Active antenna sub-system development for space-borne SAR

This paper discusses some of the innovative features incorporated in a new type of SAR front-end antenna subsystem, currently the subject of an R&D program at Astrium, Portsmouth. Traditionally, such active radiating ´tiles´ - used to populate the large SAR antenna aperture - have been a mixed assembly of electronic modules, structural components and passive RF units, all having different interface requirements. On the Envisat ASAR antenna, for example, this has necessitated the extensive use of wiring looms, flexible RF cable interconnects and mechanical devices such as isostatic blades (to offset CTE mismatch). The build cost, especially at AIT level, has proved to be unacceptably high and has led to the ´Integrated Front-End Sub-System´ concept (IFESS). To this end, Astrium are preparing a partially integrated X-band tile to demonstrate the key technology areas. Critical system parameters are listed.