i read sweep function of these pll ics. But velocity is radio wave is nearly 300 000 000 m/s. pll lock time is nearly 100uS. a target at 20 meter above , radio waves go and reflect in a few nanoseconds but at this time pll frequency is constant for this how can IF frequency generate? lo-rf(reflected)=0 Hz please look at image, triange sweep must not wait for new frequency how can these chips used in fmcw radars?