Cast core fabrication of helically wound antenna

Communications: radio wave antennas – Antennas – Spiral or helical type

Reexamination Certificate

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Details

C343S745000, C029S600000

Reexamination Certificate

active

06181296

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates in general to the manufacture and assembly of helical antennas for very high frequency applications (e.g., several tens of GHz), and is particularly directed to a cast core-based fabrication of a very small precision wound helical antenna having readily repeatable configuration parameters for use in a phased array antenna.
BACKGROUND OF THE INVENTION
Continuing improvements in circuit manufacturing technologies in developing smaller sized components for achieving higher operational frequencies (smaller wavelengths) has been accompanied by a need to reduce the dimensions of both signal processing and interface circuitry support hardware and their associated radio frequency antenna structures. In such reduced size, high frequency communication systems, helically wound antennas, such as those supported by low loss foam cores, are particularly attractive, as their radiation characteristics and relatively narrow physical configurations readily lend themselves to implementing physically compact phased array architectures that provide for electronically controlled shaping and pointing of an antenna's directivity pattern.
However, as operational frequencies have reached into the multidigit GHz range, achieving dimensional tolerances in large numbers of like components has become a major challenge to system designers and manufacturers. For example, in a relatively large number element phased array antenna operating at frequency in a range of 15-35 GHz, and containing several hundred to a thousand or more antenna elements, each antenna element may have on the order of twenty turns helically wound within a length of only several inches and a diameter of less than a quarter of an inch.
While conventional fabrication techniques, such as those which employ crossed-slat templates, diagrammatically illustrated in
FIG. 1
at
11
and
12
to form a winding
14
, may be sufficient to form helical windings for relatively large sized applications (since relatively small variations in dimensions or shape may not significantly degrade the electrical characteristics of the overall antenna), they are inadequate for very small sized elements (multi-GHz applications), where minute parametric variations are reflected as substantial percentage of the dimensions of each element. As a consequence, unless each element is effectively identically configured to conform with a given specification, there is no assurance that the antenna will perform as intended. This lack of predictability is essentially fatal to the successful manufacture and deployment of a high numbered multi-element antenna structure, especially one that may have up to a thousand elements.
SUMMARY OF THE INVENTION
In accordance with the present invention, the drawbacks of using conventional helical antenna fabrication techniques for high frequency designs are effectively obviated by a precision cast core-based manufacturing process to construct any number of very small helically wound antenna elements, each of which has readily repeatable configuration parameters. Pursuant to the invention, a dielectric core member upon which the helical antenna is wound is formed by shaping a solid mandrel to conform with the intended contour of the core member, and such that the eventually realized core member provides the intended characteristic impedance of the antenna. In addition, a precision helical groove is machined in the surface of the mandrel, to a shape and depth that provide for precision seating of the antenna wire that is wound around the dielectric core member.
After machining the mandrel to its intended shape, a silicone mold is formed around the mandrel and cured. The mandrel is then extracted, leaving the silicone mold with a shaped cavity having an embossed helical ridge that replicates the shape of the groove in the mandrel. The mandrel may now be repeatedly used to make additional dielectric cores of the identical shape and dimensions. A dielectric core epoxy—glass bead mixture is then injected into the silicone mold's cavity, and cured.
The silicone mold is then removed, and a length of antenna wire that is slightly longer than the length of helical groove is tightly wound in the dielectric core's helical groove, leaving wire extensions that project from the base and distal ends of the core. The antenna wire is then adhesively secured in the core groove at selected locations, thereby realizing a dielectric core-supported helical winding that is dimensionally stable, conforming exactly with the precision helical groove machined in the outer surface of the original mandrel.
The antenna wire-wrapped core is then mechanically and electrically attached to a baseplate laminate structure, so that the antenna may be physically mounted to a support member and connected to an associated transmit—receive module. The baseplate laminate structure includes a microstrip tuning circuit connected between the feed end of the helical antenna wire and the center pin of a standard self-mating connector, which provides a direct low loss connection to the transmit—receive module.


REFERENCES:
patent: 4862184 (1989-08-01), Ploussios
patent: 5329287 (1994-07-01), Strickland
patent: 5341149 (1994-08-01), Valinaa et al.
patent: 5604972 (1997-02-01), McCarrick
patent: 5914697 (1999-06-01), Seki
patent: 5973646 (1999-10-01), Engblom
patent: 5977931 (1999-11-01), Openlander
patent: 5986607 (1999-11-01), Rudisill

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