Frequency Modulated Continuous Wave Radar

Basics of FMCW Radar and its applications

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FMCW Radar:
CW Radar with Frequency Modulation
DR Sanjeev Kumar Mishra
Lecture 22-23

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•CW Radar limitations
•Cannot measure distance
•Most developers realized that modulating the
frequency will allow distance to be calculated.
Introduction

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•FMCW Radar is a low cost technique, often used in shorter range
applications.
• Applications include,
•altimetry for aircraft landing,
•speed guns,
•laboratory test instruments,
•education, runway debris monitoring,
•avalanche detection,
•volcano eruption onset and many more“
•The technology is simple to fabricate but requires care to obtain high
accuracy.
•The technique has the same conceptual basis as pulse compression
and high resolution"

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•…Frequency Modulated Continuous Wave (FMCW)
•Chirp pulse compression …
•FMCW-Radar with classic sawtooth or triangle shaped frequency shift
(Chirp-radar);
•FSK-FMCW (frequency shift keying FMCW);
•SFMCW (Stepped FMCW) for interferometric measurements;
•FMiCW (Interrupted FMCW) for better isolation between transmitter
and receiver PMCW (phase modulated CW) with pseudorandom
codes.

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sweeptime
sweepBW
T
B
T
ff
f
s
sweep



mod
01
'
time
amplitude
time
frequency
f
0
Down-chirp
Up-chirp

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A radar transmitting a continuous carrier modulated by a periodic
function such as a sinusoid or saw tooth wave to provide range data
(IEEE Std. 686-2008).
time
amplitude
time
frequency
f
0
triangular

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FMCW Radar: Principle 'tfFrequencyBeat  '
2
f
c
r
 Stationary Target

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time
frequency
Radar

range R
sweep time T
s
frequency excursion,
sweep bandwidth B
sweep

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time
frequency
Radar

range R
sweep time T
s
frequency excursion,
sweep bandwidth B
sweep
beat frequency f
b c
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
Beat Frequency and Range

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Moving single target
time
frequency
Radar

range R
sweep time T
s Dff
beat frequency

A moving target induces a
Doppler frequency shift 2
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

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Moving single target
time
frequency
Radar

range R Dff radial velocity
r
v
time
beat frequency
f
bu f
bd f
bu f
bd bu 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 as  
4
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

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Transmitted and received triangular LFM signals and beat frequency for
stationary target
Triangular type modulation For Stationary Target

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Moving Target [Non-stationary Target]
Transmitted and received LFM signals and beat frequency, for a moving target.

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•94 GHz radar
•reasonable penetration for certain materials (thickness)
•High accuracy
•Resistance for outdoor and indoor use
•Could be used for imaging or non-imaging
•Low emitted power – no health concern
•Can be remotely deployed

Why FMCW for concealed Weapon Detection

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Radar Transmitter

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Radar Receiver

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Summary and Conclusion
•The advantages of FM-CW Radar are:
•(1) low cost
•(2) good sensitivity
•(3) high spatial resolution
•(4) high reliability
•(5) portability
•(6) simplicity
•(7) safety
•FM-CW radar is capable of producing range-resolved velocities.
•FM-CW radar has limited range.

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