ASOLANT: Design and Breadboarding of Advanced Solar Antennas (ASOLANT) based on Amorphous Silicon (Si) and Gallium Arsenide (GaAs) Solar Cells
Project: ASOLANT.
Title: Design and Breadboarding of Advanced Solar Antennas (ASOLANT)
based on Amorphous Silicon (Si) and Gallium Arsenide (GaAs) Solar Cells"
Duration: June 2000 - October 2001
Prime contractor: OHB-Teledata, Bremen (D)
Sub-contractor: LEMA-EPFL, IMT Neuchatel
Technical Partners: CESI Milano (I), Carlo Gavazzi Space Milano (I),
Galileo Avionica Milano (I)
Introduction and motivation:
The Advanced SOLar ANTenna project ASOLANT (AO/1-3543/99/NL/SB),
founded by ESA-ESTEC, is the continuation of the former project SOLANT ((AO/1-3308/97/NL/NB)
which dealt with basic work on the integration of amorphous silicon solar cells
and microstrip antennas into a single device (fig. 2). In the ASOLANT project,
the effort was continued and directed towards four specific goals: 1) enlarging
the range of candidate antennas to other planar structures like slot antennas,
2) using high efficiency space qualified GaAs solar cells, 3) meeting the specifications
applicable to a real satellite mission, 4) further integration of final devices.
The selected mission was the MITA-AGILE spacecraft (fig. 1). This project has
shown that an ASOLANT combination can advantageously replace the standard MITA
antennas while providing extra solar cells power.
ASOLANT Project
Team Organisation
DESIGN APPROACH
The basic idea was to demonstrate that the ASOLANT concept could
replace the standard MITA antennas and even add new capabilities like higher
gain or beam tilt. Thus, it was decided to introduce a design of two combined
antennas with two different functions:
A1: A wide beam low gain antenna covering both the up- and down-link bands.
A2: A narrow beam high gain antenna covering only the down-link band.
Two different breadboards have been designed, built and measured
aiming at testing two different solar cells technology and two different antenna
radiation patterns.
The know-how developed during this project allows mounting solar cells in such
a way that cells and interconnections have a controllable effect on the antenna
behaviour and do not degrade the antenna performances.
Amorphous Silicon ASOLANT (ASOLANT-S-1)
In ASOLANT-S-1 we use amorphous silicon (a-Si:H) solar cells. These cells are
cheap, provide the best power/weight ratio and can be tailored to match any
antenna shape, as clearly demonstrate here.
ASOLANT-S-1 is composed by two antennas, a low gain antenna (A1) and a higher
gain array (A2). The low gain antenna is composed by four linear slots in sequential
rotation in order to obtain circular polarization.
The directional array is composed by 16 circularly polarized cross slots and
each cross integrates an amorphous silicon solar module. The solar modules have
been especially designed to fit the antenna shape. This was possible thanks
to the flexibility offered by the a-Si:h solar cells. The cross slot are fed
thanks to a specially designed printed beam forming network. Here, the purpose
was to demonstrate the ASOLANT capability for beam tilting. An interesting radiation
with maxima at +/- 45 degrees was obtained.
Galium Arsenide ASOLANT (ASOLANT-G-3)
ASOLANT-G-3 is composed by two antennas, a low gain antenna (A1) and a
high gain array (A2). The low gain antenna is composed by four linear slots
in sequential rotation in order to obtain circular polarization.
The directional array is composed by 4 circularly polarized cross slots. The arrangement was selected by the need of using predefined square solar cells. Despite this limitation, the increase in gain was noticeable. The crosses integrates 16 GaAs solar cells of 4x4 cm, connected in series. The solar cells are glued on a Kapton sheet that insulates them from the antenna ground plane. The solar cells and their interconnecting wires have practically no effect on the antenna behaviour.
Publications
S. Vaccaro, J.R. Mosig, P. de Maagt, "Patch and slot antennas integrating high efficiency GaAs solar cells for space applications", Journées Internationales de Nice sur les antennes (JINA'02), Nice, 12-14 novembre 2002, vol. II, pp. 117-120.