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Tapered Microstrip Line on Multilayer Substrate (EM Quasi-Static): MMTAPER

Symbol

Summary

MMTAPER models a segment of inhomogeneous microstrip line on multilayered substrate GMSUB. The width of microstrip tapers smoothly between ports. This model allows linear and exponential width tapers. The substrate may be suspended, covered by a metal cover, or placed into a metal enclosure.

Topology

Parameters

MMTAPER$ is a Microstrip iCell and has no W1 or W2 parameters. See “Intelligent Cells (iCells)” for more information.

Name Description Unit Type Default
ID Name   MT1
W1 Conductor width @ node 1 Length W[1]
W2 Conductor width @ node 2 Length W[1]
L Length of taper Length L[1]
NL Number of the substrate layer carrying conductor   1
GMSUB Substrate definition Text TMSUB#[2]
Taper Linear/Exponential switch   Linear

[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 the schematic contains multiple substrates. See the “Using Elements With Model Blocks” for details.

Parameter Details

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.

Taper. This parameter provides two options. The "Linear" option provides linear taper, that is, an outline of the strip is a trapezoid. The "Exponential" option provides exponential taper, that is, an outline of the strip is trapezoid-like with longitudinal sides made with concave exponents.

Parameter Restrictions and Recommendations

  • 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 into 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 onto 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 taper line metal. Note that the GMSUB parameter T is actually a vector, but MMTAPER 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 MMTAPER.

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.

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.

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 NUM_EXP_POINT that is valid if Taper=Exponential. This parameter specifies the number of points used for drawing a curved outline of exponential taper. The default value of NUM_EXP_POINT is 50.

References

This is an Cadence® Developed Model. The reference for the straight section Microstrip line follows:

[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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