天绘二号双星方位向天线方向图在轨测量关键技术

Key technologies for on-orbit azimuth antenna pattern measurement of TH-2 dual satellites

对星载SAR天线方向图进行在轨测量,是进行星载SAR定标、性能调优以及指标测试必不可少的环节。实际测试中通常将SAR天线方向图分为距离向和方位向分别测量。天绘二号卫星组由两颗卫星构成,在轨测试初期,两颗卫星采用一前一后间隔约40 km的跟飞模式,并各自工作于SAR模式以便于分别进行单颗卫星的定标、调优与测试。在进行方位向SAR天线方向图测试时,出现了地面接收机中两星信号交叠在一起的情况,导致现有的针对单颗SAR卫星设计的方位向天线方向图测试方法难以直接使用。针对这一问题,本文提出了一种高效的全自动的双星方位向天线方向图信号分离方法。在对地面接收机信号进行建模与分析的基础上,提出了基于关键脉冲上升沿提取、脉冲位置估计、脉冲幅度估计3个主要部分的信号分离方法,实现了地面接收机中两星信号的分离。在实现信号分离的基础上,后续方向图测量可按照传统单星的测量方法进行,试验结果表明本文方法的有效性。该方法保证了天绘二号卫星在轨测试的顺利进行,并使得测试效率相比于每颗星单独测试得以翻倍。该方法可用于未来相似型号卫星的在轨测试中。

On-orbit(inflight) measurement of the antenna pattern of space-borne synthetic aperture radar(SAR) is an indispensable and important procedure for SAR calibration, performance tuning and index test. Usually, in practical on-orbit(inflight) measurement of the SAR antenna pattern, it is separated into the vertical(elevation) and the horizontal(azimuth) directions respectively. The TH-2 satellite set is made up of two satellites to enable bistatic interferometry SAR(InSAR) observation. At the beginning of the on-orbit tests, the two satellites adopted a “following” flying formation in which one satellite flew about 40 km away after the other one. In this phase, the two satellites worked independently in SAR observation model to facilitate calibration, tuning and test of the satellites individually. When conducting the azimuth antenna pattern measurement, the collected signals from the two satellites in the ground receiver were overlapped(interleaved) and superposed, leading to the difficulty of measurement with the method designed for only one satellite. Aiming at solving this problem, an efficient and fully automated signal separation method for azimuth antenna pattern measurement is proposed. Based on the modeling and analysis of the sampled signal in the ground receiver, a novel signal separation method based on three main parts: key pulse rising edge extraction, pulse position estimation and pulse amplitude estimation is proposed to realize the separation of the signals from different satellites. After signal separation, the subsequent antenna pattern measurement tasks can be done using the traditional single-satellite method. Experimental results sufficiently show the effectiveness of the proposed method. This method escorted the on-orbit tests of the satellites smoothly, and the test efficiency can be doubled compared with the individual test of each single satellite. The proposed method can be used in the on-orbit tests of similar satellites in the future.