Research On Space-time Processing Techniques Of Virtual Aperture In MIMO Radar

Because the transmitted signals of airborne MIMO radar are orthogonal, we can make an equivalent transmit beam-forming at the receiving end. When the antenna array of MIMO radar is sparse, it can get a larger continuous virtual aperture, which can improve the spatial resolution of MIMO radar. Especially, when the transmitting array is sparse and the receiving array is compact, the MIMO radar uses wide transmitting mode and creates no grating lobes, which has very high research value. This paper’s research object is just such virtual aperture which is generated by sparse-transmitting and compact-receiving array. We have studied and analyzed the antenna pattern, clutter features, MTD algorithms and STAP algorithms of such virtual aperture. The main job we have done is as follows:1. We studied the echo signal model of airborne MIMO radar and derived the principle of virtual array from the equivalent beam-forming of receiving and transmitting array. According to the theoretical derivation, when one end of the transmitting and receiving end is sparse and the array element spacing meets certain conditions, we can get maximum continuous virtual aperture. By simulating the joint pattern of MIMO virtual aperture, we can get that MIMO virtual aperture has narrower main lobe and it has much higher spatial resolution. As the MIMO radar transmits orthogonal signal, it belongs to wide transmitting mode. When the transmitting array is sparse, MIMO radar generates no high gain grating lobes, which is in favor of radar’s stealth. From above all, we will get that the virtual aperture of MIMO radar has very high research value.2. Beginning with the composition of airborne radar ground clutter, we have studied some features of the main-lobe clutter, side-lobe clutter and altitude clutter. We have also learned some common methods of clutter simulation and the non-ideal factors of clutter. We deduced the principle of equidistance-scattering-unit-integration method and the calculation method of minimum variance spectrum. In the simulation experiment, we compared the clutter spectrum of phased array, compact-array MIMO and virtual-array MIMO, and get that the virtual-array MIMO has better performance in clutter rejection.3. We introduced the process of non-adaptive signal processing and studied the principle of the four modules which include matched filtering, transmit and receive beam-forming, MTD and CFAR. In the simulation experiment, we processed the signals of compact-array MIMO and virtual-array MIMO with non-adaptive signal processing algorithm. Comparing the simulation results, we can get that virtual-array MIMO has better performance in moving target detection.4. We have studied the adaptive processing algorithms of MIMO radar and processed the signals of compact-array MIMO and virtual-array MIMO with STAP algorithm. By comparing the simulation results, we obtained that the MIMO virtual aperture has greater advantage in moving target detection.