134 lines
4.3 KiB
Matlab
134 lines
4.3 KiB
Matlab
%
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% Stripline to Microstrip Line Transition
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%
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% Description at:
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% <http://openems.de/index.php/Tutorial:_Stripline_to_MSL_Transition>
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%
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% Tested with
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% - Octave 4.0
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% - openEMS v0.0.35
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%
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% (C) 2017 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-6; % specify everything in um
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line_length = 15000; % line length of strip line and microstrip line
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substrate_width = 6000;
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air_spacer = 4000; % air spacer above the substrate
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msl_width = 500;
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msl_substrate_thickness = 254;
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strip_width = 500;
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strip_substrate_thickness = 512;
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connect_via_rad = 500/2;
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connect_via_gap = 1250/2;
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substrate_epr = 3.66;
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substrate_kappa = 1e-3 * 2*pi*2.45e9 * EPS0*substrate_epr; % substrate losses
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f_max = 10e9;
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resolution = 250;
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edge_res = 25;
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feed_shift = 2500;
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meas_shift = 5000;
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%% Setup FDTD Parameters & Excitation Function
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FDTD = InitFDTD();
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FDTD = SetGaussExcite( FDTD, f_max/2, f_max/2);
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BC = {'PML_8' 'PML_8' 'PEC' 'PEC' 'PEC' 'MUR'};
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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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edge_mesh = [-1/3 2/3]*edge_res; % 1/3 - 2/3 rule for 2D metal edges
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mesh.x = SmoothMeshLines( [-connect_via_gap 0 connect_via_gap], 2*edge_res, 1.5 );
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mesh.x = SmoothMeshLines( [-line_length mesh.x line_length], resolution, 1.5);
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mesh.y = SmoothMeshLines( [0 msl_width/2+edge_mesh substrate_width/2], resolution/4 , 1.5);
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mesh.y = sort(unique([-mesh.y mesh.y]));
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mesh.z = SmoothMeshLines( [linspace(-strip_substrate_thickness,0,5) linspace(0,strip_substrate_thickness,5) linspace(strip_substrate_thickness,msl_substrate_thickness+strip_substrate_thickness,5) 2*strip_substrate_thickness+air_spacer] , resolution );
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CSX = DefineRectGrid( CSX, unit, mesh );
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% Create Substrate
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CSX = AddMaterial( CSX, 'RO4350B' );
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CSX = SetMaterialProperty( CSX, 'RO4350B', 'Epsilon', substrate_epr, 'Kappa', substrate_kappa );
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start = [mesh.x(1), mesh.y(1), -strip_substrate_thickness];
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stop = [mesh.x(end), mesh.y(end), +strip_substrate_thickness+msl_substrate_thickness];
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CSX = AddBox( CSX, 'RO4350B', 0, start, stop );
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% Create a PEC called 'metal' and 'gnd'
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CSX = AddMetal( CSX, 'gnd' );
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CSX = AddMetal( CSX, 'metal' );
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% Create strip line port (incl. metal strip line)
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start = [-line_length -strip_width/2 0];
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stop = [0 +strip_width/2 0];
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[CSX,port{1}] = AddStripLinePort( CSX, 100, 1, 'metal', start, stop, strip_substrate_thickness, 'x', [0 0 -1], 'ExcitePort', true, 'FeedShift', feed_shift, 'MeasPlaneShift', meas_shift );
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% Create MSL port on top
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start = [line_length -strip_width/2 strip_substrate_thickness+msl_substrate_thickness];
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stop = [0 +strip_width/2 strip_substrate_thickness];
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[CSX,port{2}] = AddMSLPort( CSX, 100, 2, 'metal', start, stop, 'x', [0 0 -1], 'MeasPlaneShift', meas_shift );
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% transitional via
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start = [0, 0, 0];
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stop = [0, 0, strip_substrate_thickness+msl_substrate_thickness];
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CSX = AddCylinder(CSX, 'metal', 100, start, stop, connect_via_rad);
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% metal plane between strip line and MSL, including hole for transition
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p(1,1) = mesh.x(1);
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p(2,1) = mesh.y(1);
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p(1,2) = 0;
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p(2,2) = mesh.y(1);
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for a = linspace(-pi, pi, 21)
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p(1,end+1) = connect_via_gap*sin(a);
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p(2,end) = connect_via_gap*cos(a);
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endfor
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p(1,end+1) = 0;
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p(2,end ) = mesh.y(1);
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p(1,end+1) = mesh.x(end);
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p(2,end ) = mesh.y(1);
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p(1,end+1) = mesh.x(end);
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p(2,end ) = mesh.y(end);
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p(1,end+1) = mesh.x(1);
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p(2,end ) = mesh.y(end);
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CSX = AddPolygon( CSX, 'gnd', 1, 'z', strip_substrate_thickness, p);
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%% Write/Show/Run the openEMS compatible xml-file
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Sim_Path = 'tmp';
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Sim_CSX = 'strip2msl.xml';
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[status, message, messageid] = rmdir( Sim_Path, 's' ); % clear previous directory
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[status, message, messageid] = mkdir( Sim_Path ); % create empty simulation folder
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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 );
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%% Post-Processing
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close all
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f = linspace( 0, f_max, 1601 );
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port = calcPort( port, Sim_Path, f, 'RefImpedance', 50);
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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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plot(f/1e9,20*log10(abs(s11)),'k-','LineWidth',2);
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hold on;
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grid on;
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plot(f/1e9,20*log10(abs(s21)),'r--','LineWidth',2);
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legend('S_{11}','S_{21}');
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ylabel('S-Parameter (dB)','FontSize',12);
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xlabel('frequency (GHz) \rightarrow','FontSize',12);
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ylim([-40 2]);
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