What is Doppler frequency shift in radar?

When a radar pulse reflects off a moving target, the returned signal has a slightly different frequency than the transmitted one. This frequency difference — the Doppler shift — is proportional to the target's radial velocity. Positive shift means the target is approaching; negative shift means it is moving away.

How is target velocity calculated from Doppler shift?

The formula is v = (fd × c) / (2 × ft × cos θ), where fd is the Doppler frequency shift, c is the speed of light (299,792,458 m/s), ft is the transmitted frequency, and θ is the angle between the radar beam and the target's direction of travel. At zero angle (head-on), cos θ = 1.

What radar bands are supported?

The calculator covers common bands: L (1–2 GHz), S (2–4 GHz), C (4–8 GHz), X (8–12 GHz), Ku (12–18 GHz), K (18–27 GHz), Ka (27–40 GHz), and W (75–110 GHz). You can also enter a custom frequency for any system.

Why does the angle affect speed calculation?

Doppler radar measures only the radial (along-beam) component of velocity. If the target is moving at an angle relative to the beam, the true speed is higher than the measured radial speed by a factor of 1/cos θ. At 30° off-axis, the true speed is about 15.5% higher than the measured value.

What is the difference between monostatic and bistatic radar in this context?

This calculator assumes monostatic radar — where the transmitter and receiver are co-located — which is the standard configuration for police radar, speed guns, and most weather radar. Bistatic configurations (separated transmitter and receiver) require a more complex geometry correction not covered here.

Doppler Shift Radar Calculator

Calculate Doppler frequency shift and target velocity for radar systems from transmitted and received frequencies.

Radar Parameters

Radar Band

Transmitted Frequency (Hz)

9.500 GHz

Received Echo Frequency (Hz)

9.500 GHz + 1,585 Hz shift

Beam Angle to Target Path (θ)

0° = head-on, 90° = perpendicular (no shift)

Results

Enter frequencies and click Calculate

—

m/s

—

km/h

—

mph

Parameter	Value
Doppler shift (f_d)	—
Transmitted freq (f_t)	—
Received freq (f_r)	—
Beam angle (θ)	—
Radial velocity (v_r)	—
True velocity (v = v_r / cosθ)	—

Formula Used

v = (f_d × c) / (2 × f_t × cosθ)

where c = 299,792,458 m/s (speed of light)

Common Radar Bands Reference

Band	Freq (GHz)	Shift per 1 m/s	Typical Use
L	1.5	10 Hz	Air traffic control
S	3.0	20 Hz	Weather radar (WSR-88D)
C	5.6	37 Hz	Weather, ship radar
X	9.5	63 Hz	Marine, airborne
K	24.15	161 Hz	Police speed gun
Ka	33.8	225 Hz	Police radar (most common)
W	76.5	510 Hz	Automotive radar (ACC)

Summary

Calculate Doppler frequency shift and target velocity for radar systems from transmitted and received frequencies.

How it works

Select the radar band or enter a custom transmitted frequency.
Enter the received (echo) frequency detected from the target.
Choose the observation angle if the radar is not head-on.
Click Calculate to compute the Doppler shift and target velocity.
Review the results showing speed in m/s, km/h, and mph.

Use cases

Verify police speed radar readings for traffic enforcement calibration.
Analyze weather radar Doppler shifts to estimate storm wind speeds.
Design and test speed guns for sports applications such as tennis or baseball.
Cross-check airborne radar returns for aircraft velocity measurement.
Educational demonstrations of the Doppler effect in physics courses.
Validate radar system performance against known target velocities.

Frequently Asked Questions

Last updated: 2026-09-20 · Reviewed by Nham Vu