Principle of FMCW radar

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

1. Remote Sensing of the Environment
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Delft
University of
Technology
Principle of FMCW Radars
Tobias Otto

2. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
Contents
I.Principle of FMCW radar
II.FMCW radar signal processing
III.Block diagram of an FMCW radar
for precipitation measurements

3. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
Principle of FMCW radar
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).
time
amplitude
time
frequency
f
0
up-chirp

4. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
Principle of FMCW radar
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).
time
amplitude
time
frequency
f
0
down-chirp

5. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
Principle of FMCW radar
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).
time
amplitude
time
frequency
f
0
triangular

6. Remote Sensing of the Environment
A
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M
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A
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Delft
University of
Technology
Single target
time
frequency
Radar
range R
sweep time T
s
frequency excursion,
sweep bandwidth B
sweep

7. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
Single target
time
frequency
Radar
range R
sweep time T
s
frequency excursion,
sweep bandwidth B
sweep beat frequency f
bc
R
t
d
2 db
s sweep
tf
TB 2
sb
sweep
cT f
R
B
receiver
output
time
modulus of
the spectrum
f
b frequency
Fourier
transformation range

8. Remote Sensing of the Environment
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A
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Delft
University of
Technology
Moving single target
time
frequency
Radar
range R
sweep time T
sDff
beat frequency
A moving target induces a
Doppler frequency shift2
r
D
v
f
with the radar wavelength λ.radial velocity
r
v
frequency excursion,
sweep bandwidth B
sweep
The beat frequency is not
only related to the range
of the target, but also to
its relative radial velocity
with respect to the radar.
f
D

9. Remote Sensing of the Environment
A
T
M
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S
A
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O
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Delft
University of
Technology
Moving single target
time
frequency
Radar
range RDff radial velocity
r
v
time
beat frequency
f
bu f
bd f
bu f
bdbu b d
f f f 2sweep
b
s
B R
f
Tc 2
r
D
v
f bd b d
f f f
Beat frequency components
due to range and Doppler
frequency shift:
that are superimposed as4
s
bd bu
sweep
cT
R f f
B 4
r bd bu
v f f
so range and radial velocity
can be obtained as

10. Remote Sensing of the Environment
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Delft
University of
Technology
Atmospheric FMCW radar
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.
the phase of the received signal is2
2R
tr
the change of the phase of the received signal with time is given by44
r
r
d dR
v
dt dt
and the change of the phase of the received signal from sweep to sweep is given as4
r
r
s
v
T 4
r
r
s
v
T

11. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
Contents
I.Principle of FMCW radar
II.FMCW radar signal processing
III.Block diagram of an FMCW radar
for precipitation measurements

12. Remote Sensing of the Environment
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Delft
University of
Technology
FMCW radar signal processing
time
frequency
FFT FFT FFT FFT
FFT .. fast Fourier transformation
time
range
FFT
Doppler
frequency
range

13. Remote Sensing of the Environment
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Delft
University of
Technology
FMCW radar signal processing
time
frequency
Data: IDRA, TU Delft
samples
sweeps
samples
sweeps
in-phase
component
quadrature
component
window function
2D FFT
range
Doppler frequency
spectrogram of the received power

14. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
Contents
I.Principle of FMCW radar
II.FMCW radar signal processing
III.Block diagram of an FMCW radar
for precipitation measurements

15. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
General block diagram of an FMCW radar
high-power
microwave amplifier
low-noise amplifier
and filtering
power
divider
mixer
radar control and
signal processing
modulated
oscillator
amplifier and
low-pass filter
beat frequency f
b

16. Remote Sensing of the Environment
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Delft
University of
Technology
IDRA –TU Delft IRCTR Drizzle radar
IDRA is mounted on
top of the 213 m high
meteorological tower.
CESAR
–
Cabauw Experimental Site for Atmospheric Research
Specifications
•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
•1.8antenna half-power beamwidth
Reference
J. FiguerasiVentura: “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
Processed and raw data available at:
http://data.3tu.nl/repository/collection:cabauw

17. Remote Sensing of the Environment
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Delft
University of
Technology
IDRA -IRCTR Drizzle radar
transmitter
receiver

18. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
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Delft
University of
Technology
IDRA -IRCTR Drizzle radar (transmitter)
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

19. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
IDRA -IRCTR Drizzle radar (transmitter)
receiver
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 amplifier

20. Remote Sensing of the Environment
A
T
M
O
S
A
T
M
O
S
Delft
University of
Technology
IDRA -IRCTR Drizzle radar (receiver)
receiver
-two-channel receiver to receive simultaneously the horizontal and vertical polarised echoes,
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 90phase 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
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21. Remote Sensing of the Environment
A
T
M
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S
A
T
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Delft
University of
Technology
Principles and Applications of FMCW Radars
Tobias Otto
e-mail [email protected]
web http://atmos.weblog.tudelft.nl