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Suspended Substrate Stripline Step In Width with Offset (EM Based): SSSTEPX2

Symbol

Summary

SSSTEPX2 models a step in width at the asymmetric junction of two striplines placed on the top surface of a suspended substrate (suspended substrate is a single layer substrate sandwiched between the infinite grounded planes and separated from them with air layers). This model allows the relative offset of lines.

This model is constructed as an X-model (table-based interpolation) using the results of a EM analysis based on Method of Moments. For a more detailed discussion of the X-models see the EM-based Models (X-models).

This model does not include the effects of dielectric/conductor/radiation losses; it also implies that conductor thickness is zero.

SSSTEPX2$ is the corresponding intelligent cell (iCell). An iCell model is identical to its non-iCell equivalent with the following exception: Certain dimension-related parameters are not explicitly user-specified; rather, they are automatically and dynamically determined by the dimensions of the attached elements. See “Intelligent Cells (iCells)” for a detailed discussion of how to use iCells, their advantages, and their limitations.

Note: SSSTEPX2 is recommended for use instead of SSSTEPX due to improved SSSTEPX2 behavior at lower frequencies.

Topology

Parameters

Name Description Unit Type Default
ID Element ID Text SS1
W1 Conductor Width @ Node 1 Length W[1]
W2 Conductor Width @ Node 2 Length W[1]
Offset Centerline Offset Dimension Length W[1]
SPSUB Substrate definition Text See[2][3]
*AutoFill AutoFill dataBase if not equal to 0   0

[1] User-modifiable default. Modify by editing under $DEFAULT_VALUES in the default.lpf file in the root installation directory.

[2] If only one SPSUB is present in the schematic, this substrate is automatically used. If multiple SPSUB substrate definitions are present, you must specify which to use.

[3] Modify only if the schematic contains multiple substrates.

* indicates a secondary parameter

Parameter Details

W1, W2. Conductor widths are independent parameters.

Offset. Offset is an independent parameter.

SPSUB. Suspended substrate parameters are listed in the SPSUB model documentation.

Autofill. The AutoFill parameter is a hidden input which allows you to specify that the entire interpolation table should be filled automatically at the current values. To instigate this filling process, this parameter should be set equal to 1. During normal operation, this parameter should be set equal to zero. You can access the hidden parameter by double-clicking on the schematic element.

Parameter Restrictions and Recommendations

  1. SSSTEPX2 implies that the ratio Wmax/H2 lies within a predefined range of 0.1≤Wmax/H2≤16 , the ratio Wmin/Wmax lies within a predefined range of 0≤Wmin/Wmax≤1 , and Offset/Wmax lies within a predefined range of 0≤Offset/Wmax≤0.5, where H2 is substrate thickness, Wmax is the maximum value of W1, W2; Wmin is the minimum value of W1, W2. Outside of these ranges, this model extrapolates output parameters and issues a warning.

  2. Step is modeled as a two-port discontinuity. Reference planes corresponding to ports are located as shown in the "Topology" section.

  3. Cover height above substrate H1, substrate thickness H2, substrate elevation above ground H3, nominal dielectric constant ErNom, dielectric tangent Tand, and relative conductor bulk resistance Rho are fixed parameters. Cadence® AWR® Microwave Office® software provides pre-generated (pre-filled) tables for several typical values of SSSTEPX2 fixed parameters. Changes to any fixed parameter may start the automatic filling process if Autofill is set to 1. However, changes to Tand and Rho do not affect results and do not instigate the tables filling.

  4. You can change any fixed parameter to create corresponding tables.

  5. The dielectric constant Er of the substrate SPSUB is a statistical parameter. It means that models account for relative deviation of Er from ErNom within 20%; larger deviation demands a new fill of model tables.

  6. The frequency limits of this model are dynamic with respect to the dimensions of the bend as discontinuity, to the line width. This dynamic frequency limit is displayed via warning messages for the relative size, and dielectric in use. Note that this recommended frequency limit changes as a function of the largest width in the discontinuity for a given substrate definition. The frequency limit warns you that at least one of the transmission lines constructing the discontinuity is approaching the frequency limit where multiple modes can propagate. See “Upper Frequency Limitations” for more information.

Implementation Details

This model was developed under research performed at Cadence Design Systems, Inc. The full set of details of the implementation are considered proprietary in nature.

Layout

This element uses line types to determine its layout. By default, the layout uses the first line type defined in your Layout Process File (LPF). You can change the element to use any of the line types configured in your process:

  1. Select the item in the layout.

  2. Right-click and choose Shape Properties to display the Cell Options dialog box.

  3. Click the Layout tab and select a Line Type.

  4. Click OK to use the new line type in the layout.

See “Cell Options Dialog Box: Layout Tab ” for Cell Options dialog box Layout tab details.

See “The Layout Process File (LPF)” for more information on editing Layout Process Files (LPFs) and to learn about adding or editing line types.

Recommendations for Use

To create new tables for the substrate dielectric constant different from those supplied with AWR Microwave Office software, you must set ErNom = Er = needed-value-of-dielectric-constant, set AutoFill = 1 and simulate. Allow several hours (the actual time depends on your computer capabilities) for generating tables.

In exchange for speed increase, small errors resulting from the interpolation should be expected and the range of the input parameters is restricted.

Note: SSSTEPX2 is recommended for use instead of SSSTEPX due to improved SSSTEPX2 behavior at lower frequencies.

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