== Running PO Simulations ==
=== Once you have set up your structure in EM.Illumina, have defined sources and observables and have examined the quality of the structure's mesh, you are ready to run a Physical Optics simulation. EM.Illumina offers five simulation modes (click on each type to learn more about it): * '''[[#Running A Basic a Single-Frequency PO Analysis ===| Single-Frequency Analysis]]'''* '''[[Parametric_Modeling,_Sweep_%26_Optimization#Running_Frequency_Sweep_Simulations_in_EM.Cube | Frequency Sweep]]''' including uniform and adaptive frequency sweeps * '''[[Parametric_Modeling,_Sweep_%26_Optimization#Running_Parametric_Sweep_Simulations_in_EM.Cube | Parametric Sweep]]'''* '''[[Parametric_Modeling,_Sweep_%26_Optimization#Optimization | Optimization]]'''* '''[[Building_Reusable_Models#Running_an_HDMR_Sweep | HDMR Sweep]]'''
[[File:PO27.png|thumb|400px|EM.Illumina's Simulation Run dialog.]]
You can set the simulation mode from EM.Illumina's "Simulation Run Dialog". A single-frequency analysis is a single-run simulation. All the other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain [[parameters]] are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree. === Running A Single-Frequency PO Analysis === To open EM.Illumina's Simulation Run dialog, click the '''Run''' [[File:run_icon.png]] button of the '''Simulate Toolbar''' or select '''Menu > Simulate > Run...'''or use the keyboard shortcut '''{{key|Ctrl+R'''}}. To start the simulation click the '''{{key|Run''' }} button of this dialog. Once the PO simulation starts, a new dialog called '''Output Window''' opens up that reports the various stages of PO simulation, displays the running time and shows the percentage of completion for certain tasks during the PO simulation process. A prompt announces the completion of the PO simulation. At this time, [[EM.Cube]] generates a number of output data files that contain all the computed simulation data. These include current distributions, near field data, far field radiation pattern data as well bi-static or mono-static radar cross sections (RCS) if the structure is excited by a plane wave source.
=== Setting The Numerical Parameters ===
You can also use higher- or lower-order integration schemes for the calculation of field integrals. [[EM.Cube]]'s PO simulation engine uses triangular cells for the mesh of the physical surface structures and rectangular cells for discretization of Huygens sources and surfaces. For integration of triangular cells, you have three options: '''7-Point Quadrature''', '''3-Point Quadrature''' and '''Constant'''. For integration of rectangular cells, too, you have three options: '''9-Point Quadrature''', '''4-Point Quadrature''' and '''Constant'''.
=== PO Sweep Simulations ===
[[Image:po_phys52.png|thumb|300px|EM.Illumina's Frequency Settings dialog.]]
You can run EM.Illumina's PO simulation engine in the sweep mode, whereby a parameter like frequency, plane wave incident angles or a user defined variable is varied over a specified range at predetermined samples. The output data are saved into data files for visualization and plotting. EM.Illumina currently offers three types of sweep:
# Frequency Sweep
# Parametric Sweep
To run a PO sweep, open the '''Simulation Run Dialog''' and select one of the above sweep types from the '''Simulation Mode''' dropdown list of this dialog. If you select either frequency or angular sweep, the '''Settings''' button located next to the simulation mode dropdown 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:
# Fix mesh at the highest frequency.
# Fix mesh at the center frequency.
# Re-mesh at each frequency.
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]]'s '''[[Variables]] Dialog'''.
== Working with PO Simualtion Data ==