How do I design a simple FMCW radar for educational or prototyping purposes?
Simple FMCW Radar Design
Building an FMCW radar is an excellent educational project that demonstrates: transmitter design, receiver design, signal processing (FFT, windowing), and electromagnetic wave propagation. Several open-source radar projects are available.
| Parameter | Pulsed | CW/FMCW | Phased Array |
|---|---|---|---|
| Range Resolution | c/(2B) | c/(2B) | c/(2B) |
| Velocity Resolution | PRF dependent | Direct from Doppler | Coherent processing |
| Peak Power | High (kW-MW) | Low (mW-W) | Moderate per element |
| Complexity | Moderate | Low | High |
| Typical Application | Surveillance, weather | Altimeter, automotive | Tracking, multifunction |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
Frequently Asked Questions
What is the cheapest FMCW radar I can build?
The cheapest approach: use an HB100 Doppler radar module ($5-15 on Amazon/eBay). While the HB100 is a CW Doppler module, it can be modified for FMCW by applying a sawtooth voltage to the VCO tuning input. Budget: $20-50 total (HB100 + op-amp + Arduino + antennas). Performance: limited bandwidth (approximately 50-100 MHz), limited range (a few meters), but: it works and demonstrates the FMCW principle. A more capable approach: use the Infineon BGT24MTR12 radar frontend ($50-100 for the evaluation board). This provides a complete 24 GHz transmitter and receiver. Add an Arduino/STM32 for chirp generation and a computer for FFT processing.
What processing is needed?
Minimum processing: 1. Generate the sawtooth chirp waveform (microcontroller DAC or function generator). 2. Digitize the beat signal (soundcard for audio-range beat frequencies; ADC for MHz beat frequencies). 3. Window the data (apply a Hanning or Blackman window to reduce FFT spectral leakage). 4. FFT the beat signal (each chirp period produces one FFT; each FFT bin corresponds to a range). 5. Display the range profile (the FFT magnitude vs. range). For range-Doppler processing: collect multiple chirps, FFT across chirps (slow time) to extract the Doppler (velocity) dimension. This produces a 2D range-Doppler map.
What regulatory issues apply?
FMCW radar transmission requires: unlicensed ISM band operation: transmit within ISM bands (2.4 GHz, 5.8 GHz, 24 GHz, 60 GHz) with power below the regulatory limit (varies by region; typically less than 100 mW EIRP for 2.4 GHz ISM). FCC Part 15: low-power radar at ISM frequencies is permitted under Part 15 rules without a license. For higher power or non-ISM frequencies: an experimental license (FCC Part 5) is needed. For 24 GHz: the 24.0-24.25 GHz ISM band is commonly used for low-power FMCW radar. Power limits: 200 mW EIRP (US) or 100 mW (EU). This is sufficient for detection ranges of 10-100 m with modest antenna gain.