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Intro MEFiSTo (Multipurpose Electromagnetic Field Simulation Tool) is a Transmission Lines Method, or TLM, 3D time domain electromagnetic solver that is ideal analyzing complicated structures. Amplifiers, high-speed transistors, other devices can be included as spice equivalent circuits in the electromagnetic simulations. All the parameters can be expressed as variables and used in repeated, batch processes, optimizations, nonlinear problems, user defined sources, etc. MEFiSTo can be run from Matlab with various parameters inside an optimization procedure, and also can include Matlab functions in simulations instead of equivalent circuits. MEFiSTo takes advantage of your hardware by fully using multiprocessor configurations or 64 bit processors. Also for fast pre-design include a 2D version and tutorials on the mapping of microstrip and waveguide structures into 2D structures for quick results. Unique features: Time domain radiation pattern calculations. Negative index materials (metamaterials) - MEFiSTo is the only commercially available tool that can include metamaterials in simulations. Inclusion of equivalent circuits in EM simulations. Preprocessor You can define 3D structures very easily in MEFiSTo. There are predefined shapes like rectangular boxes, circular and elliptical cylinders, and you can define arbitrary polygonal surfaces that can be extruded in the third dimension. Objects can be inserted totally or partially into other objects, creating various structures. All this can be done in the graphical interface or can be done in a text file that describes the structure. All parameters, dimensions and material constants can be defined as variables. Solver There are three different solvers included. A 2D EM solver, a 3D EM solver and a thermal solver. Postprocessor MEFiSTo calculates and represents in 3D the electric and magnetic field distributions, plots the frequency dependence of the S parameters, frequency and time domain probe fields, radiation patterns, etc. Examples  Coaxial to microstrip transition, electric field magnitude. 
Horn antenna radiation pattern and electric field distribution. 
It is well known that the FDTD algorithm gives phase errors, not only that but also the phase error is direction dependent - more exactly with respect to the grid axes. The dispersion error is the dominant error in the discretized approximation of a continuous structure. Advanced TLM schemes like those used by MEFiSTo are much less dispersive, including a much smaller angular dependence. To illustrate this consider a very simple 2D example of a oscillating line source (point source in 2D) in an uniform medium. The waves (phase lines) should be perfectly circular. You can see in the figure on the left that the FDTD simulation gives a distorted solution (almost square phase lines) due to the different phase error along different directions. The TLM simulation with the same grid step gives a much more accurate solution, as illustrated on the right side. 
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