Transcript Slide 1

D.Poljak et al.: Time Domain Analysis....
Time Domain Analysis of the Multiple
Wires Above a Dielectric Half-Space
Poljak[1], E.K.Miller[2], C. Y. Tham[3] , S. Antonijevic [1], V. Doric [1]
[1]
Department of Electronics, University of Split, R.Boskovicaa bb, 21000 Split, Croatia
[2]597 Rustic Ranch Lane, Lincoln CA 95648, USA
[3]Faculty of Engineering and Science, Tunku Abdul Rahman University Jalan Genting
Klang, Setapak, 53300 Kuala Lumpur, Malaysia
D.Poljak et al.: Time Domain Analysis....
CONTENTS
Introduction
Time domain integral equation formulation for thin wire arrays
Time domain energy measures for transient response
Computational examples
Conclusion
D.Poljak et al.: Time Domain Analysis....
1 INTRODUCTION
• This work deals with the energy aspect of transient radiation from wire arrays
• The time variation of the total energy of the field shows the character of the
antenna energy loss by radiation.
• Determining the currents along the wires, by solving the Hallen integral equation
set, TD energy measures are obtained by spatially integrating the square of the
current and charge along the wire as a function of time.
• Computational examples related to the wire antenna array and multiple
transmission lines are presented in the paper.
D.Poljak et al.: Time Domain Analysis....
2 TIME DOMAIN INTEGRAL EQUATION FORMULATION FOR THIN WIRE
ARRAYS
An array with an arbitrary number of elements, operating in either antenna or
scattering mode is considered,
z
Vg(t)
Hinc
Einc
z
L
C
B
A
d2
d1
(x02, y02, z02)
a
B'
  o
  o
y
(xL1, yL1, zL1)
  r o
  o
h
d2
a
(xLM, yLM, zLM)
(x01, y01, z01)
h
A'
(x0M, y0M, z0M)
d1
(xL2, yL2, zL2)
  o
  o
  r o
  o
C'
x
Multiple wires above a dielectric half-space:
a) antenna mode, b) scattering mode
y
x
D.Poljak et al.: Time Domain Analysis....
Space-time currents along the wires are governed by the set of the coupled
Pocklington integral equations:
 L I n ( x' , t  Rnm / c)

dx
'



exc
N
2
4

R
E xm
 2

1 
nm
0


 2 

2 
t
L
*

t
c t  n 1 
I n ( x' , t  R nm / c)
 x
   r ( ,  )
dx' d 
*
4R nm
   0

, m  1,2,...N W
w
where Eincxm denotes the incident field on m-th wire, In is the transient current
induced on the n-th wire, Nw is the total number of wire elements, and r(θ,t) is the
space-time reflection coefficient
4  e - t 
n+1
r(  ,t)= A (t)+
(-1
n An I n(  t) ,
)

2
1-  t n=1
| x - x,|
 = arctg
,
2h
D.Poljak et al.: Time Domain Analysis....
The corresponding Hallén equation set can be readily derived from the Pocklington
equation performing a straightforward convolution:
t L
 L I ( x' , t  R / c)

I ( x' , t  R / c)
dx'   r ( ,  )
dx' d dx' d 


4R
4R
n 1  0
 0

L
x  x'
x
Lx
exc
F0 m (t  )  FLm (t 
)   E xm ( x' , t 
)dx' , m  1,2,...N w
c
c
c
0
Nw
The unknown functions F0A(t) and FLA(t) are related to the multiple reflections from
the wire ends.
The Hallen integral equation set can be handled via time domain version of the
Galerkin Bubnov Indirect Boundary Element Method (GB-IBEM).
D.Poljak et al.: Time Domain Analysis....
3 TIME DOMAIN ENERGY MEASURES FOR TRANSIENT RESPONSE
The energy measures represented by the current and charge induced on an object
yield insight into where and how much the object radiates as a function of time.
The charge distribution along the wire can be determined from the relation:
t
q = 
0
I x' , t 
dt
x'
where q is the linear charge distribution along the wire configuration.
The H-field energy is represented by the following relation:
0 L 2
,
(
x
'
,
t
)
WI=
dx
I
4 0
while the E-field energy is measured by the integral over squared charge:
Wq=
1
4
L
2
q
 (x' ,t)dx'
0
D.Poljak et al.: Time Domain Analysis....
4 SOLUTION OF THE SPACE TIME INTEGRAL EQUATION
The local approximation for unknown current can be expressed in the form:
I ( x' , t ' )   f  I 
T
The space boundary discretization of Hallen equation set results in the local
equation system:
   f  j  f i
1
T
l j li

  f  j  f i
T
l j li


F0 (t 
l j
1
2Z 0
 
l j li
4 R
dx ' dx  I 
t
R
c
 r cos    r  sin 2 
 r cos  
1
dx ' dx  I 

*
2
R*
4

R
 r  sin 
t
c
x
Lx
)  f  j dx   FL (t 
)  f  j dx 
c
c
l j
Exexc ( x ', t 
x  x'
c
)  f  j dx ' dx
D.Poljak et al.: Time Domain Analysis....
The solution in time on the i-th space segment can be expressed:
Nt
I i (t ' )   I ikT k (t ' )
k 1
where Iik are the unknown coefficients and Tk are the time domain shape functions.
Choosing the Dirac impulses as test functions, the recurrence formula for the
space-time varying current can be written as:
Ng
  ( A ji I i
Ij

tk
i 1
tk 
R
c
 A *ji I i
1
tk 
R*
) gj *
1
all retarded times
c
A jj
where Ng denotes the total number of global nodes Aji are the global matrix terms,
gjl* is the whole right-hand sidecontaining the excitation and the currents at previous
instants.
D.Poljak et al.: Time Domain Analysis....
5 COMPUTATIONAL PROCEDURES FOR ENERGY MEASURES
First, the charge distribution is obtained by the solution of integral:
M
Nt
q   
i 1 k 1 tk

 f Ti I i dt
x'
which can be carried out analytically:

1 M Nt m
q    I i 1  I im11  I im  I im 1
2c i 1 m 1

where M and Nt denotes the total number of segments and time steps, respectively.
D.Poljak et al.: Time Domain Analysis....
The H-field energy measure is obtained by evaluating the integral:
0
WI 
4


2

T
 f i I i dx'


i 1 t x'
M
k
The solution is available in the closed form and is given by:
x
W I =10
3
7
 I   I
M
i l
k 2
i
k k
i i l
I

 I ikl  , k  1, 2,, N t .
2
The E-field energy is obtained from the integral:
Wq 
1
4 0
M

i 1 tk

x '
 f  q  dx '
2
T
i
i
for which the solution is then:
2
1 x M  k 2
k k
k
, k=1,2,..., Nt
Wq 
q

q
q

q





i
i
i

1
i

1

4 0 3 i 1 
and the total energy measure is given by sum of WI and Wq.
ICEAA 2005, Turin,Italy, September 2005
D.Poljak et al.: Time Domain Analysis....
5 COMPUTATIONAL EXAMPLES

a single wire in free space operating in antenna mode
- the wire dimensions:
L=1m, a=2mm
- excitation:
v(t )  V0 e
 g 2 (t t0 )2
- parameters:
V0 = 1.0V
g=2 109 s-1
t0 = 2ns
Time domain energy variation for dipole excited by a Gaussian voltage pulse
D.Poljak et al.: Time Domain Analysis....

a single wire in free space operating in scatterer mode
- the wire dimensions:
L=1m, a=2mm
- excitation:
E(t )  E0 e
 g 2 (t t0 )2
- parameters:
E0 = 1.0V
g=2 109 s-1
t0 = 2ns
Time domain energy variation for scatterer excited by a Gaussian incident plane wave field
D.Poljak et al.: Time Domain Analysis of the Energy Stored....

2-wire array above a PEC ground plane
The coupled wires are located above PEC ground at height h=0.25m.
- the wire dimensions:
L=1m, a=2mm, d=0.5 m.
Active wire
- excitation:
v(t )  V0 e
- parameters:
 g 2 (t t0 )2
V0 = 1.0V, g=2 109 s-1, t0 = 2ns
Passive wire
D.Poljak et al.: Time Domain Analysis of the Energy Stored....

3-wire array above a dielectric half-space
The array is located above dielectric medium (r =10) at height h=1 m.
- the wire dimensions:
L=1m, a=2mm, d=0.5 m.
Active wire
- excitation:
v(t )  V0 e
- parameters:
 g 2 (t t0 )2
V0 = 1.0V, g=2 109 s-1, t0 = 2ns
Passive wires
Transient current induced at the center of the active and passive wire
D.Poljak et al.: Time Domain Analysis....

3-wire array above a dielectric half-space
The array is located above dielectric medium (r =10) at height h=1 m.
- the wire dimensions:
L=1m, a=2mm, d=0.5 m.
Active wire
- excitation:
v(t )  V0 e
- parameters:
 g 2 (t t0 )2
V0 = 1.0V, g=2 109 s-1, t0 = 2ns
Passive wires
The H-field (WI) E-field (Wq) and total energy (Wtot) energy measures as a function of time for the active and
passive wires, respectively
D.Poljak et al.: Time Domain Analysis of the Energy Stored....

3-wire transmission line above a PEC ground
The wires are located above PEC ground at height h=5m.
- the wire dimensions:
- excitation:
L=30m, a=cm, d=3m
Central wire
E (t )  E0  e at  ebt 
- parameters:
E0=65kV/m, a=4*107s-1, b= 6*108s-1.
Side wires
Transient current induced at the center of the central and side wires, respectively
D.Poljak et al.: Time Domain Analysis....

3-wire transmission line above a PEC ground
The wires are located above PEC ground at height h=5m.
- the wire dimensions:
L=30m, a=cm, d=3m
Central wire
- excitation:
E (t )  E0  e at  ebt 
- parameters:
E0=65kV/m, a=4*107s-1, b= 6*108s-1.
Side wires
The H-field (WI) E-field (Wq) and total energy (Wtot) energy measures as a function of time
D.Poljak et al.: Time Domain Analysis....
5 CONCLUDING REMARKS
• The work deals with time domain energy measures describing the behaviour of
multiple thin wires (operating in antenna or scattering mode) located in a half-space
configuration.
•The analysis of time domain energy measures makes possible to view the
electromagnetic behaviour of wire array.
• The formulation of the problem is based on the corresponding set of the spacetime Hallen integral equations.
•The integral equations are handled by the space-time Galerkin Bubnov scheme of
the Boundary Integral Equation Method (GB-BIEM).
• Determining the currents and charges along the wires the time domain energy
measures are calculated by spatially integrating the squared current and charge.
•The total energy dissipates more slowly when parasitic wires are present than for
the case of the single wire excited by the same pulse.
More or less, that’s it!
Thank you