Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
2000-11-09
2001-10-09
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S799000, C343S810000, C343S891000
Reexamination Certificate
active
06300915
ABSTRACT:
RELATED INVENTIONS
(Not Applicable)
FEDERALLY SPONSORED RESEARCH
(Not Applicable)
BACKGROUND OF THE INVENTION
This invention relates to antennas to broadcast VHF data from a differential GPS ground station to supplement GPS reception for aircraft landings and, more generally, to elliptically-polarized omnidirective phase-progressive sub-arrays, vertical array antennas including a plurality of such sub-arrays, and cut-and-bend dipoles usable in such sub-arrays.
Enhanced accuracy applications of Global Positioning System (GPS) signals, such as use in aircraft landing and local control operations, can be enabled by derivation and local broadcast of Differential GPS (DGPS) signals to permit in-aircraft correction of local and other errors inherent in basic GPS signals. These errors may include ionospheric, tropospheric and satellite clock and ephemeris errors. To provide such DGPS signals, accurate local reception of GPS satellite signals is followed by derivation and local broadcast of the DGPS signals.
For such GPS signal reception, antenna systems providing a circular polarization characteristic in all directions horizontally and upward from the horizon, with a sharp cut-off characteristic below the horizon are described in U.S. Pat. No. 5,534,882, issued to the present inventor on Jul. 9, 1996, which is hereby incorporated herein by reference. Antennas with such characteristics are particularly suited to reception of signals from GPS satellites.
For local broadcast of DGPS data signals at VHF frequencies (e.g., for FAA Local Area Augmentation System (LAAS) for VHF Data Broadcast (VDB) applications) different antenna performance is required. Particular antenna requirements and characteristics may include accurate and reliable omnidirective broadcast of elliptically polarized VHF data signals, with elevation gain uniformity. Signal fades caused by ground reflections must also be minimized.
Objects of the present invention are, therefore, to provide new and improved antennas usable for such applications, and antennas, dipole arrays and cut-and-bend dipoles having one or more of the following characteristics and advantages:
omnidirective elliptical polarization;
omnidirective phase-progressive radiation;
low VSWR VHF band coverage via double-tuned dipoles:
optimized sub-array excitation for low elevation lobing;
dipoles with isolated frontal conductor for double-tuned performance;
frontal divided transmission line structure for double tuning, provided via frontal conductor;
low cost cut-and-bend construction; and
economical and reliable dipole construction consisting basically of only two sheet-metal strips.
SUMMARY OF THE INVENTION
In accordance with the invention, a vertical array antenna, including a plurality of four-dipole sub-arrays, comprises a support mast aligned vertically, lower, middle and upper sub-arrays and an excitation arrangement. Each sub-array includes four dipoles extending from the mast at 90 degree azimuth separations, with each dipole comprising:
(a) left and right conductive L-shaped strips having (i) respective left and right parallel portions extending outward from the mast in parallel spaced adjacent relation and (ii) left and right arm portions extending laterally from the respective parallel portions, oppositely from each other and diagonally to horizontal, and
(b) a conductive frontal strip extending in parallel spaced adjacent relation to a portion of the combined length of said left and right arm portions to form a frontal divided transmission line structure. The excitation arrangement is coupled to intermediate points along the parallel portions of the L-shaped strips of each dipole to provide omnidirective phase-progressive excitation of each sub-array, with (i) the middle sub-array having phase-progressive excitation of reference amplitude and phase, (ii) the lower sub-array having phase-progressive excitation of nominally 70 percent amplitude and plus 90 degrees phase rotation relative to the reference amplitude and phase, and (iii) the upper sub-array having phase-progressive excitation of nominally 70 percent amplitude and minus 90 degree phase rotation relative to the reference amplitude and phase.
Also in accordance with the invention, a cut-and-bend dipole includes two L-shaped strips and a conductive frontal strip. The first L-shaped conductive strip has a first portion extending from a mounting portion outward and an arm portion bent normal to the first portion. The second L-shaped conductive strip has a parallel portion extending from a mounting portion outward in parallel spaced adjacent relation to the first portion and an arm portion bent normal to the parallel portion and extending oppositely from the arm portion of the first L-shaped strip. The conductive frontal strip extends in parallel spaced adjacent relation to a portion of the combined length of the oppositely extending arm portions to form a frontal divided transmission line structure. The strips may be formed from sheet stock, with each L-shaped strip having a normal bend to provide an arm portion.
For economical and reliable construction, of such a dipole, the first and second L-shaped conductive strips may be formed in one continuous strip with the first portion and parallel portion bent normal to a bridging section, which connects those portions and comprises the mounting portion. Typically, the frontal strip extends linearly in front of nominally 80 percent of the combined length of the oppositely extending arm portions and is dielectrically supported in centered relation to that combined length.
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: 5534882 (1996-07-01), Lopez
patent: 6025812 (2000-02-01), Gabriel et al.
patent: 6028563 (2000-02-01), Higins
patent: 6201510 (2001-03-01), Lopez et al.
Bae Systems Aerospace Inc. Advanced Systems
Ho Tan
Onders Edward A.
Robinson Kenneth P.
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