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Stripline Step in Width (Mode Matching): SSTEP2




SSTEP2$ is an iCell. See “Intelligent Cells (iCells)” for an explanation.

Name Description Unit Type Default
ID Element ID Text SL1
W1 Conductor width @ node 1 Length W[1]
W2 Conductor width @ node 2 Length W[1]
Modes # Of higher order modes   4
SSUB Substrate definition Text [2]

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

[2] If only one SSUB is present in the schematic, this substrate is automatically used. If multiple SSUB substrate definitions are present, the user must specify.

Implementation Details

The model assumes a TEM mode of incident and reflected propagating waves and also calculates the stored energy in higher order evanescent waves. The model is based on the Full Wave Solution of an equivalent parallel plate wave guide impedance step and incorporates the frequency-dependent nature of the parasitic inductance and capacitance and further incorporates the effects of dispersion. The model does not incorporate the resistive effects due to radiation or dielectric and conductive losses. The parameters W1 and W2 (Strip Widths) are lengths entered in the default length units. The parameter SSUB specifies the Stripline Substrate element, which defines additional cross sectional parameters of the transmission line. The Modes parameter (Number of Higher Order Even Modes) indicates the number of modes to sum to determine the amount of stored energy in the junction. As the number of modes increase, the accuracy and calculation time increases. Further, as the aspect ratio (W1/W2) deviates away from unity (1) the number of modes required for a given accuracy increases.


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.


Zo>94.25/(εr)1/2 (for T≠0) εr≤16.0 Recommended
T/B≤0.1 Recommended 1≤εr Required
1≤Modes≤30 Recommended 0.05≤W1/Wr2≤20 Recommended

Recommendations for Use

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


[1] Menzel, W. and Wolff, I. "A Method of Calculating the Frequency Dependent Properties of Microstrip Discontinuities" IEEE Trans. On MTT Vol.25 pp.,107-112 February 1977

[2] Chu, T.S., Itoh, T. and Shih, Y.C. "Comparative Study of Mode-Matching Formulations for Microstrip Discontinuity Problems" IEEE Trans. on MTT Vol-33 No.10 Oct. 1985

[3] Chu, T.S. and Itoh, T. "Analysis of Microstrip Step Discontinuity by the Modified Residue Calculus Technique" IEEE Trans. on MTT Vol-33 No.10 Oct 1985

[4] Gupta, K.C. "Microstrip Lines and Slotlines" Artech 1996 pp.190

[5] Itoh, Tatsuo, "Numerical Techniques for Microwave and Millimeter-Wave Passive Structures" John Wiley & Sons Inc. 1989 p. 466-472

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