Alcatel developed a new generation of dual-frequency radar altimeter (POSEIDON 2) which works in C and Ku band. This article discusses about the radiofrequency unit (RFU) which plays a major role for the stringent performances of the altimeter. The compact RF unit has been designed with a modular concept. It uses the new advanced technologies: extensively use of MMIC, pHemt LNA and hybrid HFET power amplifiers. The transmitted peak power level is greater than 23W in C band and 7W in Ku band.