Sparse-array Synthetic Impulse and A perture Radar (SIAR) can isotropicly radiate by etnploying multiple frequencies (synthetic pulse) and multiple antennas(synthetic antenna) without beam spanning. The detection ability to low RCS targets(especially to stealthy targets) is improved by use of VHF band and long-time coherent integration. An effective methed to reduct its range sidelobes with frequency-coding agility among these frequencies is presented. Also
the bandwidth of transmitting signals is raised by stepped-frequencies. The high range resolution is obtained by stepped-dfrequency synthesis and impulse synthesis of SIAR. A simple appoch for comensating the effect of target velocity on stepped frequencies is presented. Finally