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다음은 PACRIM Training Course (Workshop)
의 강의 Note 중에서
1.1 Wave Properties 만을 발췌한 것으로,
전파의 성질을 이해하는데 도움이 될 것입니다.
Wave Polarization,
Polarimetric SAR, and
Polarimetric Scattering Models
Yisok Oh
Dept. of Radio Engineering, Hong-Ik University
Seoul National University, February 16-19, 2000
1
Contents
1. Wave Polarization
1.1 Wave Properties
1.2 Polarization Synthesis
2. Polarimetric Radar System
2.1 A Scatterometer System
2.2 NASA/JPL POLSAR System
3. Polarimetric Scattering Models
3.1 Surface Scattering
3.2 Volume Scattering
2
1.1 Wave Properties
-. What is the “Field”?
-. Waves : Electromagnetic Waves by Maxwell
-. Planewave Propagation in free space
-. Polarization : Basic concepts
-. Microwave Generation : DC to AC
-. Microwave Guidance by Waveguides/ Trans. lines
-. Microwave Radiation by Antennas
-. EM Wave Reflection from infinite planes
-. Microwave Scattering from
-. Point Targets
-. Distributed Targets
3
Electromagnetic Fields
Fields: Spatial distribution of a physical quantity.
Electromagnetic Fields
Static Fields
: DC
No time-variation
Separation of
Electric Field and
Magnetic Field
Dynamic Fields
: AC
Time-varying Fields
Co-existence of
Electric and
Magnetic fields
4
Electrostatic Fields
E : Electric Field
(showing flux lines)
V
+
-
E
d
Conducting Plates
Assuming infinite plates,
V
E 
d
V / m 
Direction of E : From + charges to - charges
5
Magnetostatic Fields
I
I : Current
H
H : Magnetic Field
(showing flux line)

IEEE
Emblem
voltage
Electric Fields
current
Magnetic Fields
Assuming an infinite current line,
H 
Direction of H : Right-hand rule,

 A / m
I
2
Hˆ  Iˆ  Rˆ

6
Dynamic (Time-Varying) Fields
B
 E  
t
 H  J 
D
t


B
 c E  dl   S t  ds 




D
 c H  dl  SJ  ds  S t  ds 


Electromotive
Force
(Voltage Source)
Time-varying
Electric Field
E(r,t)
Conduction
Current
Maxwell’s
Equations
Displacement
Current
Time-varying
Magnetic Field
H(r,t)
7
Waves
Consider Water wave in a pond.
Cut water surface at once
(t=t0) with Kwan-Woo’s
Sword (청룡언월도) and look
Wave Height
Log the height of
Fishing Buoy (x=x0)
as a time function
Wave Height
X
(Spatial Displacement)
t
(Time)
Even though the wave comes toward me,
the water doesn’t !
8
Electromagnetic (EM) Waves
An Example of an EM wave:
E (r , t )  E0 cost  kz  0 xˆ
Magnitude
(source,
distance,
etc.)
Ex
Sinusoidal
Wave
Time
Variation
2

T
Z-directed
propagation
2
k

Vector
(Polarization)
T
Time
Ex

z, distance
9
Phase Velocity
Assume these circles are surfing boards.
t  kz  0 = constant
Same Phase
Phase velocity = velocity of the equi-phase point
 t  0  const 


z

k


vp 


t
t
k
Poynting Vector:
S r , t   E r , t  H r , t 
: Real Power Flow (Magnitude and Direction)
10
Time-Harmonic Fields
Time-harmonic Assumption:
E ( r )  E0 e
 jkz
e
j t
xˆ
Time variation
(Phasor form)
  E   jH (Maxwell Equation)
E0  jkz
H (r ) 
e yˆ

xˆ  yˆ  zˆ



 377
in vacuum
z : wave prop. direction
11
Planewave Propagation
Planewave: wavefront is plane
Approximate Planewave
Spherical wave
near an antenna
in the Far-zone
x

2D 2 
 R 

 

E (r )  E0 e  jkz xˆ
Ex
z
Hy
y
E  H  zˆ
Z-directed propagating
Linear polarized (x-direction)
Wave
12
Polarization
: shape of the locus of the E vector tip
at a given point in space as a function of time.

E z   ax xˆ  a y yˆ e
Polarization
Linear
Circular
Elliptical
Conditions
  0, 
j
e
 jkz
Examples
E ( z )  E0 e
 jkz
xˆ

ax  a y ,   
E z   xˆ  j yˆ e  jkz
2
Other Cases
E z   xˆ  j 2 yˆ e  jkz
13
Exercise (determination of polarization)
Find polarization of the wave,
E z   2 xˆ  yˆ e jkz
E z, t   Re E z  exp  jt 
 2 xˆ  yˆ  cost  kz
E 0, t   2 xˆ  yˆ cos t 
Find instantaneous
electric field:
Ey
Plot electric field:
t  0
1

2
Determine
polarization
t  
Linear pol. with
  tan 1 2
Ex
1
14
Polarization Ellipse
Lin. Pol.
0
0
Circular Pol.
  90 0
  450
tan 2  tan 2  cos 
tan 2  sin 2  sin 
 = Rotation Angle
 = Ellipticity Angle
15
Various Polarization States
Left
Circular pol.
Wave direction
Electric Field
Thumb
Other fingers
of left hand
16
Microwave Generation
Oscillators
Tubes
Solid State
Klystron
TWT
Magnetron
A MESFET
Oscillator:
High
Power
Gunn Diode
MESFET
HEMT, etc.
Instability
Microwave
(A.C.)
Resonator
Amplifying
Light,
Cheap
D.C. Power
17
Microwave Guidance
Waveguides
Two
Conductors
Coaxial Cable
Two-wire
Microstrip
TEM wave
Single
Conductor
No
Conductor
Rectangular,
Circular
Waveguides
Dielectric
Waveguide
(Optical fibers)
TE, TM waves
(Transverse
ElectroMagnetic)
A Coaxial Cable :
E
H
direction
18
Microwave Radiation
Dipole Antenna :
Transmission
Line
(Wave guider)
Radiator
(Discontinuity)
* Current : temporal
Variation
of charges
19
Antennas
Wire
Antenna
Aperture
Antenna
Reflector
Antenna
Printed
Antenna
Electric
Field Lines
Coaxial Cable
Microstrip Antenna
20
EM Wave Reflection
Ei
Hi
z
H
x
Perpendicular Polarization
Electric field is perpendicular
to the incidence plane
Electric field is horizontal
to Earth surface
z


Horizontal Polarization
i
E
Infinite
plane
i
x
Parallel Polarization
Electric field is parallel
to the incidence plane
Vertical Polarization
Magnetic field is horizontal
to Earth surface
21
Microwave Scattering
Radar
System
Radar
System
Point
Target
Pr  Pt
Gt Gr 2
4
3
R4

 : Radar Cross Section m2 

0
Distributed
Target
: Scattering Coefficient
Pr  Pt
Gt 0 Gr 0 2
43
where Aill 

illum .
area
Aill 0
gt g r , 
R , 
4
ds
22