US3381371A - Method of constructing lightweight antenna - Google Patents

Description

May 7, 1968 E. D. RUSSELL METHOD OF CONSTRUCTING LIGHTWEIGHT ANTENNA 2 Sheets-Sheet 1 Filed Sept. 27, 1965 Earl D. Russell ATTORNEY y 7, 1968 E. D. RUSSELL 3,381,371

METHOD OF CONSTRUCTING LIGHTWEIGHT ANTENNA Filed Sept. 27, 1965 2 Sheets-Sheet 2 Figure 4A Earl D, Russell INVENTOR BY M D/M ATTORNEY United States Patent METHOD OF CONSTRUCTING LIGHTWEIGHT This invention relates to an improved method of constructing an antenna and is a continuation in part of my earlier filed application Ser. No. 160,451, entitled Lightweight Spiral Antenna, filed Dec. 19, 1961, now abandoned. More specifically, it relates to a method of constructing an antenna having a strip-like radiating element spaced from a reflecting surface that is formed on a dielectric support. The support is cast of a foam material and painted with a conducting paint to form the reflecting surface. The construction is substantially simpler than prior techniques and provides a lightweight antenna readily fabricated at low cost.

Antennas often have conducting surfaces spaced behind the radiating elements to reflect signals and thus form directional radiation patterns. Prior antenna constructions of this type require rigid, self-supporting reflectors, fabricated from sheet metal or castings, and, accordingly, they are heavy and bulky. In addition, the prior constructions are costly, since they require several fabricating operations. Furthermore, relatively bulky fastening devices are required to secure the heavy reflector to the assembly.

Accordingly, it is a principal object of the present invention to provide an improved method of constructing an antenna having a reflecting surface spaced from the radiating element.

A more specific object is to provide a method of constructing a directional antenna having a substantially plane radiating element, that is substantially less costly and light in weight than prior antennas of this type.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others to form the article possessing the features, properties and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a top plan view partly broken away of an antenna constructed in accordance with the present invention.

FIGURE 2 is a sectional view taken on the line 2-2 of FIGURE 1,

FIGURE 3 is a sectional view similar to FIGURE 2, of another embodiment of an antenna constructed in accordance with the present invention,

FIGURE 4 is a sectional view of a mold utilized in the construction of the antenna shown in FIGURES 1 and 2, and

FIGURE 4A is an enlarged portion of a section of the mold shown in FIGURE 4, illustrating the various layers of materials utilized in the present invention.

In general, the present antenna construction features a rigid, light-weight insulator that is painted with a conducting film and mounted behind a radiating element. The film reflects signals so that the antenna radiates a directional pattern.

3,381,371 Patented May 7, 1968 ice The insulator is preferably a foamed material, cast in a mold which is coated with the conducting film and secured to the radiating element. When the mold is removed, the film adheres to the hardened insulator. In this manner, the reflector is fabricated in the desired shape and secured to the radiating element in a single operation to provide a low-cost, light-weight antenna.

Referring to FIGS. 1 and 2, the antenna has a substantially flatradiating element 10, such as a double Archimedean spiral, energized by means of acoaxial feed cable 12 having a conductor connected to each of thespirals 10a and 10b. Areflector 14 is supported by a substantiallyrigid insulator 16 secured to a dielectric board orsheet 18, to which the spirals: 10a and 1% are bonded. A conductingsleeve 20 ensures a good electrical connection between thereflector 14 and theouter condoctor 12a of thecable 12.

Theinsulator 16, preferably a cylinder made of lightweight dielectric foam, effectively supports thereflector 14 at the desired distance from theradiating element 10, so that the antenna radiates in a predetermined directional pattern.

The antenna is preferably constructed by forming the Archimedeanspirals 10a and 10b of thin high-conductivity metal on one or both sides of thedielectric board 18, using, for example, printed circuit techniques. The radiating element can also be an equiangular element or other type of broad band radiator of which log periodic is a type.

Thefeed cable 12 is then connected to the radiating element through ahole 18a (FIG. 2) formed in theboard 18. With the double Archimedean spiral shown, the coaxialinner conductor 12b is connected to thespiral 10a, and theouter conductor 12a is connected to the spiral 101;. It is apparent that a waveguide or strip transmission line feed system can be used instead of the coaxial line shown.

Theinsulator 16 is preferably made of a dielectric foam cast in a mold 11 (FIG. 4) having acavity 13 with the desired shape for the insulator and anaperture 15 for thecable 12. The mold is coated with amold release agent 17 and then with a conductingpaint 19 such as a silver-epoxy. Thecable 12 is then secured to theboard 18 and the latter is secured to the mold, e.g., by clamps, and theinsulator 16 foamed in place according to wellknown techniques, for example, by adding a suitable catalyst to the dielectric material before closing the mold. The material preferably has a low dielectric constant and forms a unicellular foam. A suitable material is phenolic or epoxy foam. As the foam hardens, it adheres to the conducting paint, which serves as thereflector 14. It also adheres to theboard 18 to form a unitary structure of the entire assembly. Thefeed cable 12 may be anchored within the insulator, as shown, prior to foaming of theinsulator 16.

The aperture that accommodates the conductingsleeve 20 may be molded in place or formed after the mold has been removed. The assembly of the antenna is then completed by securing the sleeve in place. Alternatively, thesleeve 20 may be inserted into the mold after the release agent is applied and before the application of the conducting paint, as shown in FIGS. 4 and 4A. The paint then adheres to the sleeve to form an efficient connection thereto. A suitable coating, indicated by thedashed line 21, may be applied to protect thereflector 14 after the unit is removed from the mold.

As shown in FIGS. 1 and 2, theinsulator 16 is preferably a solid right cylinder, and the electrical distance between theelement 10 and the reflector portion 14a parallel to the element, is preferably a quarter-wavelength at the geometric mean of the design frequency. This spacing generally provides the optimum combination of antenna radiation pattern and impedance. The connection between the feed cableouter conductor 12a and thereflector 14 maintains the reflector at substantially ground potential.

Using the foregoing process, the antenna can be con structed with low-cost materials, and its size and weight are substantially reduced as compared to similar antennas constructed according to prior techniques. For example, .an S-band antenna, operating between 2 and 4 kmc., is 80% lighter than a similar prior antenna having a cast aluminum reflector.

In addition, thereflector 14 is fabricated and secured in place in substantially a single process, whereas the prior construction required the machining of a casting and securing it to thedielectric board 18.

Referring now to FIG. 3, according to an alternative construction, thereflector 14 is formed on a can-shaped insulator 22 secured withsuitable adhesive 23 to thedielectric board 18. A conductingfillet 24 of solder or the like connects thereflector 14 to the feed cableouter conductor 12a.

More specifically, theinsulator 22 is preferably cast in the desired shape using, for example, a phenolic material. Thereflector 14 may be formed on either the inside or the outside of the insulator by painting the insulator or a mold, which is not shown but which is similar to mold 11, with a silver or other conducting epoxy. Thefeed cable 12 is then fed through theinsulator 22 and secured to theradiating elements 10a and 10!) by soldering, for example. Theadhesive 23, a low-loss epoxy or other cement, fastens thedielectric board 18 to the support and the conductingfillet 24 is then formed between theouter conductor 12a and thereflector 14. A protective film, shown dotted at 26, is preferably sprayed over thereflector 14 on the outside of theinsulator 22.

The intenna constructed with the hollowcylindrical insulator 22 is even lighter than the antenna described above with reference to FIGS. 1 and 2, in addition to retaining its small size and low cost. It will be apparent that the radiating element and associated surface of the dielectric board may have a surface shape other than planar. For example, the surface may be conical with the apex of the cone pointing away from the reflector.

It will thus be seen that the objects set forth above,

among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

What is claimed is:

1. A process for constructing an antenna having a radiating clement, said process comprising the steps of securing said radiating element to a dielectric board, securing to said dielectric board a dielectric support projecting substantially transverse to the plane thereof by casting a dielectric foam in a mold having a cavity closed by said dielectric board, and forming a thin conductor on said dielectric support to reflect electromagnetic signals radiated by said element.

2. A process for constructing an antenna comprising the steps of fabricating a strip-like radiating element on a dielectric sheet, electrically connecting a feed system to said radiating element, coating a mold cavity having a substantially cylindrical configuration with a release agent and then with a conducting epoxy, closing said cavity with said sheet, said feed system extending axially through said cavity, casting a solid cylinder of dielectric foam in said mold cavity and permitting the same to harden therein, whereby said hardened foam adheres to said dielectric sheet and said epoxy, removing said cylinder from said mold cavity, and connecting said epoxy to a conductor of said feed system.

References Cited UNITED STATES PATENTS 2,863,145 12/ 1958 Turner 343-895 X 3,049,711 8/1962 Hooper 34389 X 3,131,394 4/1964 Wheeler 343-895 3,143,770 8/1964 Jeske 26445 X 3,169,311 2/1965 Small et al 343-912 X CHARLIE T. MOON, Primary Examiner.

R. W. CHURCH, Assistant Examiner.

Claims (1)

1. A PROCESS FOR CONSTRUCTING AN ANTENNA HAVING A RADIATING ELEMENT, SAID PROCESS COMPRISING THE STEPS OF SECURING SAID RADIATING ELEMENT TO A DIELECTRIC BOARD, SECURING TO SAID DIELECTRIC BOARD A DIELECTRIC SUPPORT PROJECTING SUBSTANTIALLY TRANSVERSE TO THE PLANE THEREOF BY CASTING A DIELECTRIC FOAM IN A MOLD HAVING A CAVITY CLOSED BY SAID DIELECTRIC BOARD, AND FORMING A THIN CONDUCTOR ON SAID DIELECTRIC SUPPORT TO REFLECT ELECTROMAGNETIC SIGNALS RADIATED BY SAID ELEMENT.

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