Doppler shift calculator

Doppler shift and radial velocity

An approaching target returns a higher frequency; a receding target returns a lower frequency. In a monostatic radar, the outward and return paths produce the factor of two in the Doppler equation:

Only radial velocity, the component along the radar’s line of sight, produces a Doppler shift. At θ = 0°, the full target speed is radial. At θ = 90°, radial velocity and Doppler shift are zero at that instant.

At 300 m/s radial velocity and a radar frequency of 10 GHz, the Doppler shift is approximately 20 kHz. Coherent receivers measure this shift relative to the transmitted signal.

Clutter rejection

Returns from terrain, buildings and the sea can be much stronger than an aircraft echo at a similar range. Doppler processing helps distinguish moving targets from this background clutter.

For a stationary radar, stationary terrain produces returns near zero Doppler. Moving target indication (MTI) suppresses these returns to improve detection of targets with a different Doppler shift.

Other applications include weather radar wind measurements, speed measurement and airborne detection of moving ground targets.

A target crossing at θ = 90° has zero radial velocity, so its return may fall within the clutter rejection band. Adjust the angle to see the target return move towards the filter notch.