The primary function of a radome is to protect the enclosed antenna system while having minimal effect on the transmission of the electromagnetic signal. Saint-Gobain SHEERGARDTM RF transparent materials are used for a variety of applications including air-supported radomes, electromagnetic windows, antenna Covers and other special configurations of structures. These materials are extremely robust yet thin and flexible allowing a large variety of uses to protect antenna systems.
SHEERGARD materials use either high strength Kevlar® or fiberglass fabrics, depending on the application. The finished materials typically have dielectric constants of less than 2.8 and loss tangents below 0.008. These properties, combined in a thin, high tensile strength composite result in an electrical thickness that typically measures only a small fraction of the RF wavelength. This provides superior RF transmission performance. This extremely low transmission loss also results in minimal scattering of energy into the antenna sidelobe pattern. Effect on cross polarization and noise temperature contribution is also minimal.
The graph shows transmission loss vs operating frequency for a variety of Saint-Gobain SHEERGARD materials.
Air Supported radomes utilize SHEERGARD high strength materials to create the protective spherical envelope. Since it is supported by internal air pressure, the radome requires no rigid structural framework that can cause additional disruption and scattering of the electromagnetic signal. This provides the best broadband electromagnetic performance of any radome type
The selection of material for an air supported radome is based on size and the maximum wind speed requirements. The chart below shows typical maximum diameters for spherical radomes designed for 150 or 200 mph wind speeds for the most widely used materials. These maximum diameters are a general guide only and can be verified for a specific application by contacting (link) Saint-Gobain.
|SHEERGARD Spherical Air Supported Radome Material Application|
|SHEERGARD Material||Maximum Diameter in ft. (m)||Maximum Wind Speed in mph (m/s)||Transmission Loss at 10 GHz|
|K40||70 (21.3)||150 (67)||0.1 db|
|K60||110 (28)||150 (67)||0.1 db|
|Q65||125 (38)||200 (90)||0.5 db|
Permanent Hydrophobic Surface
Hydrophobicity of a radome outer surface is critical to reducing additional transmission loss during rain conditions. Since water has a high dielectric constant and loss tangent, even a thin film of water on the radome surface during rain conditions will produce much higher transmission losses. A hydrophobic radome surface causes the water to form small beads and to run off in small rivulets instead of forming a sheet of water in front of the entire antenna aperture.
|93 ft. (28.4m) Diameter SHEERGARD K60 Radome Transmission loss at 19.5 GHz|
|Dry Conditions SHEERGARD||10 mm/hr rain |
|10 mm/hr rain |
|0.3 db||0.8 db||5.3 db|
SHEERGARD High Performance radome materials have PTFE as an integral part of the surface. This PTFE surface will maintain its hydrophobic characteristics throughout the life of the radome and never needs recoating or refurbishment. This eliminates the need for the expensive refurbishing of radome surfaces by painting or other time consuming processes. Other types of surfaces that produce an initial hydrophobic effect but eventually lose it over time between refurbishing events will see a gradual deterioration of the transmission performance in the rain. Additionally, as those surfaces receive new coats of material to reinstate their hydrophobicity, that buildup of surface coating contributes to additional dry and wet radome transmission loss.
SHEERGARD permanent hydrophobic surfaces provide: