Transcript ppt
ECEN5633 Radar Theory
Lecture #5
27 January 2015
Dr. George Scheets
www.okstate.edu/elec-eng/scheets/ecen5633
Read 14.1 & 14.2 (RCS)
Problems 2.10 & 19, 2014 Quiz #1
20 point Quiz #1, Next Time
Open
book & notes
Signal & Noise Power
Use appropriate Link Equation to estimate Pr
Calculate Tosys & find Wn to get noise
Pr
Nant
+
+
+
N1 =
+
+
kToW
n
N2 =
Decision
Box
+
kToW
n
N3 =
kToW
n
Need Signal &
Noise power
in here
Pr
N = kTosysWn
Ratio of Signal and Noise power at input
is same as ratio of Signal and Noise power at output
Signal & Noise Power
Noise Figure F = SNRin/SNRout
Antenna Temp changes? F changes.
Pr
Nant
+
+
+
N1 =
SNRin
+
+
kToW
n
N2 =
Decision
Box
+
kToW
n
N3 =
kToW
n
SNRout
Need Signal &
Noise power
in here
Time Averaged Autocorrelation
of
Infinite Length Baseband Pulse Stream
RXX(τ)
Pave
…
-T
-Tp 0
…
Tp
τ (sec)
T
Can be thought of as a triangle
convolved with an
infinite length stream of delta functions.
F.T. of Triangle
Peak value is
area under the
triangle
= Pavg*Tp
Nulls are at
integer
multiples of
1/pulse width
= 1/Tp Hz
F.T. of Infinite Length Time
Domain Stream of Delta Functions
Is an infinite length stream of delta
functions in the frequency domain.
δ(t)
in time domain → δ(f)/T in freq domain
T seconds spacing in time domain →
1/T Hz spacing in frequency domain
Convolution in Time Domain
Is multiplication in Frequency Domain
Power spectrum of baseband pulse
stream…
Delta
Functions
are
= 1/T Hz
apart
Peak value is
= PavgTp/T
… …
f(Hz)
Pulse Radar vs CW Radar
Sort of Opposites
Good waveform for CW Radar
Constant
amplitude sinusoid
Delta function in frequency domain
Easy to measure frequency shifts
Good waveform for Pulse Radar
Delta
function in time domain
Constant amplitude in frequency domain
Easy to measure time shifts
RCS of WWII A-26 Invader
source: Wikipedia
Small angle changes can
cause big change to σ
due to…
Reflections
Scatter Directions
Phase Cancellations
Absorption
Thru Transmission
National Radar Cross Section Test Facility
Source http://www.urs.com/projects/national-radar-cross-section-test-facility/
EM Waves and You
MHz
GHz
THz
PHz
EHz
source: http://hyperphysics.phy-astr.gsu.edu/
Metal:
Reflects
everything.
Gamma
can punch
thru thin
sheets.
2D Corner Reflector
source: naples.cc.sunysb.edu
3D Corner Reflector [Demo]
lecturedemo.ph.unimelb.edu.au/Optics/Mirrors-Lenses/Oa-6-Corner-Reflector
Deliberate Use
Buoy
in
San Diego Bay
Stealth in the Sky
Stealth on the Water
F-22 Raptor