The Comparison of the Stability on the Extended 3-
D LOD-FDTD and ADI-FDTD Methods Including
Lumped Elements
Fen Xia
1
and Qing-Xin Chu
1, 2
#1School of Electronic and Information Engineering, South China University of Technology, Guangzhou, Guangdong 510640,
China. #2 The State Key Laboratory of Millimeter Waves, Southeast University, Nanjing, Jiangsu 210096, China
xia.fen@mail.scut.edu.cn, qxchu@scut.edu.cn
Abstract-The stability comparison of the extended three-
dimensional locally one-dimensional finite difference time
domain (3-D LOD-FDTD) and alternating-direction implicit
finite-difference time-domain (ADI-FDTD) including lumped
elements is analyzed, and three common elements are
investigated: resistor, capacitor, and inductor. The elements are
inserted into the LOD-FDTD and ADI-FDTD in the explicit,
semi-implicit and implicit schemes. Stability analysis shows that
the extended LOD-FDTD and ADI-FDTD methods are
unconditionally stable in the semi-implicit and implicit schemes
while conditionally stable in the explicit scheme, and its stability
criterion depends on both the values of the element and the mesh
sizes. Finally, a simple microstrip circuit including an inductor is
simulated in the extended methods to demonstrate the validity of
the stability analysis, and the extended LOD-FDTD method is
shown to consume less CPU time.
I. INTRODUCTION
The traditional finite-difference time-domain (FDTD)
method [1] has been one of the most popular and attractive
means to solve a wide range of electromagnetic problems.
However, the traditional FDTD method is an explicit method,
and the time step size is constrained by the Courant-
Friedrichs-Lewy (CFL) condition, which affects its
computational efficiency when fine meshes are required.
Recently, to overcome the CFL condition, some
unconditionally-stable FDTD methods such as alternating
direction implicit (ADI) [2] and locally-one-dimensional
(LOD) FDTD [3] methods were developed. Moreover, the
LOD-FDTD method can be considered as the split-step
approach (SS1), which consumes less CPU time than that of
the ADI-FDTD method [3].
With the use of increasing higher frequencies and of high-
density microwave integrated circuits, the extended FDTD
method seems to be one of the best efficient and powerful
global electromagnetic tools as it can successfully analyze the
complex microwave circuits and bridge the gap between
electromagnetic-field and circuit-based simulators [4].
Recently, the study of stability of the FDTD and ADI-FDTD
method including passive and active lumped elements were
reported in [5-6], and three different formulations were
analyzed, i.e. the explicit, semi-implicit and implicit schemes.
Moreover, the 3-D LOD-FDTD method was extended to a
voltage source with impedance and a lumped load [7].
However, the stability of extended 3-D ADI-FDTD is
analyzed on energy concept [6]. Furthermore, the lumped load
in [7] is only given in the implicit scheme, and the stability
analysis of the extended LOD-FDTD is not studied.
In this paper, the formulations of the extended LOD-FDTD
and ADI-FDTD methods are generated and the stability
analysis of the formulations is studied by means of the von-
Neumann method. The theoretical results show that: in the
semi-implicit and implicit schemes, both the methods are
unconditionally stable. However, in the explicit scheme, the
methods are conditionally stable. For the numerical
computations are different between the LOD-FDTD and ADI-
FDTD method, the extended LOD-FDTD method is shown to
consume less CPU time than that of the ADI-FDTD method.
II. E
XTENDED THREE-DIMENSIONAL LOD-FDTD AND ADI-
F
DTD INCLUDING LUMPED ELEMENTS FORMAT
Assume the analytical region is in homogeneous isotropic,
non-dispersive and lossless media and the lumped element is
replaced along the +z direction.
A. Extended 3-D LOD-FDTD method
The LOD-FDTD E
z
updating equations can be written as:
sub-step 1:
1/2
1/2 1/4
2
nn
yy
nn n
zz L
HH
tt
EE I
xx xy
HH
§·
ww
''
¨¸
¨¸
ww ''
©¹
. (1a)
sub-step 2:
11/2
11/2 3/4
2
nn
nn n
xx
zz L
HH
tt
EE I
yy xy
HH
§·
ww
''
¨¸
ww ''
©¹
. (1b)
B. Extended 3-D ADI-FDTD method
Similarly, the ADI-FDTD E
z
updating equations can be
written as:
sub-step 1:
1/2
1/4
1/4
11
n
n
n
y
n
x
z
L
H
H
E
I
txyxy
HH
§·
w
w
w
¨¸
¨¸
www''
©¹
. (2a)
sub-step 2:
1/2
1
3/4
3/4
11
n
n
n
y
n
x
z
L
H
H
E
I
txyxy
HH
§·
w
w
w
¨¸
¨¸
www''
©¹
.(2b)
For sub-step 1 of the extended methods, at the time step t =
(n+1/4)t, the voltage and current characteristic equations of
three lumped elements are discussed below through three
978-1-4673-2185-3/12/$31.00 ©2012 IEEE