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2 Suspended Substrate Broadside Coupled Microstrip Lines (EM Quasi-Static Based): MSBCPLX



MSBCPLX models a section of two equal width broadside coupled microstrip lines with conductor strips placed on the top and bottom surfaces of a suspended substrate (suspended substrate is a single layer substrate elevated above the infinite grounded plane). Lateral offset is allowed for the bottom line.

MSBCPLX is constructed as an X-model (table-based interpolation) using the results of an EM 2-D quasi-static cross-sectional analysis based on Method of Moments. For a detailed discussion of X-models see EM-based Models (X-models). EM 2-D quasi-static analysis is the same method as that used in the MSBCPL model, however, MSBCPLX gains large computational speed increases due to the table-based interpolation.



Name Description Unit Type Default
ID Element ID Text TL1
W Conductors width Length W[1]
Offset Offset of bottom conductors Length W[1]
L Line length Length L[1]
Acc Accuracy parameter   1
MPSUB Substrate definition Text See[2]
*AutoFill Autofill database if not equal to 0   0
SNAME1 Structure name from lpf file for top conductor Text TOP_BCLIN
SNAME2 Structure name from lpf file for bottom conductor Text BOT_BCLIN

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

[2] If only one MPSUB is present in the schematic, this substrate is automatically used. If multiple MPSUB substrate definitions are present, you must specify which to use.

* indicates a secondary parameter

Parameter Details

W. Conductor width is an independent parameter.

Offs. The offset of the bottom conductor is an independent parameter.

Acc. The input parameter Acc is an accuracy parameter influencing the EM 2-D quasi-static cross-sectional analysis, and can range from 1 to 10. This value is used to automatically fill the model tables if the necessary table is missing and if Autofill is set to 1. Higher values of Acc may improve accuracy but also may slow the filling process. MSBCPLX does not use Acc in normal, table-based interpolation mode.

MPSUB. Suspended substrate parameters are listed in the MPSUB model description.

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

Parameter Restrictions and Recommendations

  1. MSBCPLX implies that the ratio W/H1 lies within a predefined range of 0.05≤W/H1≤18 and the ratio Offs/H1 lies within a predefined range of 0.025≤S/H1≤70 (H1 is substrate thickness). Outside of these ranges, the model extrapolates output parameters and issues a warning.

  2. Substrate thickness H1, substrate elevation above ground H2, nominal dielectric constant ErNom, dielectric tangent Tand, relative conductor bulk resistance Rho, and accuracy Acc are fixed parameters. Cadence® AWR® Microwave Office® software provides pre-generated tables for several typical values of MSBCPLX fixed parameters. Changes to any fixed parameter may start the automatic filling process (if Autofill is set to 1), the length of which depends on the Acc value. You can change any fixed parameter to create the corresponding tables.

  3. The dielectric constant Er of the substrate SPSUB is a statistical parameter. This means that models account for the relative deviation of Er from ErNom within 20%; a larger deviation demands a new fill of the model tables.

  4. SNAME1 and SNAME2 are for layout only and have no effect on the electrical performance.

Implementation Details

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


When you specify SNAME1 and SNAME2, the structures with corresponding names are identified in a $STRUCT_TYPE_BEGIN section of the LPF file. If a structure with the corresponding name is not found, the name of the missing structure is drawn on the error layer. The structure named SNAME1 must contain a text line starting with the line type name used for the top conductor. A structure named SNAME2 must contain a text line starting with the line type name used for the bottom conductor. In a structure named SNAME1=TOP_TRACE and SNAME2= BOT_TRACE with line type names "Top Copper" and "Bot Copper", you need to add the following code to the LPF file (user defined line types may contain any number of layers; structures must contain only one text line):

		! -> Layer 		offset 		minWidth 		flags
		"Cu_1"		0		5e-005		0
		! -> Layer 		offset 		minWidth 		flags
		"Cu_2"		0		5e-005		0
   "Top Copper"	0 0 0	
   "Bot Copper"	0 0 0	

Note that text inside structures contains line type names in quotation marks followed by three blank separated zeros.

Recommendations for Use

To create new tables for the substrate dielectric constant different from those supplied with AWR Microwave Office software, you must set ErNom = Er = needed-value-of-dielectric-constant, set AutoFill = 1 and simulate.

In exchange for a speed increase, you should expect small errors resulting from the interpolation, and the range of the input parameters is restricted.

If you want to implement values outside of the specified ranges of W/H1, Offs/H1 (see the "Parameter Restrictions and Recommendations" section), you can use the MSBCPL element.


[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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