121 lines
3.5 KiB
Matlab
121 lines
3.5 KiB
Matlab
%
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% EXAMPLE / waveguide / coaxial cable
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%
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% This example demonstrates how to:
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% - setup a coaxial waveguide
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% - use analytic functions for waveguide excitations and voltage/current
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% calculations
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%
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%
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% Tested with
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% - Matlab 2009b
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% - openEMS v0.0.17
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%
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% (C) 2010 Thorsten Liebig <thorsten.liebig@uni-due.de>
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close all
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clear
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clc
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%% switches & options...
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postprocessing_only = 0;
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use_pml = 0; % use pml boundaries instead of mur
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openEMS_opts = '';
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% openEMS_opts = [openEMS_opts ' --disable-dumps'];
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%% setup the simulation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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numTS = 5000; %number of timesteps
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length = 1000; %length of the waveguide
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unit = 1e-3; %drawing unit used
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coax_rad_i = 100; %inner radius
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coax_rad_ai = 230; %inner radius of outer cladding
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coax_rad_aa = 240; %outer radius of outer cladding
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mesh_res = [5 5 5]; %desired mesh resolution
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physical_constants;
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%excitation
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f0 = 0.5e9;
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epsR = 1;
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%% create sim path %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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Sim_Path = 'tmp';
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Sim_CSX = 'coax.xml';
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if (postprocessing_only==0)
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[status, message, messageid] = rmdir(Sim_Path,'s');
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[status, message, messageid] = mkdir(Sim_Path);
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end
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%% setup FDTD parameter & excitation function %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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FDTD = InitFDTD(numTS,1e-5);
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FDTD = SetGaussExcite(FDTD,f0,f0);
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BC = {'PEC','PEC','PEC','PEC','MUR','MUR'};
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if (use_pml>0)
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BC = {'PEC','PEC','PEC','PEC','PML_8','PML_8'};
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end
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FDTD = SetBoundaryCond(FDTD,BC);
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%% setup CSXCAD geometry & mesh %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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CSX = InitCSX();
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mesh.x = -coax_rad_aa : mesh_res(1) : coax_rad_aa;
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mesh.y = mesh.x;
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mesh.z = SmoothMeshLines([0 length], mesh_res(3));
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CSX = DefineRectGrid(CSX, unit, mesh);
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%%% coax
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CSX = AddMetal(CSX,'copper');
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start = [0,0,0];
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stop = [0,0,length/2];
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[CSX,port{1}] = AddCoaxialPort( CSX, 10, 1, 'copper', '', start, stop, 'z', coax_rad_i, coax_rad_ai, coax_rad_aa, 'ExciteAmp', 1,'FeedShift', 10*mesh_res(1) );
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start = [0,0,length/2];
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stop = [0,0,length];
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[CSX,port{2}] = AddCoaxialPort( CSX, 10, 2, 'copper', '', start, stop, 'z', coax_rad_i, coax_rad_ai, coax_rad_aa );
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%% define dump boxes... %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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CSX = AddDump(CSX,'Et_','DumpMode',2);
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start = [mesh.x(1) , 0 , mesh.z(1)];
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stop = [mesh.x(end) , 0 , mesh.z(end)];
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CSX = AddBox(CSX,'Et_',0 , start,stop);
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CSX = AddDump(CSX,'Ht_','DumpType',1,'DumpMode',2);
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CSX = AddBox(CSX,'Ht_',0,start,stop);
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%% Write openEMS
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if (postprocessing_only==0)
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WriteOpenEMS([Sim_Path '/' Sim_CSX],FDTD,CSX);
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CSXGeomPlot([Sim_Path '/' Sim_CSX]);
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RunOpenEMS(Sim_Path, Sim_CSX, openEMS_opts);
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end
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%%
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freq = linspace(0,2*f0,201);
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port = calcPort(port, Sim_Path, freq);
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%% plot s-parameter
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figure
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s11 = port{1}.uf.ref./port{1}.uf.inc;
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s21 = port{2}.uf.inc./port{1}.uf.inc;
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plot(freq,20*log10(abs(s11)),'Linewidth',2);
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hold on
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grid on
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plot(freq,20*log10(abs(s21)),'r--','Linewidth',2);
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xlim([freq(1) freq(end)]);
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xlabel('frequency (Hz)')
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ylabel('s-para (dB)');
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%% plot line-impedance comparison
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figure()
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ZL_a = ones(size(freq))*Z0/2/pi/sqrt(epsR)*log(coax_rad_ai/coax_rad_i); %analytic line-impedance of a coax
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ZL = port{2}.uf.tot./port{2}.if.tot;
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plot(freq,real(port{1}.ZL),'Linewidth',2);
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xlim([freq(1) freq(end)]);
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xlabel('frequency (Hz)')
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ylabel('line-impedance (\Omega)');
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grid on;
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hold on;
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plot(freq,imag(port{1}.ZL),'r--','Linewidth',2);
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plot(freq,ZL_a,'g-.','Linewidth',2);
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legend('\Re\{ZL\}','\Im\{ZL\}','ZL-analytic','Location','Best');
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