Yngve Steinheim SINTEF ICT/NINA -...
Transcript of Yngve Steinheim SINTEF ICT/NINA -...
ICT 1
RADAR An introduction to basic performance
International workshop: Trends in Radar Ornithology National Environmental Research Institute (NERI), Aarhus Denmark
21st January 2010
Yngve SteinheimSINTEF ICT/NINA
ICT 2
Radar
What is a radar, and what can it do?
Detection and location of objects by radio waves
Emits a particular type wave form, and detects the nature of the
return
How well can it do it?
Detection capability
Accuracy and resolution
Tx
Rx
Duplx
ICT 3
Transmission equation (1)
24 RPS t
t
tt
t GR
PS 24Pt
: Transmitted power
R: Range
Gt
: Tx
antenna gain
St1
St2
St1
> St2
R
ICT 4
Transmission equation (2)Radiated energy is intercepted by an object with a radar cross section σ:
24 RGPSP tt
ti
222 44 RGP
RPS tti
s
Captured energy is scattered isotropically:
σ: Target radar cross section
ICT 5
Transmission equation (3)Reflected energy is received by an antenna with effective area Ar
:
rtt
rsr ARGPASP 224
4
2r
rGA
Ar
: Receiver antenna effective area
Gr
: Receiver antenna gain
λ: Radar wavelength
ICT 6
Free space transmission equation
43
2
4 RGGPP rtt
r
22 44 RA
RGPP r
ttr
Effective radiated power x intercepted by target x captured by Rx antenna
ICT 7
Example
Received power from a (large) bird with RCS 0.01 m2
at 2000 m illuminated by a S-band ship radar:
Pt
=30 kW
R=2000 m
Gt
=Gr
= 26dB (400)
σ=0,01 m2
λ=0,1 m
WWPr 150000000000,0105,12000)4(
01,01,040040030000 1123
2
ICT 9
General transmission equation (4)
Free space antenna pattern
Effect of ”lobing”
Csc2
antenna pattern
LRFGGP
P rttr 43
42
4
ICT 10
Noise in the radar receiver
Tx
Rx
Duplx
Ground noise in lower sidelobe
Solar or galactic noise
Solar or galactic noise
Atmospheric noise
WG and duplexer noise
Receiver noise
ICT 12
Radar range equation
ns
rtt
BkTLRFGGP
NS
43
42
min 4)/(
4
min3
42
max )/(4 ns
rtt
BkTLNSFGGP
R
ICT 15
Resolution and accuracy
Radar operates in a 4-dimensional space:
Time (Range)
Two angles: (Usually) azimuth and elevation
Frequency (doppler)
A target is resolved if it can be separated from other targets in at least one of these coordinates
After having detected and resolved a target, the radar must deliver an estimate of its position
ICT 16
Range (time)
2cR
Resolution (for a rectangular pulse)
RMS Error (for a rectangular pulse)
)/(42 NSBc
R
ICT 17
Angular resolution and accuracy
Resolution: When separated by 1 half-power beam width
angle
amplitude
θ3
θ3
RMS error:
nNS
)/(5.0 3
ICT 20
Summary
Radar: Detection
and location of
objects
Fundamental performance
Detection
in the
clear. (Pd, Pfa)
Resolution
and accuracy
ICT 21
References
Skolnik
M. I. (1980): Introduction
to radar systems, McGraw-Hill
(2nd
ed).
Barton
David K (1988): Modern
Radar System Analysis, Artech
House
Blake Lamont
V. (1986): Radar Pange-Performance Analysis, Artech
House
http://www.radartutorial.eu/