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Microstrip Step In Width Offset (EM Based): MSTEPX



MSTEPX models a step in width at the asymmetric junction of two microstrip lines. Model allows 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 effects of dielectric/conductor/radiation losses; it also implies that conductor thickness is zero.

MSTEPX$ 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 specified by the user; 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.



Name Description Unit Type Default
ID Element ID Text MS1
W1 Conductor width @ node 1 Length W[1]
W2 Conductor width @ node 2 Length W[1]
Offset Centerline offset dimension Length W[1]
MSUB 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 MSUB is present in the schematic, this substrate is automatically used. If multiple MSUB substrate definitions are present, you must specify which to use.

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

* indicates a secondary parameter

Parameter Restrictions and Recommendations

0.05 ≤ W1&W2 ≤ 8.0 Recommended Offset/Wwidest ≤ 0.5 Recommended
0.05 ≤ W1/W2 ≤ 20 Recommended εr nominal ≤ 16 Recommended
0 ≤ Frequency ≤ Fmax 1 ≤ εr nominal Required
(100*|εrr nominal|)/εr nominal ≤ 10% Recommended (100*|εrr nominal|)/εr nominal ≤ 20% Required

Fmax: The frequency limits of this model are dynamic with respect to the dimensions of the discontinuity. This dynamic frequency limit is displayed to the user via warning messages for the relative size, and dielectric in use. Importantly, this recommended frequency limit will change as a function of the largest width in the discontinuity for a given substrate definition. The frequency limit warns the user that at least one of the transmission lines constructing the discontinuity is approaching the frequency limit where multiple modes can propagate. See the section marked "Upper Frequency Limitations" in the General Discussion of the X-models.

Implementation Details

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


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 substrate dielectric constant different from those supplied with Cadence® AWR® Microwave Office® software user must set ErNom = Er = needed-value-of-dielectric-constant, set AutoFill = 1 and simulate. Allow several hours (actual time depends on the computer that runs AWR Microwave Office software) for generating tables.

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

Discontinuity models function most accurately when attached to lines that match their corresponding edges. Directly connecting discontinuity models to one another reduces their accuracy.

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