US3430248A

US3430248A - Artificial dielectric material for use in microwave optics

Info

Publication number: US3430248A
Application number: US519165A
Authority: US
Inventors: William M Lightbowne
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1966-01-06
Filing date: 1966-01-06
Publication date: 1969-02-25
Anticipated expiration: 1986-02-25

Description

EXAMiNE:

5/ 9 Mr Feb. 25, 1969 w. M. LIGHTBOWNE 3, 3 8

ARTIFICIAL DIELECTRIC MATERIAL FOR USE IN MICROWAVE OPTICS Sheet of 2 Filed Jan.

a m mm h N 0. W M ma 2 M J Y B ARTIFICIAL DIELECTRIC MATERIAL FOR USE IN MICROWAVE OPTICS Filed Jan. 6, 1966 Feb. 25, 1969 w. M. LIGHTBOWNE FIG. 4

William M.L|ghtbowne,

INVENTOR. M m. BY (AM! J. M )W M M e. M

United States Patent ()1 lice 8 Claims Int. Cl. H011] 15/08 ABSTRACT OF THE DISCLOSURE An artificial dielectric material wherein an array of discrete dipoles formed by wraping cylinders of foil around plastic rods is interspersed and oriented in a three-dimensional repeating pattern, identical in the three principal planes, and supported by a lattice of insulating material.

This invention relates to artificial dielectric materials whose refractive index is precisely controlled by the physical dimensions of its component parts and which exhibits superior properties in respect to bandwidth, isotropy, power factor, ruggedness, stability, cost and availability.

Prior art dielectrics for the higher frequencies have been developed in which small metal strips, flakes or platelets are dispersed by various means throughout the mass of a foamed natural dielectric-usually polystyrene. This type of material, known as loaded foam, is the only known method of augmenting the refractive properties of natural dielectrics. It is heavy, expensive, lossy, and non-uniform in texture. For the lower frequencies, in the VHF and UHF bands, satisfactory materials have been developed, however, these materials have not been found suitable for production.

The present invention overcomes the disadvantages of the prior art materials and consists of (1) an array of discrete dipoles, interspersed and oriented in a three dimensional repeating pattern of cubic cells, having identical aspects in the three principle planes; and (2) a supporting lattice. Inasmuch as the dipoles are physically discontinuous, the supporting lattice must provide all the desired structural properties of the material. Furthermore, since the supporting lattice is part of the propagating medium, it must also possess compatible electrical properties.

It is an object of the present invention to provide an artificial dielectric possessing sufficient isotropy for use in the fields of radar and microwave optics.

Another object of this invention is to provide an artificial dielectric that can be economically produced in large quantities.

These and other objects and advantages of the invention will become readily apparent upon an inspection of the following detailed description and the accompanying drawing in which:

FIGURE 1 is an illustration of the structure of a dipole member according to the invention;

FIGURE 2 is an illustration of an alternate form of the dipole member;

FIGURE 3 is a perspective view of supporting lattice according to a first embodiment of the invention; and

FIGURE 4 is a perspective view of a second embodiment of the invention.

Referring now to FIGURE 1, dipole member is shown to consist of cylinders of foil or sheet metal 12 wrapped around plastic rod 14. Rods 14 are cut to about one wavelength at the desired center frequency. To minimize anisotropy and frequency dispersion, there should be about twelve dipoles per wavelength.

3,430,248 Patented Feb. 25, 1969 An alternate form of the dipole member 10 is shown in FIGURE 2. This form is obtained by taking a long flat strip of plastic 16 and cementing metal foil elements 18 thereon. This strip is then curled into long tubes.

The supporting lattice consists of a cube 20 whose side is the same length as rod 14 which bears the dipoles. Cube 20 is composed of expanded polystyrene foam and has groups of

holes

22, 24, and 26 molded or drilled therein normal to each face of the cube. The holes in each face are equally spaced and the number of holes is equal to the square of the number of dipoles on a rod 14. The holes have a diameter approximately equal to that of dipole member 10.

The diameter of dipole member 10 shall be such that when

holes

22, 24, and 26 are formed in cube 20 from three mutually perpendicular faces of the cube, no two holes shall intersect, and the clearance between all holes passing tangent to one another shall be approximately equal.

A second embodiment of the invention is shown in FIGURE 4 and differs from that of FIGURE 1 mainly in that the cube is formed from a plurality of square polystyrene tubes. In FIGURE 4, the dipoles 31 are discrete strips, crosses, 0r squares of foil or sheet metal which have been cemented to, in a regular pattern, large sheets of thin insulating material. The insulation material should be dimensionally stable, mechanically strong, and have the electrical properties of extremely low loss and low dielectric constant at the desired operating frequency. One example of such a material is biaxially-oriented extruded polystyrene sheet.

These sheets, with their laminated patterns, are carefully cut into rectangles. The rectangles are then folded or formed into long tubes, which may be square, octagonal, or circular in cross-section. The folds are so positioned with respect to the dipole pattern that the resulting tube is symmetrical about two principal planes, whose intersection is the axis of the tube, and which pass either normal to the sides or diagonally through the corners, of the tube. Metal dipoles 31 may be located either on the inside or the outside surface of

tubes

32, 34, and 36. The length of the tubes must be uniform and each should contain an even number of dipole patterns. A preferred length, as in FIGURE 1, would be one wavelength with twelve sets of dipoles along eachc side of a tube. In crosssection, the side of the tube should precisely equal the spacing of the dipole patterns.

With these dimensions established, a number of these

tubes

32, 34, and 36 can be constructed in the longitudinal, lateral and vertical axes as shown in FIGURE 4 to form cube 30. The addition of a cement or solvent at each interface creates a rigid, continuous, cubic lattice which possesses a characteristic mechanical symmetry.

It can be seen from the above that any dipole arrangement, in accord with the above described embodiments, provides a cell of dipoles in three dimensions, at the intersection of each tube with any other tube or with any tube in an adjacent block similarly oriented. This cell will also possess triaxial symmetry which provides the dielectric with sufficient isotropy for many applications of microwave optics. Specifically, the artificial dielectric described herein is suitable "for use in Luneberg Lens receiver antennas. It should also be noted that any desired refractive index can be obtained in any of the embodiments of the invention simply by adjusting the physical dimensions of the dipole array, the dipoles, or both.

While this invention has been described with reference to particular embodiments thereof, the following claims are intended to include those modifications and variations that are within the spirit and scope of my invention.

I claim:

1. An artificial dielectric material comprising an array of discrete dipoles interspersed and oriented in a three dimensional repeating pattern having identical aspects in the three principal planes, and a supporting lattice of insulating material for supporting said poles in said pattern.

2. An artificial dielectric material comprising: a cube of expanded plastic material, said cube having holes formed therein from three mutually perpendicular faces, and dipole members disposed in said holes and formed of alternate sections of dipoles and insulators, said dipole members having a length equal to a side dimension of said cube.

3. An artificial dielectric material as set forth in claim 2 wherein the number of holes formed in each face of said cube is equal to the square of the number of dipoles in a dipole member.

4. An artificial dielectric material as set forth in claim 2 wherein said dipole member is in the form of a rod of insulating material having bands of metal wrapped therearound at spaced positions along the length thereof.

5. An artificial dielectric material as set forth in claim 2 wherein said dipole member is in the form of long flat sheet of plastic material to which metal elements have been cemented and said sheet has been curled to form :1 tube.

6. An artificial dielectric material comprising a cubical body of insulating material and a plurality of dipoles distributed uniformly throughout said body, said body being formed of a plurality of discrete tubular insulating members disposed along three mutually perpendicular axes in a lattice configuration.

7. An artificial dielectric material as set forth in claim 6 wherein said tubular members are formed of rectangular sheets of insulating material having said dipoles cemented thereto in a regular pattern and folded so as to form a tube that is symmetrical about two principal planes, intersecting at the axis of the tube.

8. An artificial dielectric material as set forth in claim 2 wherein said expanded plastic is polystyrene foam.

References Cited UNITED STATES PATENTS 2,579,324 12/1951 Kock 343-911 2,936,453 5/1960 Coleman 343-915 3,165,750 1/1965 Tell 343-911 3,254,345 5/1966 Hannan 343-911 3,293,649 12/1966 Fox et al. 343-911 FOREIGN PATENTS 665,747 1/1952 Great Britain.

ELI LIEBERMAN, Primary Examiner.