Communications: radio wave antennas – Antennas – With means for moving directive antenna for scanning,...
Reexamination Certificate
1999-07-09
2001-07-10
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
With means for moving directive antenna for scanning,...
C343S771000
Reexamination Certificate
active
06259415
ABSTRACT:
FEDERALLY SPONSORED RESEARCH
(Not Applicable)
BACKGROUND OF THE INVENTION
This invention relates to economical beam-steered array antennas and, more particularly, to such antennas using mechanical beam steering in both azimuth and elevation, and configured to minimize antenna protrusion above the surface of an airframe.
Many types of antennas are available for aircraft and other airborne applications. Particular constraints in choice of antennas for use on commercial airliners, for example, are size, weight, protrusion above the surface and complexity of installation. Cost is also a significant consideration, particularly for applications not pertaining to aircraft operation or safety systems. Such applications include receiving of television programming for airline passenger entertainment.
For applications such as airborne reception of television signals from a satellite, the aircraft antenna must provide an antenna beam pattern which is steerable both in azimuth and in elevation. Beam steering in azimuth and elevation is necessary in order to permit the relatively narrow antenna beam to be pointed at the satellite, so that the antenna can successfully receive a relatively weak satellite signal.
The required capability could be provided by a flush-mounted, electronically steered phased-array antenna providing a fully steerable beam. However, such phased-array antennas are typically both expensive and complex, with respect to the electronic circuitry required. Thus, while electronically beam steered antennas may provide the required operating and low protrusion characteristics, cost is typically a constraint foreclosing use for applications such as entertainment systems. In contrast, mechanical arrangements, such as a rotatable antenna with dish reflector, are less expensive in so far as the basic antenna is concerned. However, in an aircraft installation a rotating dish typically has a large, above-surface protrusion requiring a large radome and resulting in unacceptable drag and other disadvantages which are controlling for aircraft installations. Alternatively, a dish antenna can be internally located below the aircraft skin to reduce radome height, however this requires cutting a large hole in the aircraft fuselage which substantially increases installation costs.
In an effort to provide an economical solution to this problem, U.S. Pat. No. 5,420,598, utilizes an array antenna providing a beam normal to the array face. The antenna is mechanically rotated and tilted to enable reception from satellites at any azimuth and over a range of elevation angles. However, with a beam normal to the array face, the antenna of this patent would have to be tilted from horizontal to a tilt angle of 70 degrees to enable reception from a satellite at 20 degrees elevation. To aim the beam at the satellite the antenna must be tilted to the complementary angle of the satellite elevation (90°−20°=70° array tilt). Thus, while objectives are partially met, low antenna protrusion (i.e., low array tilt) for reception from low elevation satellites is not possible with the antennas of this patent.
Objects of the present invention are, therefore, to provide new and improved types of mechanically beam-steered aircraft array antenna systems and such antenna systems providing one or more of the following capabilities and advantages:
fixed-tilt antenna beam from flat radiating array;
array tilt limited by provision of fixed-tilt beam;
20 to 70 degree elevation coverage with array tilt limited to 25 degrees;
no requirement for electronic beam steering;
mechanical beam steering by rotating and tilting the radiating array;
economical individual rotate motor and tilt motor configuration;
omnidirectional azimuth beam steering;
light weight, economical construction using linear array of fixed-focus slotted waveguide radiators; and
small installation hole in aircraft for motor drive, thereby minimizing installation cost.
SUMMARY OF THE INVENTION
In accordance with the invention, a mechanical beam steer array antenna system, to enable satellite reception from a moving vehicle with limited antenna protrusion uses a fixed-beam array antenna positioned by an elevation tilter. The fixed-beam array antenna includes a plurality of slotted waveguide radiator columns positioned in a side-by-side array, each radiator column having a series of radiating slots spaced along its length with the slots dimensioned to provide maximum signal reception at a fixed acute angle (&agr;) relative to column length, and a feed arrangement, without beam scan capability, coupled to the radiator columns to couple signals to provide a fixed antenna beam at the fixed acute angle (&agr;) above an aperture plane of the side-by-side array of radiator columns. The elevation tilter is arranged to mechanically tilt the array antenna to enable reception from a satellite at an elevation angle (&bgr;) by mechanically tilting the aperture plane to a tilt angle nominally equal to the angle complementary to the satellite elevation angle (90°−&bgr;), less the acute angle (&agr;). The antenna tilt angle (90°−&bgr;) required for reception from low-elevation satellites is thereby limited.
In the exemplary case where the slotted waveguide slots are dimensioned to provide maximum signal reception at a fixed acute angle (&agr;) of 45 degrees, the required antenna tilt is reduced to 25 degrees for reception from a satellite at 20 degrees elevation. This compares to a required antenna tilt of 70 degrees for such reception by a prior antenna with a beam normal to the antenna face.
Also in accordance with the invention, a method of mechanically steering an antenna beam for satellite reception from a moving vehicle, includes the steps of:
(a) providing a fixed-beam array antenna configured to provide an antenna beam at a fixed acute angle (&agr;) above an antenna aperture plane, the array antenna having no adjustable beam scan capability; and
(b) to receive signals from a satellite at an elevation angle (&bgr;) above horizontal, mechanically tilting the array antenna to position its aperture plane at a tilt angle nominally equal to the angle complementary to the satellite elevation angle (90°−&bgr;), less the acute angle (&agr;) thereby limiting the antenna tilt angle (90°−&bgr;−&agr;) required for reception from low-elevation satellites.
The above method may also typically include the additional step of:
(c) mechanically rotating the array antenna to direct the antenna beam in an azimuth direction appropriate to receive signals from the satellite.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.
REFERENCES:
patent: 5420598 (1995-05-01), Uematsu et al.
patent: 5579019 (1996-11-01), Uematsu et al.
Kumpfbeck Richard J.
Merenda Joseph T.
Pedersen John F.
BAE Systems Advanced Systems
Onders Edward A.
Robinson Kenneth P.
Wimer Michael C.
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