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General Multilayer Substrate Definition: GMSUB

Symbol

Summary

GMSUB provides a stratified inhomogeneous substrate (dielectric stack) definition used either for stripline (optional metallic cover present) or microstrip (no cover) GMnLIN (n=1..16), GMCLIN, and GFMCLIN schematic elements. The substrate may be elevated over the infinite backing ground plate, thus providing suspended substrate. All layers may have an arbitrary height and may be made of various materials. Each layer may carry any number of conductors. All conductor on the same layer have the same thickness; conductor thickness may vary between layers. The number of conductors is specified in the respective model. In addition to metallic cover, GMSUB may define perfectly conducting side walls thus confining the whole structure into metallic box.

Topology

Open grounded substrate (no cover)

Open suspended substrate (no cover)

Covered grounded substrate

Covered suspended substrate

Parameters

Name Description Unit Type Default
N Number of substrate dielectric layers   1
Er Substrate relative dielectric constants (vector)   Er[1]
Tand Substrate loss tangents (vector)   0
H Heights of substrate layers (vector) Length H[1]
ErC Relative dielectric constants of layer adjacent to cover   1
TandC Loss tangent of layer adjacent to cover   0
HC Cover height over the substrate Length H[1]
HB Substrate elevation over the backing ground plane Length H[1]
T Conductors thicknesses (vector) Length T[1]
Rho Metal bulk resistivity relative to gold   1
Cover Switch "Metallic Cover" / "No Cover"/Metallic Box   "No Cover"
Gnd Switch "Suspended Substrate" / "Grounded Substrate"   "Grounded Substrate"
SW Separation of vertical metallic walls from extreme left/right conductors (optional) Length L[1]
Name Substrate name Text GMSUB1[2]
SWRight[3] Separation of RIGHT vertical metallic wall from extreme right conductor (optional) Length 0
SigmaC[3] Bulk conductivity (S/m) of layer adjacent to cover   0
Sigma[3] Substrate bulk conductivity (S/m) (vector)   0
RhoV[3] Metal bulk resistivity relative to gold of conductor metals in layers (vector)   1
Undercut[3] Conductor etching undercut (vector)   0
MuP[3] Real part of substrate relative magnetic permeability (vector)   1
MuPP[3] Imaginary part of substrate relative magnetic permeability (vector)   0
Rgh[4] Surface roughness (RMS surface profile height) Length 0

[1] User-modifiable default. Modify by editing under $DEFAULT_VALUES in the default.lpf file in the root installation directory. See AWR Microwave Office Layout Guide for details.

[2] Modify only if schematic contains multiple substrates. See “Using Elements With Model Blocks” for details.

[3] For use with element GFMCLIN only

[4] For use with elements GMCLIN, GM1LIN, GMnCLIN only

Parameter Details

N. Number of dielectric layers that may carry conductors on their top surface. Layers are enumerated from top to bottom. Note that if switch parameter Cover is set to "Metallic Cover" the topmost layer adjacent to cover is not included in count; likewise, if switch parameter Gnd is set to "Suspended Substrate" the bottom air layer is not included in count.

Er. Relative dielectric constants of substrate layers are specified as values of vector Er components. You can assign values to vector components via array of constants (or equation variables) on the corresponding parameter field (for example, {3.8,4.1,12,12.5}). The same assignment might be implemented in equation. Models GMnCLIN, GMCLIN check if the length of vector Er is equal to the specified number of layers N.

Tand. Substrate loss tangents of substrate layers are specified as values of vector Tand components. You can assign values to vector components via array of constants (or equation variables) on the corresponding parameter field (for example, {0.001,1e-6,0}). The same assignment might be implemented in equation. Models GMnCLIN, GMCLIN check if the length of vector Tand is equal to the specified number of layers N.

H. Heights of substrate layers are specified as values of vector H components. You can assign values to vector components via array of constants (or equation variables) on the corresponding parameter field (for example, {10,20,20,10}). The same assignment might be implemented in equation. Models GMnCLIN, GMCLIN check if the length of vector H is equal to the specified number of layers N.

ErC. If switch Cover is set to "Metallic Cover" or "Metallic Box" this parameter specifies relative dielectric constant of a layer that adjoins the cover. If switch Cover is set to "No Cover" parameter ErC is not used.

TandC. If switch Cover is set to "Metallic Cover" or "Metallic Box" this parameter specifies loss tangent of a layer that adjoins the cover. If switch Cover is set to "No Cover" parameter TandC is not used.

HC. Specification of height over the substrate HC is mandatory if switch Cover is set to "Metallic Cover" or "Metallic Box" . If switch Cover is set to "No Cover" parameter HC is not used.

HB. Specification of substrate elevation over the backing ground plane is mandatory if switch Gnd is set to "Suspended Substrate". If switch Gnd is set to "Grounded Substrate" parameter HB is not used.

T. Thicknesses of conductors for each layer are specified as values of vector T components. All conductors on the same layer have identical thickness. Thicknesses may vary between layers. Each dielectric layer must have corresponding entry in vector T even if this specific layer does not carry conductors. For example, if model GM1LIN (single line model) is used and number of layers is five, vector T must contain five entries no matter that only one entry corresponds to the layer that actually carries single conductor. All entries may be set to the same value. You can assign values to vector components via array of constants (or equation variables) on the corresponding parameter field (for example, {10,20,20,10}). The same assignment might be implemented in equation. Models GMnCLIN, GMCLIN check if the length of vector T is equal to the number of dielectric layers that may carry conductors (that is, N if switch Gnd is set to "Grounded Substrate" and N+1 if Gnd is set to "Suspended Substrate").

Rho. All conductors have the same metal bulk resistivity relative to gold Rho (relevant only to GMnCLIN, GMCLIN models). GFMCLIN does not use this parameter.

Cover. This switch can be set to one of three selections: "Metallic Cover", "No Cover", "Metallic Box." "Metallic Cover" provides a covered structure typical for striplines; HC, ErC, TandC are used. "No Cover" provides an open structure typical for microstrips; HC, ErC, TandC are not used. Selections "Metallic Cover" as well as "Metallic Box" imply that layer immediately under the cover is excluded from layer count; material properties of this layer are defined via parameters ErC and TandC. Selection "Metallic Box" installs metallic cover and adds side metallic walls thus confining the whole structure into rectangular metallic enclosure. Note that for models GMnCLIN and GMCLIN distance from the leftmost conductor to the left wall is always equal to the distance from the right-most conductor to the right wall; this distance is set by parameter SW. (see below section Examples).

Gnd. This switch can be set to one of two selections: "Suspended Substrate" or "Grounded Substrate." "Suspended Substrate" provides an elevated structure typical for suspended substrates. Selection "Metallic Cover" implies that air layer adjacent to the ground plane is excluded from substrate layer count; material properties of this layer are defined inside the model. Nevertheless, this air layer potentially may carry conductors (obviously, conductors, if any, are affixed to the substrate but they stick out downwards and are recessed into the air layer) so suspended substrate uses HB and demands vector T to be of length N+1. "Grounded Substrate" places a backing ground plane back to back with substrate; in this case vector T has length N and HB is not used.

SW. Distance from the left-most/right-most conductor to the left/right wall. GMnCLIN/GMCLIN use SW as (equal) distances to the left and right wall because GMnCLIN/GMCLIN imply that the modeled structure sits symmetrically between the side walls. See the GMnCLIN documentation "Parameter Restrictions and Recommendations" section for additional explanations and examples. The SW parameter is used only if the Cover parameter is set to "Metallic Box."

NOTE: GFMCLIN uses SW as distance to the left wall only. Actual interpretation of the SW parameter depends on the setting of the GFMCLIN element IsGndStraps parameter. See GFMCLIN documentation for details.

Additional parameters used by the GFMCLIN model only. See GFMCLIN for details.

SWRight. Same as SW, but defines distance to the right wall only. This parameter is used only if the Cover parameter is set to "Metallic Box." The actual interpretation of this parameter depends on the GFMCLIN IsGndStraps parameter setting. See GFMCLIN for details.

SigmaC. Bulk conductivity of layer adjacent to cover. If switch Cover="No Metallic Cover" this parameter is irrelevant.

Sigma. This vector parameter must contain exactly N entries. Each entry provides bulk conductivity of respective layer counting from top layer.

RhoV. This vector parameter must contain exactly N entries if switch Gnd="Grounded Substrate" and N+1 (exactly) entries if Gnd="Suspended Substrate". Each entry provides bulk conductivity of respective conductor metal layer counting from top.

Rho. GFMCLIN does not use this parameter.

Undercut. GFMCLIN optionally uses this vector parameter to apply its values as etch undercuts to conductors on each layer. Etch undercut specifies non-rectangular (trapezoidal) distortion of conductor cross-section due to manufacturing errors. Undercut may take positive, zero, and negative values. All conductors that belong to the same layer have an identical undercut equal to the corresponding entry of vector Undercut. Vector parameter Undercut must contain exactly N entries if the GMSUB Gnd parameter is "Grounded Substrate", and exactly N+1 entries if Gnd is "Suspended Substrate".

MuP, MuPP. GFMCLIN optionally (if parameter IsMagSub=Magnetic substrate) uses these vector parameters to apply its values as real and imaginary parts of relative magnetic permeability of dielectric layers. Vector parameters MuP and MuPP must contain exactly N entries each.

Rgh. Surface roughness (RMS surface profile height). Models GMCLIN, GM1LIN, and GM2CLIN..GM10CLIN use Rgh to evaluate effect of metal surface roughness.

Implementation Details

Figures in Topology section demonstrate various implementations of GMSUB. Note that suspended substrate (parameter Gnd is set to "Suspended substrate") implies that layer N+1(air) is placed automatically under the layer N; grounded substrate (parameter Gnd is set to "Grounded substrate") implies that ground plane immediately backs layer N.

Covered substrate (parameter Cover is set to "Metallic Cover") implies that additional unnumbered layer (carrying cover) is automatically placed above layer 1. Material parameters of this layer must be set via parameters ErC and TandC.

Evaluation of the surface roughness impact is based on the improved Hammerstad formula.

Layout

This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.

Recommendations for Use

GMSUB must either be present on the schematics that contain elements using GMSUB or be placed on the Global Definitions window. In the latter case, models using a global definition of GMSUB must refer to it explicitly.

The following examples demonstrate how to configure GMSUB parameters for modeling commonly used single layer (N=1) substrates.

See GMnCLIN documentation for example of configuration of GMSUB enclosed in metallic box.

NOTE: Large ratios for SW/Hstack and HC/Hstack (Hstack stands for total height of dielectric stack plus optional HC and HB) should be avoided with models GFMnCLIN and GMCLIN due to a possible reduction in accuracy. It is not recommended to set these ratios above 30-40.

Examples

Centered Stripline Substrate

Off-center Stripline Substrate

Suspended (Inverted) Stripline Substrate

Substrate allows to arrange conductors at both sides of layer with Er=9.7. Air layers are not included into layer count due to usage of options Cover=Metallic Cover and Gnd=Suspended Substrate. Only middle layer with Er=9.7 is included in layer count. Note that vector T has two entries because the air layer under the substrate may "carry" conductors that stick out from the substrate bottom, but are recessed into the air layer. The negative thickness of these conductors is imposed (sign of second entry of vector T gets effectively overridden) by models GM1LIN, GMnLIN, and GMCLIN.

Alternative implementation of Suspended (Inverted) Stripline Substrate

This example demonstrates how we can alternatively (and less effectively) describe same substrate as above not using option Gnd = Suspended Substrate. Substrate allows to arrange conductors at both sides of layer with Er=9.7. Let us include bottom air layer as well as middle layer into layer count. Note that vector T has two entries because the air layer under the substrate may "carry" conductors that stick out from the substrate bottom but are recessed into the air layer. Thus, we must set second entry of vector T explicitly to negative value; must do this explicitly because in case Gnd = Grounded Substrate models do not change sign of T. Models ignore parameter HB at specified setting of Gnd so HB is set to arbitrary value. We must also set explicitly each of two entries of vectors Er, Tand, and H. Evidently, option Gnd=Suspended Substrate simplifies description of this substrate.

TWO-LAYER INVERTED AND SUSPENDED STRIPLINE SUBSTRATE

Covered substrate allows to arrange conductors only at bottom boundary of layer with Er=9.7 (inverted arrangement). We cannot use Gnd= Suspended Substrate and must assume that air layer is included in layer count. Conductors must recess into air layer so T is set explicitly to negative value. Models ignore parameter HB at specified setting of Gnd so HB is set to arbitrary value. All parameters of layer with Er=9.7 are entered as parameters of layer adjacent to cover (ErC, TandC, and HC).

Microstrip Substrate

Suspended (Inverted) Microstrip Substrate

Note that vector T has two entries because the air layer under the substrate may carry conductors that stick out from the substrate bottom, but are recessed into the air layer. The negative thickness of these conductors is provided by GM1LIN, GMnLIN, and GMCLIN models.

CONDUCTING SUBSTRATE (FOR USE WITH GFMCLIN)

This three-layer substrate features two conducting layers. Conductivity of these layers are specified in vector Sigma. Note that length of vector Sigma must be equal to number of layers (this requirement refers equally to vectors RhoV and T).

Covered Microstrip Substrate

Elements Used with GMSUB

LINES
GFMCLIN
GMnCLIN
GM1LIN
GMCLIN
MXOVER2

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