US 3287732 A
Description (OCR text may contain errors)
Nov. 22, 1966 FIG.I
J. ALTMAYER RADIO ANTENNA CONSTRUCTION Filed Nov. 15, 1963 INVENTOR. JOHN ALTMAYER United States Patent This invention relates tothe art of radio antennas and more particularly to an improved antenna construction. The invention is particularly adapted to base mounted or whip antenna constructions and will be described with particular reference thereto although it will be appreciated that theinvention may be applied to horizontal antenna constructions where the elements are based or end supported.
It is well known that whip antennas for mobile equipment should combine the following: light weight, flexibility and good electrical characteristics.
Whip antenna constructions in the prior art include metal telescoping antennas. good'electrical characteristics with some degree of flexibility due to itstelescoping portions which are of consecutively smaller cross section to permit fiexure. However, the degree of flexibility provided by the telescoping portions -is limited due to the elastic limit of the metals employed. Further, installation of such an antenna on a vehicle frequently subjects it to violent vibrations as the vehicle moves which fatigues the metal so as to render the antenna liable to breakage upon stress.
' To offset the above disadvantages of such metal telescoping antennas, another construction has been conceived in the prior art; namely, the provision of a highly flexible non-conductive rod, e.g., glass fibre impregnated plastic, with an external spirally wound wire on the rod or with an internal wire coaxially fixed within the rod. Such :constructions have inferior'electrical characteristics compared to the metal telescoping antennas.
The present invention relates to an improved antenna construction which overcomes the above-mentioned difficulties of the prior art constructions.
In accordance with the present invention, there is provided an antenna construction comprised of an elongated, flexible rod of electrical insultating material and a braided sleeve of electrically conducting wires enveloping the rod over at least a portion of its length. The rod and sleeve are together light in weight and sufficiently flexible transversely of the longitudinal axis of the rod to bend freely when subjected to transverse forces, and sufficiently rigid to minimize the degree of such bend. Further, the braided conductor sleeve has a maximum surface for a given diameter such as to have the best electrical characteristics for an antenna; namely, lower input impedance, and high capacity to ground.
In accordance with another aspect of this invention, the antenna construction includes a tough, non-conductive, flexible, protective cover enveloping the longitudinal surface of the braided sleeve so as to provide a high degree of protection against weather conditions and other external effects upon the antenna.
The antenna construction according to the present invention exhibits greater flexibility, greater capacity to ground, and lower losses and improved impedance characteristics.
The primary object of the present invention is to provide an antenna construction which incorporates light weight, flexibility, mechanical strength and good electrical characteristics.
Another object of the present invention is to provide an antenna construction having a high degree of protection against weather and other external effects upon the an- Such an antenna combines I tenna.
A still further object of the present invention is the construction of an antenna which is flexible, exhibits large capacitance to ground, has low electrical losses and good input impedance characteristics.
A still further object of the present invention is to provide an antenna construction including a flexible rod having a braided conductive sleeve enveloping the rod along the length of the rod whereby the sleeve exhibits good flexibility and provides a high ratio of conductive surface to weight of conductive material.
A still further object of the present invention is to provide a tough non-conductive, protective cover enveloping the longitudinal surface of the braided sleeve so as to provide a high degree of protection against weather and other external effects upon the antenna.
These and other objects and advantages will become apparent from the following description used to illustrate the preferred embodiments of the invention, as read in connection with the accompanying drawings in which:
FIGURE 1 is an elevational view of a whip antenna construction in accordance with the present invention, with portions of a protective cover broken away.
FIGURE 2 is an enlarged fragmentary elevational view illustrating one embodiment of the present invention.
FIGURE 3 is a cross-sectional view taken along line 3-3 in FIGURE 2.
FIGURE 4 is an enlarged fragmentary elevational view illustrating another embodiment of the present invention.
FIGURE 5 is a cross-sectional view taken along line 5-5 in FIGURE 4.
Referring now to the drawing, wherein the showings are for the purpose of illustrating preferred embodiments of the invention and not for limiting same, FIGURE 1 illustrates a whip antenna mounted at one end to a suitable clamp 10 which in turn may be secured to a vehicle fender or the like. Portions of a protective cover 12 are broken away at A, B and C to illustrate a braided sleeve 14.
In FIGURES 2 and 3 there is illustrated one preferred embodiment of the whip antenna construction comprising a flexible rod 16 enveloped by a braided sleeve 14 along the length of the rod. Preferably the rod 16 is of dielectric, flexible, light weight material, such as fiber glass, although other suitable material within the scope of the invention is contemplated. The rod 16 may be solid or hollow, although in its preferred form, as illustrated, is solid and of substantially circular cross-section. Preferably'the rod 16, which may be tapered slightly from its fixed to its free end, is sufiiciently rigid to maintain its shape when supported at one end, but yet sufficiently resilient to flex and then return to its normal position when subjected to and thereafter relieved of forces transversely of its longitudinal axis LA. Such forces, for example, may result from vehicle vibrations, wind conditions or by the antenna contacting obstructing objects, such as a garage roof.
The braided sleeve 14 preferably comprises a plurality of light weight wires 18 of relatively small diameter, such as 30 to 40 gauge, of conductive material, such as copper, braided to form a tubular sleeve about the rod 16. The wires 18 may be silver plated so as to minimize the high frequency surface resistance. When assembling the antenna the sleeve may be constructed by separately braiding the tubular sleeve 14 which when longitudinally compressed defines an inner diameter substantially greater than that of rod 16. The compressed sleeve 14 may then be placed about the rod 16 at one end thereof and stretched longitudinally so as to cover the rod along sub- 3 stantially its entire length. When stretching the sleeve 14in a longitudinal direction its inner diameter decreases whereby the sleeve tightly grasps the rod 14. Alternatively, the sleeve 14 may be assembled by directly tightly braiding the wires 18 about the rod 16 along substantially the entire length of the rod. In either case, the Wires 18 are preferably braided in such a manner to perrnit the antenna to flex transversely of its longitudinal axis LA.
The advantage of the braided sleeve 14 over a solid sleeve is its greater flexibility, which is of paramount importance for whip antenna use. Further, the advantage of sleeve 14 over a single helically wound wire is the higher ratio of conductive surface to weight of conductor material provided as well as providing greater capacity to ground. Thus, the braided sleeve 14 combines the desirable features of good flexibility with a high percentage of conductive surface area. Also, it has been found that an antenna construction according to the present invention exhibits low electrical losses and good input impedance characteristics.
Referring now to FIGURES 4 and 5, there is shown another preferred embodiment of the invention, which is essentially that as illustrated in FIGURES 2 and 3 except for a protective cover 12 which envelopes the sleeve 14 along its outer longitudinal surface. Preferably the cover 12 takes the form of tough, flexible, tubular insulating material, such as extruded synthetic plastic. The cover 12 may be mounted to the sleeve 14 in any suitable manner, but preferably by heat shrinking the cover to the contour of the sleeve. This may be done, for example, by heating a cover 12, having an internal diameter initially not greater than that of the outer diameter of the sleeve 14 sufliciently for it to expand radially outward, inserting the rod 16 with the sleeve 14 thereon into the bore of the cover, and thereafter permitting the cover to cool so as to shrink fit to the contour of the sleeve and tightly grasp the sleeve with the rod 16 serving as backing.
The cover 12 should be of sufficient length to envelope the sleeve 14 throughout its entire length and should exhibit at least the same degree of flexibility as that of the rod 16 and sleeve 14 taken together so as not to impair the flexibility of the antenna. Further, the cover 12 should be non-porous so as to seal the braided sleeve 14 from weather conditions. tenna, a cap 20 may be installed on the free end of the rod 16, as shown in FIGURE 1. Not only does the pro- To completely seal the an- 4 tective cover 12 serve to seal the sleeve 14 from weather conditions, but is also sufliciently tough to provide protection from other external effects on the antenna, such as obstructions which might damage or even sever one of the wires 18 of the sleeve. I Finally, the cover 12 is of light weight so as to further minimize the weight of the antenna in accordance with attaining the objects of the invention.
The invention has been described in connection with two preferred embodiments, but is not to be limited to the same. Various modifications may be made without departing from the scope and spirit of the present invention as defined by the appended claims.
Having thus described my invention I claim:
1. An antenna comprising:
an elongated nonconductive rod-like member, said member being constructed of resilient material and exhibiting a suificient degree of flexibility transversely of its longitudinal axis so as to bend slightly when subjected to transverse forces;
a sleeve constructed of conductive material enveloping said member for substantially the entire length of said member and supported thereon, said sleeve including a plurality of braided conductors braided in a manner to permit flexure transversely of the longitudinal axis of said member; and,
a protective cover of relatively tough, non-conductive, flexible material enveloping the outer longitudinal surface of said sleeve and exhibiting a degree of flexibility transversely of the longitudinal axis of said member which is at least equal to that of said member and said sleeve taken together so as not to impair the flexibility of the antenna.
2. An antenna as claimed in claim 1, wherein said protective cover is heat shrunk fitted to said sleeve.
References Cited by the Examiner UNITED STATES PATENTS 2,373,660 4/1945 Closson 343-900 2,681,412 6/1954 Webster 343900 2,938,210 5/1960 Harris 343-895 2,972,744 2/ 1961 Rickards et al 343-888 3,102,268 8/1963 Foley 343-895 HERMAN KARL SAALBACH, Primary Examiner. C. BARAFF, Assistant Examiner.