222 lines
7.0 KiB
Matlab
222 lines
7.0 KiB
Matlab
%
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% microstrip line example
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%
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% this example shows how to use a MSL port
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%
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% The MSL is excited at the center of the computational volume. The
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% boundary at xmin is an absorbing boundary (Mur) and at xmax an electric
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% wall. The reflection coefficient at this wall is S11 = -1.
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%
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close all
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clear
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clc
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physical_constants
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postprocessing_only = 0;
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%% setup the simulation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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drawingunits = 1e-6; % specify everything in um
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MSL_length = 10000;
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MSL_width = 1000;
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substrate_thickness = 254;
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mesh_res = [200 0 0];
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max_timesteps = 20000;
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min_decrement = 1e-6;
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f_max = 8e9;
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%% setup FDTD parameters & excitation function %%%%%%%%%%%%%%%%%%%%%%%%%%%%
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FDTD = InitFDTD( max_timesteps, min_decrement, 'OverSampling', 10 );
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FDTD = SetGaussExcite( FDTD, f_max/2, f_max/2 );
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BC = [2 0 0 0 0 1];
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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 = -MSL_length : mesh_res(1) : MSL_length;
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mesh.y = linspace(-MSL_width/2,MSL_width/2,10); % discretize the width of the MSL with 10 cells
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temp1 = linspace(-4*MSL_width,mesh.y(1),20);
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temp2 = linspace(mesh.y(end),4*MSL_width,20);
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mesh.y = [temp1(1:end-1), mesh.y, temp2(2:end)]; % add coarser discretization
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mesh.z = linspace(0,substrate_thickness,5); % discretize the substrate with 5 cells
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temp1 = linspace(substrate_thickness,2*substrate_thickness,5);
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mesh.z = [mesh.z temp1(2:end)]; % add same space above the strip
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temp1 = linspace(2*substrate_thickness,5*substrate_thickness,10);
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mesh.z = [mesh.z temp1(2:end)]; % coarser discretization
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CSX = DefineRectGrid( CSX, drawingunits, mesh );
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%% Material definitions
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CSX = AddMetal( CSX, 'PEC' );
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CSX = AddMaterial( CSX, 'RO4350B' );
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%% substrate
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CSX = SetMaterialProperty( CSX, 'RO4350B', 'Epsilon', 3.66 );
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start = [mesh.x(1), mesh.y(1), 0];
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stop = [mesh.x(end), mesh.y(end), substrate_thickness];
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CSX = AddBox( CSX, 'RO4350B', 0, start, stop );
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%% MSL port
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CSX = AddExcitation( CSX, 'excite', 0, [0 0 1]);
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portstart = [ 0, -MSL_width/2, substrate_thickness];
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portstop = [ MSL_length, MSL_width/2, 0];
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[CSX,portstruct] = AddMSLPort( CSX, 1, 'PEC', portstart, portstop, [1 0 0], [0 0 1], 'excite' );
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%% MSL
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start = [-MSL_length, -MSL_width/2, substrate_thickness];
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stop = [ 0, MSL_width/2, substrate_thickness];
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CSX = AddBox( CSX, 'PEC', 0, start, stop );
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%% define dump boxes... %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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CSX = AddDump(CSX,'Et_','DumpType',0,'DumpMode',0);
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start = [mesh.x(1) , mesh.y(1), substrate_thickness/2];
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stop = [mesh.x(end), mesh.y(end), substrate_thickness/2];
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CSX = AddBox(CSX,'Et_',0 , start,stop);
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CSX = AddDump(CSX,'Ht_','DumpType',1,'DumpMode',0);
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CSX = AddBox(CSX,'Ht_',0,start,stop);
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%% define openEMS options %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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openEMS_opts = '';
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openEMS_opts = [openEMS_opts ' --disable-dumps'];
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% openEMS_opts = [openEMS_opts ' --debug-material'];
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% openEMS_opts = [openEMS_opts ' --debug-operator'];
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% openEMS_opts = [openEMS_opts ' --debug-boxes'];
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% openEMS_opts = [openEMS_opts ' --engine=sse-compressed'];
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% openEMS_opts = [openEMS_opts ' --engine=multithreaded'];
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openEMS_opts = [openEMS_opts ' --engine=fastest'];
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Sim_Path = 'tmp';
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Sim_CSX = 'MSL2.xml';
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if ~postprocessing_only
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rmdir(Sim_Path,'s');
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end
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mkdir(Sim_Path);
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%% Write openEMS compatible xml-file %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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WriteOpenEMS( [Sim_Path '/' Sim_CSX], FDTD, CSX );
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%% cd to working dir and run openEMS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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savePath = pwd;
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cd(Sim_Path); %cd to working dir
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args = [Sim_CSX ' ' openEMS_opts];
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if ~postprocessing_only
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invoke_openEMS(args);
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end
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cd(savePath);
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%% postproc & do the plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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U = ReadUI({'port_ut1A','port_ut1B','et'},'tmp/');
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I = ReadUI({'port_it1A','port_it1B'},'tmp/');
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delta_t_2 = I.TD{1}.t(1) - U.TD{1}.t(1); % half time-step (s)
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% create finer frequency resolution
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f = linspace( 0, f_max, 1601 );
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for n=1:numel(U.FD)
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U.FD{n}.f = f;
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U.FD{n}.val = DFT_time2freq( U.TD{n}.t, U.TD{n}.val, f );
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end
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for n=1:numel(I.FD)
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I.FD{n}.f = f;
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I.FD{n}.val = DFT_time2freq( I.TD{n}.t, I.TD{n}.val, f );
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I.FD{n}.val = I.FD{n}.val .* exp(-1i*2*pi*I.FD{n}.f*delta_t_2); % compensate half time-step advance of H-field
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end
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% interpolate et to the time spacing of the voltage probes
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et = interp1( U.TD{3}.t, U.TD{3}.val, U.TD{1}.t );
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f = U.FD{1}.f;
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% Z = (U.FD{1}.val+U.FD{2}.val)/2 ./ I.FD{1}.val;
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% plot( f*1e-9, [real(Z);imag(Z)],'Linewidth',2);
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% xlabel('frequency (GHz)');
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% ylabel('impedance (Ohm)');
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% grid on;
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% legend( {'real','imaginary'}, 'location', 'northwest' )
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% title( 'line impedance (will fail in case of reflections!)' );
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% figure
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% plotyy(U.TD{1}.t/1e-6,[U.TD{1}.val;U.TD{2}.val],U.TD{1}.t/1e-6,et);
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% xlabel('time (us)');
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% ylabel('amplitude (V)');
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% grid on;
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% title( 'Time domain voltage probes and excitation signal' );
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%
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% figure
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% plot(I.TD{1}.t/1e-6,[I.TD{1}.val;I.TD{2}.val]);
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% xlabel('time (us)');
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% ylabel('amplitude (A)');
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% grid on;
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% title( 'Time domain current probes' );
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%% port analysis
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[S11,beta,ZL] = calcMSLPort( portstruct, Sim_Path, f );
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figure
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plot( sin(0:0.01:2*pi), cos(0:0.01:2*pi), 'Color', [.7 .7 .7] );
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hold on
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plot( 0.5+0.5*sin(0:0.01:2*pi), 0.5*cos(0:0.01:2*pi), 'Color', [.7 .7 .7] );
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plot( [-1 1], [0 0], 'Color', [.7 .7 .7] );
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plot( S11, 'k' );
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plot( real(S11(1)), imag(S11(1)), '*r' );
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axis equal
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title( 'Reflection coefficient S11 at the measurement plane' );
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figure
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plot( f/1e9, [real(S11);imag(S11)], 'Linewidth',2 );
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legend( {'Re(S11)', 'Im(S11)'} );
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ylabel( 'amplitude' );
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xlabel( 'frequency (GHz)' );
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title( 'Reflection coefficient S11 at the measurement plane' );
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figure
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plotyy( f/1e9, 20*log10(abs(S11)), f/1e9, angle(S11)/pi*180 );
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legend( {'abs(S11)', 'angle(S11)'} );
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xlabel( 'frequency (GHz)' );
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title( 'Reflection coefficient S11 at the measurement plane' );
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figure
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plot( f/1e9, [real(beta);imag(beta)], 'Linewidth',2 );
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legend( 'Re(beta)', 'Im(beta)' );
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ylabel( 'propagation constant beta (1/m)' );
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xlabel( 'frequency (GHz)' );
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title( 'Propagation constant of the MSL' );
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figure
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plot( f/1e9, [real(ZL);imag(ZL)], 'Linewidth',2);
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xlabel('frequency (GHz)');
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ylabel('impedance (Ohm)');
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grid on;
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legend( {'real','imaginary'}, 'location', 'northeast' )
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title( 'Characteristic line impedance ZL' );
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ylim( [-2*mean(real(ZL)) 2*mean(real(ZL))] );
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% reference plane shift (to the end of the port)
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ref_shift = abs(portstop(1) - portstart(1));
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[S11,beta,ZL] = calcMSLPort( portstruct, Sim_Path, f, ref_shift );
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figure
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plotyy( f/1e9, 20*log10(abs(S11)), f/1e9, angle(S11)/pi*180 );
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legend( {'abs(S11)', 'angle(S11)'} );
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xlabel( 'frequency (GHz)' );
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title( 'Reflection coefficient S11 at the reference plane (at the electric wall)' );
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figure
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plot( sin(0:0.01:2*pi), cos(0:0.01:2*pi), 'Color', [.7 .7 .7] );
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hold on
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plot( 0.5+0.5*sin(0:0.01:2*pi), 0.5*cos(0:0.01:2*pi), 'Color', [.7 .7 .7] );
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plot( [-1 1], [0 0], 'Color', [.7 .7 .7] );
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plot( S11, 'k' );
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plot( real(S11(1)), imag(S11(1)), '*r' );
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axis equal
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title( 'Reflection coefficient S11 at the reference plane (at the electric wall)' );
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