Counter to find the delay between a radar and an object

Do you have any pulse triggered by transmitter that informs fpga about start of pulse. Then use that to start a counter.

On the ADC side you will receive a signal and you can directly check if amplitude passed a certain threshold then stop counter.

The count value would indicate delay in periods(so smaller period = better resolution) but yo need to subtract delays caused by your system if you are after measuring absolute delays(not so if relative delay is your target)