Low frequency ultra wideband (UWB) synthetic aperture radar (SAR) has shown a great potential when vehicle-size objects are obscured in foliage. The studies imply an aperture angle of at least 180° to include the strongest (broadside) response when the target orientations are unknown. However, the aperture angle of the linear SAR (LSAR) is limited. By using circular traces, the aperture angle of the radar data acquisition has been increased, and the detection capabilities could be improved. An airborne circular SAR (CSAR) data acquisition experiment was carried out in Shaanxi by the National University of Defense Technology (NUDT). The data was acquired by using P-band UWB SAR system along a circular trajectory with the beam spotted on the same area. Compared with LSAR, this imaging mode has a better understanding of the scattering properties of targets, high resolution with low frequency band, and the capability for a 3-D target reconstruction. In this paper, the airborne multiple orbit CSAR data acquisition experiment and the processing of such data are presented.