106 lines
3.3 KiB
Matlab
106 lines
3.3 KiB
Matlab
%
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% Tutorials / Circ_Waveguide
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%
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% Describtion at:
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% http://openems.de/index.php/Tutorial:_Circular_Waveguide
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%
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% Tested with
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% - Matlab 2011a / Octave 3.4.3
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% - openEMS v0.0.31
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%
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% (C) 2010-2013 Thorsten Liebig <thorsten.liebig@gmx.de>
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close all
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clear
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clc
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%% setup the simulation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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physical_constants;
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unit = 1e-3; %drawing unit in mm
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% waveguide dimensions
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length = 2000;
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rad = 350; %waveguide radius in mm
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% frequency range of interest
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f_start = 300e6;
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f_stop = 500e6;
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mesh_res = [10 2*pi/49.999 10]; %targeted mesh resolution
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%% setup FDTD parameter & excitation function %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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FDTD = InitFDTD('EndCriteria',1e-4,'CoordSystem',1);
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FDTD = SetGaussExcite(FDTD,0.5*(f_start+f_stop),0.5*(f_stop-f_start));
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% boundary conditions
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BC = [0 0 0 0 3 3]; %pml in pos. and neg. z-direction
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FDTD = SetBoundaryCond(FDTD,BC);
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%% setup CSXCAD mesh %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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CSX = InitCSX('CoordSystem',1); % init a cylindrical mesh
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mesh.r = SmoothMeshLines([0 rad], mesh_res(1)); %mesh in radial direction
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mesh.a = SmoothMeshLines([0 2*pi], mesh_res(2)); % mesh in aziumthal dir.
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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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%% apply the waveguide port %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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start=[mesh.r(1) mesh.a(1) mesh.z(8)];
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stop =[mesh.r(end) mesh.a(end) mesh.z(15)];
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[CSX, port{1}] = AddCircWaveGuidePort( CSX, 0, 1, start, stop, rad*unit, 'TE11', 0, 1);
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start=[mesh.r(1) mesh.a(1) mesh.z(end-13)];
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stop =[mesh.r(end) mesh.a(end) mesh.z(end-14)];
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[CSX, port{2}] = AddCircWaveGuidePort( CSX, 0, 2, start, stop, rad*unit, 'TE11');
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%% define dump box... %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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CSX = AddDump(CSX,'Et','FileType',1,'SubSampling','4,4,4');
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start = [mesh.r(1) mesh.a(1) mesh.z(1)];
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stop = [mesh.r(end) mesh.a(end) mesh.z(end)];
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CSX = AddBox(CSX,'Et',0 , start,stop);
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%% Write openEMS compatoble xml-file %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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Sim_Path = 'tmp';
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Sim_CSX = 'circ_wg.xml';
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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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WriteOpenEMS([Sim_Path '/' Sim_CSX],FDTD,CSX);
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RunOpenEMS(Sim_Path, Sim_CSX)
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%% postproc %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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freq = linspace(f_start,f_stop,201);
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port = calcPort( port, Sim_Path, freq);
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s11 = port{1}.uf.ref./ port{1}.uf.inc;
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s21 = port{2}.uf.ref./ port{1}.uf.inc;
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ZL = port{1}.uf.tot./port{1}.if.tot;
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%% plot s-parameter %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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figure
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plot(freq*1e-6,20*log10(abs(s11)),'k-','Linewidth',2);
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xlim([freq(1) freq(end)]*1e-6);
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grid on;
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hold on;
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plot(freq*1e-6,20*log10(abs(s21)),'r--','Linewidth',2);
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l = legend('S_{11}','S_{21}','Location','Best');
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set(l,'FontSize',12);
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ylabel('S-Parameter (dB)','FontSize',12);
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xlabel('frequency (MHz) \rightarrow','FontSize',12);
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%% compare analytic and numerical wave-impedance %%%%%%%%%%%%%%%%%%%%%%%%%%
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figure
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plot(freq*1e-6,real(ZL),'Linewidth',2);
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hold on;
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grid on;
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plot(freq*1e-6,imag(ZL),'r--','Linewidth',2);
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plot(freq*1e-6,port{1}.ZL,'g-.','Linewidth',2);
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ylabel('ZL (\Omega)','FontSize',12);
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xlabel('frequency (MHz) \rightarrow','FontSize',12);
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xlim([freq(1) freq(end)]*1e-6);
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l = legend('\Re(Z_L)','\Im(Z_L)','Z_L analytic','Location','Best');
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set(l,'FontSize',12);
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