What are they for?
Antennas are devices expressly designed for transmitting and receiving radio waves. They are a key element of any ESA spacecraft, both in terms of communications and data transfer system and often as scientific sensors in their own right.
Other antennas on the ground complete the communication link with space, forwarding satellite signals to ground stations and vice versa
Antennas also enable global navigation services such as Galileo and broadcasting and communications services of telecommunication satellites which have transformed daily life.
Simultaneously, antennas have also evolved into an indispensable tool for radio-based space science, exploration and Earth observation, allowing in-depth characterisation of many proprieties of distinct space bodies, such as galaxies, planets, stars, and comets, enabled through the use of imaging radar, scatterometry and radiometry.
To serve this variety of applications, a broad portfolio of different antenna technologies are continuously being developed, from small navigation antennas overlooking the whole sky, to dish-shaped 'high-gain' antennas, which concentrate the radio signals they send or receive into a very small area to maximise signal strength. Typically operating across thousands of kilometres, if their pointing direction is off by even a tiny fraction of a degree then their radio beam may end up weakened, or hundreds of kilometres away from their intended target.
Modern antennas are often extremely complex: the current generation of telecommunication satellites transmit multiple small beams instead of a single main beam. Antenna dishes are carefully shaped to optimise signal strength across the region being served and enable frequency reuse for different channels while avoiding 'cross-talking'. Additionally, radio-based instruments for space science research, planetary exploration and Earth observation make use of a very large frequency spectrum, from a few megahertz up to (sub)-millimetre waves, operating well beyond 500 GHz.
The Antenna Testing Laboratories have the challenging task of testing these complex space antennas. By doing this they reduce the risks inherent in adopting state-of-the-art instruments within ESA programmes and allow future missions to be selected with confidence. They are made up of four test facilities, the Compact Antenna Test Range (CATR), the Hybrid European RF and Antenna Test Zone (HERTZ) and the Microwave and (Sub) mm-wave Material RF Characterization Laboratories.
Both CATR and HERTZ are anechoic chambers, screened against external electromagnetic radiation and their inside walls are covered with pyramid-shaped non-reflective foam to absorb signals and prevent unwanted reflections. The CATR can handle antennas of up to 1m in diameter while HERTZ performs measurements on larger antennas or complete satellite payloads. The HERTZ laboratory is also located within a cleanroom area to allow testing of flight hardware.
The Microwave and (Sub) mm-wave Material RF Characterization Laboratories are quasi-optical set-ups based on high performance corrugated horns, grids and refocusing mirrors to allow the determination of complex material properties for antenna applications. The (Sub) mm-wave set-up is installed in a controlled cleanroom environment ensuring adequate conditions for flight hardware testing.