Lecture 2
TARGET INFO
Dr. Aamer Iqbal BhattiRadar Signal Processing
Dr. Aamer Iqbal Bhatti 1
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Range (distance from RADAR)
Radial Velocity
Angular Direction
Size (Radar Cross-section), and
Shape (signature - image processing)
Note: All the above information can not be provided by a single
radar system.
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Target position is described in spherical coordinates.
Range R.
Azimuth angle ø or θAZ.
Elevation angle θ or θEL. R
ø
θ
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Transmitted waveform has four basic characteristics:
◦ Carrier frequency
◦ Pulse width (τ sec)
◦ Modulation (if any) within or between the pulses
◦ Rate at which the pulses are transmitted (pulse repetition
frequency) or Pulse Repetition Interval (PRI=T sec)
PRF=1/PRI.
Time Corresponds to Distance or
Range R through S=vt.t
T
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Range is accomplished by measuring time delay between the
radar’s transmission and the detection of the target’s signal
echo.
Ref: www.radartutorial.eu
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
We transmit a pulse and receive an echo after time t sec.
which is roundtrip time.
c is the velocity of time and R is the Range.
Substituting and considering time in
μsec, we get
where t is number of μsec or each 1 μsec delay
corresponds to range of 150 meters
Target Echo
Transmitted Pulse
t
2
tcR
smc /103 8
tR 150
t : Delay between
transmitted pulse and
received echo.
T : Pulse Repetition
Interval.
t : Pulse Width.
t corresponds to the Range
R of target.
T corresponds to the
maximum unambiguous
range Ru.
t corresponds to minimum
range or range resolution
ΔR.
t
t
T
Transmitted PulseReceived Pulse
Hzkm
skm
R
cf
u
r 50)3000(2
/103
2
5
sf
Tr
02.01
B
ccR
22
t
kmHz
skm
B
cR 45
)103.3(2
/103
2 3
5
r
uf
ccTR
22
smskHzB
t 3003.033.3
11
• Consider a radar system with an unambiguous range of 3000 km and a bandwidth of 3.33 kHz. Find the required PRF (fr),IPP (T), R, and t.
t T (dt=1.5%)
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Pulse repetition interval corresponds to maximum
unambiguous range.
Pulse width corresponds to minimum range or range
resolution.
r
uf
ccTR
22
Angular Position
Antenna pointed away from target Antenna pointed towards target
Processed
pulse widthUnresolved Near resolved resolved
Processed
pulse widthUnresolved Near Resolved resolved
Range Resolution
Power and Energy
We relate following power and energy concepts with
radar waveforms.
o Energy.
o Peak Power.
o Average Power.
Power is rate of flow of energy. Backscattered energy is
what a radar detects.
Peak power determines both voltage levels and energy
per unit of pulse width.
TimePowerEnergy
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Average Power: A radar’s average transmitted power is
the power of the transmitted pulses averaged over the
interpulse period.
The ratio, t/T, is called the duty factor of the transmitter.T
PPavg
t
Three Ways to increase Average Power
Angular resolution is the ability to separate multiple
targets at different angles
Resolution in cross range is determined by the antenna’s
effective beamwidth, with narrow antenna beams
resolving more closely spaced targets.
The criterion for cross range resolution is that targets at
the same range separated by more than the antenna
beam width will be resolved.
Angular and Cross range resolution
θ
Angular and Cross range resolution
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
A wave radiated from a point source when stationary
(a) and when moving
(b) Wave is compressed in direction of motion, spread out in
opposite direction, and unaffected in direction normal to
motion.
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Transmitted Wave
Received from an approaching target
Received from moving away target
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Suppose we have a pulse incident on a target which is
moving towards the radar at speed v.
vIncident pulse
leading
edge
trailing
edge
t=t0
During the time t it takes the trailing edge to reach the
target, it has moved a distance d=vt into the pulse.
vReflected pulse
trailing
edge
leading
edge
t=t0+t
And the reflected leading edge is even with the incident
trailing edge.
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
So the pulse has been compressed.
vIncident pulse
leading
edge
trailing
edge
t=t0
Reflected pulse
trailing
edge
leading
edge
t=t0+t
s=ct
L=ct’
d
We need to find out how t’ relates to t.
First find an expression for d.
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
c
dcvd
tt
cv
vcd
Positions of the trailing edge give: ct-d=ct and
substituting in d=vt from before gives.
vIncident pulse
leading
edge
trailing
edge
t=t0
Reflected pulse
trailing
edge
leading
edge
t=t0+t
s=ct
L=ct’
d
ttttcv
vcc
cv
vc
cv
c
cv
vctcc
22
'
ttvc
vc
'
tcv
vcd
Positions of the leading edge give: s=ct=ct.
Now, L=ct’=s-d. So that,
c
dct
t
vIncident pulse
leading
edge
trailing
edge
t=t0
Reflected pulse
trailing
edge
leading
edge
t=t0+t
s=ct
L=ct’
d
fvc
vcff
''t
t
Since phase is an invariant (there are the same number of
wave cycles in each pulse), we must have and
will be the received frequency
v is positive towards the radar
and negative away from it
vIncident pulse
leading
edge
trailing
edge
t=t0
Reflected pulse
trailing
edge
leading
edge
t=t0+t
s=ct
L=ct’
d
fttf
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
fvc
vff
vc
vcfffd
2'
fc
vfd
2
And finally, the Doppler shift is defined as the difference
fd=f ’-f:
But since v<<c and c=lf:
(where v is the line-of-sight velocity)
or
f
fcv d
2
v is positive towards the radar
and negative away from it
Must sample received signal fast
enough to avoid “Doppler aliasing”
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Noise
Clutter
Electromagnetic countermeasures
Electromagnetic interference
Spillover
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Radar Signal Processing
Dr. Aamer Iqbal Bhatti
Detection:
Detection determines whether or not a target is present.
Detection Principles
Target? Detection? Result
No No Correct
Yes Yes Correct
Yes No Error
No Yes Error (false
Alarm)
Radar Signal Processing
Dr. Aamer Iqbal Bhatti