telephone system. One such cellular system is Global System for Mobile Telecommunications (GSM) which operates over the 890 to 960 MHz frequency band while another cellular system that the radiotelephone may be required to operate on is the Personal Communication Network (PCN) which operates over the 1710 to 1880 MHz frequency band.
Antennas designed for radiotelephones are typically made of simple cylindrical coil or helical antennae or whip antennae made from a straight conductor. Where its electrical length, which should be a specific part of the wavelength of the radio frequency used, determines the resonant frequency of an antenna. For radiotelephones the size of the antenna is minimised by choosing an electrical length which is a fraction of the wavelength used. For a helical and whip antennae the electrical length should preferably be 3&lgr;/8 or &lgr;/4, where &lgr; is the wavelength. However, the characteristics of these antennae do not allow the radiotelephone to operate satisfactorily over two different frequency ranges which differ significantly from one another.
One solution to this problem has been to provide radiotelephones with two interchangeable antennae which have different resonant frequencies. Where the user attaches to the radiotelephone the antenna which corresponds to the frequency range of the system in use at any one time. However, continued exchange of the antenna can result in damage to the antenna connector and may cause contact disturbance. Further, a user could easily misplace the antenna currently not in use.
A second solution to this problem has been to attach, during manufacture, two separate antennae to the radiotelephone, each antenna designed to operate over different frequencies. Where the user or radiotelephone selects the antenna according to which system the radiotelephone is operating in. However, this solution increases the complexity of the radiotelephone design and thus increases the manufacturing costs of the radiotelephone.
European Patent 0 825 672 A1 describes an antenna which can operate at two separate frequencies. However, the antenna has three distinct specially designed elements which interact in a complex manner to provide the two frequencies. As such, this increases the complexity of the antenna design.
European Patent 0 593 185 A1 describes an antenna which has two separate resonating elements mounted within a common housing which allows the antenna to operate at two separate frequencies.
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention there is provided an antenna for a mobile communication device, the antenna comprising a housing; a first resonator element with a first feed point having a first resonant frequency; and a second resonator with a second feed point having a second resonant frequency, wherein the housing has an outer portion supporting the first resonator element and an inner portion supporting the second resonator element, the inner portion being positioned within the outer housing such that the first and second feed points are coupled to provide a feed point for the antenna thereby allowing the antenna to operate with the first resonant frequency and the second resonant frequency.
This invention has the advantage that the first and second resonator elements are supported by a housing that allows certain characteristics of the element to be accurately determined (e.g. the pitch of a resonator element). This invention also allows the antenna to be easily assembled.
This invention provides a dual frequency antenna where each resonant frequency is dependent upon an isolated resonator element. Hence, the antenna frequency characteristic can be determined by simply summing the individual resonator elements frequency characteristics. Therefore, one resonator element can be independently designed to operate over the frequency range of one cellular system and the other resonator element can be independently designed to operate over another cellular system.
Preferably the first resonator element is mounted on the outer portion. This ensures that the housing is interposed between the first and second resonator element. This can aid the de-coupling of the two resonator elements.
Preferably the second element is housed within the volume circumscribed by the outer portion of the housing.
Therefore, with this invention it is possible to design a dual frequency antenna which has substantially the same dimensions as a conventional antenna.
It is desirable that the outer and inner portions of the antenna housing are releasably connected.
This simplifies the manufacturing process and allows a user to replace either the outer or inner portion should it be necessary for the radiotelephone to operate over a different cellular system.
Preferably each of the first or second elements are formed as a helical electrical element.
By using helical elements this has the advantage that the overall size of the antenna can be minimized.
Each electrical element is preferably a monopole. This has the advantage that the length of the element is half that of a corresponding dipole.
By increasing the number of housing portions and correspondingly the number of resonator elements it is also, however, possible for the antenna to have more than two operational frequencies.
In addition a third resonator element with a third feed point having a third resonant frequency is mounted on the antenna housing such that the third feed point is coupled to the first and second feed points to provide a feed point for the antenna thereby allowing the antenna to operate with the first resonant frequency, the second resonant frequency and the third resonant frequency.
For a better understanding of the present invention and to understand how the same may be brought into effect reference will now be made, by way of example only, to the accompanying drawings, in which:
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Nokia Mobile Phones Ltd.
Perman & Green LLP
Tran Chuc D
Wong Don
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