new example: directional coupler in stacked microstrip technology
Sebastian Held
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function directional_coupler
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%
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% EXAMPLE / microstrip / directional_coupler
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%
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% Stacked directional coupler in microstrip technology.
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%
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% This example demonstrates:
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% - simple microstrip geometry
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% - S-parameter calculation using the ypar-method
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% - display of coupler parameters
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% - display of S11 (smith chart)
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%
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%
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% Tested with
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% - Matlab 2010b
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% - Octave 3.3.54
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% - openEMS v0.0.17
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%
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% (C) 2010 Sebastian Held <sebastian.held@gmx.de>
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clear
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close all
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clc
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% sim settings
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showStructure = 1;
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runSimulation = 1;
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for n=1:4
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if n > 1, showStructure = 0; end
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ports{n} = sim( n, showStructure, runSimulation );
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end
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postprocess( ports );
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function ports = sim( simnr, showStructure, runSimulation )
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physical_constants
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% setup the simulation
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drawingunit = 1e-6; % specify everything in um
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Sim_Path = ['tmp' int2str(simnr)];
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Sim_CSX = 'tmp.xml';
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f_max = 100e6;
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lambda = c0/f_max;
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% specify the coupler
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pcb1.w = 147000;
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pcb1.h = 54500;
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pcb1.t = 1524;
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pcb1.epr = 3;
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msl1.w = 135000;
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msl1.h = 2800;
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pcb2.w = 107000;
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pcb2.h = 14000;
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pcb2.t = 1524;
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pcb2.epr = 3;
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msl2.w = 95000;
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msl2.h = 4000;
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CSX = InitCSX();
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% create the mesh
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mesh.x = [-pcb1.w/2 pcb1.w/2 -pcb2.w/2 pcb2.w/2 -msl1.w/2 msl1.w/2 -msl2.w/2 msl2.w/2];
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mesh.x = [mesh.x linspace(-msl2.w/2,-msl2.w/2+msl2.h, 5) linspace(msl2.w/2,msl2.w/2-msl2.h, 5)];
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mesh.y = [-pcb1.h/2 pcb1.h/2 -pcb2.h/2 pcb2.h/2 -msl1.h/2 msl1.h/2 -msl2.h/2 msl2.h/2];
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mesh.z = [linspace(0,pcb1.t,5) linspace(pcb1.t,pcb1.t+pcb2.t,5)];
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mesh.z = [mesh.z mesh.z(end)+10*(mesh.z(end)-mesh.z(1))]; % add space above pcb
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res = lambda/sqrt(max([pcb1.epr,pcb2.epr])) / 20 / drawingunit;
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mesh.x = SmoothMeshLines2(mesh.x,res);
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mesh.y = SmoothMeshLines2(mesh.y,res);
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mesh.z = SmoothMeshLines2(mesh.z,res);
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mesh = AddPML( mesh, [8 8 8 8 8 8] ); % add space for PML
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CSX = DefineRectGrid( CSX, drawingunit, mesh );
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%% create the structure
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% microstrip
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CSX = AddMetal( CSX, 'PEC' );
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start = [-msl1.w/2, -msl1.h/2, pcb1.t];
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stop = [ msl1.w/2, msl1.h/2, pcb1.t];
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priority = 100; % the geometric priority is set to 100
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CSX = AddBox( CSX, 'PEC', priority, start, stop );
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% ground plane
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CSX = AddMetal( CSX, 'PEC_ground' );
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start = [-pcb1.w/2, -pcb1.h/2, 0];
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stop = [ pcb1.w/2, pcb1.h/2, 0];
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CSX = AddBox( CSX, 'PEC_ground', priority, start, stop );
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% substrate 1
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start = [-pcb1.w/2, -pcb1.h/2, 0];
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stop = [ pcb1.w/2, pcb1.h/2, pcb1.t];
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priority = 10;
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CSX = AddMaterial( CSX, 'substrate1' );
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CSX = SetMaterialProperty( CSX, 'substrate1', 'Epsilon', pcb1.epr );
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CSX = AddBox( CSX, 'substrate1', priority, start, stop );
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% substrate 2
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start = [-pcb2.w/2, -pcb2.h/2, pcb1.t];
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stop = [ pcb2.w/2, pcb2.h/2, pcb1.t+pcb2.t];
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priority = 10;
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CSX = AddMaterial( CSX, 'substrate2' );
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CSX = SetMaterialProperty( CSX, 'substrate2', 'Epsilon', pcb2.epr );
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CSX = AddBox( CSX, 'substrate2', priority, start, stop );
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% stripline
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start = [-msl2.w/2, -msl2.h/2, pcb1.t+pcb2.t];
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stop = [ msl2.w/2, msl2.h/2, pcb1.t+pcb2.t];
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priority = 100;
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CSX = AddBox( CSX, 'PEC', priority, start, stop );
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% connections
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start = [-msl2.w/2, -msl2.h/2, pcb1.t+pcb2.t];
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stop = [-msl2.w/2+msl2.h, -pcb2.h/2, pcb1.t+pcb2.t];
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priority = 100;
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CSX = AddBox( CSX, 'PEC', priority, start, stop );
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start = [ msl2.w/2, -msl2.h/2, pcb1.t+pcb2.t];
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stop = [ msl2.w/2-msl2.h, -pcb2.h/2, pcb1.t+pcb2.t];
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priority = 100;
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CSX = AddBox( CSX, 'PEC', priority, start, stop );
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%% ports
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% this project needs 4 simulations
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for n=1:4
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portexcite{n} = [];
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end
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portexcite{simnr} = 'excite';
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% port 1: input port
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start = [-msl1.w/2, 0, pcb1.t];
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stop = [-msl1.w/2, 0, 0];
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[CSX ports{1}] = AddCurvePort( CSX, 1, 50, start, stop, portexcite{1} );
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% port 2: output port
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start = [msl1.w/2, 0, pcb1.t];
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stop = [msl1.w/2, 0, 0];
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[CSX ports{2}] = AddCurvePort( CSX, 2, 50, start, stop, portexcite{2} );
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% port 3: coupled port
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start = [-msl2.w/2+msl2.h/2, -pcb2.h/2, pcb1.t+pcb2.t];
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stop = [-msl2.w/2+msl2.h/2, -pcb2.h/2, 0];
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[CSX ports{3}] = AddCurvePort( CSX, 3, 50, start, stop, portexcite{3} );
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% port 4: isolated port
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start = [msl2.w/2-msl2.h/2, -pcb2.h/2, pcb1.t+pcb2.t];
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stop = [msl2.w/2-msl2.h/2, -pcb2.h/2, 0];
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[CSX ports{4}] = AddCurvePort( CSX, 4, 50, start, stop, portexcite{4} );
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%% setup FDTD parameters & excitation function
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max_timesteps = 50000;
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min_decrement = 1e-6;
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FDTD = InitFDTD( max_timesteps, min_decrement );
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FDTD = SetGaussExcite( FDTD, 0, f_max );
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BC = {'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8'};
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BC = {'MUR' 'MUR' 'MUR' 'MUR' 'MUR' 'MUR'}; % faster
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FDTD = SetBoundaryCond( FDTD, BC );
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%% Write openEMS compatible xml-file
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if runSimulation
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[~,~,~] = rmdir(Sim_Path,'s');
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end
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[~,~,~] = mkdir(Sim_Path);
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WriteOpenEMS([Sim_Path '/' Sim_CSX],FDTD,CSX);
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if showStructure
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CSXGeomPlot( [Sim_Path '/' Sim_CSX] );
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end
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%% run openEMS
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openEMS_opts = '';
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openEMS_opts = [openEMS_opts ' --engine=fastest'];
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% openEMS_opts = [openEMS_opts ' --debug-material'];
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% openEMS_opts = [openEMS_opts ' --debug-boxes'];
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if runSimulation
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RunOpenEMS( Sim_Path, Sim_CSX, openEMS_opts );
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end
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function postprocess( ports )
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f = linspace( 0, 100e6, 201 );
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Y = calc_ypar( f, ports{1}, 'tmp' );
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R = 50;
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S = y2s(Y,R);
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% insertion loss
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IL_dB = -20 * log10(abs(squeeze(S(2,1,:))));
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% coupling factor
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CF_dB = -20 * log10(abs(squeeze(S(3,1,:))));
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% isolation
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I_dB = -20 * log10(abs(squeeze(S(4,1,:))));
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% directivity
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D_dB = -20 * log10(abs(squeeze(S(4,1,:) ./ S(3,1,:))));
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figure
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plot( f, [IL_dB CF_dB I_dB D_dB] );
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legend( {'insertion loss','coupling factor','isolation','directivity'} );
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title( ['performance of the coupler for a termination resistance of R=' num2str(R)] );
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grid on
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smithchart
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S11 = squeeze(S(1,1,:));
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plot( real(S11), imag(S11) );
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legend( 'S_{11}' );
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title( ['performance of the coupler for a termination resistance of R=' num2str(R)] );
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axis( [-1 1 -1 1] );
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function smithchart
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% smith chart
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figure
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if exist( 'smith', 'file' )
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% smith chart
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% www.ece.rutgers.edu/~orfanidi/ewa
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% or cmt toolbox from git.ate.uni-duisburg.de
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smith
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else
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% poor man smith chart
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color = [.6 .6 .6];
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h = plot( sin(0:0.01:2*pi), cos(0:0.01:2*pi), 'Color', color );
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hg = hggroup;
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set( h,'Parent',hg );
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hold on
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plot( hg, 0.25+0.75*sin(0:0.01:2*pi), 0.75*cos(0:0.01:2*pi), 'Color', color );
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plot( hg, 0.5+0.5*sin(0:0.01:2*pi), 0.5*cos(0:0.01:2*pi), 'Color', color );
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plot( hg, 0.75+0.25*sin(0:0.01:2*pi), 0.25*cos(0:0.01:2*pi), 'Color', color );
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plot( hg, [-1 1], [0 0], 'Color', color );
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axis equal
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axis off
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end
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