FM Doppler systems-experimental results

The authors demonstrate experimentally that a Doppler system transmitting repetitive coherent frequency-modulated signals (FM Doppler) can produce velocity profiles of the form known from a conventional pulsed-wave (PW) Doppler. The FM Doppler system utilizes two signal processing schemes that are similar to what is used in a PW Doppler. These two schemes are phase shift measurement and a method based on cross correlation. As coherent sweeps are used, vessel wall echoes can be removed by means of a stationary echo canceller. Simulations comparing the cross-correlation schemes for PW and FM and experiments comparing phase shift and cross-correlation measurements for both FM and PW Doppler systems are presented. With the present FM Doppler implementation, the accuracy of the PW Doppler appears to be better.<>