Adaptive Waveform Design For Airborne Cognitive Radar

There are practical values of radar in the following fields: life detection, the growth of crop roots, civil aviation, military and so on. With the limitations of the size and weight, the airborne radar has the characteristics of smallness in size, lightness in weight and sharing the same antennas when transmitting and receiving signals. When an airborne radar detects motion targets with low-altitude and slow-speed, the non-homogeneous clutter and interference caused by non-homomorphism clutter, complicated target background and artificial buildings have serious influence on its detection performance. In order to reduce the influence above, the concept of cognitive radar was presented. At present, the cognitive radar is still in the phase of a concept, and there are many key technical problems to solve. This article proposed a new clutter modeling method and the adaptive forming algorithm of the transmitted waveform based on the concept of cognitive radar. The contents of this paper are as follows:1. Through analyzing and comparing the structures of traditional radar system and cognitive radar system, the limitation of traditional radar was pointed out. By regonizing the basic model of cognitive radar, the cognitive radar workflow was analyzed.2. A novel clutter model of airborne cognitive radar is constructed based on digital elevation model(DEM) data. On the basis of analyzing and mining the real DEM data, four landform factors: elevation, slope, terrain relief and surface roughness were extracted to distinguish the topographic landforms. Then we create a database of topographic information on MySQL platform to store DEM data and the related topographic information. Meanwhile, considering that the radar carrier is aircraft, we designed a new algorithm to reduce the computational burden. This algorithm extracts a specific part of the data according to the aircraft position and scanning range. Based on the above algorithm, we proposed a new clutter modeling based on DEM data. Simulation results showed that the clutter constructed by the new method was in line with the actual scene, with realistic, stable and reliable advantages. And it provides effectively prior knowledge for the adaptive design of cognitive airborne radar waveform.3. We mainly used the maximum output signal-to-noise ratio(SNR) criterion to design the adaptive waveform of cognitive radar. The solution of the optimal matched waveform was obtained from two aspects: one is using the target model and the other is using the clutter data produced by the new clutter model. At the same time, under the condition of as far as possible reducing SNR loss and constant modulus constraint, the energy spectrum of optimal matched waveform was synthesized in time domain. At last, the digital beam was formed with a phased array antenna. Compared with the traditional methods, the simulation results showed that the proposed method could enhance the SNR through designing the waveform which could change with the different target or clutter, and has more practical application prospects.