This document describes how to generate equivalent circuit model for microstrip line example (Fig 4) in paper Integration of Arbitrary Lumped Multiport Circuit Networks Into the Discontinuous Galerkin Time-Domain Analysis. (A typo in paper: [Ls =0.102nH].
Step 1. Generate a half microstrip line model, only port 1 to port 2, and run DGTD to obtain the S-parameters.
- Go to folder forDeliver/halfmatchTL and execute runMPI.sh. The input pulse is set to be 4GHz -12Ghz. This will generate a folder TimeDomainVoltages.
- Run MATLAB file computeSpara.m, to generate s-parameters. Run for both S11 and S12, then a MATLAB data file halfmatchTL_S11.mat and halfmatchTL_S12.mat will be on disk and then copy them to folder matchMicroStrip.
- S11: set line 16 S11flag = 1
- S12: set line 16 S11flag = 0
Step 2. Run MATLAB file MicroStripEquiv.m.
- To choose range of data. The vector fitting may NOT work well for very complex y-parameters, so sometimes a range of frequency should be selected. As in
datarange = 1:length(freq);, all data is used. - To choose order of fitting as you need in line
opts.N=4. - routine N_PORT_circuit in this script is the working horse. See its own comments.
- Line 67 is for port 1 to port 2 and line 72 is for port 3 to port 4. Input arguments mean that the node in this circuit starts with lastNd+1; index for RLC(VCVS) starts from lastdev+1; nodes that interface with external circuit starts from port_id_start.
- Run this file, you will see MATLAB command line prompts the following:
Lid1 0 5 -1.056360e-06 Cid1 5 6 -1.583723e-15This is the SPICE netlist of circuit. Copy and paste it to file halfmicrostrip.cir. - Always this file starts with
.title XXX.
Step 3(a)
Run python script MicroStripEquiv.py. The library_path should be set correctly according to your installation of PySpice. The installation of PySpice and NgSpice shared library can be found here and here. Note, NgSpice Version 30 is recommended over others. Line 55-59 is the gap capacitor.
The input and output stage is connect in serial with a 50Ohm resistor.
So the s-parameters from equivalent should be computed as
$$
S_{11} = \frac{2V_1-V_s}{V_s}\
S_{21} = \frac{2V_2}{V_s}
$$
Then run MATLAB script MicroStripSparaCircuit.m, you will see the results as:
Step 3(b)
Since the lump port is not exactly the same as wave port where the equivalent circuit model is obtained from. So change the $Y_{22}$ to 0.02G at port 2 and port 3 by turning on Modflag in line Modflag=1 in file MicroStripEquiv.m. Then go the process stated in step 3(a) you will see.
Files included:
Folder forDelivery contains the DGTD solver in dgtd_MPI, geometry files in geo and all necessary file to obtain the s-parameter in folder halfmatchTL. To start,go to halfmatchTL and execute runMPI.sh.
In folder circuitfittingProject, there includes necessary MATLAB and python files. Each file should be commented well.
For any question, please contact shuwang12@unm.edu.