Communications: radio wave antennas – Antennas – Spiral or helical type
Patent
1994-12-23
1997-03-18
Hajec, Donald T.
Communications: radio wave antennas
Antennas
Spiral or helical type
H01Q 136
Patent
active
056127073
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a helical antenna which may be manipulated to change characteristics of the antenna. More particularly, but not exclusively, the invention relates to a "scanning mode" helix antenna in which the antenna may be manipulated to steer the beam of the antenna. The antenna of the invention is particularly suitable for use in communications applications in the 800 to 5,000 MHz range.
BACKGROUND TO THE INVENTION
Steerable beam helix antenna are used for mobile communications, including land, sea and air-borne terminals, satellite communications and/or in situations where inference sources are suppressed by manipulation of the shape of the antenna to vary its radiation pattern.
The helix antenna is well-known, as are its many modes of operation; see for example the book "antennas" by John De Kraus 2nd edition, McGraw Hill Book Company, 1950 (herein referred to as "Kraus") at page 273. The particular mode of operation depends upon parameters of the antenna, such as the number of helical conductors, the pitch angle of the conductors, antenna length and, to a lesser extent, the conductor size. One mode of operation is the so called "scanning mode" of operation. In this mode the helix is of electrically small diameter (about 0.1 wavelengths), of large pitch angle (about 60 degrees) and has several turns. This mode is referred to as the "scanning mode" as for a fixed antenna construction the beam of the antenna can scan by varying the frequency of operation. This technique may be used in radar and direction finding equipment.
Alternatively, when operating at a nominally constant frequency, the radiation pattern of the antenna can be scanned by altering parameters of the antenna.
U.S. Pat. Nos. 3,524,193; 3,510,872; 4,475,111; 3,699,585; 3,836,979 and 4,068,238 disclose helical antennas of adjustable length. However, these antennas are foldable, collapsible or telescoping only for the purpose of enabling transportation in a more compact state.
U.S. Pat. No. 4,087,820 discloses a short wave antenna which allows the height of the antenna to be varied whilst the antenna pitch remains constant. This allows the antenna to be turned to resonance within a wide frequency range. The antenna is however extremely high and the construction would be unsuitable for antenna having a large pitch angle, especially when used in mobile applications.
U.S. Pat. No. 5,146,235 discloses a UHF antenna in which the number of turns or the height of the antenna may be adjusted. The conductor is a helical spring and its height and number of turns may be adjusted by mechanical means. Such a structure would be unsuitable for an antenna having a large pitch angle. The spring would tend to resonate, which would produce distortion, especially in multifilar antennas. The problem would be particularly apparent when the antenna was mounted to a moveable vehicle.
DISCLOSURE OF THE INVENTION
It is an object of the invention to provide a scanning mode antenna suitable for use in mobile communications applications wherein parameters of the antenna may be manipulated to vary the radiation pattern of the antenna, or to at least provide the public with a useful choice.
According to the invention there is provided a helix antenna comprising a conductor secured to a dielectric sheet, the dielectric sheet being furled so that the conductor is of generally helical form, said dielectric sheet being furlable and unfurlable to alter the characteristics of the antenna.
The antenna may be rotationally or axially furled and unfurled or a combination of both methods may be used. A plurality of conductors may be provided on the dielectric sheet for multifilar applications. Multiple dielectric sheets having one or more conductor thereon may be interleaved to optimise the relative positions of the conductors. The conductors are preferably positioned so that they are evenly spaced in the axial direction of the antenna and closely radially spaced (i.e. lying substantially along the outer surface of a cylinder).
In a preferred embo
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"Antennas, " John De Kraus, 2nd Edition, McGraw Hill Book Company, 1950, p. 273.
Jenness Colin A.
Scott Neil L.
Vaughan Rodney G.
Hajec Donald T.
Industrial Research Limited
Phan Tho
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