I am learning about automotive radars and have a very basic question about them.

If two or more cars on a road have the same radar, using the same radar tech (e.g. CWFM radar) how will one car's radar reject reflections of other radars? What sort of interference will it cause since all of them operate in same frequency range?

  • 7
    \$\begingroup\$ Radars can modulate their pulses, chirp uniquely, or rotate through the frequencies they use in a unique sequence (frequency hopping). They aren't limited to just sending out pure tones at one frequency. They can also select slightly different frequencies in the same band much like your cellphone or cordless phone. \$\endgroup\$
    – DKNguyen
    Commented Jul 23, 2022 at 15:59
  • \$\begingroup\$ Frequency range ... but not the same frequency. And every transmitter has its own "signature", so "all" is rejected except the "own". \$\endgroup\$
    – Antonio51
    Commented Jul 23, 2022 at 16:49
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    \$\begingroup\$ Here's an in-depth analysis of automotive radar interference: ietresearch.onlinelibrary.wiley.com/doi/10.1049/rsn2.12096 \$\endgroup\$ Commented Jul 23, 2022 at 17:30

1 Answer 1


As @DKNguyen pointed out in the comment, use of Spread Spectrum Technology and this, Gold and Walsh-Hadamard sequences.

If I remember well, sub-modulation (PRBS of some kind) can be "inserted" within the sent pulse.
The received wave pulse is correlated with this sub-modulation and identified as its own.
Properties of PRBS are used to reject "all" other "modulation".
This work also when the received wave is well "lost" in noise ... but can be "easily" recovered.

Note that the range of the "radar" is not kilometers ... and therefore, there should be only a small amount of false "echoes".
Not all vehicles sold are equipped with this "expensive" technology.

Here perhaps a more comprehensive text ... link and this

  • \$\begingroup\$ I’m curious if any car manufacturer would not just listen for their own radar echo and determine the surroundings from that but also listen for other cars’ radar to pinpoint their location in the landscape ahead. Perhaps not needed to make adaptive cruise control work. \$\endgroup\$
    – winny
    Commented Jul 24, 2022 at 7:19
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    \$\begingroup\$ Yes. Also, they can listen to others ... something as if "I want to transmit at one frequency", let verify if "that frequency is not used", else "change frequency" for best S/N ratio. \$\endgroup\$
    – Antonio51
    Commented Jul 24, 2022 at 7:35
  • \$\begingroup\$ Those two papers seem to be discussing the use of Spread Spectrum technology in communications channels, not radar applications. \$\endgroup\$
    – SteveSh
    Commented Jul 24, 2022 at 12:09
  • \$\begingroup\$ Right. Radars or GSM or GPS can use the same techniques ... Fast "Correlators" are now part of the basic "blocks" used in general "communications. Just to show how "PRBS" is used. Same things can be assigned to radars. Note that some designs can be "military" "oriented". \$\endgroup\$
    – Antonio51
    Commented Jul 24, 2022 at 13:11

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