Abstract
The linear stepped frequency and linear frequency shift keying (FSK) signal has been widely used in radar systems. However, such linear modulation signals suffer from the range–Doppler coupling that degrades radar multi-target resolution. Moreover, the fixed frequency-hopping or frequency-coded sequence can be easily predicted by the interception receiver in the electronic countermeasures (ECM) environments, which limits radar anti-jamming performance. In addition, the single FSK modulation reduces the radar low probability of intercept (LPI) performance, for it cannot achieve a large time–bandwidth product. To solve such problems, we propose a novel chaos-based stepped frequency (CSF) synthesized wideband signal in this paper. The signal introduces chaotic frequency hopping between the coherent stepped frequency pulses, and adopts a chaotic frequency shift keying (CFSK) and phase shift keying (PSK) composited coded modulation in a subpulse, called CSF-CFSK/PSK. Correspondingly, the processing method for the signal has been proposed. According to our theoretical analyses and the simulations, the proposed signal and processing method achieve better multi-target resolution and LPI performance. Furthermore, flexible modulation is able to increase the robustness against identification of the interception receiver and improve the anti-jamming performance of the radar.
Highlights
Low probability of intercept (LPI) is important for modern radar survival [1,2,3]
The signal introduces chaotic frequency hopping between the coherent stepped frequency pulses and chaotic frequency coded in subpulse FSK/phase shift keying (PSK) composited modulation, which is called chaos-based stepped frequency (CSF)-chaotic frequency shift keying (CFSK)/PSK
For the CSF-CFSK/PSK signal, frequency spectrum splicing method possesses larger computational burden than the target pick-up algorithm based on inverse fast Fourier transformation (IFFT), but can effectively suppress the profile grating lobes around main lobe through the weighted inverse matched filter processing
Summary
Low probability of intercept (LPI) is important for modern radar survival [1,2,3]. The LPI radar typically uses a frequency shift keying (FSK) or phase shift keying (PSK) modulation signal. In the electronic countermeasures (ECM) environments, the Costas frequency-hopping code is relatively fixed, and can be predicted in a straightforward manner using the interceptor to implement precise interference, which reduces the radar anti-jamming performance and robustness against identification of the interception receiver [19,20,21]. Another previous study [22] presented the random stepped frequency signal. Chaotic frequency hopping is straightforward to generate, and the sequences are infinite and aperiodic Because they are more flexible than are the Costas and pseudorandom sequences, the CSF-CFSK/PSK signal offers relatively strong anti-jamming performance. This paper is organized as follows: Section 1 introduces the LPI radar signal features and technology disadvantages of linear stepped frequency or linear frequency-coded signals; Section 2 builds the CSF-CFSK/PSK signal model and analyzes the optimal signal parameter design; Section 3 first analyzes the signal ambiguity function and investigates the range and Doppler resolution and LPI performance; Section 4 presents the CSF-CFSK/PSK signal processing method; Section 5 describes the simulations used to validate the effectiveness of the proposed method; and Section 6 presents the conclusion
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