A DDS/PLL architecture for highly stable local oscillators

Spectral purity and source stability represent two of the primary goals in the design of high performance frequency synthesizer for modern radar systems. This paper presents a new X-band High Stable Synthesizer (HSS) architecture, which combines Phase Lock Loop (PLL), Direct Digital Synthesis (DDS) and multiplier techniques, in order to cope with low phase noise and frequency agility requirements of the next radar generations. This synthesizer offers frequency coverage in X band with a percentage bandwidth of a minimum of 10%, with fast switching time, high digitally-tunable resolution and very low phase noise. The achievement of such performance has been demonstrated by experimental results measured on a laboratory demonstrator: they show a lock-in time within 10 us and a phase noise improvement up to 30 dB compared to the current state of art Frequency Generation Unit (FGU). Moreover, for its versatility, the architecture is able to provide an intermediate output covering the needs for new S-L band application.