Avionics
Intermediate

Radar Doppler Shift

Frequency shift of an echo from a moving target; the factor of two accounts for the round trip to the target and back.

Formula

fd=2vrλf_d = \dfrac{2v_r}{\lambda}

Variables

f_dDoppler shift (Hz)
v_rRadial velocity (m/s)
λWavelength (m)

Example

Target closing at 150 m/s, λ 0.03 m: f_d = 2×150 ÷ 0.03 = 10 kHz

Did You Know?

Doppler processing lets a radar separate a fast-moving aircraft from stationary ground clutter — the basis of moving-target indication and airborne weather radar.

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