Passive and active RADAR using Software Defined Radio (WHY2025)

RAdio-frequency Detection And Ranging (RADAR) aims at using electromagnetic signals for detecting target location and motion. We demonstrate in this talk various RADAR architectures using dual-channel coherent Software Defined Radio (SDR) receivers and the associated signal processing techniques relying heavily on cross-correlations. Embedded systems are tackled, with a Raspberry Pi providing enough computational power for recording and post-processing. RAdio-frequency Detection And Ranging (RADAR) aims at using electromagnetic signals for detecting target location and motion. Being constantly illuminated with electromagnetic smog, we can benefit from existing radiofrequency emitters meeting RADAR requirements -- strong power and wide bandwidth -- for passive RADAR measurements where no active emitter is needed, using only coherent passive dual-channel Software Defined Radio (SDR) receivers for passive recording of existing signals. If existing signals are unsuitable, we can use the same principle with non-cooperative emitters such as a Wi-Fi dongle in an active RADAR setup. All processing flowcharts are implemented using GNU Radio for real time acquisition, and GNU/Octave or Python for post-processing: generic principles will be demonstrated, applicable to all sorts of receiver hardware. We will conclude with Synthetic Aperture RADAR (SAR) where antenna motion is used to simulate wide aperture receiving antennas, adding azimuth resolution to range resolution. Supporting documents are found a https://github.com/jmfriedt/SDR-GB-SAR or https://github.com/jmfriedt/passive_radar or https://github.com/jmfriedt/sentinel1_pbr Addendum following feedback on the presentation: 1/ I should have made it clear that the first part of the presentation (pulse, FMCW, FSCW) involved emitting a signal which is often not legal, while the subsequent part involves PASSIVE radar using existing emitters, and hence becoming legal. 2/ the core parameter determining maximum target range is NOT emitted power but isolation between emitter and receiver (especially on a monostatic setup). Increasing TX power if saturating RX and hence reducing RX gain does not help: this is especially true in the VNA implementation when selecting between S11 measurement (limited by the circulator isolation) and S21 (limited by emitting/receiving antenna coupling) 3/ the rail system presented in the SAR part of the discussion uses a WiFi dongle broadcasting random signals as illuminating signal, halfway between passive (a WiFi signal can be many other things than for RADAR measurements) and active (we are controlling the WiFi emission) Thank you for attending or looking at this followup. Reach me (email on the front slide) for more information or corrections. Licensed to the public under https://creativecommons.org/licenses/by/4.0/ about this event: https://program.why2025.org/why2025/talk/YMLNME/