COMSOL 6.2 - Release from Far-Field Radiation Pattern

	This feature requires at least one of the following licenses: RF Module, Wave Optics Module. In addition, this feature is only available if the ray intensity or power is solved for. Select an appropriate option from the Intensity computation list in the physics interface Intensity Computation section.

Use the node to release rays with an intensity and power distribution based on a far-field radiation pattern. The far-field radiation pattern must first be solved for in a previous study.

The node can be used for multiscale electromagnetics modeling. First, the Electromagnetic Waves, Frequency Domain interface should be used to compute the electric field in the immediate vicinity of a radiation source, such as an antenna or waveguide. The node and its default subnode, , should be added to this instance of the Electromagnetic Waves, Frequency Domain interface. In this wavelength-scale model, the mesh must be fine enough to resolve individual oscillations of the electric field, fulfilling the Nyquist criterion. Typically this requires 10 linear elements or 5 second-order elements per wavelength.

Then, in the same model component or a different component, the Geometrical Optics interface can be used to extend the far field over an arbitrarily large number of wavelengths, because the ray tracing approach does not require a finite element mesh fine enough to resolve individual oscillations of the electric field.

The node is only available in 3D. However, the far-field function used to initialize the ray intensity and polarization can be defined either in a 3D model component or a 2D axisymmetric model component. If the previous model component was a 2D axisymmetric component, the intensity distribution of released rays will also be assumed to be axisymmetric.

See Release for information on the section and the optional section.

Select an option from the list: (the default) or .

Enter based on space dimension (qx,0, qy,0, and qz,0) for the ray positions or click the button (

) to select and define a range of specific coordinates.

If is selected, the number of initial coordinates entered for each space dimension must be equal, and the total number of rays released is equal to the length of one of the lists of initial coordinates. If is selected, the total number of rays released is equal to the product of the lengths of each list of initial coordinates.

In the section, you can click the

and

buttons to visualize the ray release positions. Clicking will cause a point to appear in the Graphics window for every release position. Clicking will cause a bounding box to appear, indicating the spatial extents of the released rays.

Select an option from the list: (the default), , or .

•

For a number of rays are released at each point, sampled from a spherical distribution in wave vector space. Enter the Nw (dimensionless). The default is 50.

•

For a number of rays are released at each point, sampled from a hemispherical distribution in wave vector space. Enter the Nw (dimensionless). The default is 50. Then select an option from the list: or . For enter coordinates for the r based on space dimension.

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For a number of rays are released at each point, sampled from a conical distribution in wave vector space. Enter the Nw (dimensionless). The default is 50. Then select an option from the list: or . For enter coordinates for the r based on space dimension. Then enter the α (SI unit: rad). The default is π/3 radians.

Note that unlike the Release from Grid feature, the options and are not available here. In addition, if is selected, the cone must be isotropic. This is because each ray is assumed to subtend approximately the same solid angle, so direction distributions that give unequal weight to some directions (like ) or options with no direction distribution at all (like ) cannot initialize the ray intensity and power in a consistent and physically meaningful way.

Enter an expression for the . The default expression is Efar. This expression must match the variable name in a corresponding feature.

Use the settings in this section to orient the ray source. This allows, for example, the release of rays from an antenna to be modeled with the antenna oriented in many different directions, while only solving for the far-field radiation pattern once.

Enter the . The labels Z-X-Z indicate the order in which rotation about the different axes is performed. First, the local coordinate system of the radiation pattern is rotated about its Z-axis by the angle α. Then it is rotated about its X-axis (which is now at an angle α to the global x-axis) by the angle β. Finally, this local coordinate system is rotated about its new Z-axis by the angle γ. All three inputs are plane angles (SI unit: rad) with default values of 0.

This section is only shown if is selected from the list in the physics interface section.

The check box is selected by default. While this check box is selected and the feature is active, the frequency or vacuum wavelength of released rays will be determined by the or study in the section of the solver settings. Usually, this previous study was used to solve for the far-field radiation pattern using the Electromagnetic Waves, Frequency Domain interface.

While this check box is selected and the node is active, the frequency or wavelength specified in the Ray Properties node is ignored.