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

1. A
T
M
O
S
Principle of FMCW Radars
Tobias Otto
Delft
University of
Technology Remote Sensing of the Environment

2. A
T Contents
M
O
S
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. A
T Principle of FMCW radar
M
O
S
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. A
T Principle of FMCW radar
M
O
S
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. A
T Principle of FMCW radar
M
O
S
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
R
sweep 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. A
T Moving single target
M
O
S 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. A
T Moving single target
M
O Beat frequency components
S 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 fbu
beat frequency 4 Bsweep
vr fbd fbu
fbu fbd fbu fbd 4
time
Delft
University of
Technology Remote Sensing of the Environment

10. A
T Atmospheric FMCW radar
M
O
S
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. A
T Contents
M
O
S
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. A
T FMCW radar signal processing
M
O
S 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. A
T FMCW radar signal processing
M
O frequency
S
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. A
T Contents
M
O
S
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. A
T General block diagram of an FMCW radar
M
O
S
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. A
T IDRA – TU Delft IRCTR Drizzle radar
M
O
S 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. A
T IDRA - IRCTR Drizzle radar
M
O
S
transmitter
receiver
Delft
University of
Technology Remote Sensing of the Environment

18. A
T IDRA - IRCTR Drizzle radar (transmitter)
M
O
S
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. A
T IDRA - IRCTR Drizzle radar (transmitter)
M
O
S
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. A
T IDRA - IRCTR Drizzle radar (receiver)
M
O - 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. A
T
M
O
S
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