3.7. In Chapter 1 we developed an expression for the Doppler shift associ- ated with a CW radar (i.e.. fd = 2v/h, where the plus sign is used for clos- ing targets and the negative sign is used for receding targets). CW radars can use the system shown below to determine whether the target is closing or receding. Assuming that the emitted signal is A cos of and the received signal is kA cos ((0,0,)t + 0), show that the direction of the target can be deter- mined by checking the phase shift difference in the outputs y,

(f) and y2(t).