Setting Matrix Convergence Criteria

For designs with ports.

You can specify different stopping criteria for specific entries in the S-matrix. This is done in the Matrix Convergence dialog box. The adaptive analysis will continue until the magnitude and phase of the entries change by an amount less than the specified criteria from one pass to the next, or until the number of requested passes is completed.

To set the matrix convergence:

1. Under the General tab of the Solution Setup dialog box, select Use Matrix Convergence.
2. Click Set Magnitude and Phase.

   The Matrix Convergence dialog box appears.

3. Select one of the following from the Entry Selections drop-down menu:
   

   All	Sets all of the matrix entries at once. (The default).
   Diagonal/Off-Diagonal	Sets all of the diagonal matrix entries at once, all off-diagonal matrix entries at once, or both diagonal and off diagonal entries at once.
   Selected Entries	Sets individual matrix entries that you will select.

   
   

   For the selection All, enter the convergence criteria for the Maximum Delta (Mag S) and the Maximum Delta (Phase S) in the fields to the right.

   For the selection Diagonal/Off-Diagonal, first check Diagonal Entries, Off-Diagonal Entries, or both, to enable the convergence criteria field or fields. Then enter the convergence criteria for the Maximum Delta (Mag S) and the Maximum Delta (Phase S) in the fields to the right.

   For both of these Entry Selections, you can set the Ignore Phase when Mag is less than value. See the note on technical issues under step 4 c.

4. If you chose Selected Entries, the Matrix Convergence dialog displays some new fields:
   • a table showing columns for Matrix Entry 1, Matrix Entry 2, and the Delta Mag and Delta Phase.
   • Entry 1 and Entry 2 fields, which contain drop-down menus of ports and associated modes (or terminals).
   • an Insert button with which to move selections from the port list selections to the table

   To select the desired ports and mode (or terminal) pairs, do the following:

   1. Select Entry 1 and Entry 2 from their drop-down menus.
   2. In the Magnitude box, enter the maximum change in magnitude from pass to pass from the Entry 1 to Entry 2.
   3. In the Phase box, enter the maximum change in phase, in degrees, from pass to pass from Entry 1 to Entry 2.
      Note: When the Mag S becomes small (near to zero) its phase becomes indefinite and insignificant due to mathematical issues. In HFSS 10 and 11 there was a 0.05 magnitude threshold that caused that Phase Margin to be discarded. However, some users may want to continue running additional passes to stabilize phase margins even when the S-parameter magnitude is below this threshold. For this reason, the magnitude threshold has been removed. This calls for caution if you want to see a good phase convergence for S₁₂, which is near to 1. If you set a small delta_phi with small delta_s, after a couple of passes, S₁₂ will converge, but S₁₁ never, since S₁₁ ~0 and its phase changes with the mesh noise because the phase is indefinite. In other words, under these conditions the adaptive process never stops, so you should abort it.
   4. Click Insert.

      The entries appear in the table above. If you have selected multiple entries, all combinations of matrix entry1 and matrix entry2 populate the table.

      Selecting a Row in the table enables the Delete button, if you need to remove a row from the table.

      Clicking in the Delta Mag and Delta Row fields of the selected row enables editing in those fields.

5. Click OK to apply the values and close the dialog.