The adopted antenna architecture is a single offset configuration using a 1-bit reconfigurable reflectarray and have been properly dimensioned in order to accomplish the requirements on Gain and on EIRP over RF transmit band (ETSI EN 301.428 and ITU-R S.728.1).
The selected solution provide the use of a reconfigurable main reflector in horizontal position, and the use of a sub-reflector in a fixed configuration.
This architecture allows to increase the focal distance and to reduce the overall profile of the antenna. The problem of portability and big size of the antenna remain a critical issue. For these reasons an antenna folding, which allows size reduction has been proposed.
The antenna in deployed configuration is a pentagon while in stowed position is made up by a rectangle (50cmx60cm) and three triangles folded upon it.
A subreflector, illuminated with a dual polarized elliptical feed, has been designed considering 38x48 elements. The elements are based on either two or three layers of varying-sized rectangular patches and are dimensioned in order to obtain the desired field distribution on the main reflector. In order to obtain acceptable performance the main reflector surface will necessarily employ thousands of reflecting elements.
The architecture of the elementary cell has therefore a strong impact in the overall cost and complexity, and the minimization of the number of electronic devices to be used is mandatory. To this purpose the most effective approach is the use of 1-bit elementary cells. The cell is a stacked structure made up of multiple coupled resonators in different technologies (microstrip and slotline) that allows to cover the whole operative bandwidth imposed by the specifications.
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Reconfigurability of cells is achieved employing PIN diodes and providing a proper biasing voltage the elementary cell can be switched between two different configurations with a relative phase difference of 180°.