The SAR train concept: required antenna area distributed over N smaller satellites, increase of performance by N

The concept implements the coherent combination of the N SAR flying along a same arc as seen from the ground. A particular case is with N SAR in visibility and a single transmit. A "Signal Cleaning" SAR Train keeps unchanged the maximum antenna area of each individual SAR and brings a factor N advantage on both the SNR and the ambiguity protection. The main formation constraint is the width of the tube containing the satellite trajectories on an earth frame. An "Antenna distributing" SAR Train enables the distribution of an unchanged total minimum antenna area into N smaller elementary antennas, together with the multiplication by N of the merit factor (swath over azimuth resolution ratio). Application for N > 2 requires very tight along track SAR spacing accuracy. Use of appropriate spread spectrum waveforms instead of conventional pulse waveforms removes the major part of the extra orbit constraints induced by "Antenna distributing" and enables it for any value of N. A Train of N SAR in visibility eases the metrology of the formation (DGPS) and the global energy efficiency is increased by N since with only single transmit SAR the same performance is achieved. Moreover, the orbit constraints are relaxed by 2. As part of its application, the concept can circumvent the matter of huge antenna size for SAR mission in P band or at very high altitude, all the more as in these cases the tube width constraints are reduced (function of /spl lambda/ and altitude).