Radomes are structures or enclosures designed to protect an antenna and associated electronics from the surrounding environment and elements such as rain, snow, UV light, and strong wind. The name "radome" is derived from the words radar and dome.

The protective shell enhances the pointing accuracy of antenna systems by offsetting negative impacts of UV degradation, wind load, or build-up of snow and ice. The key functionality of these structures is to extend the system's ability to perform under adverse conditions while creating a safe working environment.

Deployment of radomes also controls the costs associated with installation and maintenance of the system or equipment. Added support and protection provided by the enclosure allows for a prolonged service life and a more cost-effective architecture, for instance, by using smaller motors or foundations. These structures operate without compromising an antenna's electromagnetic performance. This is achieved by selecting proper construction materials that maximize electrical transparency, which preserves transmission efficiency without impairing electromagnetic characteristics.

Radome walls are manufactured to a precise thickness to achieve the desired radar or radio wave transparency that is critical in aviation. Properly designed solutions with appropriate materials allow for optimum system performance.

Employment of radomes extends to several fields such as telecommunications, tracking, and radio astronomy. Each application is highly dependent on the intended use. Radomes offer security in restricted environments by shielding sensitive equipment and screening it from view.

Types of Radomes

Radomes are classified into several categories based on their design, capabilities, and wall architecture as defined by the MIL-R-7705B standard, including:

Type 1: Suitable for low-frequency use at 2GHz or less

Type 2: Designed for directional guidance with directional accuracy specifications

Type 3: Suitable for narrow band application at an operational bandwidth below 10%

Type 4: Support multiple frequency bands operating at two or more narrow frequency bands

Type 5: Applicable for an operational bandwidth falling within the range of 0.100GHz to 0.667GHz

Type 6: Provides an operational bandwidth exceeding 0.667GHz

Radomes can also be classified by wall architecture. The following types further classify wall design:

Solid wall: Half wavelength (monolithic) wall made of a dielectric material.

Thin wall monolithic: Radomes integrated with panel flanges for additional support.

A-sandwich multilayered wall: These radomes consist of three layers including two high-density polymer skins and a core made of a low-density material, such as foam or honeycomb. In these radomes, the dielectric constant of the skins is higher than that of the core. The wall thickness is modified to improve the radome's ability to operate at specific frequencies. Sandwich radomes are self-supporting and require no air pressurization. Compared to other models, they demand fewer components thereby saving on construction and maintenance costs.

Multilayered wall: These radomes feature a minimum of five dielectric layers. The number of high-density layers is odd while the number of core layers is even. Broadband frequency performance improves with each added layer.

Other designs: This category includes the remaining wall construction designs such as B-sandwich models combining a high-density core and two skins made of a low-density material.

How Radomes Work

Radomes are constructed from materials having no interference with radio waves sent and received by antennas. An assortment of shapes exists to match the specific applications. They appear as aircraft nose cones or as covering on the fuselage to protect the antennas and provide a streamlined profile by reducing aerodynamic drag.

Stationary antennas are subject to impedance mismatch caused by ice build-up, affecting the performance of the transmitter and possibly causing it to overheat. A radome prevents this by covering the antenna with a rigid, weatherproof material such as fiberglass.

Radar dishes are enclosed in a large dome-shaped structure. They shield the rotational equipment and electronics and supply heat to avoid ice and snow accumulation.

Radome geometry has a profound effect on antenna transmission properties. Certain geometrical patterns generate scattering errors at particular frequencies. Radomes with multi-panel or quasi-random panel configurations prevent scattering errors across panels.

Water exerts a substantial disrupting effect on the radome performance by forming a thin film on its surface that blocks signal transmission. To avoid signal attenuation, radomes come with hydrophobic coatings that result in water beading up and rolling off the surface. Panel flange and joint framework are designed based on industry standards to avoid adverse effects on the electromagnetic performance due to phase shifting or signal loss.

Radome design and performance for the aerospace industry is gaining important due to the increased prevalence of advanced radar applications. For innovative techniques such as Doppler wind shear detection and other advanced radar processes, standard radomes are not ideal. These techniques require specialized or custom-designed radomes.

Radomes contain materials with a low dielectric constant to reduce reflection and detrimental effects on the electromagnetic signals. Several substances such as balsa and plywood were utilized in the early construction of radomes. Modern structures are made of composite materials including quartz and fiberglass as well as aramid fibers bound by resins like epoxy. Honeycomb cores comprised of low-dielectric-constant materials exist between the radome layers to improve structural robustness.

Applications

Use of radomes applies to a range of industries that require the protection of sensitive equipment, electronic components, and personnel. These include:

• Weather radar
• Aviation
• Maritime communications
• Surveillance
• Satellite communications
• Coastal surveillance
• Military and civil flight simulation
• Military and civil radar
• Microwave
• Broadcast equipment

Selecting Radomes

Radome performance varies depending on the type and individual characteristics of a specific radome structure. To select a radome, first investigate the model designed for an intended purpose. Multiple factors must be considered such as environmental characteristics of the placement zone, frequency of use, antenna transmission properties, power availability, and maintenance costs. The majority of standard radome models are adequate for high-power and low-frequency purposes. However, sites using specialized equipment, such as Doppler radar or 3D surveillance radar, rely on modern radome technology to avoid frequency attenuation.

Specifications and Standards

Government and commercial standards apply to the construction, testing, and use of radomes. Agencies and organizations maintaining standards and specifications include:

• US military: MIL-Spec and MIL-STD
• Federal: FAA, FED-STD
• Commercial: ASTM, ASME, ASCE, ISO

Relevant standards include:

AIA/NAS ARTC-4 - Electrical test procecures for radomes and radome materials

FAA-E-2773 - Fixed ground antenna radome

MIL-R-5082 - Radome for CTV-2 pilotless aircraft

References

Image credits:

FDS ITALY SRL | Australian Radome Services | PRI Radomes