lecture 2 target info dr. aamer iqbal bhatti · pdf fileref: . radar signal processing dr....

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.



Target position is described in spherical coordinates.

Range R.

Azimuth angle ø or θAZ.

Elevation angle θ or θEL. R

ø

θ



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



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



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%)



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



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



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.



Transmitted Wave

Received from an approaching target

Received from moving away target



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.



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.



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



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”



Noise

Clutter

Electromagnetic countermeasures

Electromagnetic interference

Spillover



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)

lecture 2 target info dr. aamer iqbal bhatti · pdf fileref: . radar signal processing dr....

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