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Justification of requirements to the digital signal processing system for small-size FMCW SAR with accounting amplitude-frequency correction of signals and oversampling


L.B. Ryazantsev – Ph.D. (Eng.), Senior Lecturer, MTSC Air Forces «MAA named professor N.E. Zhukovsky and Y.A. Gagarin» (Voronezh)

The radar with synthesized aperture of continuous radiation due to their small mass, dimensions and relative simplicity of design are one of the most promising types of radar systems for small unmanned aerial vehicles. An example of such radars is the foreign radar MiniSAR, ImSAR, and the domestic system developed by the authors.

In the development of FMCW SAR, the choice of the AD converter resolution is performed based on the dynamic range of the echo signals at the output of the receiver, which, in comparison with the pulse radar, is characterized by large values because its upper limit is determined by the total power not a separate resolved band of range, but the total echo strength of the entire mapping surface within the trace of the antenna pattern. At the same time, the realization of traditional approaches to expand the dynamic range used in pulsed radars (sensitive time control, cosecant antenna pattern) is not possible due to the frequency principle of range measurement and stringent restrictions on the mass-dimensional characteristics of antenna systems. As a result, the dynamic range of signals can reach values of the order of 90...110 dB, which implies the use of an AD converter more than 16 bits and a sampling rate of up to several tens of megahertz.
In the paper it is shown that despite the large dynamic range of signals, the consideration of the effect of oversampling and the use of amplitude-frequency correction of signals in substantiating the requirements for a digital signal processing system for small-size FMCW SAR makes it possible to reduce the AD converter up to a binary quantizer without significant loss of generated radar images quality.
Taking into account the effect in combination with amplitude-frequency correction of signals, it is possible to reduce the amount of recorded information during the operation of the SAR, which will ensure a reduction in the requirements for the computation system in the synthesis of radar images (including on board the carrier) and the capacity of the radio channel for the transmission of the registered signal to the ground control station in the number of times proportional to the decrease AD converter bit width.

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