Changes

Open the [[EM.Cube]] application by double-clicking on its icon on your desktop. By default, [[EM.Cube]] opens a blank project with the name “UntitledProj1” “UntitledProj0” in its [[Building_Geometrical_Constructions_in_CubeCAD | CubeCAD]] Module. You can start drawing objects and build up your physical structure right away. Or you can initiate a new project by selecting the <b>New</b> [[Image:fdtd_newb.png]] button of the System Toolbar or using the keyboard shortcut {{key|Ctrl+N}}. This opens up the '''New Project Dialog''', where you can enter a title for your new project and set its path on your hard drive. From the same dialog, you can also set the project’s length units, frequency units, center frequency and bandwidth.

Click on the <b>Wire Dipole Wizard</b> [[Image:WireDipoleIconx.png]] button of the Wizard Toolbar or select the menu item '''Tools &rarr; Antenna Wizards &rarr; Wire Dipole Antenna'''.

The wizard also initiated a far-field radiation pattern observable. Right-click on the item "FF_1" under '''Far-Field Radiation Patterns''' in the navigation tree and select '''Properties...''' from the contextual menu. The Radiation Pattern dialog opens up. The values of the "Angle IncrementIncrements (deg)" parameter for both Theta and Phi has have been set equal to 1&deg;.

[[Image:Libera L1 Fig10.png|thumb|left|480px720px|The far-field radiation pattern dialog.]]

The quality of the simulation results in a method of moments (MoM) simulation greatly depends on the quality and resolution of its mesh. The mesh of a line object consists of a number of linear cells along its length. The resolution of [[EM.Libera]]'s mesh is controlled by a parameter called <b>Mesh Density</b>, which has a default value of 120 10 Cells/&lambda;_eff. For resonant structures, a higher mesh density is recommended. A low mesh density may fail to provide an adequate level of numerical accuracy. Extremely high mesh densities, on the other hand, may lead to numerical instability.

To view the mesh, click the <b>Show/Generate Mesh</b> [[Image:fdtd_meshshow.png]] button of the Simulate Toolbar or alternatively use the keyboard shortcut {{key|Ctrl+M}}. To exit the mesh view mode and return to the normal view mode, use the keyboard’s {{key|Esc}} key or click the <b>Show/Generate Mesh</b> [[Image:fdtd_meshshow.png]] button of the Simulate Toolbar one more time.

Once the simulation is completed, the navigation tree is populated with simulation results under the current distributions and radiation patterns nodes. [[EM.Cube]]’s computational modules usually generate two types of data: 2D and 3D. Examples of 2D data are Cartesian and polar radiation patterns. 2D data are graphed in <b>EM.Grid</b>. Examples of 3D data are near-field and current distributions and 3D radiation patterns. 3D data are visualized in [[EM.Cube]]’s project workspace, and the plots are usually overlaid on the physical structure.

[[Image:Libera L1 Fig15Libera_L1_Fig15_new.png|thumb|left|720px|The total current distribution on the wire dipole.]]

Next, visualize the 3D radiation pattern of the dipole antenna. You will see the familiar donut shape with a directivity of 1.64643.

A list of all the 2D output data files generated at the end of a simulation can be viewed in [[EM.PicassoLibera]]’s Data Manager. To open this dialog, click the <b>Data Manager</b> [[Image:fdtd_datamanagerb.png]] button of Simulate Toolbar, or use the keyboard shortcut {{key|Ctrl+D}}, or access the menu item <b>Simulate &rarr; Data Manager</b>, or right-click on the Data Manager item in the “Observables” section of the navigation tree and select <b>Open Data Manager…</b> The S/Z/Y parameters are written into complex data files with a “.CPX” file extension. These ASCII data files are called “S11.CPX”, “Z11.CPX” and “Y11.CPX”, respectively. You can view the contents of the these files using the {{key|View}} button of data manager.

Besides the 3D visualization of the radiation patterns, you can plot 2D graphs of the patterns at certain plane cuts. The 2D radiation patterns can be plotted as both Cartesian and polar graphs. In the data manager dialog, spot Cartesian pattern data files with a “.DAT” file extension as well as the polar (angular) data files with a “.ANG” file extension. The figure below shows the Cartesian and polar radiation pattern plots in the YZ plane cut. These are the data files called "FF_1_PATTERN_Cart_YZ.DAT" and "FF_1_PATTERN_Polar_YZ.ANG", respectively. To plot them, select their name or row in the Data Manager's list and highlight them and then click the {{key|Plot}} button. Note that you can make multiple file selections for plotting using the {{key|Ctrl}} or {{key|Shift}} keys. Besides the three principal XY, YZ and ZX plane cuts, there are also data files for one additional user defined Phi-plane cut, which by default is calculated at &phi; = 45°.

To change the definition of a variable, select and highlight its name in the variables list and click the {{key|Edit}} button of the dialog to open the "Edit Variable" dialog. In this dialog, replace the definition of the selected variable with a numeric value or any other expression. Click on the {{key|OK}} button to accept the changes.

Close this dialog to return to the run dialog and click the {{key|Run}} key to start the frequency sweep. After the completion of the sweep simulation, open the data manager and plot the data files "S11_Sweep.CPX" and "Z11_Sweep_CPX" in EM.Grid.

With [[EM.Libera]], you can also perform an adaptive frequency sweep of your physical structure. This sweep starts with a few frequency samples in the beginning and then inserts more frequency samples in between and uses a rational function interpolation to achieve a smooth frequency response. Open the frequency sweep settings dialog again and this time choose the radio button '''Adaptive''' for the sweep type. Accept the default values of the adaptive sweep parameters and run and new adaptive frequency sweep simulation of your planar structure. The program may give a warning that during the adaptive sweep, current distribution and far-field radiation pattern data will not be produced. Ignore the warning and continue. Also, after a number of sweep iterations, the program may pop up a message saying the convergence criterion hasn't been met and will ask you whether to continue the sweep process. <u>In that case, reply "No" and stop the sweep</u>. Too many adaptive sweep iterations may sometime lead to spurious spikes in the frequency response.

<table><tr><td> [[Image:Libera_L1_FigConv.png|thumb|left|480px|The convergence criterion message window.]] </td></tr></table> At the end of the sweep simulation, open the data manager and plot the data files "S11_RationalFit.CPX" and "Z11_RationalFit.CPX" in EM.Grid. From the figures below you can see that the dipole antenna's return loss |S11| reaches a minimum of -31.3dB at 957MHz. Also, the imaginary part of the input impedance of the dipole antenna Im(Z11) vanishes at about 955MHz, where its real part (input resistance) is about 71&Omega; at this frequency. In other words, the dipole antenna resonates at about 955MHz.

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