Communications: radio wave antennas – Antennas – With radio cabinet
Patent
1996-03-14
2000-03-07
Wong, Don
Communications: radio wave antennas
Antennas
With radio cabinet
343815, 343841, 343873, H01Q 124
Patent
active
060346388
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to antenna arrangements for use in portable communications devices. Embodiments thereof specifically relate to physically small antennas, directional antennas, and to electronically steerable antennas.
Portable or hand-held communications devices are to be taken to include cellular mobile telephones, radio pagers and two-way radios (walkie-talkies). Other applications for antennas embodying the invention are to be found in geophysical (such as ground probing radar and borehole tomography) and other radar systems (such as anti-collision radar for moving vehicles).
DESCRIPTION OF THE PRIOR ART
Antennas are used in a wide variety of applications both as transmitters and receivers of electromagnetic energy. In many of these applications it is desirable to maximise the directivity of the antenna. In the prior art this has been achieved by techniques such as the use of reflector screens (e.g. parabolic dish antennas, corner reflectors), reflector elements (e.g. curtain arrays, Yagi parasitic elements), slow wave structures (e.g. Yagi antennas) and multiple antenna arrays.
By way of a specific example, in mobile cellular telecommunications it is desirable to improve the directivity of the antenna of a mobile handset for reason of reducing the power consumption, hence lessening demand on the battery. Improved directivity also has benefit in increasing the range of mobile cellular telephones in relation to a cell site, and in reducing the interference between adjacent cells.
There also presently are concerns about the safety of mobile cellular telephones on users. Human tissue is a very good conductor of electricity, even at high frequencies, and it has been suggested that brain tumors 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 recommend maximum exposure to electromagnetic radiation received by, and propagated from, antennae. A directional antenna tends to minimise the radiation directed towards the user, and from this point of view is most desirable.
Shielding too is an established technique to reduce exposure. There is a trade-off, however, in that the proximity of a shield to an antenna can adversely affect the efficiency of the antenna. As a rule of thumb, a shield must be located at least 1/4 wavelength away from the antenna.
In other applications, such as geophysical systems, severe deep fading caused by multipath interference occurs when two signals are incident on the same antenna with approximately equivalent field strengths and with approximately 180.degree. phase difference. A steerable directional antenna can minimise the effect of such fading.
An example of an antenna structure that has consideration of the issues of directivity and steerability is that disclosed in U.S. Pat. No. 4,700,197 issued to Robert Milne.
Size too is an important consideration, particularly as electronic communications devices become ever more miniaturized. To some extent the reduction of the size of antennas is antagonistic to achieving improved 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 the antennas may be relatively large in more than one direction if directionality is required. Large antenna installations also are undesirable for reasons of appearance and mechanical stability.
DISCLOSURE OF THE INVENTION
The invention, in one aspect, is directed to an antenna which is directional and also compact.
Therefore, the invention discloses a compact directional antenna arrangement comprising: structure, the antenna elements being electrically connected to respective switching means, and the antenna arrangement being operable by the respective switching means to selectively switch one or more of the anten
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Lu Jun W.
O'Keefe Steven G.
Thiel David V.
Griffith University
Ho Tan
Wong Don
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