
Boundary Setup Exercise: Radiation. 1. The Boundary radio button should remain selected. 2. From the list of available boundaries, select Radiation . 3. Leave the Graphical Pick option set to Face .
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1. The Boundaryradio button should remain selected.
2. From the list of available boundaries, select Radiation.
3. Leave the Graphical Pick option set to Face.
4. Click in the graphical window to touch the air volume surrounding the structure on the three faces indicated. You may wish to rotate to facilitate your selection.
NOTE: Had this model been constructed with the air solid sitting on top of the substrate solid, instead of containing the substrate solid, we would have to pick specific faces on three sides of the substrate object as well.
5. In the Name field, type in “absorbing”, and click the Assign button.
6. The boundary should appear in the boundary list at left.
NOTE: We have assigned a Radiation boundary over where the microstrip port will need to be! This will be superceded in a step in part 2 of this exercise, following the Source discussion.
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1. The Boundaryradio button should remain selected.
2. From the list of available boundaries, select Perfect E.
3. Leave the Graphical Pick option set to Face.
4. Either rotate the model view to bring the lower face to the front, and click on it, or click as though touching the lower face of the air volume and use the “N” key to shift focus deeper to the lower surface of the air volume and substrate.
5. In the Name field, type in “ground_plane”, and click the Assign button.
6. The boundary should appear in the boundary list at left.
NOTE: Since this is being assigned a Perfect E boundary, we could have allowed the automatic “outer” boundary to take care of this face if we wished.
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Boundary Setup Exercise: Symmetry Plane1. The Boundaryradio button should remain selected.
2. From the list of available boundaries, select Symmetry.
3. Leave the Graphical Pick option set to Face.
4. Click on the face of the model which bisects the microstrip trace and coax. Once a face is selected, the options for the Symmetry boundary appear below the graphical view. Click again in the model to select the cut faces of the ‘thru_hole_in_wall’ and “coax_outer” cylinders as well. (You may wish to zoom in to assure you have the correct faces selected.)
NOTE: Again, if we had defined our air volume to sit atop rather than to contain the substrate, we would need to select the substrate face too.
5. In the parameter space for the boundary, click the radio button for Perfect H type symmetry (E-fields tangential to surface).
6. In the Name field, type in “mag_symmetry”, and click the Assign button.
7. The boundary should appear in the list at left.
THIS CONCLUDES PART 1 OF THE BOUNDARY SETUP EXERCISE. DO NOT EXIT THE BOUNDARY/ SOURCE MANAGER.
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Name Field
Ports are always named “portN”. Box also includes Assign, Clear, and Options buttons.
Lumped Gap Source Port Option
Activating enables Port Impedance entry fields.
Impedance and Calibration Line Fields
‘Edit Line’ dropdown allows setting, clearing, and relating Imped. and Calib. lines.
Mode Entry Field
Set port mode solution requirements. Set polarization. Shows impedance and calibration definitions applied, if any.
Impedance Multiplier Field
Use if symmetry planes intersect ports.
Gap Source Ports (blue)
A Coaxial Port Assignment
A Microstrip Port Assignment (includes air above substrate)
Port too narrow (fields couple to side walls)
Port too Short
(fields couple to top wall)
or
5w (3h to 4h), w < h
6h to 10h
w
h
HFSS Ports: Sizing Handbook INote: Port sizing guidelines are not inviolable rules true in all cases. For example, if meeting the height and width requirements outlined result in a rectangular aperture bigger than /2 on one dimension, the substrate and trace may be ignored in favor of a waveguide mode. When in doubt, build a simple ports-only model and test.
or
5w (3h to 4h), w < h
w
h
HFSS Ports: Sizing Handbook IIApprox 7g minimum
Larger of 4h or 4g
g
h
Larger of approx. 10g or 10s
Larger of 4h or 4g
s
h
g
Perfect E
Perfect H
Perfect H
Perfect E
Perfect H
Perfect H
Perfect H
Perfect E
Port
Extension
Port on Exterior Face of Model
Port Inside Modeled Air Volume; Back side covered with Solid Cap
Circular waveguide, showing two orthogonal TE11 modes and TM01 mode (radial with Z-component). Neglecting the TM01 mode from your solution would cause incorrect results.
In circular or square waveguide, use the calibration line to force (polarize) the mode numbering of the two degenerate TE11 modes. This is also useful because without a polarization orientation, the two modes may be rotated to an arbitrary angle inside circular WG.
For parallel lines, a virtual object between them aids mode ordering. Note virtual object need not extend entire length of line to help at port.
Which of the above field orientations is the zero degree phase reference? Calibration Line defines...
For a Coax, the impedance line extends radially from the center to outer conductor (or vice versa). Integrating the E-field along the radius of the coaxial dielectric provides the voltage difference.
In many instances, the impedance and calibration lines are the same!
Whole Rectangular WG
(No Symmetry)
Impedance Mult = 1.0
Half Rectangular WG
(Perfect E Symmetry)
Impedance Mult = 2.0
Half Rectangular WG
(Perfect H Symmetry)
Impedance Mult = 0.5
...and for Quarter Rectangular WG?
(Both Perfect E and H Symmetry)
Impedance Mult. = 1.0
1. Select the Source radio button.
2. The source list should set by default to Port.
3. Zoom in on your model, or otherwise orient it so you have clear visual access to the extended face of the coaxial line. Click on the face to select it. The port parameter entry fields will now appear.
4. Leave the port name as “port1”, and the number of modes as “1”.
5. Check the box for Use Impedance Line. This enables the Edit Line dropdown menu beside it. In the Edit Line dropdown, pick Set...
6. The side window will prompt you to Set Impedance Start. Define a starting point for the impedance line by clicking in the graphical window to snap to the vertex on the inner conductor, at the topmost point where it intersects the symmetry plane. (A first click may be necessary to activate the window before selecting vertices.)
7. Click the Enter button in the side window to confirm your point selection. The window now shifts to request the vector information. (proceed to next page)
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The interface will now show a vector from the starting point you defined to the origin. (This is merely a default ‘guess’ at the intended endpoint.) The side window shows vector entry fields.
8. In the graphical window, snap to the point radial from the starting point (on the outer conductor radius, at the topmost intersection with the symmetry plane). The vector fields should update to reflect a Z-directed vector.
9. Press the Enter button on the side window to confirm the vector end point. The side window interface closes, and the completed impedance line is displayed as a red vector with the letter “I”.
10. Check the box for Use Calibration Line. In the enabled Edit Line dropdown to the right, pick Copy Impedance. The vector will now update to include a “C” indication.
11. Press the Assign button to complete the port creation. The boundary list will now update to show “port1”
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Rotate and resize the graphical window so that you have visual access to the microstrip termination end of the model.
1. Source radio button and Port type are already selected.
2. Click on the 2D rectangle provided for the microstrip port face. If the entire face of the air volume is selected, use the Next Behind menu pick or “N” hotkey to shift the selection.
3. Leave the port name as “port2”, and the number of modes as “1”.
4. Use Impedance Line should remain checked from the prior port assignment. In the Edit Line dropdown, pick Set...
5. The side window will prompt you to Set Impedance Start. Define a starting point for the impedance line by clicking in the graphical window to snap to the vertex on the trace, at the point where it intersects the symmetry plane.
6. Click the Enter button in the side window to confirm your point selection. The window now shifts to request the vector information. (proceed to next page)
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The interface will now show a vector from the starting point you defined to the prior port’s ending point. The side window shows vector entry fields.
7. In the graphical window, snap to the point where the ground plane intersects the symmetry face.
8. Press the Enter button on the side window to confirm the end point. The side window interface closes, and the completed line is displayed.
9. Use Calibration Line should already be checked. In the enabled Edit Line dropdown to the right, pick Copy Impedance.
10. Before assigning the port, we need to set the Impedance Multiplier for the model. Enter a value of 0.5.
11. Press the Assign button to complete the port assignment. You will receive an overlap warning, because the port overlays the earlier “radiation” boundary. After the overlap warning message is dismissed “port2” will show in the boundary list.
12. We are now done with boundary assignment. To verify our assignment, pick Boundary Display from the Model menu.
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HFSS will now perform only the initial meshing necessary to subdivide the problem into tetrahedra, so that actual boundary application to the finite element mesh can be viewed.
13. The list of assigned boundaries is on the left. Note that it contains both boundaries we created, plus the boundaries “i_pinn” and “outer”. The “i_pinn” boundaries were assigned as a result of assigning a finite conductivity metal -- copper -- to the pin objects. The “outer” boundary is applied to any surface of the model we did not otherwise define. Highlight “outer” in the boundary listing.
14. Press the Toggle Displaybutton. The mesh on the selected boundary is displayed, indicating the surfaces on which this boundary is applied. Note that it provides the Perfect E definition on the outer conductor of the coax, on the outer conductor of the thru hole, and on the front face of the model which represents the metal module wall.
15. If you wish you may continue displaying additional boundaries. When you are through, press the Close button to return to the Setup Boundaries window. There, pick Exit from the File menu and save when prompted. (The overlap warning will repeat on exit.)
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