Distributed Spaceborne Radar Grating Lobe Suppression Technique

A long baseline with narrower beamwidth can be provided by distributed space-based radar at the cost of grating lobes, which can not correctly distinguish the angle of the receive signals, then generate angle ambiguity . This paper focuses on the study of grating lobes suppression technique on the distributed space-based radar.First, the work principle of distributed space-based radar is introduced. Then, the paper analyzes the effects of the Earth's rotation: the crab angle will affect the cone angle, and the crab magnitude will affect the magnitude of Doppler frequency, which cooperated affect will make the Doppler frequency shift. Next, the paper detailedly analyzes range ambiguity,Doppler ambiguity,angle ambiguity and the ground clutter distribution of the distributed space-based radar. The moving target detection performance is seriously interfered by the presence of ambiguities. Therefore, the clutter suppression problems of Doppler ambiguity,range ambiguity and grating lobes clutter are the key problems of distributed space-based radar to be resolved.Next, the paper focuses on the grating lobes suppression problem of the distributed space-based radar. Three suppression methods are proposed:1,A method of grating lobes suppression for non-uniform distributed space-based radar based on genetic algorithm. This method uses genetic algorithm(GA) to determine the satellite position vector of the ultra-sparse distributed space-based radar array, then suppress grating lobes. It improves effectively the GA's performance by real-valued coding of chromosome. When the baseline of satellites array and the minimum spacing are given, the effectiveness of this grating lobes suppression method was validated by the simulated results. As the development of the small satellite technology, the cost of small satellite is reduced, and this study will have certain reference value for the design of distributed small satellite.2,A method of grating lobes suppression using frequency diverse MIMO waveforms technique. When frequency diverse orthogonal waveforms were transmitted, the suppression effects is dependent on parameters as frequency offsetΔf , the number of transmitted waveforms as the sparse distance L is given. A largerΔf leads to larger movement of grating lobes, more transmitted waveforms means more beams can be combined to lower down grating lobes. Transmitted frequency diverse orthogonal waveforms is a effective method to eliminate ambiguity and improve the moving target detection performance.3,A method of grating lobes suppression for uniform distributed space-based radar array using frequency diversity is studied. Radar system transmits or receives three different frequencies, so as to move the location of the first grating lobes from±λM/d to±QλM/(Pd), then the effect of grating lobes can be suppressed between-(Q-1)λM/(Pd)and +(Q-1)λM/(Pd). This method effectively suppresses the grating lobes ambiguity for distributed space-based radar, then attains high angular resolution and angular accuracy at a lower cost.