US 3056131 A
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Description (OCR text may contain errors)
Sept. 25, 1962 R. MCCREARY INFLATABLE ANTENNA Filed Oct. 1, 1956 FIG 3 FIG INVENTOR.
RALPH L. MCCRLAAY 3,056,131 INFLATABLE ANTENNA Ralph L. McCreary, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed Oct. 1, 1956, Ser. No. 612,997 3 Claims. (Cl. 343-781) This invention relates to antenna systems and more particularly to inflatable antennas.
Prior methods used for directed beam radiation by antennas involved the use of reflectors with some sort of waveguide feed thereto. The form the reflector usually took was that of a dish of aluminum mesh. Unfortunate- 1y, this involved considerable weight and unwieldiness where the reflector obtained a large size such as thirty feet. Further, the problems arising from winds of gale force increased the difliculty with the prior art systems. The immediately prior form involved several days effort in setting up the antenna. The invention herein can be set up in a few hours under the same conditions.
It is an object of this invention to provide an antenna suitable for electromagnetic radiation.
Further, it is an object of this invention to provide a lightweight portable parabolic reflector system.
It is a further object of this invention to provide a waveguide feed parabolic reflector system suitable for narrow beam radiation under wide weather extremes.
It is a feature of this device that plastic sheet materials are formed in the shape of a convex lens, with the reflector portion composed of laminated metal and plastic layers.
It is a further feature of this invention that inflatable plastic materials having metallic layers therein are used to control electromagnetic energy.
Further objects, features, and advantages of this invention will become apparent from the following description and claims when read in conjunction with the drawing in which:
FIGURE 1 shows a perspective view of the antenna with a front horn feed.
FIGURE 2 shows a cross section of FIGURE 1 with an alternative rear feed, and
FIGURE 3 shows a cross section of FIGURE 1.
In FIGURE 1 a reflector system is mounted between two rings 11 and 12. Rings 11 and 12 are formed of a rigid material such as segmented, lightweight metal alloys bolted together. The mounting rings are mounted on brackets 13 and 14 by arms 15. The antenna system itself is made of thin flexible sheet material. The form of the invention shown is that of a number of wedgeshaped pieces 17 assembled over a parabolic shape by gluing or other joining methods. As will be better seen in the later figures, the reflector assembly consists of two parabolic plastic sheets joined at their rims with their concave sides facing each other. The rearward section has a reflecting property, as to electromagnetic radiation, while the frontward section is transparent to this radiation.
In FIGURE I a front horn feed 18 is shown exciting or coupling the antenna to related equipment. This waveguide 18 can be of rigid or non-rigid plastic with a metallic layer or of metal. In any case, the waveguide feed connects to electromagnetic energy at the focal point of the parabolic surface, coupling to the antenna system in a manner well known in the art.
FIGURE 3 shows a cross section of FIGURE 1. Here, mounting rings 11 and 12 clamp the edges of the two parabolic sections together. The front section 20 is made of an an electromagnetically transparent plastic. The rear parabola 21 is formed of lamellar plastic film 22, metallic film 23, and plastic film 24. This maied States Patent 0 7 3,056,131 Patented Sept. 25, 1962 terial is available in sheets in the commercial markets. The base plastic 22 is formed of a fairly flexible plastic having the desired temperature-flexibility characteristics. In the usual form available, metallic layer 23 is a very thin coating of aluminum metal. A protective plastic layer 24 is added over the metallic coating for additional strength and wear resistance.
The two parabolic sections 20 and 21 are formed either by casting a thin film or by gluing together sections as seen in FIGURE 1 over a parabolic form. The edges are joined at perimeter 25 to form an airtight vessel. A length of tubing 26 is set in wherever convenient communicating with the interior of this fluid-tight vessel for inflation thereof.
In assembly, the clamping rings 11 and 12 are bolted together and against the perimeter 25 of the plastic vessel. Through tube 26 dry air, gas, or fluid medium transparent to electromagnetic radiation is pumped into the lens-shaped vessel. Sufficient pressure is introduced to maintain the shape of the vessel against such wind pressures as may be encountered in service. Antennas having pressures in the order of one pound per square inch will not deform due to wind velocities exceeding miles per hour.
Waveguide 18 comprising a rectangular section 28 and a horn or radiating section 29 is brought up on the concave side of the mirror section 21 in a manner well known in the art. Horn section 29 faces the concave portion of the mirror and directs radiation toward the mirror from a point near or at the focal point of the mirror. Should the horn and waveguide not be self-supporting, thin supports extending radially to the clamping rings will not affect the performance of the mirror.
Another form of feed to this antenna may be used as seen in the section view of FIGURE 2. Here, waveguide 28 is brought in through the rear section and directs electromagnetic energy to a reflecting metallized layer 30 on the inside surface of the front parabola. The energy is then reflected by the main reflector 21 into the desired beam. The arrangement of this reflecting array is similar to a Cassegrainian telescope. The metallic layer 23 is removed at the center of the parabola 31 to permit transmission of the electromagnetic energy from waveguide 28 to a second waveguide 32. Waveguide 28 is formed of the same lamellar metallic plastic material as is the reflector, with the metallized layer terminating short of mirror 30 to permit its proper operation. The waveguide is arranged to be inflated similarly to the lens-shaped structure, by a hole communicating with the interior of the lens. Reinforcing wires or tubes inflated to a higher pressure are used to hold the waveguide more rigid, relatively, where circumstances require a greater rigidity.
A thirty foot antenna constructed according to the invention weighs in the hundreds of pounds as opposed to the several thousand pounds involved for a metallic antenna of the same size. It is obvious that the objects of portability and ease of use are achieved with this system.
Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as defined by the-appended claims. It is to be understood that this antenna array can be used interchangeably as a receiving or radiating device, and that terminology expressive of the geometry of the array in terms of one function covers the other direction of energy flow also.
1. An inflatable reflector for electromagnetic radiation comprising two substantially concave thin sheets of flexible plastic material, at least one of said sheets having a parabolic shape, retaining means for joining said sheets at the perimeters thereof with concave sides facing each other to form a fluid-tight vessel, said parabolic shaped sheet having a flexible metallic reflecting layer thereon, said retaining means comprising first and second rigid ring members between which the perimeters of said sheets are received and clamped, and a waveguide formed from a thin sheet of flexible plastic material having a flexible metallic layer therein, said waveguide extending toward the focal point of said parabola and opening into said fluid-tight vessel so that said Waveguide is inflatable with said reflector.
2. An inflatable reflector for electromagnetic radiation comprising two substantially concave thin sheets of flexible plastic material, one of said sheets having a parabolic shape, retaining means for joining said sheets at the perimeters thereof with concave sides facing each other to form a fluid-tight enclosure, said parabolic shaped sheet having a flexible metallic reflecting layer thereon, said waveguide extending through said enclosure and terminating adjacent to said other concave sheet, and means on said other concave sheet to reflect radiant energy to said metallic reflecting layer on said one concave sheet whereby radiant energy may be reflected therefrom into a desired beam.
3. The inflatable reflector of claim 2, wherein said waveguide is formed from a thin sheet of flexible plastic material having a flexible metallic layer therein so as to be inflatable with said reflector.
References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Silver: Microwave Antenna Theory and Design, Mc- Graw-Hill, New York, 1949 (pages 388, 480 relied on). Kraus: Antennas, McGraw-Hill, New York, 1950 (pages 336 to 343 referred to).