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Multiple Edge Coupled Microstrip Lines (EM Quasi-Static): MNCLIN

Symbol

Summary

MNCLIN models a section of several (1 to 50) edge coupled/single microstrip lines arranged on a single-layer substrate. A backing ground plane is always present. MNCLIN implements the same modeling techniques as the M2CLIN,...M16CLIN models. In addition, MNCLIN is a dynamic or scalable model; it accepts a number of lines as input parameters so the model and its schematic symbol expands/shrinks as the number of lines increases/decreases. This model uses disk cache to speed up simulation.

Topology

Parameters

Name Description Unit Type Default
ID Element ID Text TL1
N Number of conductors   2
L Conductor length Length L[1]
Acc Accuracy parameter   1
MSUB Substrate Definition Text MSUB1[2]
*SaveToFile "Save to txt file"=Yes/No   "No"
*FileName Name of text file with computed model parameters String Same as model name
Wi, i=1..nn- number of lines Width of conductor No i Length W[1]
Si, i=1..n-1n- number of lines Spacing between conductors No i and No i+1 Length W[1]

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

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

* indicates a secondary parameter

Parameter Details

See MxCLIN for a detailed description of MNCLIN parameters. MNCLIN differs from MXCLIN in parameter order only: For MXCLIN models, the L, Acc, and MSUB parameters follow the widths (Wi) and spacings(Si); for the MNCLIN model, the L, Acc, MSUB, Save to File, and FileName parameters precede the Wi and Si parameters.

SaveToFile. This parameter is hidden by default and set to "No". You can toggle the parameter to "Yes" or "No". If set to "Yes", the model creates a text file (named MnCLIN.txt) at the current project location. This text file contains a table of values of per-unit-length RLGC line parameters at each project frequency. Each row contains RLGC values computed at the frequency specified in the first column (frequency in GHz, R in ohms/m, L in H/m, G in S/m, C in F/m).

The structure of this text file is essentially the same for n>2. All models output RLGC matrices to columns that immediately follow the frequency column. Entries of each matrix are placed column-wise; the first column is first: R11, R21, R31.. Rn1; and then the second column: R12, R22, R32,..Rn2 etc. The total number of columns in the file is 4*n*n+1, where n is the number of lines.

If N=2, MNCLIN implies the existence of two modes, namely, C and P (see [2]) and places additional columns in the text file. Note that if a system of coupled lines is fully symmetrical (as might be the case with edge-coupled microstrip lines) C-mode corresponds to even mode and P-mode corresponds to odd mode.

For N=2, MNCLIN outputs complex characteristic impedances Re(Zc1), Im(Zc1), Re(Zp1), Im(Zp1), Re(Zc2), Im(Zc2), Re(Zp2), and Im(Zp2); complex effective dielectric constants Re(EeffC), Im(EeffC), Re(EeffP), and Im(EeffP) (see traditional effective dielectric constants in columns 38, 39); and losses for C and P modes LossC (dB/m), LossP(dB/m) to columns 2-15. Entries of R, L, G, and C matrices are distributed among columns 16-31 in corresponding order (see the previous). Columns 32-37 contain Re(Rc), Im(Rc), Re(Rp), Im(Rp), BetaC, and BetaP; where Rc is the ratio of C - mode voltage in the second line to C - mode voltage in the first line; Rp is the same ratio in P-mode (see details in [2], section 4.3.1) and BetaC and BetaP are propagation constants of C- and P-modes in Rad/m. Note that column 38 and 39 contain traditional effective dielectric constants ErC_Eff and ErP_Eff (they do not account for losses). The total number of columns in the file is 39 (at N=2).

If N=, MNCLIN creates a file that contains complex characteristic impedance Re(Zo) and Im(Zo), complex effective dielectric constant Re(Eeff) and Im (Eff) (see traditional effective dielectric constant in column 12), and Loss (dB/m) in columns 2-6. Columns 7-10 contain R, L, G, and C. Column 11 contains propagation constant Beta in Rad/m. Note that column 12 contains traditional effective dielectric constant Er_Eff that does not account for loss. Total number of columns in the file is 12 (at N=1).

The created text file might be linked or imported to a project as a data file and you can view the frequency behavior of any above mentioned parameter using the proper data measurement. Note that the first column (frequency) is always in GHz so these measurements might be incompatible with other Cadence® AWR® Microwave Office® software measurements placed on the same graph; you may prefer to place these data measurements on a separate dedicated graph.

FileName. By default this parameter is hidden and is set to model MnCLIN.TXT. You can change the file name for each model instance to an arbitrary name with a length not exceeding 64 symbols.

Parameter Restrictions and Recommendations

  1. The number of conductors N cannot exceed 50.

  2. For more information about restrictions and recommendations common to MNCLIN and MXCLIN, see MxCLIN.

Implementation Details

  1. Model implementation is based on the EM Quasi-Static technique described in [1]. It computes matrices of per-unit-length RLGC parameters and uses them to evaluate circuit parameters of coupled lines. This model saves frequency-independent RLGC matrices to disk cache. Before calculation of RLGC matrix models, it checks to see if the disk cache contains data that has been saved earlier with the same set of input parameters. If a match is found, the model reads RLGC matrices from a disk cache and saves time on their calculation. If no match is found, the model calculates RLGC matrices and places a new record into the disk cache. All subsequent runs of any project containing this model with the identical set of input parameters use the disk cache for speed up.

  2. This model accounts for losses in metal and in substrate dielectric. Dispersion is partly included (in part of frequency dependence of output parameters due to presence of frequency dependent losses).

  3. To apply Method of Moments for analysis, a quasi-static model creates 1D mesh covering contours of all conductors. The mesh is made of linear segments (pulses) of varying length. The length of a pulse is relatively big at the conductor center; it decreases toward conductor edges to reveal the charge distribution across conductor. If the conductor width is too large it may cause the pulse size to approach zero for pulses close to edge. In these rare cases the model may display a “Length of pulse #nnn equal to zero” error message.

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

See MxCLIN for details.

NOTE: The implementation of EM Quasi-Static models relies heavily on the involved numerical algorithms. This may lead to a noticeable increase in simulation time for schematics that employ many such models.

If a layer thickness is too small compared to the thickness of another layer, simulation time may also noticeably increase.

Caution regarding units of data in saved text files: If a project that reads saved text files uses frequency, resistance, inductance or conductance units different from GHz, ohm, henry or siemens, you may need to scale input values manually.

References

[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.

[2] R. Mongia, I. Bahl, and P. Bhartia, RF and Microwave Coupled-Line Circuits, Artech House, Norwood, MA, 1999.

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