Research On Estimation Of ISAR Amplitude-Phase Error In Pulses And Narrow-Band Interference For Waveform Optimization Method

Inverse synthetic aperture radar(ISAR)has been widely developed and applied in civil and military fields with the advantages of all-day,all-weather,long-distance detection and highresolution imaging capacity.In order to achieve higher resolution observation of the target,the transmitted signal of the ISAR system are developing towards higher-frequency and larger bandwidth.Although the resolution of ISAR imaging is improved,due to the limit of radar hardware performance,the quality of transmitted signal is inevitably affected,making the amplitude and phase consistency becoming worse.At the same time,with the development of all kinds of modern electronic communication equipment and jamming equipment,the electromagnetic environment of ISAR system is becoming more and more complex.The frequency-using-equipments will inevitably conflict with the working frequency band of the ISAR system,resulting in intentional or unintentional interference when ISAR observes the target,which affects the imaging quality.Therefore,it is meaningful for focused range imaging to estimate the internal amplitude-phase-error and external narrow-band interference,followed by the ISAR transmitted waveform optimization of amplitude-phase characteristics.From the perspective of the transmitted waveform optimization of wideband radar,this thesis will firstly study the amplitude and phase error estimation method in radar calibration process.Then,adaptive narrow-band inference detection method is studied.The amplitude and phase coefficients can be constructed to achieve the precise compensation of the internal system error and the effective suppression of external interference.Focused imaging results can be finally obtained.The research content of this thesis includes the following three parts:1.The basic principle of ISAR imaging is described.Firstly,the ISAR imaging model is established,and the basic process of range Doppler(R-D)imaging is described.Combined with the linear frequency modulation and phase coded signal waveforms,the analytical expressions of range pulse compression are deduced.Then,the typical methods of envelope alignment and autofocusing in translation motion compensation are introduced.Finally,the ISAR imaging process under two waveforms is simulated to verify the effectiveness of the above theoretical analysis.2.Aiming at the problem that the internal amplitude and phase errors in ISAR system lead to the decline of the target range imaging quality,an alternating optimization method is proposed to achieve the accurate estimation of the amplitude and phase errors,followed by the amplitude and phase error compensation coefficients construction and optimization of the transmitted signal waveform.Firstly,the amplitude and phase errors induced by ISAR transmition and receive modules are modeled as high-order polynomials.The effect of different-order parameters on range imaging quality is analyzed.Then,by selecting the entropy of the range pulse compression result as the objective function in radar calibration process,the polynomial coefficients of the amplitude and phase errors are alternating optimized through gradient descent method and particle swarm optimization(PSO)method,respectively.Finally,the experimental results based on simulation data verify the effectiveness of the proposed methods.3.Aiming at the problem that the traditional waveform optimization method cannot achieve the adaptive detection and suppression of narrow-band interference without the prior interference information,anti-narrowband interference waveform optimization methods are proposed to deal with the linear frequency modulation(LFM)and phase coded waveforms optimization.Firstly,as for LFM signal,the problem of anti-narrowband interference waveform optimization is transformed into the "0-1" amplitude modulation coefficients estimation problem of the transmitted signal power spectrum.The number and frequency band positions of the narrowband interference can be estimated by sequential genetic algorithm(GA)and PSO algorithm.Then,the power spectrum of optimized signal can be constructed to achieve the narrowband interference suppression.After that,as for the phase coded waveform,the normalized one-dimensional range profile energy is used as the optimization objective function and the phase coded sequence is optimized by GA.Meanwhile,a mismatched filter is constructed to obtain the pulse compression result with low sidelobe.Finally,the effectiveness of the proposed algorithms are verified by the experimental results.