10 range and doppler measurements in radar systems
TRANSCRIPT
1
Range & DopplerMeasurements
in RADAR Systems
SOLO HERMELIN
Updated: 09.10.08http://www.solohermelin.com
2
Range & Doppler Measurements in RADAR SystemsSOLO
Table of Contents
RADAR RF Signal
Radar Signals
Waveform Hierarchy
Doppler Effect due to Target Motion .( )0≠R
Continuous Wave Radar (CW Radar)
Basic CW Radar
Frequency Modulated Continuous Wave (FMCW)
Linear Sawtooth Frequency Modulated Continuous Wave
Sinusoidal Frequency Modulated Continuous Wave
Multiple Frequency CW Radar (MFCW)
Phase Modulated Continuous Wave (PMCW)
3
Range & Doppler Measurements in RADAR SystemsSOLO
Table of Contents (continue – 1) Pulse Waves
Pulse Compression Techniques
Stepped Frequency Waveform (SFWF)
Phase Coding
Resolution
Range Measurement Unambiguity
Unambiguous Range and Velocity
Coherent Pulse Doppler Radar
4
RADAR RF SignalsSOLO
The transmitted RADAR RF Signal is:
( ) ( ) ( )[ ]ttftEtEt 0000 2cos ϕπ +=E0 – amplitude of the signal
f0 – RF frequency of the signal φ0 –phase of the signal (possible modulated)
The returned signal is delayed by the time that takes to signal to reach the target and toreturn back to the receiver. Since the electromagnetic waves travel with the speed of lightc (much greater then RADAR andTarget velocities), the received signal is delayed by
c
RRtd
21 +≅
The received signal is: ( ) ( ) ( ) ( )[ ] ( )tnoisettttfttEtE dddr +−+−−= ϕπα 00 2cos
To retrieve the range (and range-rate) information from the received signal thetransmitted signal must be modulated in Amplitude or/and Frequency or/and Phase.
ά < 1 represents the attenuation of the signal
5
SOLO
The received signal is:
( ) ( ) ( ) ( )[ ] ( )tnoisettttfttEtE dddr +−+−−= ϕπα 00 2cos
( ) ( ) tRRtRtRRtR ⋅+=⋅+= 222111 &
We want to compute the delay time td due to the time td1 it takes the EM-wave to reachthe target at a distance R1 (at t=0), from the transmitter, and to the time td2 it takes the EM-wave to return to the receiver, at a distance R2 (at t=0) from the target. 21 ddd ttt +=
According to the Special Relativity Theorythe EM wave will travel with a constant velocity c (independent of the relative velocities ).21 & RR
The EM wave that reached the target at time t was send at td1 ,therefore
( ) ( ) 111111 ddd tcttRRttR ⋅=−⋅+=− ( )1
111 Rc
tRRttd
+⋅+=
In the same way the EM wave received from the target at time t was reflected at td2 , therefore
( ) ( ) 222222 ddd tcttRRttR ⋅=−⋅+=− ( )2
222 Rc
tRRttd
+⋅+=
RADAR RF Signals
6
SOLO
The received signal is:
( ) ( ) ( ) ( )[ ] ( )tnoisettttfttEtE dddr +−+−−= ϕπα 00 2cos
21 ddd ttt += ( )1
111 Rc
tRRttd
+⋅+= ( )
2
222 Rc
tRRttd
+⋅+=
( ) ( )2
22
1
1121 Rc
tRR
Rc
tRRtttttttt ddd
+⋅+−
+⋅+−=−−=−
+
−+−+
+
−+−=−
2
2
2
2
1
1
1
1
2
1
2
1
Rc
Rt
Rc
Rc
Rc
Rt
Rc
Rctt d
From which:
or:
Since in most applications we canapproximate where they appear in the arguments of E0 (t-td), φ (t-td),however, because f0 is of order of 109 Hz=1 GHz, in radar applications, we must use:
cRR <<21,
1,2
2
1
1 ≈+−
+−
Rc
Rc
Rc
Rc
( )
−⋅
++
−⋅
+=
−⋅
−⋅+
−⋅
−⋅≈− 2
.
201
.
1022
011
00 2
1
2
1
2
121
2
121
21
D
RalongFreqDoppler
DD
RalongFreqDoppler
Dd ttffttffc
Rt
c
Rf
c
Rt
c
Rfttf
( ) ( ) ( ) ( ) ( )[ ] ( )tnoisettttffttEtE ddDdr +−+−⋅+−≈ ϕπα 00 2cos
where 212
21
1212
021
01 ,,,,2
,2
dddddDDDDD tttc
Rt
c
Rtfff
c
Rff
c
Rff +=≈≈+=−≈−≈
Finally
Doppler Effect
RADAR RF Signals
7
SOLO
The received signal model:
( ) ( ) ( ) ( ) ( )[ ] ( )tnoisettttffttEtE ddDdr +−+−⋅+−≈ ϕπα 00 2cos
Delayed by two-way trip time
Scaled downAmplitude Possible phase
modulated
CorruptedBy noise
Dopplereffect
We want to estimate:
• delay td range c td/2
• amplitude reduction α
• Doppler frequency fD
• noise power n (relative to signal power)
• phase modulation φ
Table of Content
RADAR RF Signals
8
RADAR SignalsSOLO
Waveforms
( ) ( ) ( )[ ]tttats θω += 0cos
a (t) – nonnegative function that represents any amplitude modulation (AM)
θ (t) – phase angle associated with any frequency modulation (FM)
ω0 – nominal carrier angular frequency ω0 = 2 π f0
f0 – nominal carrier frequency
Transmitted Signal
( ) ( ) ( )[ ]{ }ttjtats θω += 0exp
Phasor (complex, analytic) Transmitted Signal
9
RADAR SignalsSOLO
Quadrature Form( ) ( ) ( )[ ]
( ) ( )[ ] ( ) ( ) ( )[ ] ( )tttattta
tttats
00
0
sinsincoscos
cos
ωθωθθω
−=+=
where: ( ) ( ) ( )[ ]( ) ( ) ( )[ ]ttats
ttats
Q
I
θθ
sin
cos
==
( ) ( ) ( ) ( ) ( )ttsttsts QI 00 sincos ωω −=
One other form: ( ) ( ) ( )[ ] ( ) ( ) ( )[ ]tjtjtjtj eeta
tttats θωθωθω −−+ +=+= 00
2cos 0
( ) ( ) ( )[ ]tjtj etgetgts 00 *
2
1 ωω −+= ( ) ( ) ( ) ( ) ( )tjQI etatsjtstg θ=+=:
Complex envelope
10
RADAR SignalsSOLO
Spectrum
Define the Fourier Transfer F
( ) ( ){ } ( ) ( )∫+∞
∞−
−== dttjtstsS ωω exp:F ( ) ( ){ } ( ) ( )∫+∞
∞−
==πωωωω
2exp:
dtjSSts -1F
( ) ( ) ( )[ ]tjtj etgetgts 00 *
2
1 ωω −+= ( ) ( ) ( )[ ]0*
02
1 ωωωωω −−+−= GGS-1FF
-1FF
( ) ( ) ( ) ( ) ( )tjQI etatsjtstg θ=+=:
( ) ( ) ( )[ ]tttats θω += 0cosInverse Fourier Transfer F -1
Complex envelope
11
RADAR SignalsSOLO
Energy ( ) ( ) ( )[ ]tttats θω += 0cos
( ) ( ) ( )[ ]{ } ( )∫∫∫+∞
∞−
+∞
∞−
+∞
∞−
≈++== dttadttttadttsEs2
022
2
122cos1
2
1: θω
Parseval’s Formula
Proof:
( ) ( ) ( ) ( )∫∫+∞
∞−
+∞
∞−
= ωωωπ
dFFdttftf 2*
12*
1 2
1
( ) ( ) ( )∫+∞
∞−
−= dttjtfF ωω exp11
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )∫∫ ∫∫ ∫∫+∞
∞−
+∞
∞−
+∞
∞−
+∞
∞−
+∞
∞−
+∞
∞−
=−=−=πωωω
πωωω
πωωω
22exp
2exp 2
*
112*
2*
12*
1
dFF
ddttjtfFdt
dtjFtfdttftf
( ) ( ) ( )∫+∞
∞−
−=πωωω
2exp*
2
*
2
dtjFtf
If s (t) is real, than s (t) = s*(t) and
( ) ( ) ( )∫∫∫+∞
∞−
+∞
∞−
+∞
∞−
=== ωωπ
dSdttsdttsEs
222
2
1:
12
RADAR SignalsSOLO
Energy (continue – 1) ( ) ( ) ( )[ ]tttats θω += 0cos
( ) ( ) ( )∫∫∫+∞
∞−
+∞
∞−
+∞
∞−
=== ωωπ
dSdttsdttsEs
222
2
1:
( ) ( ) ( ) ( )[ ] ( ) ( )[ ]( ) ( ) ( ) ( )
( ) ( ) ( ) ( )
−−−+−−−+
−−−−+−−=
−−+−−−+−=
−
−−
00
0000
0
*
0
*2
00
0
*
00
*
0
00
*
0
*
0
*
4
1
4
1
ϕϕ
ϕϕϕϕ
ωωωωωωωωωωωωωωωω
ωωωωωωωωωω
jj
jjjj
eGGeGG
GGGG
eGeGeGeGSS
For finite band signals (see Figure)
( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )∫∫∫
∫∫∞+
∞−
∞+
∞−
∞+
∞−
+∞
∞−
−+∞
∞−
=−−−−=−−
≈−−−=−−−
ωωωωωωωωωωωωω
ωωωωωωωωωω ϕϕ
dGGdGGdGG
deGGdeGG jj
*
0
*
00
*
0
2
0
*
0
*2
00 000
( ) ( )∫∫+∞
∞−
+∞
∞−
≈= ωωπ
ωωπ
dGdSEs
22
2
1
2
1
2
1:
Table of Content
13
SOLO Waveform Hierarchy
Radar Waveforms
CW Radars Pulsed Radars
FrequencyModulated CW
PhaseModulated CW
bi – phase & poly-phase
Linear FMCWSawtooth, or
Triangle
Nonlinear FMCWSinusoidal,
Multiple Frequency,Noise, Pseudorandom
Intra-pulse Modulation
Pulse-to-pulse Modulation,
Frequency AgilityStepped Frequency
FrequencyModulate Linear FM
Nonlinear FM
PhaseModulatedbi – phase poly-phase
Unmodulated CW
Multiple FrequencyFrequency
Shift Keying
Fixed Frequency
14
Range & Doppler Measurements in RADAR SystemsSOLO
( )tf
2
τ2
τ−
A
∞→t
2τ+T
2
τ−T
A
2
τ+−T2
τ−−T
A
t←∞−
T TA
t
A
t
A
LINEAR FM PULSECODED PULSE
T T
PULSED (INTRAPULSE CODING)
t
( )tf
A
2
τ2
τ−T
AA
T T
A
22
τ+T2
2τ−T
A
T T
A
2
τ− 2
τ+T
TN
t
( )tf
A
2
τ2
τ−T
AA
T T
A
22
τ+T2
2τ−T
A
T T
A
2
τ− 2
τ+T
TN
PHASE CODED PULSES HOPPED FREQUENCY PULSES
PULSED (INTERPULSE CODING)
t
( )tf
A
T
2/τ−
LOW PRFMEDIUM PRF
PULSED( )tf
T T T T
2/τ+
τ
HIGH PRF
TT T T
A Partial List of the Family of RADAR Waveforms
15
Range & Doppler Measurements in RADAR SystemsSOLORadar Waveforms and their Fourier Transforms
16
Range & Doppler Measurements in RADAR SystemsSOLORadar Waveforms and their Fourier Transforms
17
Range & Doppler Measurements in RADAR SystemsSOLO
Table of Content
18
Doppler Effect due to Target Motion .
SOLO
ΔT – time from point A to travel from radar to target at range R0 (at transmission time t0) is
c
TRRT
∆+=∆
0
Rc
RT
−=∆ 0
Total round-trip is 2ΔT . Therefore point A returns to radar at
Rc
RTT
−+= 0
01
2
Point B returns to radar atRc
RTTT RF −
++= 102
2
where andRFRF
RF fT
ωπ21 ==
RFTRRR += 01
( )
−+=
−+=
−−+=−=
Rc
RcT
Rc
TRT
Rc
RRTTTT RF
RFRFRF
22
:' 0112
λ
λ Rf
c
Rf
cRcR
fT
f RF
fc
RF
c
R
RF
RF
221
1
1
'
1'
/1
−=
−≈
+
−==
=<<
λR
fDoppler2−=
Two WayDoppler Frequency Shift
( )0≠R Range & Doppler Measurements in RADAR Systems
19
Range & Doppler Measurements in RADAR SystemsSOLO
The received signal is:
( ) ( ) ( ) ( )[ ] ( )
( ) ( ) ( )tnoisec
RRtRRtftE
tnoisettttfttEtE
fc
dddr
+
+−++−=
+−+−−==
2121
0000
/
00
22cos
2cos
00
ϕλππα
ϕπαλ
If we consider only (c = speed of light) then the frequency of the electromagneticwave that reaches the receiver is given by:
ctd
Rd <<
+
−≈
+
+−=
+−+
+−=
c
td
Rd
td
Rd
f
c
tdRd
tdRd
ud
dff
c
RRt
c
RRtf
td
df
21
0
21
0~
00
21210
1
2
1
22
1
ϕπ
ϕππ
λ
+
−=tdRd
tdRd
fd
21
is the doppler frequency shift at the receiver
Christian Johann Doppler first observed the effect in acoustics.
20
2-Way Doppler Shift Versus Velocity and Radio Frequency SOLO
Table of Content
λλ logloglog −=⇒−=td
Rdf
td
Rdf dd
21
SOLO
• Transmitter always on
• Range information can be obtained by modulating EM wave [e.g., frequency modulation (FM), phase modulation (PM)]
• Simple radars used for speed timing, semi-active missile illuminators, altimeters, proximity fuzes.
• Continuous Wave Radar (CW Radar)
Table of Content
22
SOLO • Continuous Wave Radar (CW Radar)
The basic CW Radar will transmit an unmodulated (fixed carrier frequency) signal.
( ) [ ]00cos ϕω += tAtsThe received signal (in steady – state) will be.
( ) ( ) ( )[ ]00cos ϕωωα +−+= dDr ttAtsα – attenuation factor
ωD – two way Doppler shiftc
RfRff
fc
DDD
0
/ 22&2
0
−=−===λ
λπω
The Received Power is related to the Transmitted Power by (Radar Equation):
4
1~RP
P
tr
rcv
One solution is to have separate antennas for transmitting and receiving.
For R = 103 m this ratio is 10-12 or 120 db. This means that we must have a good isolation between continuously transmitting energy and receiving energy.
Basic CW Radar
23
SOLO • Continuous Wave Radar (CW Radar)
The received signal (in steady – state) ( ) ( ) ( )[ ]002cos ϕπα +−⋅+= dDr ttffAts
We can see that the sign of the Doppler is ambiguous (we get the same result for positiveand negative ωD).
To solve the problem of doppler sign ambiguity we can split the Local Oscillator into two channels and phase shifting theSignal in one by 90◦ (quadrature - Q) with respect to other channel (in-phase – I). Both channels are downconverted to baseband.If we look at those channels as the real and imaginary parts of a complex signal, we get:
has the Fourier Transform: ( ){ } ( ) ( )[ ]DDv ts ωωδωωδπ ++−=F
After being heterodyned to baseband (video band), the signal becomes (after ignoring amplitude factors and fixed-phase terms): ( ) [ ]tts Dv ωcos=
( ) ( ) ( )[ ] tjDDv
Detjtts ωωω2
1sincos
2
1 =+= ( ){ } ( )Dv ts ωωδπ −=2
F
Table of Content
24
SOLO • Frequency Modulated Continuous Wave (FMCW)The transmitted signal is: ( ) ( )[ ]00cos ϕθω ++= ttAts
The frequency of this signal is: ( ) ( )
+= t
dt
dtf θω
π 02
1
For FMCW the θ (t) has a linear slope as seen in the figures bellow
Table of Content
25
SOLO • Frequency Modulated Continuous Wave (FMCW)
The received signal is:
( ) ( ) ( ) ( )[ ]00cos ϕθωωα +−+−+= ddDr ttttAts
α – attenuation factor
( ) ( )
−++= dDr ttdt
dfftf θ
π2
10
ωD – two way Doppler shiftλ
πω Rff DDD
2&2 −==
td – two way time delay
c
Rtd
2=
The frequency of received signal is:
λ – mean value of wavelength
Linear Sawtooth Frequency Modulated Continuous Wave
26
SOLO • Frequency Modulated Continuous Wave (FMCW)
To extract the information we must subtract the received signal frequency fromthe transmitted signal frequency. This is done by mixing (multiplying) those signalsand use a Lower Side-Band Filter to retain the difference of frequencies
( ) ( ) ( ) ( ) ( ) Ddrb fttdt
dt
dt
dtftftf −
−−
=−= θ
πθ
π 2
1
2
1The frequency of mixed signal is:
( ) ( ) ( ) ( )[ ]00cos ϕθωωα +−+−+= ddDr ttttAts
( ) ( )[ ]00cos ϕθω ++= ttAts
( ) ( ) ( ) ( )[ ]
( ) ( ) ( ) ( )[ ]ddD
ddDdr
ttttttA
ttttttAts
−++−+++
−−+−−=
θθωωωα
θθωωα
002
02
cos2
1
cos2
1
Lower Side-BandFilter
Lower SB Filter
Linear Sawtooth Frequency Modulated Continuous Wave
27
SOLO • Frequency Modulated Continuous Wave (FMCW)
The returned signal has a frequency change due to:
• two way time delayc
Rtd
2=
• two way doppler additionλR
fD2−=
From Figure above, the beat frequencies fb (difference between transmitted to received frequencies) for a Linear Sawtooth Frequency Modulation are:
Dm
Ddm
b fRTc
fft
T
ff −∆=−∆=+ 4
2/
Dm
Ddm
b fRTc
fft
T
ff −∆−=−∆−=− 4
2/
( )28
−+ −∆
= bbm ff
f
TcR ( )
2
−+ +−= bbD
fff
We have 2 equations with 2 unknowns R and fD
with the solution:
Linear Sawtooth Frequency Modulated Continuous Wave
28
SOLO• Frequency Modulated Continuous Wave (FMCW)
The Received Power is related to the Transmitted Power by (Radar Equation):
For R = 103 m this ratio is 10-12 or 120 db. This means that we must have a good isolation between continuously transmitting energy and receiving energy.
4
1~RP
P
tr
rcv
One solution is to have separate antennas for transmitting and receiving.
Linear Sawtooth Frequency Modulated Continuous Wave
29
SOLO • Frequency Modulated Continuous Wave (FMCW)Linear Sawtooth Frequency Modulated Continuous Wave
Performing Fast Fourier Transform (FFT) we obtain fb+ and fb.
( )28
−+ −∆
= bbm ff
f
TcR
( )2
−+ +−= bbD
fff
From the Doppler Window we get fb+ and fb
-, from which:
30
SOLO • Frequency Modulated Continuous Wave (FMCW)
The received signal is:
( ) ( ) ( ) ( )[ ]00cos ϕθωωα +−+−+= ddDr ttttAts
α – attenuation factor
( ) ( )
−++= dDr ttdt
dfftf θ
π21
0
ωD – two way Doppler shiftλ
πω Rff DDD
2&2 −==
td – two way time delay
c
Rtd
2=
The frequency of received signal is:
λ – mean value of wavelength
Linear Triangular Frequency Modulated Continuous Wave
31
SOLO • Frequency Modulated Continuous Wave (FMCW)
To extract the information we must subtract the received signal frequency fromthe transmitted signal frequency. This is done by mixing (multiplying) those signalsand use a Lower Side-Band Filter to retain the difference of frequencies
( ) ( ) ( ) ( ) ( ) Ddrb fttdt
dt
dt
dtftftf −
−−
=−= θ
πθ
π 2
1
2
1The frequency of mixed signal is:
( ) ( ) ( ) ( )[ ]00cos ϕθωωα +−+−+= ddDr ttttAts
( ) ( )[ ]00cos ϕθω ++= ttAts
( ) ( ) ( ) ( )[ ]
( ) ( ) ( ) ( )[ ]ddD
ddDdr
ttttttA
ttttttAts
−++−+++
−−+−−=
θθωωωα
θθωωα
002
02
cos2
1
cos2
1
Lower Side-BandFilter
Lower SB Filter
Linear Triangular Frequency Modulated Continuous Wave
32
SOLO • Frequency Modulated Continuous Wave (FMCW)
The returned signal has a frequency change due to:
• two way time delayc
Rtd
2=
• two way doppler additionλR
fD2−=
From Figure above, the beat frequencies fb (difference between transmitted to received frequencies) for a Linear Triangular Frequency Modulation are:
Dm
Ddm
b fRTc
fft
T
ff −∆=−∆=+ 8
4/
positiveslope
Dm
Ddm
b fRTc
fft
T
ff −∆−=−∆−=− 8
4/
negativeslope
( )28
−+ −∆
= bbm ff
f
TcR ( )
2
−+ +−= bbD
fff
We have 2 equations with 2 unknowns R and fD
with the solution:
Linear Triangular Frequency Modulated Continuous Wave
33
SOLO • Frequency Modulated Continuous Wave (FMCW)
The Range Unambiguity is given bythe FMCW time period Tm:
Range Resolution is a function of FMCW bandwidth and the linearity of FM:
msunambiguou Tc
R2
=
To preserve this Range Resolution the non-linearity must be:
For Linear Triangular FMCW the bandwidth is: fB ∆= 2
For a perfect Linear Triangular modulation the Range Resolution is given by:
f
c
B
cR
∆== 2δ
mmm
sunambiguou TfTBTcBc
R
Rtynonlineari
∆===<<2
11
2
2δ
Linear Triangular Frequency Modulated Continuous Wave
34
SOLO• Frequency Modulated Continuous Wave (FMCW)
The Received Power is related to the Transmitted Power by (Radar Equation):
For R = 103 m this ratio is10-12 or 120 db. This means that we must have a good isolationbetween continuously transmittingenergy and receiving energy.
4
1~RP
P
tr
rcv
But solutions with a commonantenna for transmitting andreceiving, and with a goodisolation between them, do exist.
One solution is to have separateantennas for transmitting andreceiving.
35
SOLO • Frequency Modulated Continuous Wave (FMCW)
One Target Detected
Performing FFT for the positive slope we obtain fb
+.
Performing FFT for the negative slope we obtain fb
-.
( )28
−+ −∆
= bbm ff
f
TcR
( )2
−+ +−= bbD
fff
Two Targets Detected
Performing FFT for each of the positive and negative slopes we obtain two Beats in each Doppler window and we cannot say what is the pair in the other window. A solution to solve this is to add an unmodulated segment (see next slide)
36
SOLO • Frequency Modulated Continuous Wave (FMCW)Two Targets Detected
Performing FFT for each of the positive, negative and zero slopes we obtain two Beats in each Doppler window.
To solve two targets we can use the Segmented Linear Frequency Modulation.
In the zero slope Doppler window, we obtain the Doppler frequency of the two targets fD1 and fD2.Since , it is easy to find the pair from Positive and Negative Slope Windows that fulfill this condition, and then to compute the respective ranges using:
( )2
−+ +−= bbD
fff
( )28
−+ −∆
= bbm ff
f
TcR
This is a solution for more than two targets.
One other solution that can solve also range and doppler ambiguities is to use manymodulation slopes (Δ f and Tm).
Table of Content
37
SOLO • Frequency Modulated Continuous Wave (FMCW)
Sinusoidal Frequency Modulated Continuous Wave One of the practical frequency modulations is the Sinusoidal Frequency Modulation.
Assume that the transmitted signal is:
( ) ( )
∆+= tff
ftfAts m
m
ππ 2sin2sin 0
The spectrum of this signal is:
( ) ( )
( )[ ] ( )[ ]{ }
( )[ ] ( )[ ]{ }
( )[ ] ( )[ ]{ }
+
−++
∆+
−++
∆+
−++
∆+
∆=
tfftfff
fJA
tfftfff
fJA
tfftfff
fJA
tff
fJAts
mmm
mmm
mmm
m
32sin32sin
22sin22sin
2sin2sin
2sin
003
002
001
00
ππ
ππ
ππ
πwhere Jn (u) is the Bessel Functionof the first kind, n order and argument u.
Bessel Functions of the first kind
38
SOLO • Frequency Modulated Continuous Wave (FMCW)
Sinusoidal Frequency Modulated Continuous Wave One of the practical frequency modulations is the Sinusoidal Frequency Modulation.
Assume that the transmitted signal is:
( ) ( )
∆+= tff
ftfAts m
m
ππ 2sin2sin 0
The transmitted and received signal are heterodyned in a mixer to give the differencefrequency
The received signal is:
( ) ( ) ( ) ( )[ ]
−∆+−⋅+= dmm
dD ttff
fttffAtr ππα 2sin2sin 0
Lower Side-BandFilter
( )ts
( )tr( )[ ] ( )[ ] ( )
∆−−∆+−+ tf
f
fttf
f
fttftfA m
mdm
mdDd πππα 2sin2sin2cos 0
2
( )[ ] ( )
−∆−−+=
22cossin
22cos 0
2 dmdm
mdDd
ttftf
f
fttftfA πππα
39
SOLO • Frequency Modulated Continuous Wave (FMCW)
Sinusoidal Frequency Modulated Continuous Wave
Since td << Tm=1/fm we have
( ) ( )[ ] ( )
−∆−−+=
22cossin
22cos 0
2 dmdm
mdDd
ttftf
f
fttftfAtm πππα
Lower Side-BandFilter
( )ts
( )tr
( )tm
( ) ( )[ ]
−∆−−+≈
22cos22cos 0
2 dmddDd
ttftfttftfAtm πππα
The frequency is obtained by differentiating the argument of this equation with respect to time
( )[ ]
( )
−∆+=
−∆−−+=
22sin2
22cos22
2
10
dmmdD
dmddDdb
ttfftff
ttftfttftf
td
df
ππ
ππππ
( ) mm
dmm f
dmdmD
f tfd
mmdD
m
f
b
m
b
ttftfffdt
ttfftff
f
dtf
f
f2
1
0
2
1
0
12
1
0 22cos2
22sin2
211
211
−∆−≈
−∆+== ∫∫
< <
ππππ
The average of the beat frequency over one-half a modulating cycle is:
40
SOLO • Frequency Modulated Continuous Wave (FMCW)
Sinusoidal Frequency Modulated Continuous Wave
Lower Side-BandFilter
( )ts
( )tr
( )tm
Rc
ffftffff mDdmD
tf
b
dm ∆+=∆+≈=< <
+
84
1π
The average of the beat frequency over one-half a modulating cycle is:
( ) ( )
∆+= tff
ftfAts m
m
ππ 2sin2sin 0
By changing the phase of the sinusoidal modulationby 180 degree each modulation cycle, we will get:
( ) ( )
∆−=− tff
ftfAts m
m
ππ 2sin2sin 0
Rc
ffftffff mDdmD
tf
b
dm ∆−=∆−≈=< <
−
84
1π
The average of the beat frequency over one-half a modulating cycle is:
41
SOLO • Frequency Modulated Continuous Wave (FMCW)
Sinusoidal Frequency Modulated Continuous Wave
Lower Side-BandFilter
( )ts
( )tr
( )tmR
c
ffftffff mDdmD
tf
b
dm ∆+=∆+≈=< <
+
84
1π
A possible modulating is describe bellow, in which we introduce a unmodulated segmentto measure the doppler and two sinusoidal modulation segments in anti-phase.
From which we obtain:
Rc
ffftffff mDdmD
tf
b
dm ∆−=∆−≈=< <
−
84
1π
The averages of the beat frequency over one-half a modulating cycle are:
28−+
−∆
= bbmff
f
TcR
2−+
+= bb
D
fff
(must be the same as in unmodulated segment)
Note: We obtaind the same form as for Triangular Frequency Modulated CW
Table of Content
42
SOLO • Multiple Frequency CW Radar (MFCW)
Assume that the transmitted signal is: ( ) [ ]tfAts 02sin π=The received signal is: ( ) ( ) ( )[ ]dD ttffAtr −⋅+= 02sin πα
c
Rt
c
Rff dD
2,
210 ≈−≈
( ) ( )
⋅−⋅−⋅+=
c
Rf
c
RftffAtr DD
22
222sin 00 πππα
where:
Therefore:
We can see that the change in received phase Δφ is related to range R by:
2/2
22
22
22
/
00
00
λππππϕ
λ R
c
Rf
c
Rf
c
Rf
cfff
D
D =>>
=⋅≈⋅+⋅=∆
The maximum unambiguous range is given when Δφ=2π : 2/λ=sunambiguouR
( ) ( )GHzfmmBandLGHzfcm 956.1115 00 =÷→==λ
We can see that the maximum unambiguous range is too small, when we use a single transmitted frequency, for any practical applications.
43
SOLO • Multiple Frequency CW Radar (MFCW)
Assume that the transmitted signal is: ( ) [ ]tfAts 02sin π=The received signal is: ( ) ( ) ( )[ ]dD ttffAtr −⋅+= 02sin πα
c
Rt
c
Rff dD
2,
210 ≈−≈
( ) ( )
⋅−⋅−⋅+=
c
Rf
c
RftffAtr DD
22
222sin 00 πππα
where:
Therefore:
We can see that the change in received phase Δφ is related to range R by:
2/2
22
22
22
/
00
00
λππππϕ
λ R
c
Rf
c
Rf
c
Rf
cfff
D
D =>>
=⋅≈⋅+⋅=∆
The maximum unambiguous range is given when Δφ=2π : 2/λ=sunambiguouR
( ) ( )GHzfmmBandLGHzfcm 956.1115 00 =÷→==λ
We can see that the maximum unambiguous range is too small, when we use a single transmitted frequency, for any practical applications.
The maximum unambiguous range can be increased by using multiple transmitted frequencies.
44
SOLO
Assume that the transmitter transmits n CW frequencies fi (i=0,1,…,n-1)
Transmitted signals are: ( ) [ ] 1,,1,02sin −== nitfAts iii πThe received signals are: ( ) ( ) ( )[ ]dDiiiii ttffAtr −⋅+= πα 2sin
c
Rt
c
Rf
c
Rfff d
i
jjDi
2,
2210
10 ≈−≈
∆+−≈ ∑
=
where:
1,,2,11 −=∆+= − nifff iii
Since we want to use no more than one antenna for transmitted signals and one antenna for received signals we must have
1,,2,101
−=<<∆∑=
niffi
jj
We can see that the change in received phase Δφi , of two adjacent signals, is related to range R by:
( )c
Rf
c
R
c
Rf
c
Rf
c
Rff
c
Rf i
cR
iiDDii ii
22
222
22
22
22
2
1⋅∆≈⋅⋅∆+⋅∆=⋅−+⋅∆=∆
<<
−πππππϕ
The maximum unambiguous range is given when Δφi=2π :
isunambiguou f
cR
∆=2
• Multiple Frequency CW Radar (MFCW)
45
SOLO • Multiple Frequency CW Radar (MFCW)
Table of Content
46
SOLO • Phase Modulated Continuous Wave (PMCW)
Another way to obtain a time mark in a CW signal is by using Phase Modulation (PM).PMCW radar measures target range by applying a discrete phase shift every T secondsto the transmitted CW signal, producing a phase-code waveform. The returning waveformis correlated with a stored version of the transmitted waveform. The correlation processgives a maximum when we have a match. The time to achieve this match is the time-delaybetween transmitted and receiving signals and provides the required target range.
There are two types of phase coding techniques: binary phase codes and polyphase codes. In the figure bellow we can see a 7-length Barker binary phase code of the transmittedsignal
47
SOLO • Phase Modulated Continuous Wave (PMCW)
In the figure bellow we can see a 7-length Barker binary phase code of the receivedsignal that, at the receiver, passes a 7-cell delay line, and is correlated to a sampleof the 7-length Barker binary signal sample.
Digital CorrelationAt the Receiver the coded pulse enters a7 cells delay lane (from left to right),a bin at each clock.The signals in the cells are summed
-1 = -1
+1 -1 = 0
-1 +1 -1 = -1
-1 -1 +1-( -1) = 0
+1 -1 -1 –(+1)-( -1) = -1
+1 +1 -1-(-1) –(+1)-1= 0
+1+1 +1-( -1)-(-1) +1-(-1)= 8
+1+1 –(+1)-( -1) -1-( +1)= 0
+1-(+1) –(+1) -1-( -1)= -1
-(+1)-(+1) +1 -( -1)= 0
-(+1)+1-(+1) = -1
+1-(+1) = 0-(+1) = -1
0 = 0
-1-1 -1
clock
123456789
1011121314
+1+1+1+1
Table of Content
48
SOLO Waveform Hierarchy
• Pulse Waves
• Range Resolution is determined by the system bandwidth
B
ccR
B
FilterMatched 22
/1 ττ ===∆
200 MHz 1 meter 325 MHz 2 feet 650 MHz 1 foot1300 MHz 6 inch
• Use short pulse (τ) for high resolution, or, bandwidth can be achieved by:
• Pulse Compression – intra-pulse coding
• Frequency Modulated Continuous Wave (FMCW)
• Stretch Processing
• Stepped Frequency Waveform (SFWF) – pulse-to-pulse coding
Table of Content
49
SOLO Waveform Hierarchy
• Pulse Compression Techniques• Wave Coding
• Frequency Modulation (FM)
- Linear
• Phase Modulation (PM)]
- Non-linear
- Pseudo-Random Noise (PRN)
- Bi-phase (0º/180º)
- Quad-phase (0º/90º/180º/270º)
• Implementation
• Hardware
- Surface Acoustic Wave (SAW) expander/compressor
• Digital Control- Direct Digital Synthesizer (DDS)
- Software compression “filter”Table of Content
50
SOLO Waveform Hierarchy
• Stepped Frequency Waveform (SFWF)
The Stepped Frequency Waveform is a Pulse Radar System technique for obtaining high resolution range profiles with relative narrow bandwidth pulses.
• SFWF is an ensemble of narrow band (monochromatic) pulses, each of which is stepped in frequency relative to the preceding pulse, until the required bandwidth is covered.
• We process the ensemble of received signals using FFT processing.
• The resulting FFT output represents a high resolution range profile of the Radar illuminated area.
• Sometimes SFWF is used in conjunction with pulse compression.
51
SOLO Waveform Hierarchy
• Stepped Frequency Waveform (SFWF)
52
SOLO Waveform Hierarchy• Pulse Compression Techniques
53
SOLO Waveform Hierarchy• Steped Frequency Waveform (SFWF)
Table of Content
54
SOLO Waveform Hierarchy• Pulse Compression Techniques
55
56
57
SOLO Waveform Hierarchy• Pulse Compression Techniques
58
SOLO Waveform Hierarchy• Pulse Compression Techniques
Phase CodingA transmitted radar pulse of duration T is divided in N sub-pulses of equal durationτ = T/N, and each sub-pulse is phase coded in terms of the phase of the carrier.
The complex envelope of the phase codedsignal is given by:
( ) ( ) ( )∑−
=
−=1
02/1
1 N
nn ntu
Ntg τ
τ where:
( ) ( ) ≤≤
=elsewhere
tjtu n
n 0
0exp τϕ
59
-1
Pulse bi-phase Barker coded of length 3
Digital Correlation At the Receiver the coded pulse enters a 3 cells delay lane (from left to right), a bin at each clock.The signals in the cells are multiplied according to ck* sign and summed.
clock
-1 = -11
+1 -1 = 02
-( +1) = -15
0 = 06
+1 +1-( -1) = 33
+1-( +1) = 04
SOLO Pulse Compression Techniques
1
2
3
4
5
6
0
+1+1
0 = 00
60
-1 = -1
+1 -1 = 0
-1 +1 -1 = -1
-1 -1 +1-( -1) = 0
+1 -1 -1 –(+1)-( -1) = -1
+1 +1 -1-(-1) –(+1)-1= 0
+1+1 +1-( -1)-(-1) +1-(-1)= 8
+1+1 –(+1)-( -1) -1-( +1)= 0
+1-(+1) –(+1) -1-( -1)= -1
-(+1)-(+1) +1 -( -1)= 0
-(+1)+1-(+1) = -1
+1-(+1) = 0
-(+1) = -1
0 = 0
-1-1 -1
Pulse bi-phase Barker coded of length 7
Digital CorrelationAt the Receiver the coded pulse enters a7 cells delay lane (from left to right),a bin at each clock.The signals in the cells are summed
clock
1
2
3
4
5
6
7
8
9
10
11
12
1314
SOLO Pulse Compression Techniques
+1+1+1+1
61
-1 = -1
-j +j = 0
+j -1-j = -1
+1 +1+1+1 = 4
-j-1+j = -1
+j - j = 0
Pulse poly-phase coded of length 4
At the Receiver the coded pulse enters a 3 cells delay lane (from left to right), a bin at each clock.The signals in the cells are multiplied by -1,+j,-j or +1 and summed.
clock
SOLOPoly-Phase Modulation
1
2
3
4
5
6
7
8
1+
1+j+
1+j+j−
1+j+j−1−
j+j−1−
j−1−
1−
1− 1+j+ j−
-1 = -1
0
Σ
62
Range & Doppler Measurements in RADAR SystemsSOLO
Resolution
Resolution is the spacing (in range, Doppler, angle, etc.) we must have in order todistinguish between two different targets.
first targetresponse
second targetresponse
compositetarget
response
greather then 3 db
DistinguishableTargets
first targetresponse
second targetresponse
compositetarget
response
UndistinguishableTargets
less then 3 db
The two targets are distinguishable ifthe composite (sum) of the received signal has a deep (between the twopicks) of at least 3 db.
63
Range & Doppler Measurements in RADAR SystemsSOLO
Pulse Range Resolution
Resolution is the spacing (in range, Doppler, angle, etc.) we must have in order todistinguish between two different targets.
Range Resolution
RADAR
τ
c
R
RR ∆+
Target # 1Target # 2
Assume two targets spaced by a range Δ R and a radar pulse of τ seconds.
The echoes start to be receivedat the radar antenna at times: 2 R/c – first target 2 (R+Δ R)/c – second target
The echo of the first target endsat 2 R/c + τ
τ τ
time from pulsetransmission
c
R2 ( )c
RR ∆+2τ+
c
R2
ReceivedSignals
Target # 1 Target # 2
The two targets echoes can beresolved if:
c
RR
c
R ∆+=+ 22 τ2
τcR =∆ Pulse Range Resolution
64
Range & Doppler Measurements in RADAR SystemsSOLO
Pulse Range Resolution (continue)
time from pulse transmission
c
R2 ( )c
RR ∆+2τ+
c
R2
Received Signals
Target # 1 Target # 2Rcvτ Rcvτ
2
τcR =∆Pulse Range Resolution
To improve the Pulse Range Resolution we must decrease theReceived pulse duration τRcv.
This is done by Pulse Compressiontechnique:
• Linear or Nonlinear Frequency Modulation
• Phase Modulation (bi-phase, poly-phase)
The Pulse Range Resolution therefore is given by
1/
2 2
Rcv RcvBWRcv
Rcv
c cR
BW
ττ ≈
∆ = =
65
Range & Doppler Measurements in RADAR SystemsSOLO
Angle Resolution
Resolution is the spacing (in range, Doppler, angle, etc.) we must have in order todistinguish between two different targets.
Angle Resolution
RADAR
Target # 1
Target # 2
R
R
3θ
2
cos 3θR
33
2sin2 θθ
RR ≈
Angle Resolution is Determined by Antenna Beamwidth.
33
2sin2 θθ
RRRC ≈
=∆
Angle Resolution is considered equivalent to the 3 db Antenna Beamwidth θ3.
The Cross Range Resolution is given by:
66
Range & Doppler Measurements in RADAR SystemsSOLO
Doppler Resolution The Doppler resolution is defined bythe Bandwidth of the Doppler FiltersBWDoppler.
Doppler Dopplerf BW∆ =
67
Range & Doppler Measurements in RADAR SystemsSOLO
Resolution Cell
Resolution is the spacing (in range, Doppler, angle, etc.) we must have in order todistinguish between two different targets.
Resolution Cell
RADAR
R∆ 3θR
3φR
The Volume Resolution Cell is the volume defined by the subtended solid angle and range resolution.
RRRRRRR
V
rrectangulaofarea
ellipseofarea
∆≈∆=∆
=∆
33
2
33
2
785.0
33
422φθφθπφθπ
Volume Resolution Cell increases with R2.
68
Range Measurement Unambiguity( )tf1
t
2
τ2
2τ−T
TA
T T T
2
τ−2
2τ+T
2
τ−T2τ+T
1 2 3c
Rt2
=
( )tf1
t
2
τ2
2τ−T
RA
T T T
2
τ−2
2τ+T
2
τ−T2
τ+T
1 2 3
Transmitted Pulses
Received Pulses
SOLO
The returned signal from the target located at a range R from the transmitter reaches the receiver (collocated with the transmitter) after
c
Rt2
=
To detect the target, a train of pulses must be transmitted.
PRT – Pulse Repetition Time PRF – Pulse Repetition Frequency = 1/PRT
To have an unanbigous target range the received pulse must arrive before the transmissionof the next pulse, therefore:
PRFPRT
c
Runabigous 1
2=<
PRF
cRunabigous
2<
Range & Doppler Measurements in RADAR Systems
69
Range measurementSOLO
70
SOLO
71
SOLO
72
Resolving Range Measurement Ambiguity
SOLO
To solve the ambiguity of targets return we must use multiple batches, each with different PRIs (Pulse Repetition Interval). Example: one target, use two batches
First batch: PRI 1 = T1
Target Return = t1-amb
R1_amb=2 c t1_amb
Range & Doppler Measurements in RADAR Systems
Second batch: PRI 2 = T2
Target Return = t2-amb
R2_amb=2 c t2_amb
To find the range, R, we must solve for the integers k1 and k2 in the equation:
( ) ( )ambamb tTkctTkcR _222_111 22 +=+=We have 2 equations with 3 unknowns: R, k1 and k2, that can be solved becausek1 and k2 are integers. One method is to use the Chinese Remainder Theorem .
For more targets, more batches must be used to solve the Range ambiguity.
See Tildocs # 763333 v1
73
SOLO
74
SOLO
75
SOLO
76
Doppler Frequency Shifts (Hz) for Various Radar Frequency Bands and Target Speeds
Band 1 m/s 1 knot 1 mph
L (1 GHz)S (3 GHz)C (5 GHz)X (10 GHz)
Ku (16 GHz)Ka (35 GHz)
mm (96 GHz)
6.6720.033.366.7107233633
3.4310.317.134.354.9120320
2.988.9414.929.847.7104283
RadarFrequency Radial Target Speed
SOLO
77
Coherent Pulse Doppler RadarSOLO
• STALO provides a continuous frequency fLO
• COHO provides the coherent Intermediate Frequency fIF
• Pulse Modulator defines the pulse width the Pulses Rate
Frequency (PRF) number of pulses in a batch • Transmitter/Receiver (T/R) (Circulator) - in the Transmission Phase directs the Transmitted Energy to the Antenna and isolates the Receiving Channel
• IF Amplifier is a Band Pass Filter in the Receiving Channel centered around IF frequency fIF.• Mixer multiplies two sinusoidal signals providing signals with sum or differences of the input frequencies
- in the Receiving Phase directs the Received Energy to the Receiving Channel
21 ff >>
2f
1f21 ff +
21 ff −
78
SOLO Coherent Pulse Doppler Radar
An idealized target doppler response will provide at IF Amplifier output the signal:
( ) ( )[ ] ( ) ( )[ ]tjtjdIFIF
dIFdIF eeA
tAts ωωωωωω +−+ +=+=2
cos
that has the spectrum:f
fIF+fd-fIF-fd
-fIF fIF
A2/4A2/4 |s|2
0
Because we used N coherent pulses ofwidth τ and with Pulse Repetition Time Tthe spectrum at the IF Amplifier output
f
-fd fd
A2/4A2/4|s|2
0
After the mixer and base-band filter:
( ) ( ) [ ]tjtjdd
dd eeA
tAts ωωω −+==2
cos
We can not distinguish between positive to negative doppler!!!
and after the mixer :
79
SOLO Coherent Pulse Doppler Radar
We can not distinguish between positive to negative doppler!!!
Split IF Signal:
( ) ( )[ ] ( ) ( )[ ]tjtjdIFIF
dIFdIF eeA
tAts ωωωωωω +−+ +=+=2
cos
( ) ( )[ ]
( ) ( )[ ]tAts
tA
ts
dIFQ
dIFI
ωω
ωω
+=
+=
sin2
cos2
Define a New Complex Signal:
( ) ( ) ( ) ( )[ ]tjQI
dIFeA
tsjtstg ωω +=+=2
ffIF+fd
fIF
A2/2|g|2
0
f
fd
A2/2|s|2
0
Combining the signals after the mixers
( ) tjd
deA
tg ω
2=
We now can distinguish between positive to negative doppler!!!
80
SOLO Coherent Pulse Doppler Radar
Split IF Signal:
( ) ( )[ ]
( ) ( )[ ]tAts
tA
ts
dIFQ
dIFI
ωω
ωω
+=
+=
sin2
cos2
Define a New Complex Signal:
( ) ( ) ( ) ( )[ ]tjQI
dIFeA
tsjtstg ωω +=+=2
ffd
A2/2|s|2
0
Combining the signals after the mixers
( ) tjd
deA
tg ω
2=
We now can distinguish between positive to negative doppler!!!
From the Figure we can see that in this case the doppler is unambiguous only if:
Tff PRd
1=<
Because we used N coherent pulses ofwidth τ and with Pulse Repetition Time Tthe spectrum after the mixer output is
81
Resolving Doppler Measurement Ambiguity
+=
+= ambDambD f
Tkf
TkV _2
22_1
11
1
2
1
2
λλ
SOLO
To solve the Doppler ambiguity of targets return we must use multiple batches, each with different PRIs (Pulse Repetition Interval). Example: one target, use two batches
First batch: PRI 1 = T1
Target Doppler Return in Range Gate i = fD1-amb
V1_amb=(λ/2) fD1_amb
Range & Doppler Measurements in RADAR Systems
To find the range-rate, V, we must solve for the integers k1 and k2 in the equation:
We have 2 equations with 3 unknowns: V, k1 and k2, that can be solved becausek1 and k2 are integers. One method is to use the Chinese Remainder Theorem .
Second batch: PRI 2 = T2
Target Doppler Return in Range Gate i = fD2-amb
V2_amb=(λ/2) fD2_amb
For more targets, more batches must be used to solve the Doppler ambiguity.
See Tildocs # 763333 v1
Return to Table of Content
82
SOLO Coherent Pulse Doppler Radar
83
Range & Doppler Measurements in RADAR SystemsSOLO
Phase Comparison Monopulse
dα
Port A
Port B
S
Dαcos
d
AntennaBoresight
αλπψ cos2
d=
wavefrontfor a point
sourceat infinity
To illustrate the Monopulse Antennaassume thsat the RF is received throughonly two ports A and B.
When the rays are received froma direction ά relative to the Antennaboresight, we obtain a phase difference of between port A and port B:
αλπψ cos2
d=
AeB jψ= Let compute
( )2
cos2
sin2
cos2)sincos1(1:ψψψψψψ AjAjAeBAS j
+=++=+=+=
( ) ( )2
sin2
sin2
cos2)sincos1(1:ψψψψψψ AjAjjAejBAjDj j
+=−−=−=−=
=2
tanψ
SDj
84
Range & Doppler Measurements in RADAR SystemsSOLO
Transmitted RF signal (in phasor form) is ( ) ( )tpetS tj
TrRFω=
p (t) - the pulse train function
At the front-end of the Antenna we receive a shifted and attenuated version of the transmitted pulse:
( ) ( ) ( )cRtpeVtS tj
cvTRF /2Re −= −ωω
ωRF - the RF angular velocity
ωT - the target’s Doppler shift
2 R/c time delay between transmission and reception
V – random complex voltage strengthc – velocity of light
We assume that from the Antenna emerge radar signal of the Sum S and Difference D
( ) ( )( ) ( ) ( )cRtpFeVD
cRtpeVStj
tj
TRF
TRF
/2
/2
−∆=
−=−
−
ψωω
ωω
85
Range & Doppler Measurements in RADAR SystemsSOLO
Receiver
The Superheterodyne Receiver translates the high RF frequency ωRF to a lower frequency for a better processing. This is done my mixing (nonlinear multiplication) the input frequency ωRF- ωT with ωRF± ωIF to obtain ωIF - ωT
IFAmp
IFAmp
Band Passat IF
Band Passat IF
S
D'D
'S
( ) tjst IFRFeLO ωω ±1
Mixer
Mixer
First Intemediate Frequaency (1st IF)
( ) ( )( ) ( ) ( )cRtpFeVD
cRtpeVStj
tj
TRF
TRF
/2
/2
−∆=
−=−
−
ψωω
ωω
The Receiver translates the high RF frequency ωRF to a lower frequency to abetter processing. This is done my mixing (nonlinear multiplication) the input frequency ωRF- ωT with ωRF± ωIF to obtain ωIF - ωT .
The IF signal is amplified and bandpass filtered to produce an output at IF frequency( ) ( )
( ) ( ) ( )cRtpFeVD
cRtpeVStj
tj
TIF
TIF
/2''
/2''
−∆=
−=−
−
ψωω
ωω
If the mixing frequency is centered at ωRF± ωIF than the output is centered atωIF and at the image 2 ωRF± ωIF .
86
Range & Doppler Measurements in RADAR SystemsSOLO
Receiver (continue – 1)
A second mixing frequency is sometimes added to avoid potential problems withimage frequency.
IFAmp
'S''S
( ) tjnd IFIFeLO ωω 22 ±
Mixer
Second Intemediate Frequaency (2nd IF)
IFAmp
'D
''D
Mixer
PhaseShifter
AGC
AGC Band Passat 2nd IF
Band Passat 2nd IF
( ) ( )( ) ( ) ( )cRtpFeVD
cRtpeVStj
tj
TIF
TIF
/2"
/2"2
2
−∆=
−=−
−
ψωω
ωω
The output of the Second Intermediate Frequency (2nd IF)
( ) ( )( ) ( ) ( )cRtpFeVD
cRtpeVStj
tj
TIF
TIF
/2''
/2''
−∆=
−=−
−
ψωω
ωω
87
Range & Doppler Measurements in RADAR SystemsSOLO
Receiver (continue – 2)
A second mixing frequency stage the signal consists of sinusoidals that possessesan arbitrary phase relationship with respect to the radar’s phase reference.
"'IS
I/Q Detection
VideoAmplifier A/D
Mixer
VideoAmplifier A/D
Mixer
VideoAmplifier A/D
Mixer
VideoAmplifier A/D
Mixer
2/π
2/π
''S
''D
"'QS
"'QD
"'ID "'ijI
D
"'ijQ
D
"'ijQ
S
"'ijI
S
tj IFe 2ω−
[ ] ( )[ ] ( )cRtpeVS
cRtpeVStj
Q
tj
I
T
T
/2"Im'"
/2"Re'"
−=−=
ω
ω
For a coherent Doppler andmonopulse processing is necessary to digitize the signal.
I/Q Detection
To find the phase and reduce the signal frequency to Video
with two 2nd IF signals at 90◦
(cos => I = in phase, sin => Q = quadrature).
[ ] ( ) ( )[ ] ( ) ( )cRtpFeVD
cRtpFeVDtj
Q
tj
I
T
T
/2"Im'"
/2"Re'"
−∆=−∆=
ψψ
ω
ω
'"'"'" QI SjSS +=
'"'"'" QI DjDD +=
88
SOLO Coherent Pulse Doppler Conceptual Operation
89
SOLO Signal Processing
Range – Doppler Cells in Σ and ΔAz, ΔEl
After Fast Fourier Transform (FFT) of the signals of the Batch in each Range Gatewe obtain Σ, ΔAz, ΔEl Rang-Doppler Maps.
90
SOLO Signal Processing
Parameters of Σ , ΔAz, ΔEl Range – Doppler Maps
f
fM
R
RN sunambiguousunambiguou
∆=
∆= &
The Parameters defining the Range – Doppler Maps are:
Δ R – Map Range Resolution
Δ f – Map Doppler Resolution
RUnambiguous – Unambiguous Range
fUnambiguous – Unambiguous Doppler
Range – DopplerCell
Range – DopplerMap
Range Gates are therefore i = 1, 2, …, NNumber of Range-Doppler Cells = N x M
Doppler Gates are therefore j = 1, 2, …, M
Note: The Map Range & Doppler resolution (Δ R, Δ f) may change as function of Seeker task (Search, Detection, Acquisition, Track). This is done by choosingthe Pulse Repetition Interval (PRI) and the number of pulses in a batch.
resolutionresolution ffRR ≥∆≥∆ &
91
SOLO Signal Processing Generation of Σ , ΔAz, ΔEl Range – Doppler Maps (continue – 1)
( ) ( )[ ] ( ) ( )ttTktttTkttfCts ddkdkrk
rk ++≤≤++−= τθπ2cos
The received signal from the scatter k is:
Ckr – amplitude of received signal
td (t) – round trip delay time given by ( )2/c
tRRtt kk
d
+=
θk – relative phase The received signal is down-converted to base-band in order to extract the quadrature components. More precisely sk
r (t) is mixed with:( ) [ ] τθπ +≤≤+= TktTktfCty kkk 2cos
After Low-Pass filtering the quadrature components of Σk, ΔAz k or ΔEl k signals are:
( ) ( )( ) ( )
==
tAtx
tAtx
kkQk
kkIk
ψψ
sin
cos
( ) ( )
+−≅−=
c
tR
c
Rfttft kkkdkk
2222 ππψ
The quadrature samples are given by:( ) ( )
+−≅=
c
tR
c
RfjAjAtX kkkkkkk
222expexp πψ
Ak - amplitude of Σk, ΔAz k or ΔEl k signals ψk - phase of Σk, ΔAz k or ΔEl k signals
( )
+−
+≅+=
c
tR
c
RfAj
c
tR
c
RfAxjxtX kk
kkkk
kkQkIkk
222sin
222cos ππ
92
SOLO Signal Processing Generation of Σ , ΔAz, ΔEl Range – Doppler Maps (continue – 2)
The received signal from the scatter k is:
The energy of the received signal is given by: ( ) ( ) 2kkkk AtXtXP == ∗
( )
+−
+≅+=
c
tR
c
RfAj
c
tR
c
RfAxjxtX kk
kkkk
kkQkIkk
222sin
222cos ππ
where * is the complex conjugate.
Therefore:kk PA =
93
94
Range & Doppler Measurements in RADAR SystemsSOLO
References on RADAR
Skolnik, M.I., “Introduction to Radar Systems”, McGraw Hill, 1962
Scheer, J.A., Kurtz, J.L., Ed., “Coherent Radar Performance Estimation”, Artech House, 1993
Schleher, D.C., “MTI and Pulsed Doppler Radar”, Artech House, 1991
Barton, D.K., Ward, H.R., “Handbook of Radar Measurements”, Artech House, 19
Morris, G.V., “Airborne Pulse Radar”, Artech House, 2nd Ed., 19
Maksimov, M.V., Gorgonov, G.I., “Electronic Homing Systems”, Artech House, 19
Wehner, D.R., “High Resolution Radar”, Artech House, 19
Hovanessian, S.A., “Introduction to Sensor Systems”, Artech House, 19
Barton, D.K., “Modern Radar System Analysis”, Artech House, 19
Berkowitz, R.S., “Modern Radar Analysis, Evaluation and System Design”, John Wiley & Sons, 1965
95
SOLO
TechnionIsraeli Institute of Technology
1964 – 1968 BSc EE1968 – 1971 MSc EE
Israeli Air Force1970 – 1974
RAFAELIsraeli Armament Development Authority
1974 – 2013
Stanford University1983 – 1986 PhD AA
96
Range & Doppler Measurements in RADAR SystemsSOLO
Chinese Remainder Theorem The original form of the theorem, contained in a third-century AD book by Chinese mathematician Sun Tzu and later republished in a 1247 book by Qin Jiushao.
Suppose n1, n2, …, nk are integers which are pairwise coprime. Then, for any given integers a1,a2, …, ak, there exists an integer x solving the system
1 1 1 1 1
2 2 2 2 2
1 2
0
0
0
, , , integersk k k k k
k
x n t a n a
x n t a n a
x n t a n a
t t t are
≡ + > >≡ + > >
≡ + > >L L L L L
L
or in modern notation
( )mod 1,2, ,i ix a n i k≡ = L ai is the reminder of x : ni
x
97
Range & Doppler Measurements in RADAR SystemsSOLO
Chinese Remainder Theorem (continue – 1)
A Constructive Solution to Find x
( )mod 1,2, ,i ix a n i k≡ = L
x
Define 1 2: kN n n n= L
For each i, ni and N/ni are coprime.
Using the extended Eulerian algorithm we can therefore find integers ri and si such that
( )/ 1i i i irn s N n+ =Define
Therefore ei divided by ni has the remainder 1 and divided by nj (j≠i) has the remainder 0,because of the definition of N.
( ): / 1i i i i ie s N n rn= = −
( ) ( )1 mod 0 modi i i je n and e n i j= = ∀ ≠Because of this the solution is of the form
1
k
i ii
x a e=
= ∑ But also ( )1
modk
i ii
a e x N=
=∑
98
Range & Doppler Measurements in RADAR SystemsSOLO
Chinese Remainder Theorem (continue – 2)
A Constructive Solution to Find x (Example)
( )mod 1,2, ,i ix a n i k≡ = L
1 2 3: 60N n n n= × =
( )( )( )
2 mod 3 ,
3 mod 4 ,
1 mod 5 .
x
x
x
≡
≡
≡1 2 33, 4, 5n n n= = =
1 2 3/ 20, / 15, / 12N n N n N n= = =
( ){ { { {
11 11
/
13 3 2 20 1sn N n
r
− + = ÷
( ){ { { {
2 2 22
/
11 4 3 15 1n s N n
r
− + = ÷
( ){ { ( )
{ {33
3 3/
5 5 2 12 1N nn
r s
+ − = ÷
( ): /i i ie s N n= ( )1 : 2 20 40e = = ( )2 : 3 15 45e = = ( )3 : 2 12 24e = − = −
1 2 32, 3, 1a a a= = =
( )1 1 2 2 3 3 2 40 3 45 1 24 191x a e a e a e= + + = × + × + × − =
Check:
191 63 3 2 47 4 3 38 5 1= × + = × + = × +
( )/ 1i i i irn s N n+ =Find ri and si such that:
Compute:
Therefore:
and ( )11 191 11 mod 60x N= ¬ = =
11 3 3 2 2 4 3 2 5 1= × + = × + = × +
99
100
101
102
SOLO Waveform Hierarchy
• Continuous Wave (CW)
103
SOLO Waveform Hierarchy
• Continuous Wave (CW)
104
SOLO Waveform Hierarchy
• Continuous Wave (CW)
105
SOLO Waveform Hierarchy
• Continuous Wave (CW)
106
SOLO Waveform Hierarchy
• Continuous Wave (CW)
107
SOLO Waveform Hierarchy
• Continuous Wave (CW)
108
SOLO Waveform Hierarchy
• Continuous Wave (CW)
109
SOLO Waveform Hierarchy
• Continuous Wave (CW)
110
SOLO Waveform Hierarchy
• Continuous Wave (CW)
111
112
SOLO Waveform Hierarchy• Steped Frequency Waveform (SFWF)
3 – 4 GHz
6 – 7 GHz
3 GHz
4 GHz
3 – 4 GHz