[[Image:FDTD116.png|thumb|250px|[[FDTD Module]]'s Radiation Pattern dialog]]
[[Image:fdtd_out26_tn.png|thumb|400px|The 3D total radiation pattern of a dipole antenna: polar type.]]
For any far field calculations in [[EM.Cube]], first you have to define a far field observable in the Navigation Tree. In [[FDTD Module]], defining a far field observable also initiates a far field box in the computational domain. This box is used to perform the near-to-far-field transformation at the end of an FDTD simulation. To insert a new far field box, follow these steps:
After closing the Far Field Dialog, a far field entry immediately appears with its given name under the '''Far Fields''' item of the '''Observables''' section in the Navigation Tree. A far field box shows up as a light blue wireframe box in the project workspace. You can right click on the far field item's name in the navigation tree and select '''Properties...''' to open up the radiation pattern dialog for further editing. Bear in mind that a full 3D radiation pattern calculation with a high angular resolution might be very time-consuming.
===Visualizing Once an FDTD simulation is finished, three far field items are added to the Far Field section of the Navigation Tree. These are the far-zone E-field component along φ direction, the far-zone E-field component along φ direction and the total far-zone E-field.The 3D Radiation Patterns===plots can be viewed in the project workspace by clicking on each item.
Once an FDTD simulation is finished, three The view of the 3D far field items are added to plot can be changed with the Far Field section available view operations such as rotate, pan and zoom. A legend box appears in the upper right corner of the Navigation Tree3D radiation pattern plot, which can be dragged around with the left mouse button. These If the structure blocks the view of the radiation pattern, you can simply hide or freeze the entire physical structure or parts of it. Note that 3D radiation patterns are always positioned at the far-zone E-field component along φ directionorigin (0, 0,0) of the far-zone E-field component along φ direction spherical world coordinate system even though the radiation center of the structure may not be located at that point. The (maximum) '''Directivity''' of the radiating structure is displayed at the bottom of the legend box and is calculated using the total far-zone E-field defined asdefinition:
:<math>|\mathbf{E_{ff,tot}}| = \sqrt{| E_{\theta}|^2 + |E_{\phi}|^2 }</math><!--[[Image:FDTD129.png]]--> The 3D plots can be viewed in the project workspace by clicking on each item. The view of the 3D far field plot can be changed with the available view operations such as rotate, pan and zoom. A legend box appears in the upper right corner of the 3D radiation pattern plot, which can be dragged around with the left mouse button. The (maximum) '''Directivity''' of the radiating structure is displayed at the bottom of the legend box and is calculated using the definition: :<math> D_0 = \frac{4\pi [S(\theta,\phi)]_{max}}{P_{rad}} = \frac{ 4\pi \big| \mathbf{E^{ff}}(\theta,\phi) \big|^2 |_{max} } { \int\limits_0^{2\pi} \int\limits_0^{\pi} \big| \mathbf{E^{ff}}(\theta,\phi) \big|^2 \sin\theta \,d\theta \,d\phi } </math><!--[[Image:FDTD113.png]]--> You can change the type of the 3D radiation pattern plot through the '''Radiation Pattern Dialog'''. In the '''3D Display Type''' section of this dialog you can choose from three options: '''3D Polar''', which is the default choice, '''Spherical Map''' and '''Cone'''. In the case of cone type, you can also set the size of the cones that are used for a vectorial visualization of the far field data. If the structure blocks the view of the radiation pattern, you can simply hide or freeze the entire physical structure or parts of it. Note that 3D radiation patterns are always positioned at the origin (0,0,0) of the spherical world coordinate system even though the radiation center of the structure may not be located at that point. Sometimes, it might be a good idea to hide the physical structure when you are viewing the 3D radiation patterns to avoid any confusion. In a 3D radiation pattern visualization, the fields are always normalized to the maximum of the total far field. For this reason, sometimes the cross-polarization component might get lost compared to the co-polarization component and you have to zoom in to make it visible. You can also change the properties of the 3D radiation pattern plot by selecting the '''Properties...''' item in the right click menu of the plot's name in the Navigation Tree or by double-clicking the legend box. This opens up the '''Output Plot Settings Dialog'''. In general, there are two scale options: Linear (which is the default option) and dB. In the case of a linear plot, the plot range varies between 0 and 1. In the case of a dB plot, the range is fixed from -50 to 0dB. You can change the '''Color Map''' option as well the foreground and background colors of the legend box. {{twoimg|fdtd_out26_tn.png|The 3D total radiation pattern of a dipole antenna: polar type.|fdtd_out28_tn.png|The 3D total radiation pattern of a dipole antenna: cone type. }} ===2D Radiation Graphs=== At the end of an FDTD simulation, the radiation pattern data E<sub>θ</sub>, E<sub>φ</sub> and E<sub>tot</sub> in the three principal XY, YZ and ZX planes plus one additional user defined phi plane cut are available for plotting on 2D graphs in '''EM.Grid'''. There are a total of eight 2D pattern graphs in the data manager: 4 polar graphs and 4 Cartesian graphs of the same pattern data. To open data manager, click the '''Data Manager''' [[Image:data_manager_icon.png]] button of the '''Simulate Toolbar''' or select '''Simulate > Data Manager''' from the menu bar or right click on the '''Data Manager''' item of the Navigation Tree and select '''Open Data Manager...''' from the contextual menu or use the keyboard shortcut '''Ctrl+D'''. In the Data manager Dialog, you will see a list of all the data files available for plotting. These include the four polar pattern data files with a '''.ANG''' file extension and the four Cartesian pattern data file with a '''.DAT''' file extension. Select any data file by highlighting its row in the table and then click the '''Plot''' button to plot the graph.
At the end of an FDTD sweep simulation, other radiation characteristics are also computed as a function of the sweep variable (frequency, angle, or any other user defined variable). These include the '''Directivity (D0)''', '''Total Radiated Power (PRAD)''' and '''Directive Gain (DG)''' as a function of the θ and φ angles. Another radiation characteristic of interest especially in circularly polarized scenarios is the Axial Ratio. In [[EM.Cube]], the axial ratio is always defined in the LCP<sub>z</sub> or RCP<sub>z</sub> sense based on the X- and Y-components of the electric field. In order to calculate the directive gain or axial ratio, you have to check the boxes labeled '''Axial Ratio (AR)''' or '''Directive Gain (DG)''' in the "Additional Radiation Characteristics" section of the '''Radiation Pattern Dialog'''. Four 2D Cartesian graphs of the axial ratio as functions of the theta angle are generated in the three principal XY, YZ and ZX planes as well as the additional user defined phi plane cut. At the end of an FDTD sweep simulation, the directive gain and axial ratio can also be plotted as functions of the sweep variable. In that case, either quantity needs to be computed at a fixed pair of θ and φ angles. These angles are specified in degrees as '''User Defined Azimuth & Elevation''' in the "Output Settings" section of the '''Radiation Pattern Dialog'''. The default values of the user defined azimuth and elevation are both zero corresponding to the zenith.
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[[File:FDTD119.png|thumb|left|250px|[[EM.Cube]]'s Data Manager dialog showing a list of 2D polar and Cartesian radiation pattern graphs.]]
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[[File:FDTD118.png|thumb|left|250px|A 2D Cartesian radiation pattern in the ZX plane cut.]]
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[[File:FDTD117.png|thumb|left|250px|A 2D Cartesian radiation pattern in the ZY plane cut.]]
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===Radiation Pattern Above A Half-Space Medium===