Since the center frequency of the project is 1GHz, the operating wavelength is:
<!-- :<math>\lambda_0 = {c){1 \times 10^9} = 0.29979m = 330mm}</math> -->[[Image:fdtd_lec1_wavelength.png|center]]
[[Image:fdtd_lec1_9_nevigationtree.png|350x|right]] For your resonant dipole to be half-wave, it can be approximated at 150mm.
<u>{{Note|If you have a mouse with a scroll wheel, you can use the scroll wheel to zoom in or zoom out while you draw the line. You can also rotate the view using the right mouse button, or pan the view using the right mouse button while holding the keyboardâs Shift Key down.</u>}}
Once your drawing is complete, you can zoom to fit your stucture into the screen using the keyboard shortcut <b>Ctrl+E</b> or by clicking the Zoom Extents [[Image:fdtd_zoomextents.png]] button of View Toolbar. After you have rotated or panned the view, you can always restore EM.Cubeâs standard perspective view using the keyboardâs <b>Home Key</b> or by clicking the <b>Perspective View</b> [[Image:fdtd_perspective.png]] 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 <i>PEC_1</i> 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 <b>Activate</b> from the contextual menu.
 ==1.4 omputational Computational Domain & Boundary Conditions==
As soon as you draw your first object in [[FDTD Module]]âs project workspace, a blue wireframe box appears which completely encloses your object. This is [[FDTD Module]]âs computational domain box. Since FDTD is a finite-domain numerical technique, it requires a computational domain of finite extents. By default, the domain box is placed a quarter free space wavelength from the largest bounding box of your physical structure. You can confirm this by opening the Domain Settings Dialog. Click the <b>Domain Settings</b> [[Image:fdtd_domainsettings.png]] button of Simulate Toolbar (or select the menu item <b>Compute → Computational Domain → Domain Settingsâ¦</b> or use the keyboard shortcut <b>Ctrl+A</b>) to bring up the domain dialog box. For the default domain type, the domain size is specified in terms of offsets along the ±X, ±Y, and ±Z directions, i.e., the distances between the largest bounding box of the geometry and all the six domain boundaries. The offsets are expressed in free space wavelengths calculated at the highest frequency of the project, which is fmax = f0 + Δf/2, where f0 is the center frequency of the project and Δf is the bandwidth.
 The boundary Conditions at the six faces of the computational domain can be set by selecting the menu item <b>Simulate ï &rarr Computational Domain ï &rarr Boundary Conditions⦠</b> or by right clicking on the âBoundary Conditionsâ item in the âComputational Domainâ section of the Navigation Tree. By default, EM.Cubeâs [[FDTD Module]] assumes an open-boundary physical structure. All the six boundaries default to <b>PML</b>, or Perfectly Matched Layer, which you are going to maintain for this tutorial lesson. But the dropdown lists allow you to also choose <b>PEC</b>, or a Perfect Electric Conducting boundary, or <b>PMC</b>, a Perfect Magnetic Conducting boundary.
[[Image:fdtd_lec1_10_domainboundary.png|center]]
==1.5 Source Definition==
[[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_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 <b>Lumped Source</b> item in the âSourcesâ section of the Navigation Tree, and select <b>Insert New Sourceâ¦</b> The Lumped Source Dialog opens up. [[Image:fdtd_lec1_12_lumpedsourcefig.png|300px350px|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 <i>Line Object </i> 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 <i>Offset </i> 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.
Your lumped source will have an <b>Amplitude </b> of 1V and a zero <b>Phase</b>. 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.