Patent Grant
8081137
This subject invention relates to radomes.
Radar systems must be protected from the environment such as rain, snow, ice, etc., in some manner, usually by a structure called a radome. The design of a radome is not elementary. It must protect the transmit/receive (T/R) modules of the radar system for sensitivity compliance, it must allow transmission of RF energy through the radome, it must not reflect RF energy back at the radar system to prevent damaging its T/R modules, and the radome must be constructed at a suitable cost.
For inflated (air-supported) radomes made of a single-layer material such as Vectran, the optimum shape, from the perspective of reducing reflected energy back at the radar system, is a sphere. But, a sphere shaped radome must be extremely large and is thus costly. So, a prolate geometry is often used. But, the prolate geometry, especially when subject to wind loading and variations in air pressure, results in radar energy reflections which may damage the radar equipment housed within the radome.
In one example, an air-supported radome 103 feet tall had a base 103 feet in diameter, a top hemispherical region with a 60 foot radius, and a prolate region at the bottom. A radome reflected power of 8 dB above the transmit/receive module power was measured which damaged the transmit and receive modules of the radar system housed within the radome.
A rigid sandwich radome structure may not suffer from these reflections, but rigid sandwich radome structures are expensive, may have undesirable seams which can cause high scattering to degrade the radar performance, and are difficult to manufacture and erect when the size of the radome is, say, a hundred feet high with a radius of 60 feet.
It is therefore an object of this invention to provide a new air-supported sandwich radome.
It is a further object of this invention to provide such a radome which better protects radar equipment housed therein.
It is a further object of this invention to provide such a radome in which any reflected RF energy is of lower power.
It is a further object of this invention to provide a method of reducing RF energy reflections in an existing radome.
It is a further object of this invention to provide such a method which can be implemented in the field.
The subject invention results from the realization that, in one embodiment, by adding a laminate including a flexible, high strength, RF transmissive, low dielectric Vectran layer and a low dielectric foam layer to at least a portion of the inside wall of an air-supported radome, transmission of the RF energy through the radome is not adversely affected but reflected RF energy power is lowered because the foam provides a 180° phase delay between the RF energy reflected of the outer radome wall and the RF energy reflected of the inner laminate layer.
The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.
The subject invention features, in one example, an air-supported sandwich radome comprising a hemispherical top region and a prolate region with a high strength, RF transmissive, low dielectric flexible wall. There is a defined region where damaging RF radiation is reflected. At least in the defined region, a flexible high strength, RF transmissive low dielectric layer is added with a low dielectric gap between the outer wall and the inner layer. This laminate construction provides a 180° phase delay between RF energy reflected off the outer wall and RF energy reflected off the inner layer to cancel the effect of said reflected RF energy on radar equipment housed by the radome.
Preferably, the outer wall and the inner layer are made of the same material such as Vectran. The gap is preferably defined by a foam ply. The inner layer may be secured to the foam ply in the shape of geodesic tiles secured to the outer wall. Or, the inner layer may be secured to the foam ply in the shape of longitudinally extending strips secured to the outer wall.
In one example, the foam ply is ¼″ thick and has a dielectric constant of less than 1.15. The foam ply may be a foam tape. To save material and to lower the cost, the geodesic tiles or strips may be secured to the outer wall only at the defined region.
The subject invention also features a method of reducing RF energy reflections in an air-supported sandwich radome. The preferred method comprises adding to the inside wall of the radome, at least at a defined region of the radome, a flexible, high strength, RF transmissive, low dielectric layer separated from the outer wall by low dielectric gap. This laminate structure provides a 180° phase delay between the RF energy reflected off the outer wall and RF energy reflected off the inner layer to cancel the effect of reflected RF energy on radar equipment housed by the radome.
One air-supported sandwich radome in accordance with this invention includes a high strength, RF transmissive, low dielectric, flexible wall, a flexible, high strength, RF transmissive, low dielectric layer, and a low dielectric gap between the outer wall and the inner layer providing a phase delay between RF energy reflected off the outer wall and RF energy reflected off the inner layer to reduce the effect of reflected RF energy on radar equipment housed by the radome. Typically, the low dielectric gap includes a foam ply between the wall and the layer.
Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:
Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.
As discussed in the Background section above, a certain region of radome 10,
In accordance with a preferred embodiment of the subject invention, laminate 20,
Vectran layer 22 may be secured to foam layer 24 in a variety of ways including the use of low dielectric adhesives or tapes. Rigid stand offs may be added between Vectran inner layer 22 and outer wall 12 to maintain the required dielectric gap spacing.
The shape of the laminate including Vectran inner layer 22 and foam layer 24 laminate may vary. As shown in
In this way, an existing air-supported radome can be modified in the field by adding, at least to a predefined region of the radome, usually on the inside wall thereof, a flexible, high strength RF transmissive, low dielectric layer separated from the outer wall by a low dielectric gap providing a 180° phase delay between the RF energy reflected of the outer wall and the RF energy reflected of the inner layer to cancel the effect of the reflected RF energy on radar equipment housed by the radome.
The result, in any embodiment, is a radome which better protects the radar equipment housed therein and wherein any reflected RF energy is of a lower power. In one simulation, focused radome reflected power was reduced to −3 dB level relative to the T/R module power which provides a good margin for transmit and receive module protection from radome reflection.
Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.
In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.
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| Number | Date | Country | |
|---|---|---|---|
| 20090091509 A1 | Apr 2009 | US |
