The Waveform Design Of Chaotic Radar And Weak Signal Detection Under Chaotic Background

The matched filter of matched filterable chaotic radar system can be implemented by low-cost analog devices and has broad engineering application prospects. But transmitted signal of this system is not a band-limited signal, causing signal in the process of propagation prone to spectrum leaked and distortion, so it is necessary to design transmitted signal in the form of band-limited signal.In addition, the present study showed that many engineering problems can be attributed to weak signal detection from strong chaotic background. For example, sea clutter suppression to reveal the weak target signal in skywave over-the-horizon radar. So weak signal detection from strong chaotic background has very broad application prospects.This thesis focuses on the researchs about waveform design of chaotic radar and weak signal detection from strong chaotic background. The main works are summarized as follows:(1) Study on waveform design of matched filterable chaotic radarAs the transmitted signal of matched filterable chaotic radar system is not a band-limited signal, this paper gives a radar waveform design method by using chaotic synchronization and filtering: in the radar transmitter, make the chaotic signal become a band-limited signal by designing a filter; in the receiver, use synchronization and filtering to recover the chaotic signal. Compared with traditional signal design methods, the proposed method is implemented in the analog domain, with an advantages of low-cost; in adittion, the method is still have good target range resolution when the signal-to-noise ratio(SNR) is as low as-20 dB.(2) Study on weak signal detection from strong chaotic backgroundFirstly gives a weak signal detection method by using echo state network, this method is essentially to use chaotic phase space reconstruction method based on Takens theory, which is the main method of weak signal detection from strong chaotic background, however, this method often requires high signal-to-interference-plus-noise ratio(SINR) and sensitive to Gaussian white noise, etc. Then according to the second-order statistical properties of chaotic signal is unchanged, and combined with optimization theory, this paper proposed a harmonic signal detection method from strong chaotic background based on optimal filter, which has stronger anti-white noise performance, meanwhile can detect weak harmonic signal under lower SINR, and can detect a greater range of signal amplitude.(3) Application of the weak signal detection method by using echo state network in skywave over-the-horizon radar sea clutter suppressionFurther more, taking into account that the weak signal detection method by using echo state network can be applied to over-the-horizon radar sea clutter suppression; this paper gives an over-the-horizon radar sea clutter suppression method based on echo state network. The method firstly analyzes the chaotic characteristics of sea clutter, then uses echo state network to reconstruct and suppress the chaotic sea clutter. Measured data processing indicates that compared with traditional cycle cancellation method and singular value decomposition method, the proposed method has better performance of sea clutter suppression in the situation of short coherent integration time and low speed.