NEC - Basic
Scattering Code
NEC-BSC
Version 4.4
Soon to be Released
Ronald J. Marhefka
The
ElectroScience Laboratory
tel: +1-614-292-5752
fax: +1-614-292-7297
email: marhefka.1@osu.edu
October 2007
The
Numerical Electromagnetic Code - Basic Scattering Code (NEC-BSC V4.4) is a
user-oriented computer code for the electromagnetic analysis of the radiation
from antennas in the presence of complex structures at high frequency. For many practical sized structures this
corresponds to UHF and above. The code
can be used to predict patterns of antennas in the presence of scattering structures,
to provide the EMC or coupling between antennas in a complex environment, and
to determine potential radiation hazards.
Simulation of the scattering structures is accomplished using
combinations of multiple flat plates, finite elliptic cylinders, composite cone
frustums, finite composite ellipsoids, and thin wires. The structures can be perfectly conducting or
composed of multilayered materials. The
plates can be transparent or opaque, that is, metal backed. The curved surfaces presently must be metal
backed.
The
analysis is based on uniform asymptotic techniques formulated in terms of the
Uniform Geometrical Theory of Diffraction (UTD). It can be successfully used to model a wide
range of practical problems. In this
particular code, the antennas can be mounted on or off flat or curved surfaces,
but not directly in materials. It can be
used to simulate the scattering from the superstructures of a ship, the body of
a truck or tank, or the fuselage, wings, and stores of an aircraft or space based
structures. The material capability can
be used as an isolated slab which can simulate a windshield or radome, or it
can be use to coat a plate or curved surface to simulate composites or an
absorber-coated ground plane, or as a semi-infinite half space to simulate the
earth. The materials modification is not
complete (i.e., surface waves and creeping waves are not included), but it is
meant to be applied to practical problems within engineering accuracy.
Antennas
are defined to be sources or receivers.
If a receiver is defined, then spatial coupling between the source and
receivers are calculated. In principle,
any antenna can be defined since the UTD solutions are based on infinitesimal
elements. If the currents are known like
from a moment method code, these currents can be numerically integrated. For efficiency sake, there are various built
in antenna types defined by their pattern factors. They include dipoles, rectangular, and
circular apertures with various current descriptions. A linear interpolation of table look up data
may also be used. All the antenna types
can be arrayed together with a large number of types of aperture
distributions. Interfaces to several other
full wave codes and methods are available.
The
fields may be calculated in the near or far zone of the structures. The antennas are assumed to be in the near
zone of the objects. The antennas can
either be fixed or moving. They can move
in spherical or linear pattern traces in any incremental step size. Single pattern traces or volumetric data can
be obtained. Either single or multiple
frequencies can, also, be calculated.
The
size of the structures should be large in term of a wavelength. The minimum size and spacing should be around
one wavelength. For engineering accuracy,
the sizes can be reduced to around a quarter - wavelength. The accuracy of the solution is also
dependent on the number of UTD terms included for the particular problem. All terms for plates are included up to third
level interaction without including double edge diffraction with intervening
plate interactions at the present time.
For geometrical optics there is up to ten reflections between
plates. Surface waves in dielectric
materials are not available either. For
curved surfaces, first order terms are included for all curved surface
descriptions. In addition, creeping wave
terms are available for only the perfectly conducting cylinders at
present. Plate-to-cylinder interactions
are not presently included. The number
of terms calculated in a given solution can be controlled, by specifying the
type of term. Particular parts of the
structures can be specified in a separate file for inclusion or exclusion
through a term processor.
The
NEC-BSC V4 has a User’s Manual which is designed to give an overall view of the
operation of the code and to instruct a user in how to use it to simulate the
scattering from structures. Examples input files are available to validity the
code by comparing various computed results against alternative codes and measured
data whenever available. The code has
been designed to run on many types of computers. It is relatively fast compared to integral
and differential based theories for large size objects. It is also efficient in its use of memory
needing only several MBs. Version 4.4 has dynamic memory allocation
through an external file that is used to set the storage size of the geometry
structures and antenna representations.
The NEC-BSC is presently distributed as a PC executable code for Windows
2000, XP and
The
NEC-BSC has a companion graphical user interface code referred to as the NEC-BSC Workbench. It is an intelligent editor for the input
files with dialog boxes to aid command definition. It can also provide visualization of the
geometry and NEC-BSC output files. It is
not essential for operation of the NEC-BSC.