Communications: radio wave antennas – Antennas – Antenna with parasitic reflector
Reexamination Certificate
1999-06-24
2001-02-13
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna with parasitic reflector
C343S912000, C343S916000
Reexamination Certificate
active
06188370
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to antennas and, more particularly, to paraboloidal grid antennas.
2. Description of the Related Art
An especially useful configuration for an antenna reflector is that of a paraboloid which is generated by rotating the arc of a parabola about its axis. In a feature of this structure, electromagnetic energy transmitted from the paraboloidal focus to the paraboloidal surface is collimated or, equivalently, received collimated energy is reflected from the paraboloidal surface to the paraboloidal focus. One performance characterization of paraboloidal grid antennas is the front-to-back ratio which is a ratio of maximum gain in the antenna's forward hemisphere to maximum gain in its rear hemisphere. This ratio is typically approximated by a power ratio of the main lobe to the rear lobe.
Paraboloidal reflectors have been constructed by replacing a solid paraboloidal surface with one formed by parallel grid members that are aligned with the polarization of a received signal. The grid members are spaced by a common space that is typically calculated to realize a selected front-to-back ratio. Although this replacement generally reduces total aperture efficiency (e.g., from a range of 0.5 to 0.7 to a range of 0.45 to 0.65) and degrades front-to-back ratio (e.g., on the order of 3 dB), it significantly lowers weight and wind loading and reduces the difficulty and cost of antenna installation.
An early description of paraboloidal grid reflectors is found in U.S. Pat. No. 2,850,735 to Harris. In order to reduce the rear lobe and thereby enhance the front-to-back ratio, U.S. Pat. No. 4,801,946 to Matz elongated each grid member in a direction parallel to the paraboloidal axis. In order to further reduce wind loading, U.S. Pat. No. 4,405,928 to Elsbernd provided the grid members with streamlined cross sections.
Modern communication systems (e.g., terrestrial digital video delivery systems) have increased the performance requirements of paraboloidal grid antennas. For example, cellular communication systems with advanced modulation techniques (e.g., quadrature amplitude modulation) and closely-spaced multiple transmitters require high front-to-back ratios (e.g., >26 dB) for subscriber antennas in order to avoid unacceptable co-channel interference and mulitpath reception.
Conventional paraboloidal grid antennas that can meet these front-to-back ratios require a large number of grid elements which increases their manufacturing cost. Because this also increases their weight and wind loading, they require more complex support structures which not only are more expensive but increase antenna installation costs.
SUMMARY OF THE INVENTION
The present invention is directed to paraboloidal grid antennas that are lighter, have less wind loading, are less expensive and are easier to install because they recognize angular variations in antenna parameters (e.g., feed gains and path losses) and use these variations to efficiently space elongate members to realize selected front-to-back radiation ratios.
In accordance with the invention, a method for achieving a selected front-to-back ratio F/B includes a first step of providing parallel elongate members that are shaped and positioned to lie upon the surface of an imaginary paraboloid that has a focus and a vertex. Thus, the elongate members have a main lobe gain G
ml
and a differential path loss L
d
&thgr;
from the focus that varies with an angle &thgr; from the vertex. In another step, an electromagnetic feed signal is radiated from the focus with a polarization substantially parallel to the elongate members and with a feed gain G
f
&thgr;
that varies with the angle &thgr;.
From the main lobe gain G
ml
, the differential path loss L
d
&thgr;
and the feed gain G
f
&thgr;
, a transmission coefficient T
&thgr;
is determined, as a function of the angle &thgr;, that realizes the selected front-to-back ratio F/B. Respective cross sections are then chosen for the elongate members and, based on their respective cross sections, adjacent pairs of the elongate members are spaced by different spaces S that realize the transmission coefficient T
&thgr;
at respective angles &thgr;.
In paraboloidal reflectors of the invention, adjacent pairs of elongate members are positioned at respective angles &thgr; from the paraboloidal vertex and spaced apart by respective spaces S that increase with increased angle &thgr; for at least two of the adjacent pairs. Generally, the spaces S increase with increased angle &thgr; for a contiguous majority of adjacent pairs and may be constant for a contiguous minority that typically adjoins the vertex. In other reflector embodiments, the spaces S increase with increased angle &thgr; for all of the adjacent pairs.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 2597339 (1952-05-01), Krutter
patent: 2729816 (1956-01-01), Crawford
patent: 2850735 (1958-10-01), Harris
patent: 3178713 (1965-04-01), Yang
patent: 4405928 (1983-09-01), Elsbernd
patent: 4801946 (1989-01-01), Mats, Jr.
patent: 5291212 (1994-03-01), Cox
patent: 5380328 (1995-01-01), Morgan
patent: 5894290 (1999-04-01), Oona et al.
Jasik, Henry,Antenna Engineering Handbook,Mc-Graw Hill, Inc., New York, 1993, pp. 17-17 to 17-22, 27-12 to 27-13 and 46-2 to 46-9.
Bulletin No. G-992, Microwave Grid Antennas 335-2700 MHz,Radiation Systems,Inc.—Mark Antennas Division.
Specification Sheets for Super Grid, GP Series and GridPak Antennas,Andrew Microwave.
Stutzman, Warren, et al.,Antenna Theory and Design,JohnWiley and Sons., New York, 1981, pp. 433-434.
California Amplifier, Inc.
Dinh Trinh Vo
Koppel & Jacobs
Wong Don
LandOfFree
Grid antennas and methods with efficient grid spacing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Grid antennas and methods with efficient grid spacing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Grid antennas and methods with efficient grid spacing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2576400