Research On 3D ISAR Imaging Algorithm Of Shipborne Radar On Moving Target

Shipborne radar is a radar that can acquire high-resolution images of non-cooperative moving targets over long distances.The range resolution comes from the wideband signal emitted by the radar.The azimuth resolution is derived from the Doppler bandwidth generated by the relative motion between the radar and the target.With the development of radar imaging technology,two-dimensional radar images have been unable to meet the needs of certain specific applications,and the demand for three-dimensional radar images has continued to increase.The ship-borne radar oscillates in three dimensions with the waves.When imaging a moving target,there is a high-order phase term in its echo signal,and these high-order phase terms contain information about the target's height.If the traditional ISAR imaging algorithm is used,not only the problem of image defocusing,but also the information of the higher-order phase term of the echo signal cannot be extracted.This article focuses on how to process high-order phase signals of shipborne radar echo signals to improve their imaging resolution.The main contents are as follows:1.Most ISAR imaging uses time-frequency analysis algorithms.Conventional time-frequency analysis algorithms cannot take into account computational efficiency,parameter estimation resolution,and decoupling of multi-component chirp signals.This paper proposes an improved fractional Fourier transform time-frequency analysis algorithm.First use the short-time Fourier transform for rough estimation.Although the short-time Fourier transform has a low resolution,it has a fast calculation speed and can quickly delineate the estimation range of the precise estimation.Then the fractional Fourier transform is used for precise estimation.Fractional Fourier transform solves the problem of coupling terms of multi-component chirp signals in the time-frequency plane,but the two-dimensional search algorithm used to find the optimal transform order has a huge amount of calculations.Through rough estimation,it can effectively reduce Two-dimensional search range.Simulation experiments show that this algorithm effectively improves the calculation efficiency and estimation accuracy.2.Traditional ship-borne radar 3D ISAR imaging uses interference technology.Interference technology not only fails to eliminate the higher-order phase terms of the echo signals from the ship-borne radar,but also requires two radars to image the target at thesame time.In this paper,a three-dimensional ISAR imaging algorithm for moving targets based on single-transmit and single-receive shipborne radar is used.The three-dimensional swing model simulates the complex movement of ship-borne radar with the waves.The function relationship between the high-order phase term parameters of the echo signal and the three-dimensional coordinates of the target scattering point is derived based on the vector relationship between the radar coordinate and the target coordinate.Combining time-frequency analysis algorithms and narrow-band radar measurement data,the three-dimensional reconstruction of the target scattering point can be achieved???Structure.The effectiveness and practicability of this algorithm are illustrated by simulation experiments.3.The ship-borne radar oscillates complexly with the waves.The image resolution is different for different imaging time periods.The optimal imaging time period needs to be selected for imaging according to the actual imaging needs.This paper uses an optimal imaging time period selection algorithm based on the image quality function,taking into account azimuth resolution,height resolution,and reconstruction accuracy to select the optimal imaging time period.The weighting coefficient is adjusted to meet the needs of different scenarios.