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Microstrip Radial Stub Shunt on Multilayer Substrate (EM Quasi-Static): MMSRSTUB



MMSRSTUB models a single microstrip radial stub on multilayer substrate that shunts microstrip line (on multilayer substrate as well). This model is a two-port through element.



Name Description Unit Type Default
ID Name Text ST[1]
Ro Outer radius of the stub Length L[2]
W Conductor width Length W[2]
Wg Width of crossing of stub and microstrip line Length W[2]
Theta Angle of the stub Angle 90 Deg
NL Number of the substrate layer carrying conductor   1
GMSUB Substrate definition Text GMSUB[3]

[1] # is automatically incremented as additional ST 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 MSUB is present in the schematic, this substrate is automatically used. If multiple MSUB substrate definitions are present, you must specify which to use.

Parameter Details

W. The conductor width of the connecting microstrip line on multilayer substrate GMSUB. Note that the connecting line must be located on the same substrate layer (specified by parameter NL).

GMSUB. Supplies parameters for multilayer dielectric substrate, conductor thickness, conductor metal properties, the presence/absence of metallic cover, and the cover height above the substrate. The GMSUB Cover parameter allows the addition/elimination of an infinite metallic plate acting as a cover/shield. Setting the Gnd parameter to "Suspended substrate" allows elevation of the dielectric stack above the backing ground. The elevation gap is filled with air and the HB parameter specifies its height.

Parameter Restrictions and Recommendations

  • Theta must be within the range 9 ≤ Theta ≤ 160.

  • Note that the substrate GMSUB's Cover parameter allows you to model the effect of either PEC substrate cover (Cover = "Metallic Cover") or PEC enclosure (cover + side walls). A secondary substrate parameter SW allows you to control the separation of the right-most/left-most conductor from the respective side wall. Conductor separations from the left and from the right wall are assumed equal.

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

  • If substrate parameter Gnd = "Grounded substrate" then the number of the substrate layer carrying conductor NL must be within limits 1≤NL≤N, where N is a number of dielectric layers in the substrate stackup. If Gnd = "Suspended substrate" then NL must be within the limits 1≤NL≤N+1. Setting NL = N + 1 implies that the taper line is located on the air layer underlying the dielectric stack. To enable the conductor (at NL = N + 1) to jut downwards (from the dielectric stack bottom), conductor thickness T should be made negative (T<0).

  • GMSUB parameter T. T specifies thickness of the stub metal. Note that the GMSUB parameter T is actually a vector, but MMSRSTUB uses only the first entry of this vector so you may enter the value of T as a scalar. It is important that the connecting line is located at the same layer (specified by parameter NL). In a multilayer stack configuration often it is convenient to have a separate GMSUB instance for MMSRSTUB.

Implementation Details

This model is constructed from a cascaded series of constant width microstrip transmission lines. Model implementation is based on an EM Quasi-Static technique[1]. The number of sections used is frequency-dependent and is constant as a function of the length divided by the guided wavelength. This model assumes a Quasi-TEM mode of propagation and incorporates the effects of dielectric and conductive losses.


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

  • The layout cell has a local parameter NSECT. This parameter specifies the number of points used for drawing a curved outline of radial stub. The default value of NSECT is 64.

  • 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] B. C. Wadell, Transmission Line Design Book, Artech House, Boston-London, 1991, pp.306-307

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