Speakers
Description
The Wavemill is an RF instrument which follows a pure along-track interferometer concept, the
'Javelin’ one. In the Javelin architecture, master and slave phase centres should be perfectly
aligned in the along track direction, and the resulting interferogram, co-located, is only sensitive to
surface motion. The objective of the Wavemill instrument is to combine along and across track radar interferometry to provide high accuracy 2D measurements of ocean current velocity, ocean current direction and
ocean topology, over a wide swath of 2 x 100 km.
Earlier studies resulted in an instrument design based on four separate antenna structures. This
concept, whilst having good predicted performance potentially experienced differential heating
across the antennas which required compensation and complicated the instrument calibration. An
alternative design called 'Javelin' based on two in-line antenna structures was therefore developed
which would experience a more uniform thermal environment and simplify in-orbit calibration.
In the frame of the Wavemill program an antenna capable of generating up to four squinted beams with
a swath of around 100km is being studied. The Wavemill instrument is composed of two subsystems, each subsystem includes two antennas and both fore and aft subsystem are separated by a baseline distance of more than 12 meters in the along-track direction. One single antenna shall transmit a dual linear polarized pulsed
signal in one beam at a time. Each antenna of the two subsystems shall receive in a dual linear
polarized mode the reflected signal within this beam. This operation shall be repeated successively
4 times, for the 4 different beams. The Javelin Wavemill instrument operation provides the required
along-track interferometric baselines with a compact spacecraft at launch.
Each antenna subsystem shall be able to produce 4 transmit beams in dual linear polarization, and
for each transmitted beam, the 2 antenna subsystems separated in along track shall be able to
produce at the same time the same beam footprint to receive the reflected radar signal in the same
polarization.
The antenna subsystem is defined as the antenna radiating aperture(s), the feeding network, the
single antenna structure, the deployment arm interconnecting the antenna to the host spacecraft,
the relevant hold-down and release system, and the deployment and pointing mechanism.
The orientation of the vertical polarization shall be perpendicular to the flight direction at mid
footprint incidence angle, horizontal polarization shall be orthogonal to the vertical one.
A Leaky wave antenna concept has been chosen as the most suitable one for Wavemill mission. A representative antenna breadboard has been manufactured and tested in Airbus Defence & Space España.
RF measurements and assessment of the results are included in this project obtaining very good agreements with the predictions.
| ESA Technical Officer | Jean-Christophe ANGEVAIN |
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