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Principle of FMCW radar
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Principle of FMCW radar

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Introduction to frequency-modulated continuous-wave radar. Please download the presentation to enjoy the animations included.

Introduction to frequency-modulated continuous-wave radar. Please download the presentation to enjoy the animations included.

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  • 1. ATMOS Principle of FMCW Radars Tobias Otto Delft University of Technology Remote Sensing of the Environment
  • 2. AT ContentsMOS I. Principle of FMCW radar II. FMCW radar signal processing III. Block diagram of an FMCW radar for precipitation measurements Delft University of Technology Remote Sensing of the Environment
  • 3. AT Principle of FMCW radarMOS frequency-modulated continuous-wave A radar transmitting a continuous carrier modulated by a periodic function such as a sinusoid or sawtooth wave to provide range data (IEEE Std. 686-2008). Modulation is the keyword, since this adds the ranging capability to FMCW radars with respect to unmodulated CW radars. We will concentrate in this talk on linear FMCW radar (LFMCW). frequency amplitude f0 time up-chirp time Delft University of Technology Remote Sensing of the Environment
  • 4. AT Principle of FMCW radarMOS frequency-modulated continuous-wave A radar transmitting a continuous carrier modulated by a periodic function such as a sinusoid or sawtooth wave to provide range data (IEEE Std. 686-2008). Modulation is the keyword, since this adds the ranging capability to FMCW radars with respect to unmodulated CW radars. We will concentrate in this talk on linear FMCW radar (LFMCW). frequency amplitude down-chirp f0 time time Delft University of Technology Remote Sensing of the Environment
  • 5. AT Principle of FMCW radarMOS frequency-modulated continuous-wave A radar transmitting a continuous carrier modulated by a periodic function such as a sinusoid or sawtooth wave to provide range data (IEEE Std. 686-2008). Modulation is the keyword, since this adds the ranging capability to FMCW radars with respect to unmodulated CW radars. We will concentrate in this talk on linear FMCW radar (LFMCW). frequency amplitude triangular f0 time time Delft University of Technology Remote Sensing of the Environment
  • 6. A T Single target M O S Radar range R frequency frequency excursion,sweep bandwidth Bsweep time sweep time Ts Delft University of Technology Remote Sensing of the Environment
  • 7. A T Single target M O S Radar range R frequency td fb Ts Bsweep frequency excursion, cTs fb Rsweep bandwidth Bsweep beat frequency fb 2 Bsweep time sweep time Ts 2R td modulus of c the spectrum receiver Fourier output transformation range time fb frequency Delft University of Technology Remote Sensing of the Environment
  • 8. AT Moving single targetMOS A moving target induces a radial velocity vr f fD Doppler frequency shift Radar 2vr fD range R with the radar wavelength λ. frequency sweep bandwidth Bsweep frequency excursion, beat frequency The beat frequency is not only related to the range fD of the target, but also to time its relative radial velocity sweep time Ts with respect to the radar. Delft University of Technology Remote Sensing of the Environment
  • 9. AT Moving single targetMO Beat frequency componentsS due to range and Doppler radial velocity vr frequency shift: f fD Radar Bsweep 2 R fb Ts c 2vr range R fD frequency that are superimposed as fbu fb fd fbd fb fd so range and radial velocity can be obtained as time cTs R f bd fbubeat frequency 4 Bsweep vr fbd fbu fbu fbd fbu fbd 4 time Delft University of Technology Remote Sensing of the Environment
  • 10. AT Atmospheric FMCW radarMOS Radar range R When the expected Doppler frequency shift of the target has a negligible effect on the range extraction from the beat frequency, it can be estimated by comparing the phase of the echoes of successive sweeps, e.g. for meteorological applications. 2 the phase of the received signal is r t 2R the change of the phase of the received signal with time is given by d r 4 dR 4 vr dt dt and the change of the phase of the received signal from sweep to sweep is given as r 4 r vr vr Ts Ts 4 Delft University of Technology Remote Sensing of the Environment
  • 11. AT ContentsMOS I. Principle of FMCW radar II. FMCW radar signal processing III. Block diagram of an FMCW radar for precipitation measurements Delft University of Technology Remote Sensing of the Environment
  • 12. AT FMCW radar signal processingMOS frequency time FFT FFT FFT FFT range range FFT time Doppler frequency FFT .. fast Fourier transformation Delft University of Technology Remote Sensing of the Environment
  • 13. AT FMCW radar signal processingMO frequencyS spectrogram of the received power range time in-phase quadrature component component samples window function sweeps samples 2D FFT Doppler frequency sweeps Data: IDRA, TU Delft Delft University of Technology Remote Sensing of the Environment
  • 14. AT ContentsMOS I. Principle of FMCW radar II. FMCW radar signal processing III. Block diagram of an FMCW radar for precipitation measurements Delft University of Technology Remote Sensing of the Environment
  • 15. AT General block diagram of an FMCW radarMOS modulated power high-power oscillator divider microwave amplifier radar control and amplifier and low-noise amplifier mixer signal processing low-pass filter and filtering beat frequency fb Delft University of Technology Remote Sensing of the Environment
  • 16. AT IDRA – TU Delft IRCTR Drizzle radarMOS Specifications CESAR – Cabauw Experimental Site for Atmospheric Research • 9.475 GHz central frequency • FMCW with sawtooth modulation • transmitting alternately horizontal and vertical polarisation, receiving simultaneously the co- and the cross-polarised component • 20 W transmission power • 102.4 µs – 3276.8 µs sweep time • 2.5 MHz – 50 MHz Tx bandwidth • 60 m – 3 m range resolution • 1.8 antenna half-power beamwidth Reference J. Figueras i Ventura: “Design of a High Resolution X-band Doppler Polarimetric Weather Radar”, PhD Thesis, TU Delft, 2009. (online available at http://repository.tudelft.nl) Near real-time display: http://ftp.tudelft.nl/TUDelft/irctr-rse/idra IDRA is mounted on top of the 213 m high Processed and raw data available at: meteorological tower. http://data.3tu.nl/repository/collection:cabauw Delft University of Technology Remote Sensing of the Environment
  • 17. AT IDRA - IRCTR Drizzle radarMOS transmitter receiver Delft University of Technology Remote Sensing of the Environment
  • 18. AT IDRA - IRCTR Drizzle radar (transmitter)MOS transmitter - GPS stabilised 10 MHz oscillator, for synchronisation of the whole system and data timestamp - direct digital synthesizer (DDS) that generates the sawtooth modulation (other waveforms can be easily programmed) - first up-conversion to the 350-400 MHz band, filtering and amplification / a power splitter provides the signal reference for the down-conversion in the receiver - second up-conversion to the radar frequency 9.45 – 9.5 GHz (X-band) - switch for transmitting either horizontal or vertical polarisation, and high-power solid-state microwave amplifiers Delft University of Technology Remote Sensing of the Environment
  • 19. AT IDRA - IRCTR Drizzle radar (transmitter)MOS transmitter receiver - GPS stabilised 10 MHz oscillator, for synchronisation of the whole system and data timestamp - direct digital synthesizer (DDS) that generates the sawtooth modulation, other waveforms can be easily programmed - first up-conversion to the 350-400 MHz band, filtering and amplification / a power splitter provides the signal reference for the down-conversion in the receiver - second up-conversion to the radar frequency 9.45 – 9.5 GHz (X-band) - switch for transmitting either horizontal or vertical polarisation, and high-power solid-state microwave amplifier Delft University of Technology Remote Sensing of the Environment
  • 20. AT IDRA - IRCTR Drizzle radar (receiver)MO - two-channel receiver to receive simultaneously the horizontal and vertical polarised echoes,S that first undergo the low noise amplification and first filtering stage - first down-conversion to the 350-400 MHz band followed by filtering and amplification - I/Q receiver, i.e. the received signal is splitted and mixed with 90 phase difference realisations of the transmitted signal at 400 MHz in order to obtain the in-phase and the quadrature-phase components of the received signal - after the analog-to-digital conversion, the received signal is sent to the radar control computer for signal processing receiver Delft University of Technology Remote Sensing of the Environment
  • 21. ATMOS Principles and Applications of FMCW Radars Tobias Otto e-mail t.otto@tudelft.nl web http://atmos.weblog.tudelft.nl Delft University of Technology Remote Sensing of the Environment