2 GHz self-aligning tandem A/D converter for SAR

A new generation of the Danish synthetic aperture radar system (EMISAR) is under development targeting a bandwidth of 800 MHz and a corresponding range resolution of around 25 cm. Two alternative approaches to achieve the wide bandwidth are considered. One is to use analog I/Q demodulation before digitizing, and the other is to digitize the signal before digital I/Q demodulation. In both cases the digitizing may be performed by a digital front end (DFE) with two parallel analog-to-digital-converters (ADCs) sampling at 1 GHz in phase or in anti-phase respectively, provided the analog bandwidth of the ADC is sufficient. In the first case each ADC has to digitize a 0-400 MHz signal, and in the second case both ADCs have to digitize a 100-900 MHz signal. In both cases the sampling time alignment is a critical parameter. The paper addresses some aspects of ADC alignment in the implementation of a DFE for the EMISAR system