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Single Conductor Coplanar Line (EM Based Quasi-Static): CPWLINX

Symbol

Summary

CPWLINX models a section of symmetric coplanar waveguide (gaps between the strip conductor and lateral grounds have equal width) on a dielectric substrate. This model accounts for an optional metallic cover, an optional backing ground plane, and allows for the arbitrary metal thickness of signal conductor and lateral ground planes. This model is constructed as an X-model (Table Based Interpolation) using the results of a quasi-static cross-sectional analysis based upon the Method of Moments. For a more detailed discussion of the X-models see EM-based Models (X-models).

Topology

Parameters

Name Description Unit Type Default
ID Element ID Text CP1
W Conductor width Length W[1]
S Gap width Length W[1]
L Conductor length Length L[1]
Acc Accuracy parameter   10
CPW_SUB Substrate definition Text [2]
*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 CPW_SUB is present in the schematic, this substrate is automatically used. If multiple CPW_SUB substrate definitions are present, you must specify which to use.

* indicates a secondary parameter

Parameter Details

CPW_SUB. Supplies parameters for dielectric substrate, conductor thickness, conductor metal properties, the presence/absence of metallic cover/backing, and the cover height over the substrate. The Cover and Gnd parameters allow the addition/elimination of infinite metallic plates acting as a cover or grounded backing. The CPWLINX model does not use the following CPW_SUB parameters: Hab, ER_Nom, H_Nom, Hcov_Nom, Hab_Nom, and T_Nom.

Acc. The accuracy parameter influencing the 2-D Quasi-Static Method of moment analysis. It can range from 1 to 10.

AutoFill. 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. To view this parameter click Show Secondary in the Element Options dialog box that displays when you double-click this element on a schematic.

Parameter Restrictions and Recommendations

  1. The Acc parameter A is limited to 1 < Acc > 10. A larger value of Acc increases the density of mesh used in computations. The accuracy of model parameters may improve slightly by increasing Acc, at the expense of a noticeably longer computation time. This model should be used at the highest ACCUR level of 10, as no additional computational burden is seen once the interpolation table is complete.

  2. 0.0325<=(W+2S)/H<=4.0

  3. 0.1<=W/(W+S)<=0.9

    NOTE: To implement values outside of these ranges, you can use the CPW1LIN element.

  4. This model does not impose restrictions on the conductor thickness (thickness may be zero, positive, or negative). Negative thickness means that the conductor is recessed into the substrate.

  5. Model parameters can be broken into groups of independent, scalable, fixed, and statistical parameters in accordance with the detailed discussion of the X-models in EM-based Models (X-models) :

Independent Parameters: W, S, L
Scalable Parameters: Frequency
Fixed Parameters: ACCUR, CPW_SUB(Tand, Rho, Is Grounded, Has Cover)
Statistical Parameters: CPW_SUB(Er, T, Hsub, Hcov)

Implementation Details

  1. This 2-D Quasi-Static analysis is the same method as that used in the CPW1LINE model, however, CPWLINX gains large computational speed increases due to the table based interpolation. In exchange for this speed increase, small errors resulting from the interpolation should be expected and the range of the input parameters have been restricted.

  2. Setting Gnd=0 implies that the substrate is not backed by a perfect conductor, but is bounded by infinite air space. Modeling results are strongly affected by thin substrate heights and might differ substantially from modeling results obtained from models that implement the common conception of a coplanar waveguide (for example, CPWLINE). To model a classic coplanar waveguide featuring an infinitely thick substrate, set Gnd=0 and H >2(W+2S), where Gnd and H are parameters of CPW_SUB.

  3. Example projects for autofilling an EM-based model are provided in the /Examples/Circuit Features/Xmodels subdirectory of the Cadence® AWR® program directory. You must initiate an autofill of the EM data table after making any changes to the CPW_SUB element.

This model was developed under research performed at Cadence Design Systems, Inc. The 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.

CPW elements have special configurations for the defined line types. The center conductor geometry draws on all the layers defined in the line type. The spacing to the ground plane is then drawn on negative layers with the same name as all of the layers in the line type. You must then draw the same layers on the positive layer to complete CPW layout. See “Negative Layers ” for more information on setting up processes for positive and negative layers.

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

References

[1] M.B. Bazdar, A.R. Djordjevic, R.F. Harrington, and T.K. Sarkar, "Evaluation of quasi-static matrix parameters for multiconductor transmission lines using Galerkin's method," IEEE Trans. Microwave Theory Tech., vol. MTT-42, July 1994, pp. 1223-1228.

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