Research On Radar Low-altitude Weak Target Detection Technology

With the gradual opening of the low-altitude field and the increasingly sophisticated low-altitude and ultra-low-altitude penetration technology,low-altitude weak target detection probability is relatively low owing to the multipath effect and small target's Radar Cross Section(RCS),the research on detection technology has also become increasingly important in the military field.This thesis aims to solve the problem of lowaltitude weak target detection,adpotes frequency agile signals to improve the multipath cancellation problem,in the meantime,utilizes long-time integration to improve the signal-to-noise ratio(SNR),and then uses Keystone transform and compensation function to correct the problem of distance movement,improves low-altitude weak target detection performance ultimately.The main works are as follows:1.Establish a low-altitude target multi-path model,and a 4-way echo signal model is built according to the established multipath model.Afterwards,some mathematical parameters such as the path difference between the direct path and the reflection path and the grazing angle of the reflection path are calculated.Next,the influence of the multipath effect on the echo power is analyzed via echo model.Further,some common approaches for improving the detection effect of weak multiple targets are also studied.2.According to the multipath factor the influence of wavelength on echo power was found,frequency agility is employed to improve the situation where the multipath echo signal cancels the direct echo signal.The characteristics and differences of the three commonly used frequency agility signals are analyzed,as well as the effect of frequency agility on the path difference and wavelength ratio in the multipath factor and the decorrelation of frequency agility,and simulation tests also verify that adopting frequency agility method can reduce the situation where multipath echo signals cancel direct echo signals.Moreover,in order to use long-time coherent integration to improve the signalto-noise ratio,frequency agile signal is redesigned and the signal grouping method is introduced for frequency agile signal.After that,extensive simulation tests are conducted to analyze and compare in terms of pulse group agile signal and the designed agile signal.3.The long-time integration method is adopted to improve the detection probability of weak targets,however,due to the shortcoming of the designed frequency agile signal with amplifying speed,this strategy can result in distance movement problem greatly.To overcome this deficiency,according to the reason of movement and signal echo analysis,Keystone transform(KT)and compensation function are utilized to solve the problem of distance movement caused by long-time integration of each group.Unfortunately,since the designed frequency agile signals are grouped,there are some differences in the results of the cumulative accumulation of the respective memory cells which are showed in the distance-Doppler diagram's doppler unit.Thus,it causes that the final constant false alarm rate(CFAR)processing result cannot been added up directly.To overcome this drawback,Keystone transform is used to reacquire the signal to solve the problem of doppler unit movement caused by the different frequency of each group.4.Based on the previously analyzed signal processing methods and signal processing flow,a radar low-altitude weak target detection scheme is designed.To be specific,this scheme includes three modules,namely,Keystone transform sampling module,distance correction module and CFAR module.Under different scenarios,each module can be modified and redesigned to meet different requirements for multiple targets.Extensive simulation tests demonstrate that the proposed scheme is effective and feasible.