Research On Sidelobe And Grating Lobe Suppression Method For SAR Image Of FJB Signal Based On GWO Algorithm

Synthetic Aperture Radar(SAR)is widely used in military and civilian fields due to its all-weather and all-weather observation capabilities.SAR based on Frequency Jump Burst(FJB)signals synthesizes multiple narrowband signals into large bandwidth signals through broadband synthesis technology,avoiding the technical and methodological difficulties caused by directly transmitting large bandwidth signals.This provides a new technical approach for achieving high-resolution range profiles and has become a research hotspot.However,the frequency stepping characteristics of FJB signal subpulses bring additional periodic grating lobes to the range direction of their SAR images.The inherent sidelobes and these grating lobes of FJB signal subpulses in the range and azimuth directions can mask or hide weak reflection targets,affecting imaging quality,causing missed detection of targets or increasing the probability of false alarms.In response to the above issues,this article conducts research on sidelobe suppression methods for SAR images based on FJB signals in the range direction from two aspects: waveform parameter design at the radar signal transmitter and signal filtering processing at the receiver.Based on the above two sidelobe suppression methods,joint sidelobe suppression is performed on 2D SAR images.The main content includes the following parts:(1)A joint suppression method based on multi-objective grey wolf optimization algorithm for distance sidelobe and gate lobe is proposed to address the uncertain high-level sidelobe problem caused by the random selection of FJB signal waveform parameters in the range compression results.This method can optimize waveform parameters with the goal of minimizing sidelobes and gate lobes under the given system resolution and maximum instantaneous bandwidth of sub pulses,and obtain a quantitative relationship between sidelobe suppression level and waveform parameters.Compared to the comparative algorithm,the Pareto solution set obtained by the multi-objective grey wolf optimization algorithm has better convergence and diversity,resulting in waveform parameter values with higher sidelobe suppression performance.(2)A strictly constrained third-order spatial apodization sidelobe suppression algorithm is proposed to address the problem of high-level sidelobes generated by the distance compression results of sub pulses of the FJB signal and high-level gate lobes caused by the frequency stepping characteristics of the FJB signal.The algorithm combines the gate lobe suppression method of sub pulse windowing,A sidelobe suppression algorithm for frequency modulated stepper radar signals is proposed based on the Triple Apodization and Three order Spatial Variant Apodization(TA-TSVA)algorithm for processing full pulses using subpulse three apodization filtering.This method combines the long-range gate lobe suppression ability of Kaiser window and the close range gate lobe suppression ability of Chebyshev window,improving the overall gate lobe suppression performance;By increasing the order of the filter,the search space for filter coefficients is expanded,and the sidelobe suppression performance is improved.The simulation results show that this algorithm can more effectively suppress the range sidelobes of SAR images while maintaining the main lobe without broadening.(3)The feasibility of two-dimensional separable sidelobe suppression of SAR images based on FJB signals was analyzed.The waveform parameter design method and signal filtering method based on distance sidelobe suppression of FJB signals were used to jointly suppress the sidelobes of two-dimensional SAR images based on FJB signals.The performance of the two methods in suppressing sidelobes of SAR images was verified.The simulation results show that the combination of waveform parameter design method and signal filtering method algorithm can effectively improve the sidelobe suppression performance of two-dimensional SAR images,and the sidelobe suppression effect is better than that obtained by using the two methods alone.