Build Your Own Radar
Using SDR
Julian Arnold
[email protected]
https://github.com/jarn0ld
25 Feb. 2015 - Cyberspectrum #4
History
• RADAR = Radio Detection and Ranging
• 1886 Heinrich Hertz discovered that radio waves could be reflected from
solid objects
• 1904 Patent by Christian Huelsemeyer for ship detection device
•
Pulsed RADAR using spark gap
• Before WW2 extensive research in several countries led to the modern
concept of radar
The RADAR Equation
• Receive power declines as the fourth power of the range!
The Doppler Effect
• Source moving towards observer at rest
𝒗𝒄
• 𝐟′ = 𝒗𝒄 −𝒗𝒔 𝒇
• For RADAR (Object moving towards source and observer)
http://en.wikipedia.org/wiki/Continuous-wave_radar#mediaviewer/File:Doppler_effect_diagrammatic.png
• Example: v = 25 Miles/h (11 m/s) and f = 2.4GHz => 𝒇𝒅 = 𝟏𝟕𝟔 𝑯𝒛
RADAR Variants
• Pulsed RADAR
• Transmit short pulse
• Measure time until reflection is received
• Needs accurate timing and ability to generate very short
pulses
RADAR Variants
• FM CW RADAR
• Transmit FM-modulated continuous wave
• FM modulation at audio frequencies
• Frequency difference between transmitted and received signal
varies with delay
• Easy-to-generate and process compared to Pulsed RADAR
RADAR Variants
• CW RADAR
• Transmit unmodulated continuous wave
• Use Doppler Effect to detect moving targets
• Very easy to realize with SDRs
Inspiration
• MIT Open Course Ware Project [1]
• Coffee Cans as Directional Antennas
• Modular RF design
[1] http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-andsynthetic-aperture-radar-imaging-january-iap-2011/
Inspiration
Inspiration
Cantennas
• Coffee cans can be used to build cheap directional antennas
• Good for operation in ISM band
• Only one hole and a waveguide coupler required
• BUT: Antennas need to be matched
Matching
• Monopole length inside can can be
used to match antenna to operating
frequency (2.4GHz)
• Network analyzer is needed
Matching S11
After some wire cutting…
S21
Data Processing
• Data processing minimal as SDR is doing most of the work on its own
• Basically only a Waterfall plot is required to display the Doppler shift
• Small Doppler shift below 1 kHz
• Good compromise between frequency and time accuracy needed
DEMO
Questions?