US3509570A

US3509570A - Flexible blade antenna

Info

Publication number: US3509570A
Application number: US763705A
Authority: US
Inventors: Jefferson F Lindsey; Gareth H Nason
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1968-09-30
Filing date: 1968-09-30
Publication date: 1970-04-28
Anticipated expiration: 1987-04-28

Description

April 1970 J. F. LINDQSEY m, ETAL 3,509,570

FLEXIBLE BLADE ANTENNA Filed Sept. 30, 1968 m mi FREQUENCY FIG. 5

Jefferson F. LindseyIH Gareth H. Nason INVENTORS ATTORNEY United States Patent Office 3,509,570 Patented Apr. 28, 1970 3,509,570 FLEXIBLE BLADE ANTENNA Jefferson F. Lindsey III, and Gareth H. Nason, Houston,

Tex., assign-ors to the United States of America as represented by the Administrator of the National Aeronautics and Space Administration Filed Sept. 30, 1968, Ser. No. 763,705 Int. Cl. H01q 1/12 U.S. Cl. 343-718 Claims ABSTRACT OF THE DISCLOSURE A flexible, resilient metallic blade is perpendicularly mounted from the surface of a solid dielectric material held in a metallic cup with the cup in turn being mounted in a flat metallic plate. A metallic shielded electrical conductor extends into the cup and through the dielectric material with the central conductor being electrically connected to the blade and the shield being electrically connected to the cup. The surface of the dielectric material is depressed to permit the blade to be bent flat and the blade is curved laterally to prevent it from kinking when bent and to increase its rigidity when erect.

The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Governmlent for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates generally to the field of antennas and more particularly to a flexible monopole antenna exhibiting a broad bandwidth characteristic and low voltage standing wave ratio over a selected frequency range.

Brief description of the prior art The prior art discloses a variety of antennas which are designed to be mounted on the surface of a vehicle or other moving body. In some instances, the primary consideration is to provide a flexible antenna which is less likely to be damaged when it is struck or bent. One such prior art antenna includes simply a thin, wire-like antenna element carried within a supporting rubber mounting.

In other areas, the primary concern may be for reducing the induced air drag of the antenna Where it is employed on rapidly mjoving bodies such as air craft. In such cases, the radiating element of the antenna may assume the form of an air foil to reduce induced air drag. US. Patent No. 2,484,817 to De Armond discloses an antenna having a radiating element in the form of a slightly curved metal blade which may be raised into or retracted from a streamlined housing. The antenna resembles a steel tape measure and is in fact coiled and uncoiled from a storage container in a fashion similar to such tape measure.

While the described prior art devices include certain desirable physical attributes, their electrical characteristics are relatively limited, partially due to the manner by which they are mounted and partially due to their overall design. Improved antenna designs have been suggested by the prior art with attendant improvement in operating characteristics. For example, US. Patents No.,2,505,751 and 2,449,562 to Bolljahn and Meier respectively, disclose improvement in mounting and design of antenna elements. The Bolljahn reference discloses a streamlined sleeve type antenna with a specific dimensional relationship between antenna components. The antenna is also adapted for effective cooperation with the surface upon which it is mounted which is employed as a ground plane. The Meier antenna is of the whip type and includes a mounting assembly which is also designed to employ the mounting surface as a ground plane. Both the Bolljahn and Meier antennas employ a driven element which is mechanically mounted within a grounded parasitic element. The radiating element is in each case electrically insulated from the parasitic element by dielectric mounting means.

While the Bolljahn and Meier antennas afford improved operating characteristics as compared with other prior art antennas, they are relatively bulky, are difficult to mount and include a large number of separate components. Moreover, the driven elements disclosed in the latter two references are relatively large and cannot be collapsed for storage where limited space is available.

SUMMARY OF THE INVENTION The blade monopole antenna of the present invention includes a single spring-metal blade which is mounted vertically in a suitable dielectric material carried in a cuplike structure with the cup in turn being countersunk in a metal plate. The center conductor of a suitable coaxial line is electrically connected to the embedded end of the blade while the outer shielding of the coaxial line is electrically connected to the cup. The plate acts as a mechanical mounting structure and also 'as a ground plane.

The blade is slightly curved laterally along its length to be self-supporting and the face of the dielectric material is depressed adjacent the blade mounting to permit the blade to be bent fiat. When not in use, the blade of the antenna may be folded against its supporting structure or ground plane to reduce the space required for storing the antenna and associated equipment.

The antenna of the present invention is capable of broad application but it is particularly advantageous for use in radio frequency communication between astronauts during extravehicular activities in space. The components employed in fabricating the antenna are dependable and sturdy and, more importantly, have small dimensions and thus require only a small volume for storage.

The dimensions and configuration of the blade and cup are designed for optimum performance on the particular equipment with which they are mounted and employed. In the case of space application, the ground plane for the blade monopole may include the metallic portions of an astronauts back pack as well as his metallized garments.

The blade monopole of the present invention is characterized by a very low voltage standing wave ratio over a relatively wide frequency band. These advantageous operating characteristics are also present when the antenna is employed with the theoretically imperfect ground plane afforded by the back pack and garments employed by astronauts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawings is a front elevation, partially broken away, of the blade monopole of the present invention;

FIG. 2 of the drawings illustrates the blade monopole of the present invention mounted on the back pack of a fully suited apollo astronaut;

FIG. 3 is a plan view of the blade monopole of the present invention;

FIG. 4 is a cross section of the blade monopole of the present invention taken along the line 4-4 of FIG. 3; and

FIG. 5 of the drawings is a graph illustrating the improved operating characteristics of the blade monopole of the present invention.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIGS. 1, 3 and 4 of the drawings, it may be seen that the antenna of the present invention includes a single, spring-steel blade mounted in a suitable dielectric potting material 11 contained in a cylindrical metallic cup 12 which is in turn counter sunk in -a metallic mounting plate 13. The plate 13 is secured to a metallic mounting surface 14 by any means such as the threaded bolts and

nuts

15 and 16. The surface 14 may comprise a portion of an astronauts back-pack or other associated or similar equipment.

As best illustrated in FIG. 4 of the drawings, a coaxial line 17 having a center conductor 17a and a metal shield 17b extends through the base of the cup 12 and connects the antenna to its associated electronic system (not illustrated). The shield 17b is D.C. coupled to the cup 12 by any suitable means, such as soldering, while the center conductor 17a is D.C. coupled to the base of the antenna blade 10 by means of nut and bolt assembly 18 which extends through an appropriate bore in the blade. The assembly 18 also acts as an anchoring means for improving the mounting of the blade 10 within the potting material 11.

As best illustrated in FIGS. 3 and 4 of the drawings, the blade 10 is laterally curved along its lengthwise axial development. The curvature in the body of the blade 10 assists in holding the blade in an erect position and also prevents it from kinking when it is forcibly bent. As a further measure to permit forcible bending of the an tenna without damage, the potting material 11 is depressed as indicated at 11a and 11b. By virtue of the described structure, the antenna blade 10 may be bent and folded into the dotted line position illustrated in FIG. 4 of the drawings. When thus bent for storage or otherwise, the blade is allowed to follow the smoothly curving contour of the potting surface at 11a which prevents the elastic limit of the blade material from being exceeded. When the bending force is released, the resiliency of the blade 10 causes it to spring back into its erect, operative position.

In one specific embodiment of the antenna, designed for use in the 259.7 mHz. to 296.8 mHz. frequency range, the blade 10 was made approximately 11% inches in length measured from the top of the cup 12, /2 inch in width and 0.005 inch in thickness, with the curve in the blade having a 0.5 inch radius. The dielectric material employed for the potting 11 was Stycast 1090SI manufactured by Emerson & Cuming, Inc. The dimensions of the cup 12 were designed to best match the characteristics of the blade 10 and included an inside diameter of 1% inches and a height of inch. The spacing between the bottom of the blade and the inside surface of the bottom on the cup 12 was A; inch, and the metallic ground plate 13 was in the form of a 2 /2 by 2 /2 inch square. The antenna was mounted on the back pack B carried by a suited apollo astronaut A as illustrated in FIG. 2 of the drawings. In this mounting, the ground plate made radio frequency contact with metallic portions of the equipment carried within the back pack B and the ground plane for the blade monopole was formed by aluminum honeycomb (not illustrated) in the cover of the back pack B and aluminized mylar in the astronauts thermal garments G.

When thus mounted, and operating as an asymetric dipole by virtue of the irregular ground plane, a 12:1 voltage standing wave ratio (VSWR) was achieved at the intermediate frequency of 279.0 mHz. with a 50 ohm resistive impedance being used as a reference for the VSWR. Distinctly improved characteristics, as compared with other antenna designs, were observed for the monopole antenna of the present invention through all changes in orientation of the astronaut A and associated ground plane of back B and garments G. The antenna Cir 4 having the stated dimensions is generally characterized by an unusually broad band width characteristic over the 259.7 mHz. to 296.8 mHz. frequency range with a 1.5 :1 or less voltage standing wave ratio at 259.7 mHz. and 1.621 VSWR at 296.8 mHz.

It was discovered that these favorable operating characteristics are attributable to the use of the blade monopole design described herein in combination with a cup having an inside diameter which is correlated with the blade length and width. In the described example, the inside diameter of the cup is the length of the blade measured from the top of the cup and 2% times the width of the blade. These ratios of cup diameter to the blade width and height are larger than analogous ratios found in prior art antennas.

FIG. 5 of the drawings illustrates the relationship between frequency and voltage standing wave ratio (VSWR) for two antennas with the curve C generally representing the performance of an antenna incorporating the features of the present invention and the curve C representing the performance of an antenna which was of similar construction but without a cup. As is clearly indicated by the curves, the operating characteristics of the antenna of the present invention are markedly superior to those of the antenna having no cup.

It will be understood that various materials are suitable for use in constructing the antenna of the present invention. By way of example rather than limitation, the potting compound 11 may be any suitable dielectric material having the desired structural strength when cured, and preferably having a dielectric constant in the range of 1.8 and a dissipation factor of 0.015 or less. Suitable potting materials in addition to Stycast 109051 include polytetrafluoroethylene, sold under the trademark Teflon or R.T.V. 560, or 60 made by the General Electric Company. The blade 10' may be constructed of Havar Steel which is sold by the Hamilton Watch Company, Simmonds Precision Sara Beacon Material made by the Simmonds Precision Company, or any other suitable metal such as stainless steel or beryllium copper. The cup 12 and plate 13 may be constructed of any suitable, conducting metal.

It will also be understood that various modifications may be made in the illustrated form of the invention without departing therefrom. By way of example rather than limitation, the single blade element 10 may be replaced with a series of similar blades which are laminated to each other to increase their rigidity. The plate 13 may also assume a variety of shapes and is not limited to the configuration illustrated in the drawings. If desirable, the base of the cup 12 may be omitted and the shield conductor 1712 may be connected directly to the cylindrical wall of the cup. Various modifications may also be made in the anchoring and attachment assembly carried at the bottom of the blade 10.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention.

We claim:

1. A blade monopole antenna comprising:

(a) an elongated metallic blade means having first and second axial ends;

(b) a dielectric means for supporting said first axial end of said blade means;

(0) an axially extending annular metallic shield means completely encircling said first axial end and a portion of the axial length of said blade means and separated from said blade means by said dielectric means; and

(d) a metallic ground plate means carried externally of said annular metallic shield means and extending laterally from said shield means.

2. The blade monopole antenna as defined in claim 1 wherein said blade curves laterally along its axial length.

3. The blade monopole antenna as defined in claim 1 or 2 above wherein said dielectric material includes a concave surface which extends toward said first axial end of said blade.

4. The blade monopole antenna as defined in claim 1 or 2 above wherein said shield means includes cylindrical walls and is concentrically disposed about said blade.

5. The blade monopole antenna as defined in claims 1 or 2 above wherein:

(a) said shield means includes a cup-shaped body having cylindrical sidewalls; and

(b) said dielectric material includes a concave surface which extends toward said first axial end of said blade.

6. The monopole blade antenna as defined in claim 1 above wherein:

(a) said blade curves laterally along its axial length;

(b) said dielectric material includes a concave surface which extends toward said first axial end of said blade;

(c) said shield means includes cylindrical Walls and is concentrically disposed about said blade; and

(d) shield means further includes a metal base extending between said cylindrical walls.

7. The blade monopole antenna as defined in claim 1, 2 or 6 further including a coaxial conductor having an inner conductor and an outer conductor with saidinner conductor connected to said first axial end of said blade and said outer conductor connected to said shield means.

8. The blade monopole antenna as defined in claim 1, 2 or 6 wherein said metallic ground plate means is electrically associated with a metallic mounting surface for forming a ground plane.

9. The blade monopole antenna as defined in claim 1, 2 or 6 including a ground plane of metallized garments.

10. The blade monopole antenna as defined in claim 1, 2 or 6 wherein said metallic ground plate means is electrically associated with a metallic mounting surface for forming a ground plane and including a further ground plane area comprising metalized garments.

References Cited FOREIGN PATENTS 873,521 3/1942 France.

ELI LIEBERMAN, Primary Examiner U.S.C1.X.R. 343 829. 888