A radome, constructed of material that minimally attenuates the electromagnetic signal, safeguards the airborne antenna while permitting the passage of radar's transmitted signals and return echoes with minimum distortion and absorption. The first in-flight radome fabricated from Plexiglas has evolved into purpose-built shells. Bi-layer radomes consist of an outside pyroceram shell of 0.079-inch thickness glass-reinforced plastic substrate of 0.166 inch. A sandwich radome has two thin outer skins solid dielectric material separated by lightweight, low-dielectric core material, and 3-layer sandwich composite foam core with a thickness of lambda of the highest RF frequency used. Radomes made of fiberglass or Kevlar, radomes specifically designed for aircraft/RF-system combination, and sandwich radomes consisting of plastic skins all share the same requirement - radome materials are extremely pure and low dielectric so that structural integrity is achieved without compromising transparency. Radomes are useful when radar frequency is low enough to permit a skin thickness which will satisfy the structural requirements.
What are the main design requirements of an aircraft radome?
Aircraft radome design requirements extend to topology, material, mechanical properties and effects on transmitted or received signals. Aircraft radomes must be designed to minimize electrical and environmental interferences to radar sensor antennas. The reflections at the radome’s surface must be minimized for transmission and reception of the signal. Aircraft radomes must have strength, stiffness, temperature resistance, resistance to moisture absorption, abrasion and erosion resistance. The device should permit passage of the radar's transmitted signals and return echoes with minimum distortion and absorption. The design must withstand aerodynamic loads, thermal stresses, and environmental conditions, and it should minimize the insertion phase delay for the spread of incidence angles. Aircraft radomes should have a certain electrical thickness (0.085 to 0.095 inches) related to their physical thickness, operating frequency, and material type.
Aircraft radomes should be designed to minimize RF distortions, dissipate static and direct lightning, must be electrically transparent to electromagnetic energy, should have a wall thickness equal to an integer multiple of the radar wavelength/2, and solid walls with no air bubbles or other material fragments inside. The device should have low dielectric constant, low loss tangent, and minimal attenuation. Aircraft radomes should be homogeneous in nature to avoid additional Dk boundaries within the radome itself. The device design incorporates diverter strips for lightning protection. Aircraft radomes should avoid metal fixings and coatings because they reduce signal strength.
Electrical thickness, determined by physical wall thickness, operating frequency, and material type, is therefore chosen to equal an integer multiple of half the radar wavelength to become nearly transparent and minimize reflection losses. It needs stiffness to provide elastic stability, temperature resistance to tolerate thermal cycling, resistance to moisture absorption to keep dielectric properties unchanged, and abrasion and erosion resistance to survive rain, hail, dust, and stone impact. Manufacturing tolerances must be tight - excessive layers of paint or minute thickness variations seriously degrade performance - and designers employ anti-static coatings and lightning-diverter strips to dissipate charge. The entire design and fabrication cost must remain far below that of the radar system it protects, assuring economic viability while meeting mechanical and electrical requirements for the specific aircraft and antenna combination.
What materials are aircraft radomes made of?
Aircraft radomes are typically made of fiberglass, Kevlar, or a combination of composite materials, most commonly glass fibre. These composite materials are designed to be transparent to radio waves while providing structural integrity and protection for the antenna. The radome's conical configuration aids aircraft aerodynamics and is constructed using materials like conventional organic resins-polyester, epoxy, or polyimide-reinforced with glass fibres.
For advanced performance, quartz fibers with cyanate ester resin systems are deemed the best materials for structural radomes due to their low dielectric constant and high impact resistance. Manufacturers like Toray supply cyanate ester and epoxy based prepregs, which are produced in carbon free, isolated facilities to prevent contamination. These materials feature the industry's lowest dielectric constant, dielectric loss tangent, coefficient of thermal expansion, and moisture absorption, guaranteeing high performance in demanding environments.
Laird incorporates a range of radome materials including resins, fabrics like quartz, fiberglass, and plastic fibers, as well as core materials like foam or honeycomb. Polyurethane foams, including products like LAST A FOAM FR 3700, FR 7100, and FR 9800, form major core materials in radome construction. These foams provide refined thermal properties and are used as protective structures on the leading edges of aircraft radomes to guard against erosion damage.
Other construction types include solid laminate around 2 mm (0.079 in) thickness, 2-layer sandwich foam between thin membranes (typical for turboprops), and 3-layer sandwich designs with composite foam cores. Reinforced plastics consisting of a resin and woven fabric are standard, with bonding resins used for adhesion between components. The exterior surface of radomes is treated with specialized paints to minimize static build-up (anti-static) and rain erosion (hydrophobic).
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.