CST2013: Asymptotic Solver Parameters

Simulation: Solver Start Simulation Asymptotic Solver

If you are not familiar with what the asymptotic solver does and what it is used for, you should first read the Solver Overview or the Asymptotic Solver Overview. The asymptotic solver allows the calculation of farfield and RCS results for PEC and surface impedance type structures in vacuum with open boundaries. Despite its limitations, it may often be the first choice for electrically very large problems which are difficult to handle by using any other simulation technique. Before you start the solver you should have made all necessary solver settings. After the simulation has finished, the calculated farfield results can be accessed through the navigation tree's Farfields folder.

Solver settings frame

Solver: This selection specifies whether the solver should use independent rays (SBR) or ray tubes (SBR Raytubes). Scattering independent rays is generally more robust for complex and inaccurate geometries whereas ray tubes provide a significantly better performance for electrically large and geometrically smooth structures.

Mode: This selection specifies whether the solver should run in Monostatic or Bistatic Scattering mode. For monostatic calculations, the observation angles are identical to the excitation angles. Therefore, for this mode the specification of an observation angle sweep is required only. For bistatic calculations, the excitation and observation angles do not need to be the same. As a consequence, the dialog box layout changes depending on the mode and offers an additional list for specifying excitation angle sweeps when the solver is used in bistatic mode.

In addition to the two scattering modes, a Field sources mode allows for antenna placement type of calculations by using field source excitations. For this mode, only the observation angles need to be specified.

Finally, the Range profiles mode uses similar observation angle definitions as the monostatic mode, but only either single point or single angle sweeps are supported. In case of a single observation point definition, a one dimensional range profile is calculated whereas for two dimensional sweep definitions, a sinogram (range vs. angle) will be generated. Please note that the reference position for the range calculation will always be located in the center of the global coordinate system (0, 0, 0).

Accuracy: This setting allows you to choose from one of the predefined accuracy configurations such as Low,  Medium or High. Low accuracy means that the simulation settings will be optimized for fast simulations whereas High accuracy implies settings optimized for obtaining very accurate results. Typically the Medium accuracy default provides a good compromise between accuracy and simulation speed. In addition to these default configurations, you may also choose Custom which enables a Settings button next to the entry field. This button allows you to enter a dialog box where you can get more detailed access to the solver control options.

Maximum number of reflections: This parameter specifies the maximum number of ray reflections which will be taken into account for the ray tracing computation.

Store all result data in cache: Check here if you want the solver results to be stored in the result data cache.  

Settings: This button opens a dialog box for more detailed control of the solver's parameters. This button becomes active only when the Accuracy field is set to Custom.

Calculate farfields for PO: This option controls whether the first order PO farfields are calculated in addition to the total farfields including all multiple reflection and diffraction effects. Comparing the two sets of results can be used for checking the influence of the higher order effects on the solution. This option is only available for the Monostatic and Bistatic scattering modes.

Incident field polarization settings frame

This frame is only visible for Monostatic or Bistatic scattering modes as well as the Range profiles mode. The list can contain a number of polarization definitions for describing the orientation of the incident plane waves' field vectors. Depending on the particular type of the polarization, each list item may either be a horizontal, vertical, left hand circular (LHCP), right hand circular (RHCP) or custom polarization. You can add or delete polarizations from the list by pressing the Add or Delete buttons. If a polarization definition is selected, you may also edit its properties by pressing the Edit button.

Note: A change of the Incident field polarization settings also changes the corresponding settings in the Monostatic RCS Sweep Properties for the Integral Equation Solver.

Field source settings frame

This frame is only visible for the Field sources excitation mode. The list contains an entry for each defined farfield source. For each source, you may specify an Amplitude and a Phase shift for the  excitation which will then be applied to the pattern of the farfield source.

In addition a Rays option can be checked in order to allow storing the rays launched from the corresponding source for visualization. Depending on the Settings, the incident rays, the scattered rays and the points where the rays initially hit the structure are stored (by default, all of these options are active). The scattered rays for a given excitation will be grouped together by observation direction, so in addition to checking the ray option for a particular field source, you will also need to check the ray option for the corresponding observation angle sweep as well.

Simultaneous excitation of field sources: Check this option to run a simultaneous excitation of all field sources. In this case only one farfield result will be calculated which contains the superposition of all field sources. If this option is unchecked, a sequence of calculations will be performed where only one field source is active for each run.

Sweep parameters frame

Frequency sweeps: This list can contain a number of frequency sweep definitions, each of which consisting of a lower bound, an upper bound and a step width. By defining more than one frequency sweep you can specify non-uniform frequency samplings as needed. You can add or delete frequency sweeps from the list by pressing the Add or Delete buttons. If a frequency sweep definition is selected, you may also edit its properties by pressing the Edit button. This list is not available for the Range profiles mode. If the Range profiles mode is selected, a number of other entry fields is shown instead of the frequency sweep list:

Center frequency: This entry field allows you to specify the center frequency for the range profile and sinogram calculation.

Fmin: The frequency range for the scattering calculation is automatically derived from the settings center frequency, range extend or bandwidth and number of samples. This non-editable field displays the currently determined minimum frequency for the calculation. It is important that this frequency is large enough such that the asymptotic approximation is valid. The minimum frequency must always be greater than zero, otherwise you will need to adjust other settings in order to obtain a valid frequency range.

Range extend: If this option is selected from the list, it allows to specify the maximum range extend for the range profile and sinogram calculation. Checking the Automatic box will determine a reasonable value for this setting automatically based on the size of the structure and the center frequency specification.

Bandwidth: If this option is selected from the list, it allows to specify the bandwidth for the range profile and sinogram calculation. Checking the Automatic box will determine a reasonable value for this setting automatically based on the size of the structure and the center frequency specification.

Number of samples: This setting allows you to specify the number of spectral samples for the range profile or sinogram computation.

Window function: This setting allows you to specify the spectral window function being used for calculating range profiles or sinograms.

Excitation angle sweeps: This list can contain a number of angular sweep definitions for describing the excitation directions from where the structure will be illuminated by plane waves. Depending on the particular type of the sweep, each sweep may either be a single point, a one dimensional theta or phi sweep or a two dimensional theta and phi sweep.

For each angular sweep, a Rays option can be set in order to allow storing the rays for the corresponding the plane wave's incident directions. Depending on the Settings, the incident rays, the scattered rays and the points where the rays initially hit the structure are stored (by default, all of these options are active). The scattered rays for a given excitation will be grouped together by observation direction, so in addition to checking the ray option for a particular excitation angle sweep, you will also need to check the ray option for the corresponding observation angle sweep as well.

By defining more than one excitation angle sweep you can specify non-uniform angular samplings as needed. You can add or delete angular sweeps from the list by pressing the Add or Delete buttons. If a angular sweep definition is selected, you may also edit its properties by pressing the Edit button. This list only becomes available for the Bistatic scattering mode.

Observation angle sweeps: The list can contain a number of angular sweep definitions for describing the observation directions for which the scattered farfields and the RCS results will be calculated. Depending on the particular type of the sweep, each sweep may either be a single point, a one dimensional theta or phi sweep or a two dimensional theta and phi sweep. By defining more than one excitation angle sweep you can specify non-uniform angular samplings as needed.

A Rays option can be set for each angular observation angle sweep in order to store the rays being scattered into these observation directions. The scattered rays are grouped together by observation direction and excitation, so in addition to the observation angle selection, in Bistatic and Field sources modes the ray option needs to be set for the corresponding excitation as well. In the Monostatic scattering or Range profiles modes, the corresponding incident direction will be identical to the observation direction and therefore specifying the rays option for the observation angle only is sufficient.

You can add or delete angular sweeps from the list by pressing the Add or Delete buttons. If a angular sweep definition is selected, you may also edit its properties by pressing the Edit button. Please note that in Range profiles mode only either single point or single angle sweeps are supported.

Note: A change of the Observation angle sweep settings also changes the corresponding settings in the Monostatic RCS Sweep Properties for the Integral Equation Solver.

Start

Store the specified settings and start the asymptotic solver.

Optimize...

This button brings you into the Optimize dialog box that allows you to set up and start an optimization run.

Parameter Sweep...

This button opens the Parameter Sweep dialog box that allows you to set up and start a sequence of parameterized simulations. Note that it is necessary for the model to contain parameterized structure elements or solver settings.

Acceleration...

Opens the acceleration dialog box to control the high performance options of the simulation run (e.g. Multithreading, Distributed Computing).

Apply

Store the specified settings without starting the calculation.

Close

Closes this dialog box without performing any further action.

Help

Shows this help text.