Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1999-08-04
2001-09-04
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S859000
Reexamination Certificate
active
06285341
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a low profile antenna, and more particularly to a mobile antenna suitable for satellite communications.
BACKGROUND OF THE INVENTION
In the last thirty years satellite services have come to play an increasingly important role in telecommunications. Antenna design is an important part of a satellite system. One type of satellite antenna suitable for satellite communications is the quadrifilar helix first disclosed by Kilgus (Resonant Quadrifilar Helix Design, Microwave Journal, December 1970). This antenna consists of four helical windings fed in phase quadrature.
This configuration exhibits many performance characteristics well suited to satellite communications, namely, a hemispherical omnidirectional radiation pattern with excellent circular polarization throughout the radiation pattern, as well as compactness and simplicity. Omnidirectional coverage is desirable to allow the earth terminal to see the satellite regardless of its relative orientation to the satellite. The geometries of this design employ a resonant matching network. Hence the operating bandwidth is typically narrow.
Recently, higher performance mobile satellite services have emerged which require increased antenna gain. Due to the location of population of the earth, the areas that many service providers have allocated high priority to are in the northern hemisphere. As a result the important converge profile is located at 20 to 60 degrees in elevation with respect to the earth terminal.
In prior art, the increase in gain at these elevations is accomplished by increasing the height of the quadrifilar helix antenna. The compact quadrifilar helix antenna, which can exhibit nearly uniform hemispherical gain, does not provide enough gain at 20 to 45 degrees in elevation for the high performance systems. More energy can be directed to the low elevation angles by increasing the height of the antenna. The tradeoff between size and performance leads to a significant increase in the height of the antenna. As low profile structures are highly desirable for mobile communications, this is a considerable disadvantage.
An object of the invention is to overcome this disadvantage.
SUMMARY OF THE INVENTION
According to the present invention there is provided a low profile antenna comprising a helical loop having a plurality of turns, said turns being closely spaced so as to provide a strong coupling therebetween and thereby force the current in said closely spaced turns to be in phase.
since the current on all the turns of the loop is forced to be phase due to the strong coupling, each of the turns of the loop behaves like a travelling wave antenna.
By modeling the helical loop antenna on the basis of the travelling-wave loop antenna operation, the radiation properties of higher order modes of the loop antenna can be exploited to direct the radiated energy of the helical loop antenna towards low elevation angles. The multiple turns of the helical loop antenna eliminate the need for a matched load on the end of the wire, increasing the radiation efficiency and thus the gain of the antenna.
The antenna is primarily intended for satellite communications, but it could be used for other applications where high gain in the 20 to 60 degree elevation is desired.
The invention eliminates the need to trade-off height for the low elevation angle coverage required by mobile satellite antenna systems. This is accomplished with the use of a helical loop that is short in height but large in diameter.
REFERENCES:
patent: 4489276 (1984-12-01), Yu
patent: 4494117 (1985-01-01), Coleman
patent: 5734353 (1998-03-01), Van Voohies
patent: 5896113 (1999-04-01), O'Neill, Jr.
patent: 6011524 (2000-01-01), Jervis
patent: 6028558 (2000-02-01), Van Voorhies
patent: 97 41695 (1997-11-01), None
patent: 98 15029 (1998-04-01), None
patent: 98 15028 (1998-04-01), None
Hisamatsu Nakano et al: “Extremely Low-Profile Helix Radiating A Circularly Polarized Wave” IEEE Transactions On Antennas and Propagation, US, IEEE Inc. New York, vol. 39, No. 6, p. 754-757 XP000209548 ISSN: 0018-926X—the whole document.
Cooper Michael
Roscoe David
(Marks & Clerk)
Tran Chuc
Vistar Telecommunications Inc.
Wong Don
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