Distributed Spaceborne Radar Echo Characteristics Analysis And Simulation

Distributed Spacborne Radar is a sparse array radar formed by a cluster of microsatellites flying in formation, Those microsatellites through collaborative work form a larger and more complex dummy satellite radar. With the advantage of single satellite radar, such as covering large scope, working all-weather and all-time and so on, Distributed Spacborne Radar can detect low speed ground target, because of its multi-aperture and longer base-line. Unfortunately, using Distributed Spacborne Radar to detect moving target faces many difficulties made by the higher orbit altitude, larger microsatellite speed, and gratinglobes coming with sparse antenna aperture.To suppress ground clutter and detect low speed moving target, the main issue of ground clutter and the ground clutter space-time characteristics in Distributed Spacborne Radar is studied in this dissertation, the main contents are as follows.In terms of the observation geometry of Distributed Spacborne Radar, five coordinate systems involving in the observation geometry are established first, and their mutual transformational relation are analyzed. Then the partition of range bins in observation region is studied, and establish the observation geometry model of Distributed Spacborne Radar finally, the established model is examined correct through simulations and analysis. The model is a foundation of studying the space-time characteristics of ground clutter and detecting of low speed moving target in Distributed Spacborne Radar.After the introduction of originates of common radar ground clutter, the main issues of the ground clutter in Distributed Spacborne Radar are studied. The earth is rotating all the time according to microsatellites, crab angle and crab magnitude come with the earth's rotation in the Doppler frequency of the return signals. Because of the larger observation region of the Distributed Spacborne Radar and the higher altitude of the microsatellite orbit, range ambiguities occur in the ground clutter. Also, the larger speed of microsatellite platform result in Doppler ambiguities in Distributed Spacborne Radar. The length between microsatellites is much bigger than half of wavelength, the low sample frequency in space results in gratinglobes in receiving antenna. Finally, on the foundation of the analysis of the clutter covariance matrix, power spectrum, clutter ridges of Distributed Spacborne Radar, the space-time characteristics of the ground clutter in Distributed Spacborne Radar are studied in detail. Theoretical analysis and simulation results show that: the clutter rank becomes bigger along with the crab angle brought by the earth's rotation, and the angle-doppler trace is changed a curve from a straight by earth's rotation. When range ambiguities happen, return signals from different range bins add together, and the width of ground clutter spectrum is made larger by range ambiguities. The clutter rank is made lager by the doppler ambiguities, also doppler ambiguities cause the clutter spectrum dispersed. Gratinglobes bring gratinglobes clutter modulated by the receive antenna.