Communications: radio wave antennas – Antennas – With housing or protective covering
Patent
1997-09-02
2000-08-29
Le, Hoanganh
Communications: radio wave antennas
Antennas
With housing or protective covering
343795, 343700MS, 343713, H01Q 140, H01Q 132
Patent
active
061115525
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an antenna, and in particular to an antenna for receiving and/or transmitting electromagnetic radiation at radio frequencies, and to an antenna assembly.
1. Background of the Invention
Antennas, often referred to as aerials, are widely used for the reception and/or transmission of electromagnetic radiation, such as the reception of radio and television signals, and more recently the reception and transmission of mobile telephone communications.
2. Description of the Prior Art
The form of the antenna may be determined by the direction from which the signal is received (as well as the wavelength). Thus, antennas for television signal reception at a fixed building, where the direction from which the signal is received is known and is also fixed, are commonly directional, being of a complex (e.g. "yagi") shape. However, antennas for mobile radio reception (e.g. for motor vehicles, where the absolute and relative direction from which the signal is received may change and/or is unknown), must be of a non-directional type, and are commonly in the form of a long wire (or "whip"), which is substantially equally responsive to a signal received from any "generally horizontal" direction.
Alternative forms of antennas are also known, such as the self-supporting symmetrical arms disclosed in WO-88/09065, U.S. Pat. No. 2,656,463, U.S. Pat. No. 3,369,245 and others. The antennas disclosed therein all have enlarged plate-like reception/transmission elements, of significant thickness, and having a greater effective area (sometimes referred to as "capture" area) than whip antennas; they can be expected efficiently to receive signals of lower strength than corresponding whip antennas. The form of the elements can determine whether these alternative antennas are partly or substantially non-directional.
Despite the availability of above alternative antennas, known mobile telephone communication systems, both for hand-held mobile telephones, and also for mobile telephones located in motor vehicles, use whip antennas. This is, we believe, because of the relative cheapness of whip antennas to manufacture, and their well-known performance characteristics. It is known, for instance, for a vehicle with both a fitted radio and a mobile telephone unit to have a whip antenna for radio reception, and a separate whip antenna for the mobile telephone.
Whip antennas operate most efficiently if their effective length is an exact multiple of one quarter of the wavelength of the signal to be received (or the central wavelength if a range of frequencies is to be received). With most vehicle radio antennas, the received signal can range from around 200 KHz (long wave) to 100 MHz (F.M.). One quarter of the wavelength at these frequencies corresponds to approximately 375 m and 0.75 m respectively, so that a disadvantage of using whip antennas in vehicles is that most vehicle antennas in practice are shorter than even the lesser of these lengths, and so are unable to operate at maximum efficiency. However, the received signal strength, and the means developed over several years for the amplification of the signal by the radio unit, are such that adequate radio performance can usually be achieved.
The mobile telephone systems of which we are aware operate at higher frequencies than those for radio transmissions; in the U.K. for example the permitted range of the ETACS and GSM systems are 875-960 MHz. At these frequencies, one quarter of the wavelength is approximately 8.3 cm, and so most whip antennas can have an effective length equal to, or equal to a multiple of, this one quarter wavelength dimension, thus permitting the use of whip antennas for mobile telephone reception and transmission for these systems.
One disadvantage of the use of whip antennas for mobile telephone reception and transmission is that, both because of the efficiency of the whip antennas at the chosen frequency, and the relatively low signal strength of mobile telephone transmissions, the effective length of the whip antenna i
REFERENCES:
patent: 4746925 (1988-05-01), Toriyama
patent: 4860019 (1989-08-01), Jiang
patent: 4994820 (1991-02-01), Suzuki
patent: 5061944 (1991-10-01), Powers et al.
patent: 5568157 (1996-10-01), Anderson
patent: 5598168 (1997-01-01), Evans et al.
Le Hoang-anh
Oathout Mark A.
LandOfFree
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