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Asymmetric Stripline Tee (EM Based): STEEX

Symbol

Summary

STEEX models a T-junction of three striplines placed on the top surface of an asymmetric substrate SSUBL (asymmetric substrate SSUBL is a two layer substrate sandwiched between two infinite grounded planes).

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

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

STEEX$ 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 details on how to use iCells, their advantages, and their limitations.

Topology

Parameters

Name Description Unit Type Default
ID Element ID Text ST1
W1 Conductor Width @ Node 1 Length W[1]
W2 Conductor Width @ Node 2 Length W[1]
W3 Conductor Width @ Node 3 Length W[1]
SSUBL Substrate definition Text See [2][3]
*AutoFill AutoFill database if not equal to 0   0
*SimName Simulator used to create the X-model   "AWR.MWOffice.EMSightIP"

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

[2] If only one SSUBL is present in the schematic, this substrate is automatically used. If multiple SSUBL 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, W3. Conductor widths are independent parameters.

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

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

Parameter Restrictions and Recommendations

  1. STEEX implies that the ratio Wwidest/H2 lies within a predefined range of 0.25≤Wwidest/H2≤16 where Wwidest is the maximum value of W1, W2, and W3 (H2 is a thickness of lower substrate layer); it also implies that the ratio Wothers/Wwidest lies within a predefined range of 0.2≤Wothers/Wwidest≤1 where Wothers are all values of W1, W2, W3 excluding Wwidest. Outside of these ranges, this model extrapolates output parameters and issues a warning.

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

  3. Dielectric layer thicknesses H1 and H2, nominal dielectric constants Er1Nom and Er2Nom, dielectric tangents Tand1 and Tand2, as well as relative conductor bulk resistance Rho are fixed parameters. Cadence® AWR® Microwave Office® software provides pre-generated (pre-filled) tables for several typical values of STEEX fixed parameters. Changes to any fixed parameter may start the automatic filling process if AutoFill is set to 1. However, changes to Tand1, Tand2, and Rho do not affect results and do not instigate table filling.

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

  5. The dielectric constants Er1 and Er2 of the substrate SSUBL are statistical parameters. STEEX accounts for relative deviation of Er1 from Er1Nom and/or Er2 from Er2Nom within 20%; a larger deviation requires 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 ErNom1 = Er1 = needed-value-of-dielectric-constant-of-layer-1, Er2Nom = Er2 = needed-value-of-dielectric-constant-layer-2, 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.

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