According to the Doppler equation, for any given velocity, the frequency shift will increase by increasing the:

• A. Doppler angle
• B. Transmit frequency
• C. Pulse length
• D. Pulse repetition frequency

Answer: (B)

The Doppler frequency shift is proportional to the transmit frequency, the velocity component along the beam, and a cosine of the angle, expressed in the common form fD ≈ (2 f0 v cos θ) / c. So, for a fixed velocity, raising the transmit frequency f0 scales the shift up directly. In other words, higher transmitted frequency means the same moving scatterer produces a larger frequency shift.

The angle matters too because of the cos θ term, but increasing the angle tends to reduce cos θ (since cos θ decreases as θ increases), which would decrease the shift rather than increase it. Pulse length and pulse repetition frequency don’t change the actual magnitude of the Doppler shift; pulse length affects spectral broadening and resolution, while PRF affects the sampling rate and potential aliasing but not the shift value itself.