An innovative antenna assembly developed to serve Europe’s coming generation of weather satellites is being tested in the ESA’s cavernous Hertz chamber, which can reproduce the boundless reaches of space. This UHF and L-band combination patch-array antenna (Developed by Thales Alenia Space Italy) has been designed to operate aboard Meteosat Third Generation Imaging satellites.
The ESA and Eumetsat’s Meteosat Third Generation (MTG) programme will extend and enlarge the services currently provided by Meteosat Second Generation (MSG) satellites from 2020 onwards. The mission requires two types of satellites, MTG-I (imaging) and the MTG-S (sounding). Planned to operate for more than 20 years, four MTG-I and two MTG-S satellites will be built. Between them, the satellites will provide key data for near-term weather forecasting as well contributing to global climate monitoring.
MTG-I satellites carry a Data Collection System that gather readings from platforms distributed across the globe, which transmit results up to the satellites in UHF for retransmission to the ground. In addition, they host Geostationary Search and Rescue (GEOSAR) transponders that pick up UHF distress signals, passing on these SOS calls to regional search and rescue centres in L-band, operated as part of the international Cospas–Sarsat satellite relay system.
A prototype antenna placed within a mock-up MTG-I underwent testing inside ESA’s Hybrid European RF and Antenna Test Zone (Hertz) chamber, in ESA’s ESTEC technical centre in Noordwijk, the Netherlands. The chamber’s metal walls form a ‘Faraday cage’ to block all external signals, isolating the facility from TV and radio broadcasts, aircraft and ship radars, even mobile calls. Pyramid foam cladding absorbs radio signals internally to create conditions simulating space’s infinite void.
The Hertz Chamber is a hybrid chamber that supports both near field and far field antenna testing techniques. The compact range built in the early 1990s has more recently been supplemented by a state-of-the-art near-field scanner that allows a full sphere sampling of the electromagnetic fields produced by the antennas under test down to frequencies in the order of a few hundred megahertz.
The near-field scanner has been used around the clock for the five-week test campaign, measuring near fields that, with appropriate mathematical transformations, allow the performance of the antennas to be derived in all directions. The data acquired by the test is still being evaluated, but the preliminary results show the antennas are performing well and the accuracy of the measurement is very close to state-of-the-art.
