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== An EM.Libera Primer ==

EM.Libera is a 3D free-space structure simulator for modeling metallic structures. It features a full-wave Method of Moments (MoM) engine for analyzing wire structures or wire-frame models of metallic surfaces and solids. Many RF systems utilize wire antennas like dipoles, monopoles, loops, or arrays of wire antennas. The [[3D Method of Moments|3D method of moments]] (MoM) based on Pocklington's integral equation can accurately model such antennas and their coupling effects. Moreover, in many applications, metallic surface or [[Solid Objects|solid objects]] can be approximately modeled as wire-frame structures. EM.Libera's Wire MoM simulator can provide an adequate numerical solution of wire-frame structures. Examples of this sort are wire antennas in the presence of large reflectors or scatterers. Wire-frame models also make a good approximation of metallic target structures for radar cross section (RCS) analysis.

EM.Libera's Wire MoM simulator is seamlessly interfaced with [[EM.Cube|EM.CUBE]]'s other simulation engines. The solution of a wire-frame structure can be imported to [[EM.Cube]]'s other modules as a set of short dipole sources with proper amplitudes and phases.

The Method of Moments (MoM) is a rigorous, full-wave, numerical technique for solving open boundary electromagnetic problems. Using this technique, you can analyze electromagnetic radiation, scattering and wave propagation problems with relatively short computation times and modest computing resources. The method of moments is an integral equation technique; it solves the integral form of Maxwell’s equations as opposed to their differential forms used in the finite element or finite difference time domain methods.

Ports are used to order and index gap sources for S parameter calculation. They are defined in the '''Observables''' section of the Navigation Tree. Right click on the '''Port Definition''' item of the Navigation Tree and select '''Insert New Port Definition...''' from the contextual menu. The Port Definition Dialog opens up, showing the total number of existing sources in the workspace. By default, as many ports as the total number of sources are created. You can define any number of ports equal to or less than the total number of sources. This includes both gap sources and active lumped elements (which contain gap sources). In the '''Port Association''' section of this dialog, you can go over each one of the sources and associate them with a desired port. Note that you can associate more than one source with same given port. In this case, you will have a coupled port. All the coupled sources are listed as associated with a single port. However, you cannot associate the same source with more than one port. Finally, you can assign '''Port Impedance''' in Ohms. By default, all port impedances are 50Σ. The table titled '''Port Configuration''' lists all the ports and their associated sources and port impedances.

[[File:port-definition.png]]

The radiation patterns of antenna arrays usually have a main beam and several side lobes. Some [[parameters]] of interest in such structures include the '''Half Power Beam Width (HPBW)''', '''Maximum Side Lobe Level (SLL)''' and '''First Null [[Parameters]]''' such as first null level and first null beam width. You can have [[EM.Cube|EM.CUBE]] calculate all such [[parameters]] if you check the relevant boxes in the "Additional Radiation Characteristics" section of the '''Radiation Pattern Dialog'''. These quantities are saved into ASCII data files of similar names with '''.DAT''' file extensions. In particular, you can plot such data files at the end of a sweep simulation.

{{Note|Using an array factor for far field calculation, you cannot assign non-uniform amplitude or phase distribution to the array elements. For this purpose, you have to define an array object.}}