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Symmetric Edge Coupled Striplines (Closed Form): SCLIN




Name Description Unit Type Default
ID Element ID Text SL1
W Conductor width Length W[1]
S Gap width Length W[1]
L Conductor length Length L[1]
SSUB Substrate definition Text SSUB[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, you must specify which to use.

Implementation Details

This circuit component models a section of coupled strip transmission lines residing in the same plane. These strips are assumed to reside on the centerline between the two ground planes and be of the same width. The model accounts for both conductive and dielectric loss and corrects for a finite strip thickness.

The parameters W1 (strip widths), S (gap between strips) and L (coupled line length) are dimensions entered in the default length units. The parameter SSUB specifies the stripline substrate element, which defines additional cross sectional parameters of the transmission line.

Important: This model has two implementations: basic implementation and modified impementation. Basic implementation provides frequency-dependent behavior that matches references [1-3]; unfortunately, formulations [1-3] are not very good in low frequency and DC region. Modified implementation improves low frequency and DC behavior but demonstrates frequency behavior somehow different from those of basic implementation at frequencies below 1 GHz. For example, in this frequency region model may underestimate total loss if dielectric loss substantially exceeds conductor loss. SCLIN is not intended for modeling substrates with exorbitant loss tangents (say, above 0.1): Loss of this magnitude should be modeled by EM Quasi-Static models.

To switch between implementation, right-click the schematic that contains the SCLIN model(s), choose Options, then on the AWR Sim tab, specify the Model compatibility version.

To set all SCLIN models in this schematic to basic implementation, select Version 5.5.

To set all SCLIN models in this schematic to modified implementation, select Version 6.0 or Version 6.5.

Circuit Model Synthesis

SCLIN supports synthesis of physical parameters based on electrical specifications using the Transmission Line Calculator. To open the Transmission Line Calculator, right-click a transmission line element in a schematic and choose Synthesize.

To perform transmission line synthesis:

  1. In the Electrical property grid, select Target check boxes for desired electrical parameters and enter a corresponding value. Note that for coupled lines, you choose between the even and odd modes for synthesis targets.

  2. In the Physical property grid, update frequency and substrate parameters if needed, then select Synthesize check boxes for transmission line physical parameters to synthesize based on the targets.

  3. Click the Synthesize left arrow to run the synthesis program. The values in both property grids update with the synthesized results. An analysis is also performed with the final physical values. If synthesis cannot achieve the target values, it shows how close it came.

  4. Click OK to update the selected transmission line element with the synthesized physical parameters. Expressions are overwritten with the new, evaluated values. You can click the Undo button on the program toolbar to revert all parameters in the schematic document to their pre-synthesized state. Parameters from substrate elements are never updated since typically substrate elements are used by more than one transmission line element. Click Cancel to close the dialog box without setting the parameters into the element.


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

Modified implementation of SCLIN better works in time-domain than basic implementation; however, in critical time-domain designs EM Quasi-Static models like S2CLIN are preferable.


W/B≥0.35 (Recommended for T≠0)(B=Ground Plane Spacing)

T/B≤0.1 Recommended B=Center Strip Thinkness

T/S≤2 Recommended

NOTE: SCLIN implies that parameter Rho specified on substrate definition SSUB represents bulk resistance of conductor metal normalized to copper. This normalization is specific to SCLIN (and SLIN as well); other transmission line models use Rho normalized to gold. So, if one obtained value of Rho normalized to gold (ρnorm to gold) than Rho normalized to copper ( ρnorm to copper ) can be evaluated as ρnorm to copper=1.7353ρnorm to gold


[1] S.B. Cohn "Problems in Strip Transmission Lines" IRE Trans MTT March, 1955 p.119-126

[2] S.B. Cohn "Shielded Coupled-Strip Transmission Line" IRE Trans MTT October, 1955 p.29-38

[3] S.B. Cohn "Thickness Corrections for Capacitive Obstacles and Strip Conductors" IRE Trans MTT November, 1960 p.638-644

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