What are Satellite Antennas?

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Oct 31, 2022

Satellite antennas are used to concentrate the satellite’s transmitting power towards a designated geographical region on earth and avoid interference from undesired signals that will deteriorate the overall quality of the signal.

Antennas that are used onboard satellites are selected based on the requirements of their physical configurations, expected to have low volume, low cost, and high antenna gain. The antenna gain is defined as the intensity at which an antenna propagates its signal in a particular direction. Antennas receiving signals can be directional/bidirectional as well as omnidirectional in nature. Directional antennas transmit/receive signals only from a particular direction and have a radius of about 45-90 degrees. However, omnidirectional antennas transmit/receive RF signal equally from all directions and provide a 360-degree radiation pattern.

Monopole Antennas

Monopole antenna consists of a straight rod-shaped conductor, often mounted perpendicularly over a surface known as the ground plane. Monopole antennas were first placed on the world’s first artificial satellite; “Sputnik-1” where 4 flexible monopoles were placed in the middle of the vehicle.

CubeSat Deployable Antennas

For certain operations that require compact & cost-effective measures, antennas that can be expanded post-launch are used on CubeSats. These antennas are folded, stowed, or packed in a Cubesat before and during launch. After the satellite is placed into orbit, they are deployed to conduct its missions. Predominantly, L-band antennas are used for these missions where four monopole antennas are placed at the edges of the CubeSat as mentioned in the image below.

Geo Satellite Communication Antennas

GEO Satellite’s main function is TV broadcast and voice data transmission. Hence, many communication satellites are geosynchronous. Since GEO satellites are about 36,000 km away from earth, they need high levels of radiated power. For this purpose, large effective reflector antennas are used with large apertures. Reflector antennas have a simple structure, high, lightweight, and mostly operate in the Ka-band. Each reflector antenna is pointed toward a specific geographical location on earth as observed in the image below which helps in the seamless broadcast of signals.

Space is a treacherous environment and several factors must be considered before deploying an antenna in space as they are the only elements that will facilitate the transmitting and receiving of signals and enable connection from space to earth and vice versa. Hence, they must be suitable to the structure on which they are used both electrically & physically. Furthermore, the durability and reliability of these antennas must also be tested and taken into account along with the following conditions and tests.

Launch phase

The launch of a spacecraft will subject the antenna to shocks, mechanical stress based on static loads, acoustic vibrations, and sudden atmospheric pressure drops that will deteriorate the performance of the antenna. Hence, these effects must be taken into consideration during the antenna design stages.

Space environment

Post-launch, when a spacecraft is exposed to the harsh environment of space the antenna will be placed in a vacuum. Also, the high-temperature change which occurs suddenly will hamper the thermal stability of an antenna if this factor was ignored during the initial thermal stages. Solar radiation and atomic oxygen oxidation are also different factors that will affect the performance of an antenna.

Verification for launch and environmental effects

To reprimand and foolproof the antenna to perform functionally in the space environment and withstand the launch effect mentioned above, some tests should be performed before the mission can officially begin. 

The tests are listed below:

  • Thermal qualification
  • Random vibration or acoustic
  • Quasi-static acceleration
  • Stiffness measurement