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Tapered Microstrip Line (Closed Form): MTAPER



MTAPER models a segment of inhomogeneous microstrip line. The width of microstrip tapers smoothly between ports. This model allows linear and exponential width tapers.



MTAPER$ 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]
MSUB Substrate definition Text MSUB#[2]
Taper Linear/Exponential switch   Linear
Method Default/Interpolation switch   Default

[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 the “Using Elements With Model Blocks” for details.

Parameter Details

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.

Method. This parameter provides two options. When the Default option is selected, the model breaks the tapered conductor into multiple constant width sections and calculates transmission line characteristics for each section. When the Interpolation option is selected, the model breaks the tapered conductor into a small number of constant width sections and creates lookup tables for transmission line parameters using width as an argument. Transmission line characteristics for multiple sections are evaluated by means of interpolation in these tables. The Interpolation option speeds up MTAPER and may be beneficial for tuning and optimization. Note that interpolation may slightly degrade accuracy, so user discretion is advised.

Also note that selecting Method=Interpolation has no effect on time-domain simulations.

Parameter Restrictions and Recommendations

0.05 ≤ W1 or 2/H ≤ 20 Recommended εr ≤ 16.0 Recommended
T/Wmin ≤ 0.5 Recommended 1 ≤ εr Required
T/H ≤ 0.5 Recommended Tand ≥ 0 Required
Rho ≤ 100 Recommended Ang ≤ 45 degs or L ≥ |W1 -W2|/2

Implementation Details

This model is constructed out of a cascaded series of constant width Microstrip transmission lines. 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 and dispersion.


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.


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

[1] E. Hammerstad and O. Jensen, IEEE MTT-S International Microwave Symposium Digest, p.407, 1980.

[2] I. J. Bahl and D. K. Trivedi, "A Designer's Guide to Microstrip Line," Microwaves, p. 174, May, 1977.

[3] S. March, "Microstrip Packaging: Watch the Last Step," Microwaves, p. 83, Dec., 1981.

[4] R. Pucel, D. J. Masse, and C. P. Hartwing, IEEE Trans. Microwave Theory Tech., Vol. MTT 16, p. 342, 1968.

[5] G. Wells and P. Pramanick, Int. J. Microwave and mmWave Computer-Aided Design, Vol. 5, p. 287, 1995.

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