HFSS15: Creating PMLs Automatically

1. Draw a PML base object at the radiation surface.

2. Depending on the design you may select either faces of the object or the entire object.

When you create a PML that completely covers an object, for example, an airbox around an antenna, you may find it convenient to select the object and have a boundary applied to all faces of the object.

You can select the faces of the PML base object to turn into PMLs. In these cases, select only external, planar faces and exclude faces defined as symmetry boundaries.

3. Click HFSS > Boundaries>PML Setup Wizard.

The PML Setup wizard appears.

4. If you have selected a non-planar object for a PML or one that completely covers another object, you can select Use Selected Object objectName as PML Cover. If you have selected object faces, select Create PML Cover Objects on Selected Faces.

5. Type the thickness of each layer in the Uniform Layer Thickness text box. You can assign a variable as the thickness value.

If you do not assign a value, you can select Use Default Formula to have HFSS calculate a value for you based on geometrical analysis.

6. If the selected faces are on a box object. you can see the option to select Create joining corner and edge objects.

Edge and corner PML objects will be created to join adjacent PML surfaces together, ensuring complete coverage.

7. Under Base Face Radiation Properties, click a radio button to specify one of the following:

• Radiating Only - the radiation surface (default).

• Incident Field - the incident field source patterns are projected on these surfaces and are backed by ABC or PML. This is like a generalized space port. HFSS knows the incident field pattern, applies it to the port and expects a reflected field pattern which radiates back. In other words, it behaves as if you excited the project by a Norton or Thevenin generator using an impedance which is the free space wave impedance.

For Radiating Only or Incident Field, you can also specify whether the surface is used as Reference for FSS, that is, as a Frequency Selective Surface - this surface becomes the input surface for calculations of the reflection/transmission coefficients. The other radiating surface automatically becomes output. Only one FSS can be defined in a given model. Using the Incident Field option together with Reference for FSS is advantageous for highly reflective and resonant structures. Reflection/Transmission coefficients for FSS designs can be viewed in the solution data panel as S-parameters or you can create an S-parameter report.

If you check Reference for FSS, the PML objects will stay visible.

8. Click Next.

HFSS creates PMLs from the faces you selected. Names are automatically given to the layers. that start with PML, which is necessary for HFSS to recognize them as PMLs.

9. Specify how the PMLs terminate by selecting one of the following:

a. PML Objects Accept Free Radiation if the PMLs terminate in free space.

• Then enter the lowest frequency in the frequency range you are solving for in the Min Frequency text box.

b. PML Objects Continue Guided Waves if the PMLs terminate in a transmission line.

• Then specify the propagation constant at the minimum frequency.

10. Specify the minimum distance between the PMLs and any of the radiating bodies in the Minimum Radiating Distance text box. You may choose to have HFSS calculate the value by clicking Use Default Formula. The default distance is based on the extent of base object geometry.

The PML material characteristics depend on the cumulative effect of their near fields at the location of the PML surfaces.

11. Click Next.

HFSS calculates the appropriate PML materials based on the settings you specified and the material of the base object, and assigns these materials to the objects in the PML group.

A summary dialog box appears, enabling you to modify the settings you specified.

12. Click Finish.