Overview of Modern Radar Electronic Protection Class Notes

Transcription

Overview of Modern Radar
Electronic Protection
Class Notes
Fall 2012
Dave Adamy
Adamy Engineering
1420 Norfolk Ave, Atwater, CA 95301
Tel(209)357-4433 Fax(209)357-4434
www.lynxpub.com
Scope of Course
• Radio Propagation
• Radar Jamming
• Electronic Protection
Handout Material
• Course Syllabus
– All visual aids + exercise work-sheets
• EW Pocket Guide
• Antenna & Propagation Slide Rule
• Scientific Calculator
EWPG page number
To Really Understand
Electronic Warfare
You need to have a real feel for Radio
Propagation
Antenna & Propagation Calculator
1 m = 3.3 ft 1ft = .3m
1
Antenna Calculations
Free Space Attenuation
Ant. Gain reduction vs surface
2
2 Ray Attenuation
Fresnel Zone
Calculate dB
Antenna Amplitude Pattern
1 m = 3.3 ft 1ft = .3m
2 Ray Attenuation
Fresnel Zone
Calculate dB
Antenna Scales
Antenna Scales
Antenna Gain & Beamwidth
Set Antenna Diameter (in ft) at Frequency (in GHz)
Antenna Gain & Beamwidth (cont)
Read Boresight Gain at Efficiency
Note 55% efficiency for Narrow Bandwidth antennas
Read 3 dB Beamwidth at 3 dB line
Read 10 dB Beamwidth at 10 dB line
First Null and Sidelobe
First
Sidelobe
First Null
Gain reduction vs. Surface Tolerance
Frequency
Gain reduction vs Surface Tolerance
Gain Reduction
Frequency
Gain Reduction
Surface Tolerance
Selection of Propagation Model
Clear
Propagation
Path
Propagation
Path
obstructed
by Terrain
Low
Link longer
Frequency, than Fresnel
Zone Distance
Wide
beams,
Link shorter
than Fresnel
Near
Zone Distance
ground
High frequency, Narrow
beams, Far from the ground
Two Ray
Line of
Sight
Calculate additional loss
from Knife Edge Diffraction
14
Also called:
Line of Sight Attenuation
Spreading Loss
Determined from: Formula
Nomograph
Slide Rule
Applicable when: Far from ground
Frequency high
Antennas narrow
Free Space Attenuation from Formula
LS = 32.44 + 20 Log(d) + 20 Log(f)
LS = Spreading loss between isotropic antennas (in dB)
d = distance in km
f = frequency in MHz
32 is a fudge factor
Warning:
This equation only works if exactly
the right units are input
Some Extra Information, not in book:
If Distance in kilometers: round 32.44 to 32 for 1 dB calculations
If Distance in staturte miles: replace 32.44 with 36.52 (round to 37)
If Distance is in nautical miles: replace 32.44 with 37.74 (round to 38)
15
Free Space Attenuation from Nomograph
Spreading Loss (dB)
20,000
160
Frequency (MHz)
140
100
1000
120
100
100
80
10
10
Transmission Distance (km)
10,000
500
60
40
1
1
15
1
sm = 1.6 km
nm = 1.15 sm
2
2 Ray Attenuation
Fresnel Zone
Calculate dB
Front of Antenna/Propagation slide rule
with line of sight attenuation scales highlighted
1
Free Space Attenuation from Slide Rule
Set Frequency
Read Attenuation at Range
Also notice short range scale (in meters)
Two Ray Attenuation
Also called:
40 Log d attenuation
distance4 attenuation
Determined from: Formula
Nomograph
Slide Rule
Applicable when: One primary reflector
Frequency low
Antennas wide
Direct and Reflected Rays close to the ground
XMTR
RCVR
Transmit
Antenna
Height
Receive
Antenna
Height
GROUND
16
Two Ray Attenuation from Formula
LS = 120 + 40 Log(d) - 20 Log(hT) - 20 Log(hR)
LS = Spreading loss between isotropic antennas (in dB)
d = distance in km
hT = height of transmit antenna in meters
hR = height of receiving antenna in meters
Warning:
This equation only works if exactly
the right units are input
Note:
There is no frequency term
Minimum antenna heights may apply
30 MHz over good soil 10 meters
(to 3 meters at 60 MHz & 1 meter at 200 MHz)
Higher over salt water
Use higher of actual or minimum antenna height
16
10
30
100
3
.1
.3
10
30
100
1
3
10
30
100
300
1000
300
300
1000
1000
3000
3000
10,000
10,000
70
80
90
100
110
120
130
140
150
160
170
Propagation Loss (dB)
3
1
Path Length (km)
1
Receiving Antenna Height (m)
Transmitting Antenna Height (m)
Two Ray Attenuation from Nomograph
16
1
2
2 Ray Attenuation
Fresnel Zone
Calculate dB
Back of slide rule
with two-ray calculation scales highlighted
2
Two Ray Attenuation from Slide Rule
Set Transmit antenna height at link distance
Two Ray Attenuation from Slide Rule
Read attenuation at receiving antenna height
Minimum Ant Height – 2 Ray Propagation
Minimum Height (meters)
200
100
80
60
40
Sea
Water
20
10
8
6
4
Good Soil
Vert Pol
Poor Soil
Vert Pol
2
Poor Soil
Hor Pol
1
.8
.6
.4
Good Soil
Hor Pol
20
500 1000
50 100 200
Frequency (MHz)
Fresnel Zone
Determines whether FREE SPACE or
TWO RAY Propagation is appropriate
If Link is shorter than FZ:
Use Free Space
If Link is longer than FZ:
Use 2 Ray
Use selected propagation for whole distance
Determined from: Equation
Slide Rule
Fresnel Zone Calculation
FZ = [hT x hR x F] / 24,000
Where:
FZ = Fresnel Zone in km
hT = Transmit antenna height in meters
hR = Receiving antenna height in meters
F = frequency in MHz
13
1
2
2 Ray Attenuation
Fresnel Zone
Calculate dB
Back of slide rule with Fresnel zone scales highlighted
2
Fresnel Zone from Slide Rule
Align transmit and receive antenna heights
(both in meters)
Fresnel Zone from Slide Rule
Read Fresnel Zone (in km) at Frequency (in MHz)
Knife Edge Diffraction Geometry
Note: Blind Zone
d1 ≥ d2
d2 ≥ d1
H
T
R
d1
d= [
d2
2 / (1 + d1/d2)]d1
If d is set to d1 there is a loss of  1.5 dB Accuracy
This is recommended, since this is only an
Approximation of the loss over a ridge line
17
Line of sight path above or below the knife edge
H
XMTR
Line of Sight
RCVR
XMTR
Line of Sight
RCVR
H
Knife Edge Diffraction Nomograph
17
Jamming Equations
Required J/S
About Jamming Equations
Note: ERP = PT + GT
(In direction of receiver)
d & R both used for range (in km)
1 sm = 1.6 km, 1 nm = 1.15 sm
Antenna gains sometimes “qualified”
GS = side lobe gain
(also called GRJ for Gain of radar antenna toward jammer)
GM = main beam gain (for self protection, just called G
RADAR RECEIVED POWER EQUATION
XMTR
RCS
RCVR
dB
or
PR = PT + 2G - 103 - 20 Log F - 40 Log R + 10 Log RCS
PR = ERP + G - 103 - 20 Log F - 40 Log R + 10 Log RCS
RWR Link
1 dBi
30 dBi
10 km
10 kw
RADAR
Rcvr Sens = -55 dBm
8 GHz
PR = ERP – Loss + GR
20 Log Reff = ERP – 32 -20 Log F + GR – Sens
Eff Range = Antilog[(20 Log d)/20]
RWR Link (2)
30 dBi
1 dBi
ERP = 100 dBm
10 km
10 kw
RADAR
Rcvr Sens = -55 dBm
8 GHz
PR = +100 – 131 + 1 = -30 dBm
20 Log Reff = 100 – 32 - 78 + 1 – ( -55) = 46
Eff Range = Antilog[(46)/20] = 199.5 km
RWR Link (3)
30 dBi
10 kw
RADAR
8 GHz
10 km
S/L = -20 dB
1 dBi
Rcvr Sens = -55 dBm
RWR Link (4)
30 dBi
10 kw
RADAR
8 GHz
ERP = 80 dBm
10 km
1 dBi
S/L = -20 dB
GS = 10 dBi
PR = 80 – 131 + 1 = -50 dBm
Rcvr Sens = -55 dBm
20 Log Reff = 80 – 32 - 78 + 1 – (-55) = 26
Eff Range = Antilog[(26)/20] = 20 km
SELF PROTECTION JAMMING
Radar Signal
RADAR
Jammer Signal
Jammer located on target
Has advantage of Radar Antenna
Can use either Cover or Deceptive Jamming
S = ERPS + G - 103 - 20 Log F - 40 Log R + 10 Log RCS
J = ERPJ + G - 32 - 20 Log F - 20 Log R
Note that distances are the same and both jammer &
radar return are received with antenna gain G
J/S = ERPJ - ERPS + 71 + 20 Log R - 10 Log RCS
J
STAND-OFF JAMMING
Radar Signal
RADAR
•Jammer remote from target
•In side lobe of Radar Antenna
•Uses cover jamming
•Prevents Acquisition
S = ERPS + GM - 103 - 20 Log F - 40 Log RT + 10 Log RCS
J = ERPJ + GS - 32 - 20 Log F - 20 Log RJ
Note that distances and antenna gains are different
J/S = ERPJ - ERPS + 71 + GS - GM - 20 Log RJ + 40 Log RT
- 10 Log RCS
J
SELF PROTECT BURN THROUGH
Radar Signal [Reduces by R4]
J
Jammer Signal [Reduces by R2]
RADAR
Rcvd Pwr
Target (& Jammer)
Approaching Radar
Jammer
Skin Return
Range
Range at which
there is no longer
adequate J/S
SELF PROTECT BURN THROUGH EQN
20 Log R = ERPS - ERPJ - 71 + 10 Log RCS + J/S (Required)
Note: RBT = R at Burn through range
RBT = Anti-Log {[20 Log R]/20}
Value of
STAND-OFF BURN THROUGH
Radar Signal [Reduces by d4]
Range at which
there is no longer
adequate J/S
Rcvd Pwr
RADAR
Jammer
Skin Return
Range
Target
Approaching
Radar
J
STAND-OFF BURN THROUGH EQN
J/S = ERPJ - ERPS + 71 + GS - GM - 20 Log RJ + 40 Log RT
- 10 Log RCS
40 Log RT = ERPS - ERPJ - 71 - GS + GM + 20 Log RJ
+ 10 Log RCS + J/S (Required)
Note: RBT = RT at Burn through range
RBT = Anti-Log{[40 Log RT]/40}
Value of
Jamming Problems
Self Protect J/S Problem
10 sm
30 dBi
10 km
10 kw
RADAR
J
100 watts
3 dBi Ant
Self Protect J/S Problem(2)
30 dBi ERP = + 100 dBm
+ 70 dBm
10 kw
10 km
RADAR
10 sm
J
100 watts
3 dBi Ant
J/S = 53 - 100 + 71 + 20 - 10 = 34 dB
ERP = + 53 dBm
Self Protect Burn Through Problem
10 sm
30 dBi
J
10 kw
RADAR
J/S (Rqd) = 2 dB
20 Log RBT = ERPS - ERPJ - 71 + 10 Log RCS + J/S (Rqd)
RBT = Antilog[(20 Log RBT)/20]
100 watts
3 dBi Ant
Self Protect Burn Through Problem(2)
10 sm
30 dBi ERP = + 100 dBm
J
10 kw
RADAR
100 watts
3 dBi Ant
J/S (Rqd) = 2 dB
ERP = + 53 dBm
20 Log RBT = ERPS - ERPJ - 71 + 10 Log RCS + J/S (Rqd)
20 Log RBT = 100 – 53 - 71 + 10 + 2 = -12
RBT = Antilog[( -12)/20] = 251 meters
Stand-off J/S Problem
30 dBi
10 sm
5 km
RADAR
10 kw
S/L = -20 dB
J
1 kw
18 dB Ant
J/S = ERPJ - ERPS + 71 + GS - GM - 20 Log RJ + 40 Log RT - 10 Log RCS
Stand-off J/S Problem (2)
30 dBi
ERP = + 100 dBm
10 sm
5 km
RADAR
10 kw
S/L = -20 dB
J
GS = 10 dBi
1 kw
18 dB Ant
ERP = + 78 dBm
J/S = 78 - 100 + 71 + 10 - 30 - 29.5 + 28 - 10 = 17.5 dB
Stand-off Burn-through Problem
30 dBi
10 sm
RADAR
10 kw
S/L = -20 dB
J/S (Rqd) = 2 dB
J
1 kw
18 dB Ant
40 Log RBT = ERPS - ERPJ - 71 – GS + GM + 20 Log RJ+ 10 Log RCS + J/S (Rqd)
Stand-off Burn-through Problem (2)
30 dBi
10 sm
ERP = + 100 dBm
RADAR
10 kw
S/L = -20 dB
GS = 10 dBi
J/S (Rqd) = 2 dB
J
1 kw
18 dB Ant
ERP = + 78 dBm
40 Log RBT = ERPS - ERPJ - 71 – GS + GM + 20 Log RJ+ 10 Log RCS + J/S (Rqd)
40 Log RBT = 100 - 78 - 71 – 10 + 30 + 29.5 + 10 + 2 = 12.5
RBT = Antilog[(12.5)/40] = 2 km
Stand-in Jamming Problem
30 dBi
10 sm
5 km
RADAR
10 kw
S/L = -20 dB
100 m
J
1 watt
ERP
Stand-in Jamming Problem (2)
30 dBi
10 sm
ERP = + 100 dBm
5 km
100 m
RADAR
10 kw
S/L = -20 dB
GS = 10 dBi
J
1 watt
ERP
ERP = + 30 dBm
J/S = 30 - 100 + 71 + 10 - 30 +20 + 28 - 10 = 19 dB
Standard Jamming Techniques
Barrage Jamming
Spot Jamming
Swept Spot Jamming
Spoked PPI Display
Power Management
DECEPTIVE JAMMING
• Range
– RGPO, RGPI, Cover Pulse
• Angle
– Inverse Gain
• Velocity
– VGPO
• Monopulse Techniques
– Formation, Formation w/range denial, Blinking
– Cross Pol, Cross Eye, Terrain Bounce,
RANGE GATE PULL-OFF
TARGET
Radar Signal
Skin Return
1
2
Jammer
Signal
3
4
JAMMER
RANGE GATE PULL-OFF
At Radar
Early Gate
Late Gate
Skin Return
1
2
Jammer
Signal
3
4
RANGE GATE PULL-OFF
Radar Resolution Cell
Leading Edge Tracking
Skin Return
Jammer
Signal
Leading
Edge
Energly
Leading Edge Tracker Ignores Delayed Jammer Leading Edge
CCM requires jammer to lead skin return
RANGE GATE PULL-IN
TARGET
Radar Signal
Skin Return
1
2
Jammer
Signal
JAMMER
3
4
RANGE GATE PULL-IN
At Radar
Early Gate
Late Gate
Skin Return
Jammer
Signal
RANGE GATE PULL-IN
Radar Resolution Cell
COVER PULSES
TARGET
Radar Signal
Skin Return
Jammer
Signal
JAMMER
Denies Radar Range Information
Theoretical Inverse Gain
INVERSE GAIN JAMMING (CONSCAN)
SKIN
RETURN
JAMMING
SIGNAL
RADAR
RECEIVED
SIGNAL
INVERSE GAIN JAMMING (CONSCAN)
RADAR TRACKING RESPONSE
Track While Scan Radar
Fan Beam
measures Elevation
Fan Beam
measures Azimuth
Reference
Target
Elevation
Target
Azimuth
Inverse Gain against TWS Radar
Angle Gate
Skin Return
Jammer
Radar
Return
Scan on Receive Only Radar
Steady Beam
On Target
Scans to create
Tracking data
INVERSE GAIN JAMMING (SORO)
SKIN
RETURN
JAMMING
SIGNAL
RADAR
RECEIVED
SIGNAL
AGC Jamming
Doppler Radar Return
Velocity Gate Pull-off
Formation Jamming
Formation Jamming with Range Denial
Blinking
Missile Track with Blinking
Terrain Bounce
Note: Last of Optional Slides
• Some techniques work against nonmultichannel radars only
• Multichannel techniques:
– Described in Section 9.9 of EW101
• Focus in this section on most complex
techniques
– Cross Pol & Cross Eye
• Others will be discussed along with EP
considerations
CROSS
POLARIZED
RESPONSE
CONDON
LOBES
PARABOLIC
DISH
FEED
SIGNAL ARRIVING
FROM OFF AXIS
DIRECTION
Cross Pol Jamming
Cross Polarization Jamming
Vert Rcv
Received
Signal
Polarization
Horr Rcv
Transmitted
Signal
Polarization
Vert Xmt
Horr Xmt
Cross Pol Issues
• Requires very large J/S to overcome
weakness of Condon Lobes
• Works best against short focus parabolic
antennas (Larger Condon Lobes)
• Defeated by polarization filters or flat plate
antennas (No Forward Geometry)
Cross Pol
Cross Eye Jamming
Wavefront with Cross Eye
Cross Eye Miss Distance
Cross Eye Implementation
180 deg
nsec
SW
nsec
SW
•
•
•
•
•
•
•
EP Techniques
Ultra-low Side Lobe
Side lobe canceller
Side Lobe Blanker
Anti Cross Pol
Mono-pulse
Pulse Compression
Pulse Doppler
– Anti Doppler pull-off
– Frequency, range rate correlation
– Anti Chaff
•
•
•
•
•
•
Anti AGC jamming
Burn through modes
Frequency Agility
PRF Jitter
Home on Jam Modes
Ultra-low Side Lobe
Reduced
ELINT Range
Target
JAMMER
Reduced J/S
Performance Relative Level Average Level
Ordinary
-13 to -30 dB
0 to -5 dBi
Low
Ultralow
-30 to -40 dB
Below -40 dB
-5 to -20 dBi
Below -20 dBi
From Schleher, EW in Info Age
Coherent Side Lobe Canceller
Main
Radar
Antenna
Appears to Radar
to be reduced signal
In Main Lobe
Signal Received
Stronger in auxiliary
Antenna.
Auxiliary
Antenna
RADAR ADDS
AUXILIARY ANTENNA
SIGNAL 180° OUT OF PHASE
(LIKES CW SIGNALS)
Coherent Sidelobe Canceller
Target
Jammers
Requires one
Canceller per
Jammer
NB
Loop
& Ph
Shift
Vulnerable
To Blinking
(pg 288)
+
NB
Loop
& Ph
Shift
+
NB
Loop
& Ph
Shift
Cross pole response
May require another
canceller
Pulse signal acts like
It has wide angle.
Requires multiple CSCs
Main Beam Signals
- Side lobe Signals
Note that loop bandwidths make CSC respond best
To continuous signals
Side Lobe Blanker
Main
Radar
Antenna
RADAR BLANKS
RECEIVER INPUT
DURING PULSE
IN SIDELOBE
Auxiliary
Antenna
Appears to Radar
to be reduced signal
In Main Lobe
Signal Received
Stronger in auxiliary
Antenna.
Sidelobe Blanker
Target
Jammers
“Side Lobe”
Antenna
Switch
High Duty Factor or
Cover pulses cover
Desired return
Note that blanker works against pulse signals in S/L
Anti Cross Pol
CROSS
POLARIZED
RESPONSE
CONDON
LOBES
Reduced Condon Lobes Make Cross Pol Jamming Ineffective
Monopulse Tracker
Angle tracking on every pulse
Deceptive Jamming Improves Radar Angle Track
Pulse Compression
Unless Jamming has correct
Bit phases, effective J/S
Reduced by code length
Digital
PULSE
With FM
Linear
FM
Unless Jamming has correct
Frequency slope, effective J/S
Reduced by compression factor
COMPRESSIVE
FILTER
Range/Velocity Correlation
Pulse Position vs. time in RGPO
Time
PD radar correlates apparent range rate with Doppler frequency
– If inconsistent, rejects jamming signal
Skin Return
Jammer
Signal
Leading
Edge
Energy
Leading Edge Tracker Ignores Delayed Jammer Leading Edge
CCM requires jammer to lead skin return
Anti AGC Jamming
Dicke Fix
Skin Return
Wideband Jamming
Wideband
Channel
Limiter
Normal
bandwidth
IF Amp
AGC Loop
Prevents narrow pulses and wideband FM generated
Noise from capturing AGC
Burn Through Modes
• Increased Power
• Increased Duty Factor
Both increase radar detection range
In presence of Jamming
PRF Jitter
PSEUDO-RANDOM PULSE POSITION
PREVENTS RGPO & EXTENDS COVER PULSE TIME
Home on Jam
• Radar detects that jamming is taking place
– Pulse Doppler Radar detects jamming
waveforms
• Homes on Jamming signal
– Mono-pulse radars use multiple apertures for
angle info on every pulse
• Makes self protection jamming impractical
– Requires stand-off, stand-in jamming or
decoys

Overview of Modern Radar Electronic Protection Class Notes

Transcription

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