The Microwaves and Radar Institute at the German Aerospace Center operate an airborne multi-frequency, polarimetric, imaging SAR system. The F-SAR sensor is equipped with a variety of different antennas, based on patch technology. A new antenna is developed for the P-Band frequency range from 400 to 470 MHz, covering the Biomass mission requirements. The size and weight of the antenna array, and therefore of each single element, is reduced to a minimum. A cavity backed, capacitive coupled stacked patch element is basis for the new PII-Band antenna array.