Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
1999-12-22
2001-09-11
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S815000, C343S841000, C343S873000
Reexamination Certificate
active
06288682
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to antennas for use in portable communications devices and particularly to a directional antenna assembly.
DESCRIPTION OF THE PRIOR ART
The prior art in relation to antennas covers a broad spectrum. Antennas are used in a wide variety of applications both as transmitters and receivers of electromagnetic energy. One important consideration in many of these applications is the directivity of the antenna. It is generally desirable to maximise the directional properties of the antenna. This has been achieved in the prior art arrangements by techniques such as reflector screens, multiple antenna arrays, electronically steerable antennas and reflector elements.
Optimised antenna directivity is of particular concern in the area of mobile cellular communications. Improved directivity increases the range of mobile cellular telephones in relation to a cell site, and reduces the interference between adjacent cells. A reduction in power consumption, and hence less demand on the mobile telephone battery, also results from improved directivity of the antenna.
There are also presently concerns about the safety of mobile cellular telephones for users. Human tissue is a very good conductor of electricity, even at high frequencies, and it has been suggested that health problems may occur with prolonged use of such devices for reason of the antenna being very close to the user's skull resulting in very high strength electromagnetic fields concentrated about the antenna penetrating the skull and damaging brain tissue. The IEEE has published Technical Standard No. C95.3 in relation to recommended maximum exposure to electromagnetic radiation from antennas. A directional antenna can minimise the radiation directed towards the user, and from this point of view is most desirable.
Reduced exposure to mobile telephone radiation can also be achieved through the use of shielding devices. Such shields seek to protect the user by reducing the amount of radiation that is emitted towards the head of the user. However, there is a trade-off in that the absorbed energy is not used in transmission, thus reducing the overall efficiency of the mobile telephone. A further disadvantage of this method is that there is a certain amount of microwave energy that is diffracted around the edges of the shield. This diffracted energy reduces the effectiveness of the shield and therefore reduces the amount of protection that is given to the mobile telephone user.
The overall size of the antenna apparatus is another important consideration, particularly as electronic communications devices become ever more miniaturised. Large antenna apparatus are undesirable for reasons of portability, mechanical stability and appearance. Size is also an important consideration in achieving increased antenna directivity. In free space, the distance between radiating elements/reflectors is a substantial part of one free space wavelength of the radiation in air. This means that the antennas may be relatively large in more than one direction if directionality is required.
Reference also can be made to International Publication No. WO 94/28595 (equivalent to Australian Patent No. 679992) that discloses forms of physically small antennas.
It is a principal object of the present invention to provide a directional antenna that provides protection to the user against electromagnetic radiation. It is a further, secondary object of the invention to provide a directional antenna that is physically small compared with prior art arrangements.
SUMMARY OF THE INVENTION
Therefore, the invention discloses a directional antenna assembly arrangement comprising:
a dielectric structure having a surface; and
an array of wire antenna elements positioned within or on the surface of the dielectric structure, at least one of the wire antenna elements being active and the remainder being passive.
The dielectric structure can be formed from a material having a dielectric constant of greater than four, or preferably greater than ten. Switching means, connected to the antenna elements is operable to selectively switch one or more of the antenna elements to be active, while the passive elements are switched to be electrically connected to ground or in a circuit condition. The switching can be directed by a direction of greatest signal strength. The antenna elements can be in a symmetric array. Further, the dielectric structure can be a hollow or solid cylinder, or a rectangular body.
In accordance with another aspect of the present invention, there is provided an antenna assembly including at least:
a substantially planar structure of dielectric material, and an array of at least three antenna elements mounted on a common surface of said structure, the array including an active element having a feed connection point, a first passive element being parallel with and spaced apart from the active element, and a second passive element being parallel with and spaced apart from the first active element in an opposed direction to said first passive element.
In one advantageous form, said antenna elements are substantially elongate. Furthermore, said second passive element has a transverse portion substantially L-shaped, and of greater length than the active element to act as a reflector, and said L-shaped second passive element is arranged to at least partially surround the active element. The first passive element can be equal or lesser length than the active element to act as a director. The second passive element passes through said dielectric structure and extend over at least a portion of the opposed surface of the structure. Furthermore, the feed point of the active element is electrically connected with a centre conductor of a coaxial feed line, being at one end of the active element. The second passive element is electrically connected to a signal ground conductor of the coaxial feed line.
The invention further discloses a communications device having an antenna assembly as described immediately above. In a preferred embodiment, the antenna assembly is mounted from the communications device in a manner such that the plane of the array is perpendicular to a user's head, with the second passive element being proximate thereto. The antenna assembly is mounted from the communications device in a manner such that the antenna assembly can pivot about its base.
Embodiments of the invention provide an antenna that has less absorption by the user's head, increased signal strength due to improved directionality and a minimal change in antenna impedance with the user's head position than those in the prior art. This then results in a reduction in power consumption of the electronic equipment to which the antenna is coupled (eg. a cellular telephone). There further is an associated health benefit, since the electromagnetic energy absorbed by the user's head will be at a lower level than in the prior art.
One other specific advantage is that, because the antenna assembly can be directly substituted for prior art antennas in portable communications devices, the foregoing benefits are gained without a need to replace the otherwise expensive device. In one example, a physically smaller antenna having improved directivity can be substituted for an existing antenna in a cellular telephone. Thus the telephone casing can further be reduced in size to provide the user with greater portability.
A further specific advantage is that the antenna assembly is capable of being arranged so as to fold down alongside a telephone casing further reducing the overall size of the device and further providing greater portability.
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patent: 3560978 (1971-02-01), Himmel et al.
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patent: 4170759 (1979-10-01), Stimple et al.
patent: 4356492 (1982-10-01), Kaloi
patent: 4367474 (1983-01-01), Schaubert et al.
patent: 4379296 (1983-04-01), Farrar et al.
pat
Lu Jun Wei
O'Keefe Steven Gregory
Thiel David Victor
Griffith University
Ho Tan
Jenkins & Wilson, P.A.
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