When designing low-signature air vehicles several disciplines have to be integrated: The signature has to be as low as possible for different threat sensor systems and aerodynamic and manoeuvre characteristics have to fulfil the requirements. A common process is needed where different concepts can be evaluated and optimizations can be made with respect to several parameters. The project reported here has been conducted during 2004-2005 within the framework of FoT8 and is coordinated with the project "Utformning lågsignaturfarkost" which is conducted in FoT25. Both projects have been carried out at FOI and the objective is to design, analyze and improve a UCAV concept (Unmanned combat air vehicle called EIKON) which is inspired by the experimental air vehicle Pegasus. The project presented here focuses mainly on sensor related issues such as requirements, signature modelling, signature measurement and signature analysis. Also, low observable materials are treated. This report presents the results obtained during the year 2005. Main topics treated are requirements, signature modelling, radar signature measurement and preliminary study concerning multi-disciplinary optimization. A summarizing final report for the project is issued at the same time.