Radome
A radome is a protective enclosure placed over an antenna to shield it from the environment while allowing radio-frequency energy to pass through with minimal loss and distortion. The word is formed from radar and dome, but radomes are widely used in satellite communications, terrestrial microwave systems, radar, radio astronomy, and mobile communications systems. In satellite communications, radomes are commonly used with Earth station antennas, maritime terminals, aeronautical terminals, vehicle-mounted terminals, and some gateway or tracking antennas.
The main purpose of a radome is environmental protection. Antennas may otherwise be exposed to wind, rain, hail, snow, ice, salt spray, sand, dust, sunlight, and temperature extremes. These conditions can damage the antenna structure, degrade pointing accuracy, change reflector shape, corrode components, or interrupt service. A radome reduces these effects by enclosing the antenna in a stable protective cover. For ship, aircraft, and vehicle terminals, the radome also provides a smoother external shape and protects moving or delicate antenna mechanisms.
A radome must be mechanically strong but electromagnetically transparent. This is a difficult compromise. The material must withstand environmental loads while introducing as little attenuation, reflection, depolarization, phase distortion, and beam distortion as possible. Common radome materials include fiberglass-reinforced composites, plastics, foams, and sandwich structures. The exact material and wall thickness are chosen according to frequency band, antenna size, structural loading, temperature range, and required radio-frequency performance.
In a satellite link budget, a radome usually appears as a small additional loss. This is known as radome loss or radome insertion loss. Even a well-designed radome absorbs and reflects a small part of the signal. On receive, this reduces the wanted carrier level and may also add thermal noise, slightly reducing G/T. On transmit, it reduces the effective isotropic radiated power in the intended direction. At higher frequencies, especially Ku-band, Ka-band, and above, radome design becomes more critical because wavelengths are shorter and small variations in material thickness, water films, ice, or surface contamination can have a greater effect.
Radomes can also affect antenna pattern performance. If the radome is not uniform, or if its curvature and thickness are poorly matched to the antenna and frequency band, it may distort the main beam, increase sidelobes, reduce cross-polarization discrimination, or introduce pointing errors. This is particularly important for high-gain antennas and systems using frequency reuse by polarization. For precision Earth stations, gateway antennas, and tracking systems, the radome must therefore be treated as part of the antenna system rather than as a simple weather cover.
Several radome shapes are used. Small satellite terminals often use compact domes over mechanically steered antennas or flat-panel arrays. Maritime satellite antennas are commonly enclosed in white spherical or near-spherical radomes mounted above the ship’s superstructure. Aircraft satellite antennas may use low-profile aerodynamic radomes mounted on the fuselage. Large fixed Earth stations may use geodesic, space-frame, or air-supported radomes, although many large dishes are left uncovered because the radome cost, wind loading, and radio-frequency loss may be unacceptable.
Radomes are especially valuable where antenna pointing or mechanical motion would otherwise be affected by the environment. A stabilized ship antenna, for example, must keep its beam locked on the satellite while the vessel rolls, pitches, and yaws. The radome protects the antenna from wind and sea spray and helps maintain reliable operation. In icy or snowy environments, a radome can prevent the accumulation of ice on the reflector and feed, avoiding severe loss or pattern distortion.
Radome design must also consider drainage, condensation, ventilation, lightning protection, maintenance access, structural attachment, and long-term aging. Water, ice, salt, dirt, and ultraviolet degradation can all change the radio-frequency properties of the enclosure over time. For this reason, radomes used in demanding satellite communications applications are often specified and tested for both mechanical and electromagnetic performance.
In satellite communications, a radome is therefore not merely a cover. It is a protective radio-frequency structure that must preserve antenna performance while allowing reliable operation in harsh environments.