Based on the concept of aperture synthesis sparse antenna

the imaging radar on the stratosphere airship for the earth observation is investigated.The multiple phase centre aperture synthesis method in time division mode is proposed to eliminate the high side lobes of sparse array.Using simulated annealing algorithm to optimize the location of antennas

so as to minimize the number of antennas used.To guarantee the power of transmitter and enhance range resolution

the multiple frequency orthogonal signals have been used to achieve multiple-input and multiple-output function.For the length of array is far less than the scene width

the sub-aperture imaging method is adopted.The curve fitting and PGA(Phase Gradient Autofocus)algorithm have been combined to compensate array error.The simulation results denote the validity of the method proposed in the paper.