Protecting Signal Strength – General Plastics' Foam for Radomes
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Protecting Signal Strength – General Plastics’ Foam for Radomes

From defense and solar system research to boats and aircraft, radome structures perform the function of protecting radar equipment. These weatherproof shells transparent to radio frequency systems, notably radar, microwave, and other antennae, are used for signal transmission and capture that do not affect the signal passing through them. Although “radome” is a blend of “radar” and “dome,” these protective structures are not always dome-shaped but come in many different types, which include flat panels covering sensitive components of antennas on large dishes and small radar systems used in naval applications.

General Plastics’ polyurethane foams are commonly used as composite materials and offer dielectric properties for constructing radomes and related housings. They provide an optimal, insulating barrier between sensitive electronics used in communication, telemetry and radar systems and environmental threats posed by rain, wind, hail, snow, sand, insects, bird strikes, UV damage and rapid fluctuations in temperature.

Wide-ranging radome applications

  • Security/Military/defense – Radomes protect and conceal electronic surveillance equipment, such as that used to intercept satellite communications and other radar air defense applications. They support military aircraft platforms for reconnaissance, electronic warfare, defense and preemptive strikes, data links and electronic countermeasures.
  • Stationary antennae – Radomes prevent debris, ice and freezing rain from accumulating directly onto the metal surface.
  • Commercial aircraft – Needed for navigation or communications, commercial flights rely on signals. Radomes used in protective structures on the noses of aircraft ensure optimal antenna functionality for weather detection.
  • Maritime satellite communications – Ships employ radomes to protect dish antennae used to continually track fixed satellite and for navigation.
  • Broadband communications – On oil tankers and large cruise ships, radomes extending more than three meters in diameter may cover antennae connecting them to voice, data television and Internet transmissions.
  • Private yachts – Small private yachts may use radomes as small as 26 cm in diameter for voice and low-speed data.
  • Solar system research – NASA uses large radar dishes in far-flung, uninhabited areas that offer minimal pollution of signal.

Why polyurethane foams are optimal for constructing effective barriers

Radomes built using suitable materials and configured properly for the application and radio frequency range are essentially invisible electronically, preventing negative impact on the performance of the signals produced or captured. Versatile, robust and cost-effective, our polyurethane foams offer high performance and low dielectric interference, with superb dimensional stability. Two reasons they don’t change over time is that these foam materials are closed-cell and hydrophobic: They do not absorb water. Water is highly polar and can cause them to lose their properties or change over time.

What’s more, in extremely cold and windy environments, foam structures surrounding radar dishes prevent snow and wind from moving them around. And, as a natural insulator, our foam material prevents cold and heat from transferring, slowing down potentially undesirable changes in temperature. For example, in the transition from night to day, an unprotected antenna in direct sunlight can heat up quickly, jeopardizing performance and longevity.

Generally, radomes are fabricated using layup or prepreg methods in which resin-reinforced laminate materials are readily bonded to low- or medium-density rigid polyurethane foams. Our polyurethane foams are already renowned for supporting composite structures, which capitalize on their high strength-to-weight ratio.

Selection considerations

All of General Plastics’ foam material holds distinct characteristics and advantages that help determine their applications. Specific General Plastics foam feature low dielectric constant and low loss tangent, making it ideal for radome applications. Material selection may also depend on the shape or contours of the sensitive electronics being covered and how imperative it is to protect them. The polyurethane foams best suited for these applications are our LAST-A-FOAM® FR-3700 Performance Core series and FR-7100 Multi-Use Core series.

FR-3700LAST-A-FOAM® FR-3700 has specifically engineered properties that make it tougher and more durable than the FR-7100. The FR-3700 is able to handle rugged environments for a given density, such as those needed for military and defense applications that dictate the highest levels of protection. This performance core series is flame-retardant, is an excellent alternative to wood, resistant to most chemicals and solvents, and has a high-strength to weight ratio.

Although not as tough as the FR-3700, our LAST-A-FOAM® FR-7100 is sufficient and more affordable for applications involving less risk. Other benefits of this multi-use core series include its fine cell structure that supports smooth finishes, dimensional stability, and its closed-cell characteristic that does not absorb water or moisture. We recommend using FR-7100 for applications that allow for more variation or have less performance requirements.

Larger radomes typically have simpler exposure requirements. For example, a very large radome in Alaska only has to handle some wind and potentially hail, whereas a naval ship or a weaponized system will call for a tougher, more significant composite to protect that radar system from loss. This is also a function of foam formulation and density driving material properties.

Proven capabilities

Testing conducted on General Plastics’ signature LAST-A-FOAM® materials (see our dielectric materials white paper for dielectric constant and loss tangent data), demonstrates how the foams performed well under a range of applied microwave frequencies without significant heat loss. Our products are proven impervious to moisture and virtually transparent to radio signals, they are the leading choice for protecting aerospace, marine and land-based microwave antennae.

Our polyurethane foams can be provided in three ways: 1) as sheet stock, which can be further modified to meet customer needs, 2) machined to shape based on a supplied drawing with dimensions noted and 3) as a molded part. In addition, for some applications, we can provide material cast to a specified shape.

Regardless of whether you are selecting foam material in boards or blocks, or you rely on General Plastics for machining or finished product, we advise contacting our Customer Solutions team early in the design process. Each query may be very specific, so tap our expertise to identify in advance the design’s impact on cost. Our technical data sheets for each product also provide valuable guidance.

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