[[Image:fdtd_lec1_9_nevigationtree.png|350x|right]] For your resonant dipole to be half-wave, it can be approximated at 150mm.
[[Image:fdtd_lec1_9_nevigationtree.png|350x|right]] Once your drawing is complete, you can zoom to fit your stucture into the screen using the keyboard shortcut Ctrl+E or by clicking the Zoom Extents button of View Toolbar. After you have rotated or panned the view, you can always restore EM.Cubeâs standard perspective view using the keyboardâs Home Key or by clicking the Perspective View button of View Toolbar.
In EM.Cubeâs [[FDTD Module]], objects are grouped together and organized by material under the âPhysical Structureâ node of the Naviation Tree. Since you selected no material for your line object, the first drawn object is automatically assigned a PEC_1 material group. The default perfect electric conductor (PEC) group is set as the active material. When a material group is set as active, its name appears in bold letters, and all subsequently drawn objects will be placed under that material node. Any material group can be set as the active material by right-clicking on its name in the Navigation Tree and selecting Activate from the contextual menu.
[[Image:fdtd_lec1_11_lumpedsource.png|400px|right]] A dipole antenna can be excited using a lumped source, which is one of the simplest source types in [[FDTD Module]]. A lumped source is a voltage source in series with an internal resistance that is placed between two adjacent nodes of the FDTD mesh. To define a lumped source, right-click on the Lumped Source item in the âSourcesâ section of the Navigation Tree, and select Insert New Source⦠The Lumped Source Dialog opens up.
[[Image:fdtd_lec1_12_lumpedsourcefig.png|300px|left]] A lumped source can only be placed on a line object. Additionally, the line must be parallel to one of the principal axes. The dropdown list labeled Line Object displays all the eligible lines in the project workspace. In this project, there is only one object, which is selected by default. A new lumped source is placed at the center of the host line object by default. The location of the source can be changed via the Offset parameter of the dialog. We will leave this at 75 for this tutorial, as we want to test a center-fed dipole. You can also change the direction of the lumped source.
[[Image:fdtd_lec1_12_lumpedsourcefig.png|300px|left]] Your lumped source will have an Amplitude of 1V and a zero Phase. This means that the voltage source will excite the dipole with a modulated Gaussian pulse waveform centered at 1GHz with a frequency bandwidth of 1GHz, where the envelope of the signal reaches a maximum voltage of 1V. You will see the lumped source in the middle of the dipole, represented by an arrow pointing in the +Z direction.
[[Image:fdtd_lec1_15_fieldprobe.png|right]] Project observables are output quantities that you would like to compute at the end of an FDTD simulation. By default, an FDTD time marching scheme does not generate any output data unless you define one or more project observables before you start a simulation.
[[Image:fdtd_lec1_16_fieldsensor.png|right]] [[Image:fdtd_lec1_17_radiationpattern.png|left]] Field Probes
The simplest observable is a Field Probe, which is used to record the field values as a function of time at a specific point inside the computational domain. To define a field probe, right click on the Field Probes item in the âObservablesâ section of the navigation Tree and selec Insert New Observable⦠In the Field Probe Dialog, select X from the dropdown list labeled Direction. This means that your probe will record the X component of electric and magnetic fields. Enter the point (5, 5, 75) as the Coordinates of the field probe. Click the OK button of the dialog to accept the changes
Field Sensors
[[Image:fdtd_lec1_16_fieldsensor.png|400px|left]] Field sensors are are used to visualize the near fields of your structure on a plane parallel to one of the three principal planes. The field sensor planes extend across the entire computational domain. To define a field sensor, right click on the Field Sensors item in the âObservablesâ section of the Navigation Tree and select Insert New Observable⦠In the Field Sensor Dialog, enter the point (0, 0, 0) for Coordinates and select X from the dropdown list labeled Direction. This means that your field sensor plane will be the YZ plane, which passes through the dipole antenna. We would like to display the fields in the frequency domain at 1GHz. Accept the other default settings in the dialog box, and select OK to continue. A new entry Sensor_1 is added to the Navigation Tree, and the field sensor is now represented in the project workspace by a purple plane across the computational domain.
Radiation Patterns
To plot the radiation patterns of a radiating structure, you need to define a far field observable. A radiation box has to be established that encloses all the radiating objects. The electric and magnetic fields on the surface of this box are used to calculate the far field. By default, the radiation box is defined 0.1 free-space wavelength away from the bounding box of the geometry. To define a far field observable, right click on the Far Fields item in the Observables section of the Navigation Tree, and select Insert New Radiation Pattern⦠In general, you can accept the default values, unless a special case is being analyzed. The radiation box appears as a cyan or light blue box around your physical structure.
Port Definition
For calculating the port characteristics of the dipole antenna such as S parameters and input impedance, you need to set up a port. To do so, right click on Port Definitions under the Observables section of the Navigation Tree, and select Insert New Port Definition⦠By default, since you have only one source, it is assigned as Port 1. Accept the default values for PORT_1 and click OK to accept these values.
[[Image:fdtd_lec1_17_radiationpatternfdtd_lec1_18_portdefinition.png|center]] ==1.8 Running the FDTD Simulation== [[Image:fdtd_lec1_19_run.png|right]] At this time, your project is ready for FDTD simulation. Click the Run Button of the Simulate Toolbar to open up the Simultion Run Dialog. Or alternatively, use the keyboard shortcut Ctrl+R, or the menu Simulate ï Run⦠The simplest simulation mode in EM.Cube is âAnalysisâ. In this mode, your physical structure is taken âAs Isâ and its mesh is passed to the FDTD simulation engine, alnog with the necessary information regarding the soures and observables. An FDTD âAnalysisâ is a wideband analysis by nature depending on your projectâs specified bandwidth. At the end of an FDTD analysis, the port characteristics are calculated over the entire bandwidth of your project. However, some frequency-domain observables like field sensors or radiation patterns are calculated only at the specified frequencies. Before you run your first FDTD simulation in EM.Cube, letâs take a closer look at the FDTD simulation engineâs settings. Click the Settings button next to the âSelect Engineâ dropdown list to bring up the FDTD Engine Settings Dialog box. The âConvergenceâ section of this dialog offers three criteria for terminating the FDTD time marching scheme. The first one is a Power Threshold of -30dB. The second one is a Maximum Number of Time Steps equal to 10,000. The third option is labeled âBothâ, which means that both of the above termination criteria will be considered until one of is met. If your computer has a CUDA-enabled Nvidia GPU, you can use EM.Cubeâs accelerated GPU FDTD solver. The default setting is to use the Multi-Core CPU solver.  In the âExcitation Waveformâ section of the dialog, you can set the temporal waveform type for the FDTD simulation. Three options are available: Sinusoidal, Gaussian Pulse and Modulated Gaussian Pulse, with the last one set as default type. Accept all the parameters with their default values and click OK. To run the simulation, click the Run button of the Simulation Run Dialog. A separate window pops up displaying messages from the simulation engine. In four separate fields, the engine reports the current time step, elapsed time, performance in MCells/second, and convergence status. Once the simulation has been completed, you can close the message window and return to the project workspace. The Navigation Tree is now populated with simulation results, most notably under Field Sensors and Far Fields nodes. [[Image:fdtd_lec1_20_enginesetting.png|center]] ==1.9 Viewing the Results== EM.Cubeâs computational modules usually generate two types of data: 2D and 3D. Examples of 2D data are probe fields, S/Z/Y parameters and polar radiation patterns. 2D data are graphed in EM.Grid. Examples of 3D data are near field distributions and 3D radiation patterns. 3D data are visualized in EM.Cubeâs project workspace and the plots are usually overlaid on the physical structure.  A list of all the 2D output data files generated at the end of a simulation can be viewed in EM.Cubeâs Data Manager. To open this dialog, click the Data Manager button of Simulate Toolbar, or use the keyboard shortcut Ctrl+D, or access the menu Simulate ï Data Manager, or right click on the Data Manager item in the âObservablesâ section of the Navigation Tree and select Open Data Managerâ¦Â Select the two data files âProbe_1_E_Timeâ and âProbe_1_H_Timeâ and click the Plot button of Data Manager to open EM.Grid. For multiple file   [[Image:fdtd_lec1_.png|500px]][[Image:fdtd_lec1_18_portdefinitionfdtd_lec1_.png|500px]][[Image:fdtd_lec1_19_runfdtd_lec1_.png|500px]][[Image:fdtd_lec1_20_enginesettingfdtd_lec1_.png|500px]][[Image:fdtd_lec1_.png|500px]][[Image:fdtd_lec1_.png|500px]][[Image:fdtd_lec1_.png|500px]][[Image:fdtd_lec1_.png|500px]]
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