Master's Thesis from the year 2013 in the subject Engineering - Aerospace Technology, University of Rome "Tor Vergata" (Engineering), course: Telecommunications, language: English, abstract: The Biomass Calibration Radar Transponder Antenna is devoted to receiving and transmitting back the radar pulses generated by the Biomass radar, operating in a 10MHz band centred at 435MHz (P-band), to allow its calibration during operations in orbit. The antenna must provide a directive pattern in double linear polarisation with low cross-polar levels (XPD > 40dB) and low radiation in the backward hemisphere. Low side-lobe levels close to the horizon are very desirable also in the forward hemisphere (SL < -45dB). The aim of my work consisted in designing a planar array which meets the requirements, leading to a good solution for the Biomass Transponder Antenna. The present report summarises the results obtained in the preliminary and advanced design of the radiating element and of the whole array, based on available data and on the preliminary performance assessment.