HFSS15: Creating PML Boundaries Manually

See Guidelines for Assigning PML Boundaries.

1. Draw the PML object at the radiation surface, and then select it.

2. In the Properties window, give the object a name with the prefix PML.

Object names that start with PML are necessary for HFSS to recognize them as PMLs.

3. Click HFSS>Boundaries>PML Setup Wizard.

The PML Setup wizard appears.

4. Select Use Selected Object as PML Cover.

5. Select the Corresponding Base Object, the object touching the PML, from the pull-down list.

6. 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.

7. Select the orientation of the PML object, the direction of outward propagation, in the relative, or local, coordinate system.

8. 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 Frequency Selective Surface (FSS), the PML objects will stay visible.

9. Click Next.

10. Specify how the PML terminates by selecting one of the following:

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

• 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 PML terminates in a transmission line.

• Specify the propagation constant at the minimum frequency.

11. Specify the minimum distance between the PML and the radiating body in the Minimum Radiating Distance text box. You may choose to let 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.

12. Click Next.

HFSS calculates the appropriate PML material based on the settings you specified and the material of the base object, and assigns this material to the PML.

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

13. Click Finish.