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Microstrip Open Ended Effect (EM Based): MSOPENX



MOPENX models an effect of the open end of a microstrip line placed on the top surface of a suspended substrate (suspended substrate is a single layer substrate elevated above the infinite grounded plane). This model should be used in conjunction with any suitable microstrip suspended line model.

This model is constructed as an X-model (table-based interpolation) using the results of EM analysis based on Method of Moments. For a more detailed discussion of the X-models see EM-based Models (X-models).

This model does not include the effects of dielectric/conductor/radiation losses; it also implies that conductor thickness is zero.

MOPENX$ 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 user-specified; 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 MO#[1]
W Conductor width Length W[2]
MPSUB Substrate definition Text See [3] [4]
*AutoFill AutoFill dataBase if not equal to 0   0

[1] # is automatically incremented as additional MO element ID's are added to the schematic.

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

[3] 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.

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

* indicates a secondary parameter

Parameter Details

W. Conductor width is an independent parameter.

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

Autofill. The AutoFill parameter is 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. You can access the hidden parameter by double-clicking on the schematic element.

Parameter Restrictions and Recommendations

  1. MSOPENX implies that the ratio W/H1 lies within a predefined range of 0.05 ≤ W/H1 ≤ 16 , where H1 is substrate thickness. Outside of these ranges, this model extrapolates output parameters and issues a warning.

  2. An open end is modeled as a one-port discontinuity. The reference plane corresponding to the port is located at the edge of the open end of the line attached to this port; MSOPENX adds a small stretch of suspended microstrip line.

  3. Substrate thickness H1, substrate elevation above ground H2, nominal dielectric constant ErNom, dielectric tangent Tand, and relative conductor bulk resistance Rho are fixed parameters. Cadence® AWR® Microwave Office® software provides pre-generated (pre-filled) tables for several typical values of MSOPENX fixed parameters. Changes to any fixed parameter may start the automatic filling process if Autofill is set to 1. However, changes to Tand and Rho do not affect results and do not instigate the tables filling.

  4. You can change any fixed parameter to create corresponding tables.

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

  6. The frequency limits of this model are dynamic with respect to the dimensions of the bend as discontinuity, actually, to the line width. This dynamic frequency limit is displayed via warning messages for the relative size, and dielectric in use. Note that this recommended frequency limit changes as a function of the largest width in the discontinuity for a given substrate definition. The frequency limit warns you that at least one of the transmission lines constructing the discontinuity is approaching the frequency limit where multiple modes can propagate. See “Upper Frequency Limitations” for more information.

Implementation Details

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


This element does not have an assigned layout cell nor does it use line types to determine its layout. The element models an open end effect.

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. Allow several hours (the actual time depends on your computer capabilities) for generating tables.

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

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