A Study On Model Building And Method To Elevation Estimation Of Low-angle Target In Meter-wave Radar

Elevation estimation of low-angle target is one of the crucial difficult problems for meter-wave radar. Meter-wave radar has occupied an increasingly important position in modern radar field due to the ability of anti-stealth, whose advantage lies in that its long-wavelength makes the common stealth technique effective for micro-wave radar, such as absorbing coating, absorbing materials and impedance loaded, have little effect. However, just because of this characteristic, meter-wave radar can not form narrow beams, which leads to low elevation resolution. And especially in low-angle tracking, the direct echoes are influenced by ground reflection, which causes the changes in signal amplitude and phase and the large errors in elevation estimation. Hence, height estimation is greatly influenced and unable to meet the actual needs. How to overcome the influence of ground reflection and obtain normal height estimation of target has, therefore, become one of the urgent problems in radar field.This dissertation researches the genesis and changes of the ground reflection path effects in the given situation by the analysis of actual surroundings and experimental data, and presents a ground reflection path model based on spheric reflection and the assumption of multi-scattering centers of target. The model explains and certifies the genesis and the characteristics of distribution. Furthermore, a processing method corresponding to the characteristics of distribution is presented, which searches a technical resolution approach. That is the core of method can directly use mature supper-resolution algorithm that guarantees the credibility and reliability of the method.The analysis of the experimental data shows that, the ground reflection path effects occurred during elevation estimation of low-angle target in meter-wave radar can be described by static and dynamic effects: (1) static effects depend on geographical conditions of radar and are basically independent of target range and height; (2) dynamic effects depend on the type and the attitude changes of target. The influences of these two effects on the observation results can be described by three intervals: credibility, incredibility and fuzzy interval, which provide the criteria to judge whether the observation results are true or not. In addition, it is also found by further analysis that the ground reflection path effects are without the characteristics of equivalent plane waves but show the characteristic of discrete peak distribution in elevation range of (-90o~90o), and the changes of position and number of peaks is dynamic.Since the size of target corresponds to the wave length in meter-wave radar, the scattering characteristic of target accords with oscillating distribution and varies with the changes of target attitude. In order to reduce the difficulty of analysis, the scattering characteristic of target is simplified in this dissertation. That means the target is regarded as a group of multi-scattering centers with discrete distribution in space that lie on the position of transient peak, which is multi-scattering assumption of target. And the ground reflected echoes come from the ground reflection paths which multi-scattering centers correspond to. To describe the ground reflection effects as much as they are, the paths of target-ground-radar in consideration of the effects of earth curvature. Hence, the ground reflection path model based on multi-scattering centers of target is built. Although the scattering characteristic is simplified in model building, the results of model simulation can explain and certify the genesis of the phenomenon in the analysis of experimental data. And that provides a technical resolution approach for following elevation estimation.Aimed at the characteristic of multi-peak distribution of echoes, an elevation estimation method of searching and canceling the"similar-plane-wave", which the peaks are simplified as, is presented. That makes the mature and widely used super-resolution technique can be applied and become the core of the method, based on which the target height correction estimator is designed and can obtain the correct estimation of target elevation by regarding the interval the observation result lies in as criteria. The processing results of lots of batches of prior and posterior data certify the credibility and reliability of the method. The method shows good stability and adaptability during the processing of many batches of data and the accuracy of estimation is better than expectation.Even if the method presented in this dissertation aims at the experimental data from one kind of geographical condition, the idea of analysis and processing method are not presented according to the geographical condition, so they can be spread and applied to other conditions. Moreover, the existence of the credibility interval can be a reference criterion for the position of radar.