A GPS Disciplined RFDAC Based C-Band Radar

Digital frequency modulation using a direct digital frequency synthesizer (DDFS) and digital to radio frequency (RF) conversion using radio frequency digital to analog converter (RFDAC) enables accurate and identical ramp generation at RF frequencies. It eliminates the trade-off between modulation bandwidth and loop bandwidth of a PLL-based frequency modulation allowing high ramp slopes. Based on a developed DDFS & RFDAC, a C-Band radar is built. The system is supplied with a GPS locked reference clock to allow long term stability. A two hour measurement against an active radar reflector which provides sufficient signal-to-noise ratio (SNR) in 72m distance is conducted. PPM deviations in range due to atmospheric effects are observed due to the high stability of the system. The measurement shows a correlation with existing propagation models.