View
24
Download
0
Category
Tags:
Preview:
Citation preview
Radar Basics
Radar
• Detects and tracks objects of interest"• Measures the location of objects remotely in range
and angle"• Generates imagery of the ground (and other
objects)"• Able to provide very wide coverage (e.g. 3600,
global)"• Operates day and night and in all weathers"• Can provide information about object type and
intent"
Schematic Diagram of a Simple Radar System
“I’m Listening”
Wavelength and Frequency
Phase and Superposition
Intensity of spherical waves
Polarization
For a wave travelling in the Z direction the electric field must lie in the x-y plane as defined by Ex and Ey ."If Ex =0, or Ey =0 then the polarization is linear. "If Ex=Ey and they oscillate in phase, the field will oscillate linearly along a 450 line in the x-y plane."If Ex=Ey and are npi/2 put of phase the polarization is circular and if Ex is not equal to Ey the polarization is elliptical."
Diffraction
Beams
Refraction and Reflection
Radar Types
Primary Air Traffic Control Radar at Heathrow Airport , London, UK
Air Traffic Control Radar (ACTR) ALE 3X5 Maccarese, Italy
Courtesy of AMS A. Farina, June 2003
Civil marine band radar used "by shipping throughout the world. "All commercial craft are legally obliged to carry such radar systems"
Civil Marine Radar
Martello – UK Air Long Range Defence Radar System
US E3-D Sentry Airborne Early Warning Radar System
Captor Radar for TYPHOON Aircraft Airborne Intercept Radar
Courtesy of BAE SYSTEMS"
BYSON – UK Experimental Radar
AEGIS AN-SPY1 Air Defence
MESAR-1 Experimental Phased Array Naval Air Defence
Early Bistatic Radar Experiments at UCL
Griffiths, H.D. and Carter, S.M., ʻProvision of moving target indication in an independent bistatic radar receiverʼ; The Radio and Electronic Engineer, Vol.54, No.7/8, pp336-342, July/August 1984 ."
94 GHz SAR Experimental System sometimes used in Missile Seekers
ERS-1 Earth Resources Satellite
SEASAT Shuttle SAR Image
Terra SAR - X
Airborne SAR Image of the Penatgon
source: Sandia Corporation -http//www.sandia.gov "
Stealth aircraft
Typical Applications
HF VHF and UHF L-band S-band C-band X-band Ku- and Ka-band V- , W- and mm-wave bands
3 - 30 MHz 30 - 1000 MHz 1 - 2 GHz 2 - 4 GHz 4 - 8 GHz 8 - 12 GHz 12 - 40 GHz 40 - 100+ GHz
Over-the-horizon radar, combining very long range with lower resolution and accuracy. More useful over the oceans."Long range, line-of-sight surveillance with low to medium resolution and accuracy and freedom from weather effects."Long-range surveillance with medium resolution and slight weather effects (200 nmi)"Short-range surveillance (60 nmi), long-range tracking with medium accuracy. Subject to moderate weather effects in heavy rain or snow."Short-range surveillance, long-range tracking with high accuracy. Subject to increased weather effects in light to medium rain."Short-range surveillance in clear weather or light rain; long-range tracking with high accuracy in clear weather, reduced to short range in rain."Short-range tracking, real and synthetic aperture imaging, especially when antenna size is limited and when all-weather operation is not required or ranges are short."Limited to short ranges in a relatively clear atmosphere, very short ranges in rain. Generally for tracking and ‘smart seekers’ with very small antennas. Remote sensing of clouds."
Radar Frequency Bands
Radar Letter Band Designations
frequency (GHz)
wavelength (cm)
0.125 0.25 0.5 1 2 4 8 16 32 64 128
240 120 60 30 15 7.5 3.75 1.87 0.94 0.47 0.23
L S C X Ku
A B C D E G I J K MF H L
K Ka RADAR BANDS
ECM BANDS
Atmospheric Attenuation – Weather
Atmospheric attenuation – clear air
mm-wave sub mm-wave Infra-red Vis. UV
micro-wave
Extra Attenuation – Foul Weather
99.8%
Atte
nuat
ion
/ dB
per
km
Tran
smis
sion
ove
r 1km
10GHz 100GHz 1THz 10THz 100THz 1000THz
1
10
100
1000
0.1
0.01
10%
80%
98%
10 % -8
10 %
mm-wave
sub mm-wave
Infra-red
Vis. UV micro-wave
94GHz
35GHz
Fog (50m vis)
Heavy rain (25 mm/hr)
Drizzle (0.25 mm/hr)
-100
Courtesy of AMS A. Farina, June 2003
RAN 20 S, radar electronic cabinet including: a) RF Generator (double conversion); RF-IF receiver; b) Signal processor (target and weather); c) Data
processor (target and weather);"
Radar Equipment Rack
Block Diagram of a Typical Radar
RF AMPLIFIER
MODULATOR POWER SUPPLY
DIPLEXER AND FILTER
EXCITER
RF PREAMPLIFIER
AND MIXER
IF AMPLIFIER AND
QUADRATURE DETECTOR
ADC and SIGNAL
PROCESSING
DATA PROCESSING AND DISPLAY
SYNCHRONISER
ANTENNA
ANTENNA
RECEIVER
TRANSMITTER
MICROWAVE EXCITER AND SYNCHRONISER
Radar Ranging
point !target!
r
radar!
pulse !
Two-way propagation delay"""hence "
2 rtc
=
2ctr =
Radar range is sometimes quoted in nautical miles (1 nmi = 1.85 km), and velocity in knots (1 kt = 1 nmi/hr) "
Range Resolution
point !targets!
radar!
pulse"duration = τ
r + Δr
r
received energy
time"
echo"duration = τ
The separation in time between the echoes from the targets is""""" "Set this = t, then""The radar echo is usually processed in"samples of range extent equal to the range"resolution, and known as range bins."
( )2 2 2 r r r rc c c+Δ Δ
− =
2cr τ
Δ =
Range Resolution (ii)
The spectrum of a rectangular pulse of length t"""" is a sinc function centered on w0"""""whose bandwidth (at -3.9 dB) is B = 1/t""""So we can write the range resolution as "
2Δ =
crB
0( ) cos 2 2
f t A t tτ τω= − ≤ ≤
( ) ( )( )
0
0
sin 22 2
Fω ω ττ
ωω ω τ
⎛ ⎞+= ⎜ ⎟⎜ ⎟+⎝ ⎠
Angular Resolution
(radians)B dλ
θ ≈
r antenna"
length = d"
azimuth resolution
Br rdλ
θ= ≈
Pulse Repetition Frequency
time
Pulses are usually transmitted at a regular interval, known as the"pulse repetition interval (PRI)"""""""""""The reciprocal of the PRI is the pulse repetition frequency (PRF)"
PRI
1PRF PRI
=
Maximum Unambiguous Range
time
Associated with a given PRF is a maximum unambiguous range, since any echo which arrives after the instant of transmission of the next pulse cannot unambiguously be associated with the original pulse.""The maximum unambiguous range is therefore or""
PRI
. PRI2
c2. PRFc
Maximum Unambiguous Range
Scanning radar
Many (but not all) radars scan in azimuth.""If the scan period is T, then the time (dwell) for which the beam illuminates a given target is :"""""Hence the number of pulses illuminating the target is :""""""The rotation rate of the antenna (in r.p.m.) is"
Bo . θ
θB(with in degrees)360
T
Bo . .
360θ PRFT
60T
Recommended