Feko is a comprehensive electromagnetic solver with multiple solution methods that is used for electromagnetic field analyses
involving 3D objects of arbitrary shapes.
EDITFEKO is used to construct advanced models (both the geometry and solution requirements) using a high-level scripting language
which includes loops and conditional statements.
One of the key features in Feko is that it includes a broad set of unique and hybridised solution methods. Effective use of Feko features requires an understanding of the available methods.
Solver methods can be categorized as either source-based methods or field-based methods. Understanding the main differences
between these two categories helps to understand and choose an appropriate solution method for each application.
The Solver includes multiple frequency and time domain solution methods. True hybridisation of some of these methods enables efficient
analysis of a broad spectrum of electromagnetic problems. You can also use more than one solver method for cross-validation
purposes.
Full wave solutions rigorously solve Maxwell's equations without making any assumptions regarding the nature of the electromagnetic
problem. The solution can be either in the frequency or the time domain.
The testing of the integral equation applies the integral equation over each triangle edge to obtain N equations with N unknowns which can readily be solved on a computer.
Summing or integrating the vector currents is the last step in the MoM procedure. This step leads to specific output parameters such as far fields and impedance.
The usage of a dense matrix in the MoM implies a limit to the size of the problem that can be solved. The limit is determined by the available computational
resources.
The multilevel fast multipole method (MLFMM) is an alternative formulation of the technology behind the method of moments (MoM) and applies to much larger structures (in terms of the wavelength) than the MoM, making full-wave current-based solutions of electrically large structures a possibility.
The relevant integral equation method can be used to solve a model to either obtain faster iterative or higher numerical
accuracy when using the MoM or MLFMM.
The adaptive cross-approximation (ACA) is a fast method similar to the multilevel fast multipole method (MLFMM) but is also applicable to low-frequency problems or when using a special Green’s function.
The finite element method (FEM) is a solution method that employs tetrahedra to mesh arbitrarily shaped volumes accurately where the dielectric properties
may vary between neighbouring tetrahedra.
The finite difference time domain (FDTD) is a full wave time domain solution method, and Fourier transforms are applied to convert the native time domain results
to the frequency domain.
Asymptotic solution methods solve Maxwell's equations, but make certain assumptions regarding the nature of the problem.
Feko provides various high frequency asymptotic solution methods that assume the frequency of interest is high enough that
the structure is much larger than the wavelength.
The windscreen antenna solution method reduces the computational requirements by meshing only metallic elements while analysing
the behaviour of the integrated windscreen antennas within their operating environment. The analysis can take into account
the physical features of windscreen antennas and their surroundings.
Feko offers state-of-the-art optimisation engines based on generic algorithm (GA) and other methods, which can be used
to automatically optimise the design and determine the optimum solution.
Feko writes all the results to an ASCII output file .out as well as a binary output file .bof for usage by POSTFEKO. Use the .out file to obtain additional information about the solution.
CADFEKO and POSTFEKO have a powerful, fast, lightweight scripting language integrated into the application allowing you to create
models, get hold of simulation results and model configuration information as well as manipulation of data and automate
repetitive tasks.
Full wave solutions rigorously solve Maxwell's equations without making any assumptions regarding the nature of the electromagnetic
problem. The solution can be either in the frequency or the time domain.
The Solver includes multiple frequency and time domain solution methods. True hybridisation of some of these methods enables efficient
analysis of a broad spectrum of electromagnetic problems. You can also use more than one solver method for cross-validation
purposes.
One of the key features in Feko is that it includes a broad set of unique and hybridised solution methods. Effective use of Feko features requires an understanding of the available methods.
Basis functions are elementary functions for the modelling of the unknown quantity on a
mesh element.
Categories of Basis Functions
There are two main categories of basis functions:
entire-domain basis functions
sub-domain (sub-sectional) basis functions
Entire-domain basis functions are defined over the entire surface of the scatterer - they
are non-zero over the entire domain. The formulation of these functions is deemed rather
trivial, provided the shape of the scatterer is regular. For most practical applications,
the shape of the scatterer is irregular and the formulation of such basis functions is near
impossible. This requires the usage of sub-domain basis functions.
In the application of sub-domain basis functions the entire surface of the scatterer is
subdivided into small surfaces. On each subdivided surface a simple function is employed to
represent the unknown quantity (such as charge or current). Sub-domain basis functions are
non-zero on only a small part of the entire domain.
Note: For FEM and VEP, the
volume is subdivided and on each volumetric element a simple function is employed
to represent the field.
Types of Sub-Domain Basis Functions
The different types of basis functions are distinguished from each other based on their
spatial variations. A few well-known ones are as follows:
constant (also known as pulse or stair-step)
linear
polynomial
piecewise sinusoidal
The Rao-Wilton-Glisson (RWG) element
The MoM in Feko is based on
a triangular mesh. Triangular meshes can approximate surfaces much better than for example,
rectangular patches. Feko makes use of linear roof-top basis
functions introduced by Rao, Wilton and Glisson in 1982. 1 These basis functions enforces current continuity
over a common edge of a triangle pair.
In Figure 1, only two triangles
are shown sharing a common edge. Each triangle also has two other edges. If these edges are
connected to triangles, then additional basis functions would be required. Therefore for a
triangle connected on all three sides, a total of three basis functions would be defined.
Within the triangle element the total current would then be the sum of these three basis
functions.
In Figure 5, the
Yagi-Uda was modelled with wire segments. Similar to triangle pairs, linear roof-top basis
functions are used across vertices between wire segment pairs.