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.
{{Note|In [[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|EM.CUBE]]]]]]]]]]]]]]]]]]]]]]]]]] you cannot assign ports to an array object, even if it contains sources on its elements. To calculate the S [[parameters]] of an antenna array, you have to construct it using individual elements, not as an array object.}}
[[File:port-definition.png]]
The wire MoM engine settings dialog.
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== More 3D MoM Simulation Types ==
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=== 3D MoM Sweep Simulations ===
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You can run [[EM.Cube|EM.CUBE]]'s MoM3D simulation engine in the sweep mode, whereby a parameter like frequency, plane wave angles of incidence or a user defined variable is varied over a specified range at predetermined samples. The output data are saved into data file for visualization and plotting. [[EM.Cube|EM.CUBE]]'s [[MoM3D Module]] currently offers three types of sweep:
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# Frequency Sweep
# Angular Sweep
# Parametric Sweep
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To run a MoM3D sweep, open the '''Run Simulation Dialog''' and select one of the above sweep types from the '''Simulation Mode''' drop-down list in this dialog. If you select either frequency or angular sweep, the '''Settings''' button located next to the simulation mode drop-down list becomes enabled. If you click this button, the Frequency Settings Dialog or Angle Settings Dialog opens up, respectively. In the frequency settings dialog, you can set the start and end frequencies as well as the number of frequency samples. The start and end frequency values are initially set based on the project's center frequency and bandwidth. During a frequency sweep, as the project's frequency changes, so does the wavelength. As a result, the mesh of the structure also changes at each frequency sample. The frequency settings dialog gives you three choices regarding the mesh of the project structure during a frequency sweep:
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# Fix mesh at the highest frequency.
# Fix mesh at the center frequency.
# Re-mesh at each frequency.
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The [[MoM3D Module]] offers two types of frequency sweep: adaptive or uniform. In a uniform sweep, equally spaced frequency samples are generated between the start and end frequencies. In the case of an adaptive sweep, you must specify the '''Maximum Number of Iterations''' as well as the '''Error'''. An adaptive sweep simulation starts with a few initial frequency samples, where the Wire MoM engine is initially run. Then, the intermediary frequency samples are calculated and inserted in a progressive manner. At each iteration, the frequency samples are used to calculate a rational approximation of the scattering parameter response over the specified frequency range. The process stops when the specified error criterion is met in a mean-square sense. The adaptive sweep simulation results are always continuous and smooth. This is due to the fact that a rational function curve is fitted through the discrete frequency data points. This usually captures frequency response characteristics such as resonances with much fewer calculated data points. However, you have to make sure that the process converges. Otherwise, you might get an entirely wrong, but still perfectly smooth, curve at the end of the simulation.
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[[File:wire_pic22.png]] [[File:wire_pic24.png]]
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The [[MoM3D Module]]'s run simulation dialog with frequency sweep selected and the frequency settings dialog.
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You can run an angular sweep only if your project has a plane wave excitation. In this case, you have to define a plane wave source with the default settings. During an angular sweep, either the incident theta angle or incident phi angle is varied within the specified range. The other angle remains fixed at the value that is specified in the '''Plane Wave Dialog'''. You have to select either '''Theta''' or '''Phi''' as the '''Sweep Angle''' in the Angle Settings Dialog. Then you can set the start and end angles as well as the number of angle samples.
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[[File:wire_pic23.png]] [[File:po_phys54.png]]
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The [[PO Module]]'s run simulation dialog with angular sweep selected and the angle settings dialog.
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In a parametric sweep, one or more user defined [[variables]] are varied at the same time over their specified ranges. This creates a parametric space with the total number of samples equal to the product of the number of samples for each variable. The user defined [[variables]] are defined using [[EM.Cube|EM.CUBE]]'s '''[[Variables]] Dialog'''. For a description of [[EM.Cube|EM.CUBE]] [[variables]], please refer to the [[CubeCAD|CUBECAD]] manual or the "Parametric Sweep" sections of the FDTD or [[Planar Module]] manuals.
== Working with 3D MoM Simulation Data ==
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|Defining an array factor in the radiation pattern dialog simply performs a post-processing calculation. The resulting far field obviously do not take into account any inter-element coupling effects as [[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|[[EM.Cube|EM.CUBE]]]]]]]]]]]]]]]]]]]]]]]]]] does not construct a real physical array in the project workspace.}}
{{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.}}
The data manager dialog showing a list of 2-D polar and Cartesian radiation pattern graphs.
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== More 3D MoM Simulation Types ==
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=== 3D MoM Sweep Simulations ===
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You can run [[EM.Cube|EM.CUBE]]'s MoM3D simulation engine in the sweep mode, whereby a parameter like frequency, plane wave angles of incidence or a user defined variable is varied over a specified range at predetermined samples. The output data are saved into data file for visualization and plotting. [[EM.Cube|EM.CUBE]]'s [[MoM3D Module]] currently offers three types of sweep:
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# Frequency Sweep
# Angular Sweep
# Parametric Sweep
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To run a MoM3D sweep, open the '''Run Simulation Dialog''' and select one of the above sweep types from the '''Simulation Mode''' drop-down list in this dialog. If you select either frequency or angular sweep, the '''Settings''' button located next to the simulation mode drop-down list becomes enabled. If you click this button, the Frequency Settings Dialog or Angle Settings Dialog opens up, respectively. In the frequency settings dialog, you can set the start and end frequencies as well as the number of frequency samples. The start and end frequency values are initially set based on the project's center frequency and bandwidth. During a frequency sweep, as the project's frequency changes, so does the wavelength. As a result, the mesh of the structure also changes at each frequency sample. The frequency settings dialog gives you three choices regarding the mesh of the project structure during a frequency sweep:
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# Fix mesh at the highest frequency.
# Fix mesh at the center frequency.
# Re-mesh at each frequency.
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The [[MoM3D Module]] offers two types of frequency sweep: adaptive or uniform. In a uniform sweep, equally spaced frequency samples are generated between the start and end frequencies. In the case of an adaptive sweep, you must specify the '''Maximum Number of Iterations''' as well as the '''Error'''. An adaptive sweep simulation starts with a few initial frequency samples, where the Wire MoM engine is initially run. Then, the intermediary frequency samples are calculated and inserted in a progressive manner. At each iteration, the frequency samples are used to calculate a rational approximation of the scattering parameter response over the specified frequency range. The process stops when the specified error criterion is met in a mean-square sense. The adaptive sweep simulation results are always continuous and smooth. This is due to the fact that a rational function curve is fitted through the discrete frequency data points. This usually captures frequency response characteristics such as resonances with much fewer calculated data points. However, you have to make sure that the process converges. Otherwise, you might get an entirely wrong, but still perfectly smooth, curve at the end of the simulation.
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[[File:wire_pic22.png]] [[File:wire_pic24.png]]
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The [[MoM3D Module]]'s run simulation dialog with frequency sweep selected and the frequency settings dialog.
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You can run an angular sweep only if your project has a plane wave excitation. In this case, you have to define a plane wave source with the default settings. During an angular sweep, either the incident theta angle or incident phi angle is varied within the specified range. The other angle remains fixed at the value that is specified in the '''Plane Wave Dialog'''. You have to select either '''Theta''' or '''Phi''' as the '''Sweep Angle''' in the Angle Settings Dialog. Then you can set the start and end angles as well as the number of angle samples.
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[[File:wire_pic23.png]] [[File:po_phys54.png]]
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The [[PO Module]]'s run simulation dialog with angular sweep selected and the angle settings dialog.
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In a parametric sweep, one or more user defined [[variables]] are varied at the same time over their specified ranges. This creates a parametric space with the total number of samples equal to the product of the number of samples for each variable. The user defined [[variables]] are defined using [[EM.Cube|EM.CUBE]]'s '''[[Variables]] Dialog'''. For a description of [[EM.Cube|EM.CUBE]] [[variables]], please refer to the [[CubeCAD|CUBECAD]] manual or the "Parametric Sweep" sections of the FDTD or [[Planar Module]] manuals.
<p> </p>
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