Research On The Waveform Design Of Random Hopping Frequency And Signal Processing

With the development of electronic countermeasures technology,the higher anti-jamming capability and detectivity of radar are required.In order to improve the anti-jamming capability of large time-bandwidth product and high resolution radar,the frequency of pulse should be changed randomly.In order to improve the detectivity of radar,the sidelobe of the ambiguity functions is required to be low enough.In this paper,signal model was modeled,analyzed,and elicited and simulated.Have a research on realizing a low sidelobe random hopping frequency signal in both waveform designing and signal processing.The main contents of this paper are as follows:First of all,the basic theory of radar signal processing is briefly introduced,which paves the way for the following chapters.Then,the waveform design methods and signal processing methods of several common large time-bandwidth product signals are introduced,include linear frequency modulation signal,stepped-frequency signal and non-linear frequency modulation signal.The advantages,disadvantages and application scenarios of different signals were analyzed and compared.After analyzing the advantages and disadvantages of these signals,the advantages and disadvantages of random hopping frequency signals were expounded,and the importance and necessity of random hopping frequency signals were presented.The signal model of random frequency hopping signals was modeled.The theoretical derivation shows that the range ambiguity function is only related to the frequency set of the pulse train,but not to the order of different carrier frequencies.We can get hopping frequency signal with different range ambiguity function by selecting different frequency sets.In the third chapter of this paper,the traditional genetic algorithm is used to optimize the frequency set which meets the set condition.It was founded that the frequency distribution after sorting conforms to the "S" curve distribution in rough,after obtained the frequency set.And higher the setting conditions,means lower amplitude peak sidelobe,the higher fitting degree of frequency distribution to the "S" curve.Then,a "S" curve model of frequency distribution was modeled according to spectral density window function,and a set of frequencies strictly conforming to "S" curve was obtained,so a random frequency hopping signal was obtained.The results of Matlab simulation show that range peak sidelobe of the random hopping frequency signal can be as low as-40 dB,and different "S" curve can even reach a lower level,which greatly improves radar resolution.Finally,the advantages and disadvantages of the two waveform design methods were analyzed.In order to obtain random hopping frequency signal with low sidelobe,we can achieve the goal of reducing range sidelobe by means of sidelobe suppression,besides the way of waveform design.The key to achieve low range sidelobe is the design of filter.In this paper,the adaptive iterative least squares algorithm is used to design filter.So the ambiguity function's sidelobe of echo signal would be compressed when the echo signal through the filter.In the traditional iterative processing,the threshold is a fixed parameter,which can not adjust the threshold parameter according to the last time.In this chapter,the threshold of the algorithm is dynamically adjusted according to the output result,which accelerates the algorithm.This scheme not only can suppress sidelobes of the ambiguity function of random hopping frequency signals,enhance the radar resolution,but also has the characteristics of easy realization.It improves the detection ability of broadband radar to the target,to a certain degree.