IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013 647
An Unconditionally Stable One-Step Leapfrog
ADI-BOR-FDTD Method
Yi-Gang Wang, Bin Chen, Member, IEEE, Hai-Lin Chen, and Run Xiong
Abstract—In this letter, an unconditionally stable one-step
leapfrog alternating-direction-implic it finite-difference time-do-
main (ADI-FDTD) method for body of revolution (BOR) is
proposed. It is more computationally efficient while preserving
the properties of the original alternating-direction-implicit body
of revolution finite-difference time-domain (ADI-BOR-FDTD)
method. Due to the s ingularity, some field components on and
adjacent to the axis are treated especially. To verify the accuracy
and efficiency of the method, the scattered field from a PEC
cylinder with a notch is calculated.
Index Terms—Alternating-dire ction-implicit (ADI) method,
body of revolution finite-difference time-domain (BOR-FDTD)
method, one-step leapfrog, unconditional stability.
I. INTRODU CTIO N
I
N SOLVING electromagnetic problems toward structures
with circular symmetry, the body of revolution finite-dif-
ference time-domain (BOR-FDTD) method has been w idely
used [1], [2]. The body of revolution symmetry allows one to
extract the known azimuthal behavior of the fields around the
axis of symmetry analytically and to reduce a three-dimen-
sional problem to a numerically concise two-dimensional one.
To overcome the Courant–Friedrichs–Lewy (CFL) limit on
the time-step, [3] presented an unco nditio nally stable scheme,
the alternating-d irection -imp licit body of revolution finite-dif-
ference time-domain (ADI-BOR-FDTD) metho d. It is based
on the t im e-split scheme where time marching over one full
time-step is broken up into two sub-time-steps. Such handling
leads to a high computational expenditure.
Recently, an unconditionally s table o ne-step leapfrog ADI-
FDTD method has b een proposed, where th e field components
do not need to be updated in two sub-tim e-steps and all the field
quantities march over a full time-step [4], [5]. The C PU time
is further reduced by introducing au xiliary field components to
the improved reformulation of th e m ethod [6]. In this letter,
an efficient one-step leapfrog ADI-BOR-FDTD method is pro-
posed. It is unconditionally stab le with respect to the choice of
time-step
and more computationally e fficient than the orig-
inal AD I-BOR-FDTD method.
Manuscript received March 21, 2013; revised April 22, 2013; accepted May
02, 2013. Date of publication May 06, 2013; date of current version May 21,
2013. This work was supported in part by the National Science Foundation of
China under Grant 61271106 and the School Foundation KYGYZLYY 1306.
The authors are with the National Key Laboratory on Electromagnetic Envi-
ronmental Effects and Electro-optical Engineering, PLA University of Science
and Technology, Nanjing 210007, China (e-mail: emcchen@163.com).
Dig
ital Object Identifier 10.1109/LAWP.2013.2261891
II. FORMULATION AND DISCUSSION
We begin by outlining the equations of the original ADI-
BOR-FDTD method [3], from which our new sch eme i s de-
rived. For linear materials, the equations of the original ADI-
BOR-FDTD method can be expressedinthefollowingmatrix
form:
(1)
(2)
at the first sub-time-step, and
(3)
(4)
at the second sub-time-step, where
Here, and are electric and magnetic component vectors,
respectively. A , B, C, and D are matrices that contain the spatial
differential o perators in the cylindrical coord inates.
A. Equations for Off-Axis C ells
With the algebraic manipulation of (1)–(4), we can get the
equations of the one-step leapfrog ADI-BOR-FDTD method.
First, substituting (2) into (1), we obtain
(5)
From (3), considering the previous time-step, we can write
(6)
Based on (4) but at one time-step backward, we can obtain
(7)
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