Research On Terahertz Radar ISAR Imaging Based On Real Data

With the breakthrough of the related devices of terahertz radar recent years,terahertz radar has gradually become one of the research focus in radar domain at home and abroad.Compared with the radar with traditional band,terahertz radar has the characteristics of small size and high resolution,which is an important choice for some unmanned platform radar systems in the future.The large bandwidth of the terahertz radar makes the high range resolution of terahertz radar possible,the short wavelength enables a higher azimuth resolution at the same synthetic aperture meanwhile.Therefore,terahertz radar imaging can obtain more elaborate characterizations of object,which is helpful for further work such as target recognition.In ISAR scenario,the moving target is imaged by static radar.The acquisition of high range resolution of radar image is relying on the large bandwidth signal transmitted by the radar,and the high azimuth resolution depends on the synthetic aperture formed by the rotation of the target relative to the radar.At the same time,ISAR imaging,the same as SAR imaging,can detect and image targets in all-weather at all time,which is of great significance for imaging recognition of land,sea,and air targets.With the increasing requirements for imaging resolution of ISAR,fine-grained imaging of targets is a trend in radar imaging.Therefore,ISAR imaging of THz radar is one of the important research directions.Based on the background above,this paper studied the ISAR imaging based on the terahertz measured data under experimental conditions with the multi-band terahertz radar system built by the laboratory.Secondly,by introducing and analyzing the constructed terahertz radar system,the processing and research of the ISAR imaging of the experimental target by the measured data of terahertz radar echo under different motion conditions are taken.The main tasks are as follows:1.The theoretical analysis and experimental verification of the nonlinear tuning of the chirp signal of the terahertz radar system are carried out.The phase noise correction of the terahertz radar system is realized by the difference frequency processing of the reference echo of the corner reflector target,and the corrected echo distance resolution tends to be theoretically derived.2.The range profile of the terahertz radar target simulation echo and the measured echo was analyzed in detail.The high range resolution of THz radar causes the echo of the target to appear as a High Resolution Range Profile(HRRP)after pulse compression.In THz radar,the cross-correlation coefficient of the target HRRP is low,and the azimuth sensitivity is large,which increases the difficulty of the envelope alignment of the ISAR imaging in some cases.3.The two-dimensional ISAR imaging of the terahertz radar turntable target was verified and analyzed.The terahertz two-dimensional ISAR imaging was obtained based on the turntable model of different frequency bands and different targets by Range-Doppler(RD)algorithm,Polar Format Algorithm(PFA),Convolution Back-Projection(CBP)algorithm,and Direct Integration Method(DIM).4.An analysis was performed for the towed sports tank target ISAR imaging.Aiming at the problem that the traditional envelope alignment is poor,a new envelope alignment processing method was designed.The results show that new method can obtain better alignment results for the recorded data.Finally,through the processing of several common phase correction methods,the two-dimensional focused ISAR image of the moving tank target was obtained.The results show that the focusing ISAR image effect obtained by the weighted multiple scatterers algorithm(WMSA)is better.