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