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March 19, 2012

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FEKO is a suite of tools that is used for electromagnetic field analysis of 3D structures. FEKO simulations are based on the Method of Moments (MoM) solution to Maxwell’s equations and features several extensions to the MoM for the solution of complex problems, including large structures and complex dielectrics or human tissue. Various output parameters can be computed and displayed in a number of formats to make FEKO a leading electromagnetic simulation software suite.

__Applications__

*Antenna Analysis *

Wire antennas, horn and aperture antennas, reflector antennas, microstrip antennas, phased array antennas, helical antennas. Many special formulations enable the analysis of practical antenna problems.

*Antenna Placement *

The MoM/FEM, MoM/PO, MOM/GO, MoM/UTD hybridisations and the MLFMM enable the analysis of antennas mounted on electrically large platforms where the interaction with the nearby structures influences the antenna characteristics, e.g. UHF antennas on aircraft or ships, GSM antennas on motor vehicle, etc.

*EMC and cable problems *

FEKO is used extensively for EMC analysis, especially in the automotive industry. It is useful for computing cable-to-cable and cable-to-device coupling and for the investigation of cable radiation effects. FEKO can solve both radiation and irradiation problems, through standard multi-conductor transmission line (MTL) theory and the combined MoM/MTL solution method.

*Planar microstrip antennas and circuits *

A full 3D MoM formulation is available for the analysis of microstrip antennas with arbitrarily oriented metallic wires and surfaces in multi-layered dielectric media. Interpolation tables are used for faster simulation times.

*Dielectric bodies (e.g. SAR computation) *

Field values can be calculated inside multiple dielectric regions, each with different dielectric parameters. These fields may be used for computation of the Specific Absorption Rate (SAR) in these regions. This functionality has found wide application in the analysis and design of mobile phones and has also been applied extensively in studies regarding the compliance of cellular base stations to international radiation exposure guidelines.

*UTD ray tracing for RF antennas *

The visualization of UTD rays can be very informative in identifying high frequency scattering and reflection points. Typical application of this technology is in the investigation of inter-antenna isolation, radiation pattern distortion, etc. Typical examples of this application include RF antennas on ship superstructures or mobile phone base stations in complex building environments.

*Radiation exposure safety studies*

The MoM or MLFMM may be used to compute near-field values around complex building and antenna structures where people work. Isosurface plots are then instrumental in determining where the safety boundaries conforming to international radiation safety guidelines are located. Such information is typically used to place signage and barriers at the site, ensuring safety of the public and personnel in proximity to the transmitters.

*Analysis of windscreen antennas *

Windscreen antennas may be modelled with a MoM-based solution method that was designed specifically for this class of problem. Multiple layers of windscreen glass can be taken into account, without meshing the glass. Antenna elements may consist of either wire or metallic elements which are located inside a layer or on the boundary between adjacent layers. Multiple windscreens may be taken into account and coupling with external geometry, e.g. a car body, is accurately modelled.

__GRAPHICAL USER INTERFACE (GUI) __

The FEKO GUI consists of CADFEKO and POSTFEKO and is available for Windows and Linux.

**CADFEKO **

** Functionality**:

- Interactive geometry specification.
- Automated or custom meshing.
- Excitation and port definition.
- Solution control.
- Optimisation setup.
- Output requirement specification.

** Features**:

- Create canonical structures (cylinders, polygons, spheres, cones, etc.) with the click of a button.
- Perform boolean operations on geometry objects (e.g. split, union, intersect and subtract).
- Define various types of curves and surfaces, including analytical curves, splines and NURBS surfaces.
- Create geometry by spinning, sweeping and lofting lines and curves.
- Translate, rotate, scale and mirror objects.
- Project points, curves and surfaces onto surfaces or solids.
- Enter parameters in terms of variables and/or mathematical expressions which may be modified to change the geometry.
- Surface meshes (triangles) and volume meshes (tetrahedra) may be created with user specifiable mesh density for any specific region of the geometry.
- Import and export filters for complex geometry or mesh models in industry standard CAD formats (such as AutoCAD, Parasolid, ACIS, Unigraphics, Pro/ENGINEER and CATIA for geometry and NASTRAN, STL, ABAQUS and Concept for meshes.)

__Solution of Electrically Large Problems __

Full-wave techniques (MoM, FEM etc.) generally suffer from poor scalability. This limits the electrical size of the problems that can be solved on typical computers. When using field based solution techniques (FEM, FDTD), the discretisation of the field introduces a very small error as a wave propagates through the mesh. For very large meshes, these errors could add up, resulting in reduced accuracy in results. The error can be reduced by using a finer discretisation, but this increases the resource requirements.

The MoM does not require field discretisation, which means that the propagation distance does not degrade the accuracy of the results. With the MoM the memory required relates to the number of basis functions squared (N2). For general structures, a basis function density of about 100 basis functions per λ2 is recommended. For 1 GByte RAM, and using no symmetry, this translates to a surface area of approximately 82λ2 that can be solved in-core. Larger problems can be solved using an efficient out-of-core solver in FEKO, but this solution is slower than an in-core solution.

The memory requirements for MoM is proportional to N2, whereas that of the MLFMM is N*log(N) (for metallic surfaces N ≈ 100*(A/λ2) with A the surface area). For large N this is a huge difference!

Although the MLFMM enables the analysis of electrically large problems, this accurate full-wave method is not sufficient for the solution of electrically huge structures.

Asymptotic high frequency techniques (PO, GO and the UTD) offer a solution to the scalability hurdles in such problems. In the PO formulation the currents on the metallic surfaces are simply calculated from the incident field. The GO works by launching rays from each MoM element and placing Huygens sources on surfaces, while with the UTD only the closed form reflection and diffraction (edge and corner) coefficients are used in the solution. The size of the object, therefore, does not influence the memory requirement. The coefficients (terms) and the number of interactions do however influence the run-time. The UTD formulation requires that the smallest dimension of the UTD objects be at least in the order of a wavelength.

Whereas the triangles (for PO and GO) are well suited to represent complex geometry, the uses of flat polygonal plates restrict the application of the UTD to geometries which can be modelled sufficiently with such plates (e.g. a ship).

In FEKO, the generally applicable MoM has been hybridised with the Physical Optics (PO), Geometrical Optics (GO) and the Uniform Theory of Diffraction (UTD). This hybridisation enables the solution of large problems on small computers. The hybridisation allows for full wave analysis where required, and approximations to be used when applicable.

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