A direct digitally synthesized exciter achieving near theoretical performance for an operational SAR system

The design of a directly digitally synthesized exciter for linear FM chirp generation in a synthetic-aperture radar (SAR) system is discussed. The exciter is implemented with integrated circuits that are contained on the Eurocard wirewrap boards. A procedure developed for analyzing the phase and amplitude errors present in the digitally synthesized exciter is also discussed. Once these errors were determined, a method for reducing them was used which was highly effective. A description of the measurement setup used, as well as measured data results is given. The measurement results show the effects of the phase errors before and after correction. Two types of plots are included. One type plots the phase error of the chirp pulse as a function of time. The other type of plot shows the compressed chirp waveform pressed in the same fashion as the radar system processes data.<
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