US 3432859 A
Description (OCR text may contain errors)
March ll, 1969 T. J. JORDAN ETAL 3,432,859
RADOME AND METHOD FOR MAKING SAME Filed Jan. 29, 1955 Sheet March 11, 1969 12.1. JORDAN ETAL 3,432,359
RADOME AND METHOD FOR MAKING SAME Filed Jan. 29, 1963 Sheet 2 of 2 Q9 7Z1 4. m
The/k ACCO/Wgg United States Patent Office 3,432,859 Patented Mar. 11, 1969 RADOME AND METHOD FOR MAKING SAME Thomas J. Jordan, Ballston Lake, and Henry T. Plant,
Schenectady, N.Y., assignors to General Electric Company, a corporation of New York Filed Jan. 29, 1963, Ser. No. 254,798
US. Cl. 343-872 Int. Cl. H01q 1/42, 15/08; E04b 1/32 The present invention relates to dielectric, microwavetransparent, panels and, more particularly, to radomes formed with such panels having high strength and rigidity coupled with a uniform dielectric constant.
For various applications, radomes are generally required to exhibit a combination of very low, uniform dielectric constant, minimum weight, high strength, and rigidity. Present materials and techniques for making radomes do not satisfy these requirements, especially with regard to uniformity of the dielectric constant.
It is quite common today to construct radomes by laminating several layers of materials having different properties, for example, dielectric characteristics and mechanical strength, in order to take advantage of the various properties. Such constructions are relatively pervious to electromagnetic radiation but are usually limited to a rather narrow range of frequencies. Additionally, such constructions are only efficient when the radiation angles of incidence vary within narrow, low angles. These limitations on the performance of conventional laminated radomes create serious disadvantages in broad-band applications where wide frequencies and incident angles are generally encountered.
In radome applications requiring weight minimization without sacrifice of strength, sandwich construction has been resorted to, wherein, the sandwich core is usually either a honeycomb construction or a foamed plastic. In order to achieve uniform dielectric properties, the skin elements of a sandwich must be spaced apart accurately and be of uniform thickness. In addition, the core must be homogeneous. The skins are often cemented to the core, thus, introducing an extraneous substance which often has adverse effects on transmitted microwave characteristics.
Accordingly, it is an object of this invention to provide a microwave transparent panel having a uniform, low dielectric constant along With low weight, high strength, and rigidity.
Another object of this invention is to provide a microwave transparent panel which efficiently transmits electromagnetic radiation over a wide range of frequencies and incidence angles.
A further object of this invention is to provide a method for fabricating microwave transparent panels havmg a uniform, low dielectric constant along with low weight, high strength, and rigidity.
A still further object of this invention is to provide a method for fabricating microwave transparent panels wherein the dielectric properties of the panel can be varied and closely controlled.
Further objects and advantages of this invention will be better understood from the following description taken 1n connection with the accompanying drawings. The features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming part of this specification.
In the drawings, FIGURE 1 is a perspective view showing a final radome configuration incorporating the principles of this invention.
FIGURE 2 is a magnified perspective view showing a panel construction suitable for a radome which comprises a plurality of layers of corrugated sheets, the corrugation 9 Claims axes of adjacent sheets being angularly disposed with respect to one another.
FIGURE 3 is a magnified perspective view depicting a different panel construction suitable for transmission of microwave energy therethrough which comprises a plurality of layers of corrugated sheets, the corrugation axes of adjacent sheets being parallel to one another.
FIGURE 4 shows a magnified cross-sectional view showing a panel construction comprising a plurality of layers of alternating corrugated and planar sheets.
FIGURE 5 is a magnified perspective view showing a panel construction comprising a plurality of layers of sheets having embossments formed therein.
FIGURE 6 is a magnified perspective view showing a panel construction comprising a plurality of layers of hollow, cylindrical elements, the longitudinal axes of the cylindrical elements of all layers being parallel to one another and the elements within a single layer having a common transverse axis.
FIGURE 7 is the same as FIGURE 6 except the longitudinal axes of elements in one layer are angularly disposed with respect to the longitudinal axes of elements in an adjacent layer.
In accordance with the various embodiments of this invention, a rigid panel having a uniformly low dielectric constant and being of low weight, high strength, and rigidity is produced by fabricating a simulated foam of plastic material having a cellular structure with controlled, welldefined air cells therein. The simulated foam is formed by laminating layers of plastic material such that the assembly defines a plurality of elongated passages therethrough. This structure is formed with alternations of air and plastic material such that, by proper geometrical design, the desired dielectric characteristics and density is attained.
Referring to the drawings, radome 1 (FIG. 1) may be fabricated from dielectric, transparent, microwave panel 2 (FIG. 2) having satisfactory mechanical and electrical properties. In this embodiment, a plurality of thin sheets 3 of plastic material are corrugated and laminated so that corrugation axes of adjacent sheets are angularly disposed with respect to one another.
In order to satisfy the strict requirements necessary for proper microwave transparency, the most important and critical step in the formation of a radome panel is production of the individual sheets 3 from which the panel is formed. Close control of the thickness dimension and uniformity is required. Starting with a homogeneous plastic material having the desired dielectric properties, it is necessary to produce a plurality of sheets 3 having a minimal thickness which, when laminated, will maintain a minimum dielectric constant. Extrusion to a minimal thickness of about .006 inch with a tolerance of about .0005 inch has been successful. After extruding the flat sheets, the subsequent corrugating step must also be closely monitored, such as by vacuum forming. It has been found that, in order to avoid deleterious reflections, corrugation heights should not exceed one-tenth of the radiation wavelength to be used.
The step after corrugation is lamination which is defined as the stacking and bonding of a plurality of layers, the layers consisting of planar of preformed sheets or a plurality of elements unitarily assembled within a single plane, such as a plurality of cylinders to be discussed below. By careful maintenance of the quality of material used and careful formation of the corrugated sheets, controlled uniform electrical and mechanical properties are precisely defined. This high degree of uniformity is readily attainable through many manufacturing processes in common use today.
The materials of construction for the layer elements are known as plastics and provide the high strength qualities needed. The term plastics encompasses synthetic organic resins and ceramics, including those which are reinforced. Ceramic and reinforced ceramic materials are particularly applicable for radomes where high temperatures or radiation are likely to be encountered.
In the laminating process for the thermoplastic sheets it has been found that bonding of the adjacent layers is best accomplished by solvent welding which does not introduce permanently any extraneous material adversely affecting the electrical properties of the laminated product.
FIGURE 3 illustrates an alternate panel construction wherein adjacent corrugated layers 4 are arranged with the axes of corrugations parallel to one another. The corrugated sheets. are arranged such that they do not nest within one another but instead are assembled so that corrugations between adjacent sheets define a plurality of elongated passages 5.
FIGURE 4 illustrates a similar panel construction utilizing corrugated sheets 6 oriented with parallel corrugation axes. In this embodiment, planar or flat sheets 7 are interposed between the corrugated sheets 6 to define elongated passages 8 between the surfaces of adjacent sheets. Obviously, the present, embodiment is merely illustrative and not exhaustive of various combinations and formations that can be achieved with corrugated and non-corrugated sheets.
An alternate configuration of the panel construction is illustrated in FIGURE 5. The individual layers for the composite member may be prepared by formation of a plurality of embossments 9 in thin sheets 10 of plastic material. The embossments 9 may be of any conceivable shape such as hemispherical, rectangular, pyramidal, etc. The embossed sheets 10 are then laminated such the the embossments are staggered in position and are contiguous with an embossed portion of an adjacent sheet. The embossments serve as spacers or short columns defining passages 14 between adjacent sheets. As with the embodiments using corrugated sheets, layers of embossed sheets may be alternated with layers of planar sheets to achieve similar results.
Another alternative configuration employs a plurality of hollow cylindrical elements 12 as illustrated in FIG- UR-ES 6 and 7. The cylindrical elements are arranged in layers such that the longitudinal axes of cylinders in each layer are parallel with the transverse axe's 13 of all cylinders in each layer being within a single plane, albeit not necessarily a fiat plane. For example, the layers may be formed into a warped plane of the shape finally desired.
Successive layers of the cylinders may be laminated having longitudinal axes parallel with respect to one another as illustrated in FIGURE 6 or transverse to one another as illustrated in FIGURE 7. The relative angle between the axes may be of any value between the extremes illustrated in FIGURES 6 and 7 such as 30 or 45 degrees.
As was described for the above embodiments utilizing corrugated sheets, the embossed sheets and layers of cylinders are preferably bonded together by solvent welding. It should also be noted that for any of the described embodiments, a single unitary panel may be fabricated to obviate the joining together of a plurality of smaller panels. In addition, the final member may be flat or formed into various shapes as may be required in the particular radome application.
While specific forms and methods of the invention have been shown and described, it will be apparent to those skilled in the art that numerous changes, combinations and substitutions of equivalents might be made. It is therefore contemplated by the claims which conclude the specification to cover all such modifications as fall within the true spirit and scope of this invention.
What we claim as new and desire to secure by Letters Patent of the United States is:
1. A rigid panel comprising a radome through which microwave energy is transmitted having substantially uni' form dielectric properties, said panel comprising a plurality of layers of preformed elements, each of said elements being made of plastic material and having a uniform thickness and uniform dielectric properties, said elements being preformed such that, upon assembly thereof into layers, a plurality of elongated passages is defined, the maximum dimension of said passages in a direction parallel to said transmitted microwave energy being not greater than one-tenth of the wavelength of said microwave energy.
2. A rigid radome as defined in claim 1 wherein said elements are hollow cylindrical bodies and wherein each of said layers comprises a plurality of the cylinders oriented to have parallel longitudinal axes and a common transverse axis, said longitudinal axes being substantially perpendicular to the direction in which said microwave energy is transmitted and wherein the hollow interiors of said cylindrical bodies constitute said elongated passages.
3. A rigid radome as defined in claim 2 wherein the longitudinal axes of the cylinders in each layer are parallel to the longitudinal axes of the cylinders in an adjacent layer.
'4. A rigid radome as defined in claim 2 wherein the longitudinal axes of the cylinders in each layer are angularly disposed with respect to the longitudinal axes of the cylinders in an adjacent layer.
5. A rigid radome through which microwave energy is transmitted having substantially uniform dielectric properties, said radome comprising a lamination of a plurality of sheets having corrugations formed therein, each of said sheets being made of plastic material and having uniform thickness and uniform dielectric properties, said corrugations defining a plurality of elongated passages, the maximum height of said corrugations being one-tenth of the wavelength of said microwaves.
6. A rigid radome as defined in claim 5 including a plurality of planar sheets being made of plastic material and having uniform thickness and uniform dielectric properties, said lamination comprising alternations of said corrugated sheets and said planar sheets.
7. A rigid radome through which microwave energy is transmitted having substantially uniform dielectric properties, said radome comprising a lamination of a plurality of sheets having a plurality of embossments formed therein, each of said sheets being made of plastic material and having uniform thickness and uniform dielectric properties, said sheets being assembled such that the embossments of one sheet are contiguous with and about an unembossed portion of an adjacent sheet thus defining a plurality of elongated passages between adjacent sheets, the maximum dimension of said passages in a direction parallel to said transmitted microwave energy being not greater than one-tenth of the wavelength of said microwaves.
8. A method for making a rigid panel through which microwave energy is transmitted having substantially uniform dielectric properties comprising thesteps of:
(a) providing a plurality of thin sheets of plastic material, each of the sheets having uniform thickness and uniform dielectric properties,
(b) offsetting portions of the sheets to form projections therefrom and,
(c) laminating the sheets such that adjacent sheets and the projections therefrom define a plurality of elongated passages each having a maximum dimension in a direction parallel to the direction in which said microwave energy is transmitted of not more than one-tenth the wavelength of the microwaves.
9. A method as defined in claim 8 wherein the step of offsetting comprises corrugating the sheets.
(References on following page) References Cited UNITED STATES PATENTS Watson 156-591 Ruppricht 161-136 Shipley et a1. 161-6'8 Wentworth et a1. 156-205 Pajak 156-207 Lincoln 16 1- 69 Meyer 161-137 X Overholt 161-89 Colman et a1 343-872 X 6 2,045,849 6/1936 Genter 161-69 3,041,223 6/1962, Sage 161-69 2,751,964 6/ 1956 Guyer 156-205 EARL M. BERGERT, Primary Examiner.
H. F EPSTEIN, Assistant Examiner.