Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives Magazine Sponsor RF Cafe Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Alliance Test Equipment Centric RF Empower RF ISOTEC Reactel RF Connector Technology San Francisco Circuits Anritsu Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Conduct RF Copper Mountain Technologies everything RF Exodus Advanced Communications Innovative Power Products KR Filters LadyBug Technologies PCB Directory Rigol TotalTemp Technologies Werbel Microwave Windfreak Technologies Wireless Telecom Group Withwave Sponsorship Rates RF Cafe Software Resources Vintage Magazines RF Cafe Software WhoIs entry for RF Cafe.com Thank you for visiting RF Cafe!
Windfreak Technologies Frequency Synthesizers - RF Cafe

Cafe Press

Espresso Engineering Workbook - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

RF Cascade Workbook for Excel

RF & Electronics Symbols for Visio

RF & Electronics Symbols for Office

RF & Electronics Stencils for Visio

RF Workbench  (shareware)

T-Shirts, Mugs, Cups, Ball Caps, Mouse Pads

These Are Available for Free

Espresso Engineering Workbook™

Smith Chart™ for Excel

RF Cascade Workbook 2018 - RF Cafe

Doppler Frequency Shift

RF Cafe Espresso Engineering Workbook™ for Excel - RF CafeA very nice Doppler calculator is included in Espresso Engineering Workbook™ for Excel - a FREE download.

Doppler Frequency Shift - RF CafeDoppler shift is an apparent change in frequency (and, correspondingly, wavelength) due to the relative motion of two objects. Per the lower right drawing, the wavefront of the moving object is compressed and shortens the wavelength in that region (increases frequency) and lengthens the wavelength (decreases frequency) in the region behind it. As shown in the upper right drawing, either one or both of the objects may be moving with respect to the ground.

Radar systems exploit the Doppler shift to provide an indication of relative speed. When the two objects are approaching each other (closing), the Doppler shift causes a shortening of wavelength (increase in frequency). When the two objects are receding from each other (opening), the Doppler shift causes a lengthening of wavelength (decrease in frequency).

For a Doppler radar system to measure speed, an accurate measurement of the original transmitted frequency and the reflected return frequency is required. The difference in the two frequencies is the termed the Doppler frequency shift, and is a direct indication of the object's speed as indicated in the equations below. The measured speed is relative to a straight line directly from the radar to the target (RHorizontal) - not its speed relative to the ground (RSlant). To calculate ground speed, the target's height relative to the radar antenna must be known, and that can be inferred from the elevation angle of the antenna (known as boresight angle, θ).

Doppler wavefront - RF Cafe

Note that the angle shown (θ) is for elevation differences only. If there is also an azimuthal angle, it must be factored into the equation as cos (α), where 'α' is the azimuth angle relative to the radar antenna boresight direction.

RHorizontal =  RSlant * cos θ.

In the following equations, distance can be expressed in any convenient units as long as they are consistent for both 'V' and 'c,' that is, km/hr, mi/hr, cm/week, furlongs/fortnight, etc. Use positive velocity (+) when the target is moving away from the radar and negative (-) when moving toward. 'c' is the speed of light. fTransmitted should have units of Hz since the Doppler shift is usually no more than a few kHz.

Note: When using these formulas, be sure to keep dimensional units consistent; i.e., do not mix kHz with MHz, mm with inches, etc. It is safer to use base units (e.g., Hz, m) for calculation, then convert result to desired units.

Here is information on propagation time, radar equation, and path loss.

Radar Doppler Frequency Shift Equation

Doppler frequency shift equation - RF Cafe

This equation applies generally to any value of VMovingTarget; however, for VMovingTarget << cVMovingTarget - c c and the equation simplifies to the ones shown below.

Note: The factor of 2 in the equation is due to a Doppler shift occurring both for the incident and reflected wave. When

          calculating Doppler shift from an emitter, such as light from a star or from a satellite, replace 2 with 1.

Example 1: An airplane moving at Mach 1 along the antenna boresight of a 10 GHz radar creates a Doppler shift of 22.87 kHz.

Example 2: The SCR-270 radar in use at Pearl Harbor during the Japanese attack on December 7, 1941, operated at 106 MHz and an A6M Zero attack aircraft had a diving speed of around 400 mi/hr. That corresponds to a Doppler shift of a mere 633 Hz.

Fixed Radar with Moving Target

Doppler frequency radar 1 moving platform equation drawing - RF Cafe

where VMovingTarget is relative to the stationary radar.

Moving Radar with Moving Target

Doppler frequency 2 moving platforms radar equation drawing - RF Cafe

where VMovingRadar and VMovingTarget are relative to a fixed point on the ground.

 

 

You might also want to check out the Doppler Shift section of the Electronic Warfare and Radar Systems Engineering Handbook. 

PCB Directory (Manufacturers)

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

Webmaster:

    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

Copyright  1996 - 2026

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website: AirplanesAndRockets.com

My Daughter's Website: EquineKingdom

RF Electronics Shapes, Stencils for Office, Visio by RF Cafe



Rigol DHO1000 Oscilloscope - RF Cafe