| Paper: | TH-A3.2 |
| Session: | Current Concepts |
| Time: | Thursday, March 29, 11:00 - 11:20 |
| Presentation: |
Oral
|
| Topic: |
Current and future satellite missions: |
| Title: |
The Radio Frequency and Calibration Assembly for the MetOp Second Generation MicroWave Imager (MWI) |
| Authors: |
Carine Bredin; Airbus DS SAS | | |
| | Jean-Claude Orlhac; Airbus DS SAS | | |
| | Thibaut Decoopman; Airbus DS SAS | | |
| | Pierre-Olivier Antoine; Airbus DS SAS | | |
| | Asma Kallel; Airbus DS SAS | | |
| | Christophe Malassingne; Airbus DS SAS | | |
| | Franck Bayle; Airbus DS SAS | | |
| | Christian Tabart; Airbus DS SAS | | |
| | Alfredo Catalani; Space Engineering Spa | | |
| | Tito Lupi; OHB Italia Spa | | |
| | Salvatore D'Addio; ESA-ESTEC | | |
| Abstract: |
The MicroWave Imager (MWI) instrument is part of the payload complement of the MetOp-SG Satellites that will continue and enhance meteorological observation from polar orbit. The MWI is a conical scanning total power microwave radiometer, providing calibrated and geolocated measurements in 26 channels ranging from 18.7GHz up to 183.31 GHz, offering dual polarization measurements up to 89 GHz.
The MWI instrument is composed of one rotating part and one fixed part. The rotating part includes the Radio-Frequency Assembly (RFA) and is completed by two electronic units: the Front End Electronics (FEE) and the Command and Data Processing Unit (CDPU). The fixed part contains the passive hot calibration target, the cold-sky view reflector and the electronics for the instrument control and interface with the platform. A scan mechanism provides continuous rotation at a constant speed of 45 rpm.
The RFA is the main element of the rotating part of the MWI. It encompasses the functions of main antenna and receivers, and it includes support functions like structure and thermal control. The RFA is composed of the following elements: the Front-End Sub-Assembly (FESA), the Low-Frequency Equipment, the Main Reflector. The RFA is mechanically interfaced with the Scan Mechanism which provides the rotation and the Launch Locking Devices which ensure the clamping of the rotating part during launch phases.
The RFA structure allows field of view for Earth scanning and towards the calibration sources. The on-board calibration target (OBCT) and the cold sky reflector are supported by a central mast forming the hub of the scan mechanism. The cold sky reflector deflects towards the horns the radiation from the cold sky, in the anti-sun side of the orbit. Thermal insulation is particularly important for the OBCT. Its temperature shall be as much as possible constant and spatially uniform. To meet this objective, the OBCT includes a baffle which prevents from sun intrusion, which is closely matched with its racetrack located on the rotating part.
The high number of channels and the broad band spectrum drives towards a technology step forward compared to former radiometers. As the number of channels increases, the RFA accommodation and especially the FESA becomes by far more challenging to design. With regard to previous instrument generation, the increase of mass and power of the RF equipment leads to a significant phase of design optimization to maintain the balanced instrument inside the very stringent mechanical specification.
The RF architecture has been broken down from the frequency channels requirements in a manner that limits the number of units, while meeting RF, accommodation and dynamic requirements. When possible, direct detection has been preferred for simplification and compactness, however for narrow band channels and high frequencies, heterodyne detection with down-converters and IF filtering are still the best solution performance wise. Receivers are simultaneously constrained by the accommodation inside the FESA and the stringent instrument radiometric sensitivity requirements. This calls for challenging envelope, mass and power consumption together with state-of-the-art noise figure performances for the receivers and a very compact design of the FESA. European cutting edge M-HEMT technologies and innovative Schottky diode technologies are extensively used to achieve outstanding receiver performances.
An overview of the instrument performance will be given at the end of the paper. The current MWI design shows compliance to the severe radiometric sensitivity requirements
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