The airborne synthetic aperture radar system, operated by the Microwaves and Radar Institute, is now equipped with a fully operational P-band subsystem. Antenna design, measurements and first results are presented. Due to the airborne platform antenna elements with reduces physical dimensions were developed, composing an antenna group of 25 dual polarized elements. With two switchable power divider networks the antenna can support a nadir looking sounder mode as well as the standard side looking SAR mode. This paper shows antenna measurements inside the Institutes antenna measurement facility and in flight performance.