198 lines
6.8 KiB
Matlab
198 lines
6.8 KiB
Matlab
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% Tutorials / bent patch antenna
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%
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% Describtion at:
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% http://openems.de/index.php/Tutorial:_Bent_Patch_Antenna
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%
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% Tested with
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% - Matlab 2011a / Octave 4.0
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% - openEMS v0.0.33
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%
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% (C) 2013-2015 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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%% setup the simulation
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physical_constants;
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unit = 1e-3; % all length in mm
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% patch width in alpha-direction
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patch.width = 32; % resonant length in alpha-direction
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patch.radius = 50; % radius
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patch.length = 40; % patch length in z-direction
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%substrate setup
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substrate.epsR = 3.38;
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substrate.kappa = 1e-3 * 2*pi*2.45e9 * EPS0*substrate.epsR;
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substrate.width = 80;
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substrate.length = 90;
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substrate.thickness = 1.524;
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substrate.cells = 4;
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%setup feeding
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feed.pos = -5.5; %feeding position in x-direction
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feed.width = 2; %feeding port width
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feed.R = 50; %feed resistance
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% size of the simulation box
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SimBox.rad = 2*100;
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SimBox.height = 1.5*200;
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%% setup FDTD parameter & excitation function
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FDTD = InitFDTD('CoordSystem', 1); % init a cylindrical FDTD
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f0 = 2e9; % center frequency
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fc = 1e9; % 20 dB corner frequency
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FDTD = SetGaussExcite( FDTD, f0, fc );
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BC = {'MUR' 'MUR' 'MUR' 'MUR' 'MUR' 'MUR'}; % boundary conditions
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FDTD = SetBoundaryCond( FDTD, BC );
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%% setup CSXCAD geometry & mesh
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% init a cylindrical mesh
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CSX = InitCSX('CoordSystem',1);
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% calculate some width as an angle in radiant
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patch_ang_width = patch.width/(patch.radius+substrate.thickness);
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substr_ang_width = substrate.width/patch.radius;
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feed_angle = feed.pos/patch.radius;
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%% create patch
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CSX = AddMetal( CSX, 'patch' ); % create a perfect electric conductor (PEC)
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start = [patch.radius+substrate.thickness -patch_ang_width/2 -patch.length/2 ];
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stop = [patch.radius+substrate.thickness patch_ang_width/2 patch.length/2 ];
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CSX = AddBox(CSX,'patch',10,start,stop); % add a box-primitive to the metal property 'patch'
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%% create substrate
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CSX = AddMaterial( CSX, 'substrate' );
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CSX = SetMaterialProperty( CSX, 'substrate', 'Epsilon', substrate.epsR, 'Kappa', substrate.kappa );
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start = [patch.radius -substr_ang_width/2 -substrate.length/2];
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stop = [patch.radius+substrate.thickness substr_ang_width/2 substrate.length/2];
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CSX = AddBox( CSX, 'substrate', 0, start, stop);
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%% save current density oon the patch
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CSX = AddDump(CSX, 'Jt_patch','DumpType',3,'FileType',1);
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start = [patch.radius+substrate.thickness -substr_ang_width/2 -substrate.length/2];
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stop = [patch.radius+substrate.thickness +substr_ang_width/2 substrate.length/2];
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CSX = AddBox( CSX, 'Jt_patch', 0, start, stop );
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%% create ground (not really necessary, only for esthetic reasons)
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CSX = AddMetal( CSX, 'gnd' ); % create a perfect electric conductor (PEC)
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start = [patch.radius -substr_ang_width/2 -substrate.length/2];
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stop = [patch.radius +substr_ang_width/2 +substrate.length/2];
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CSX = AddBox(CSX,'gnd',10,start,stop);
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%% apply the excitation & resist as a current source
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start = [patch.radius feed_angle 0];
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stop = [patch.radius+substrate.thickness feed_angle 0];
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[CSX port] = AddLumpedPort(CSX, 50 ,1 ,feed.R, start, stop, [1 0 0], true);
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%% finalize the mesh
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% detect all edges
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mesh = DetectEdges(CSX);
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% add the simulation domain size
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mesh.r = [mesh.r patch.radius+[-20 SimBox.rad]];
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mesh.a = [mesh.a -0.75*pi 0.75*pi];
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mesh.z = [mesh.z -SimBox.height/2 SimBox.height/2];
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% add some lines for the substrate
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mesh.r = [mesh.r patch.radius+linspace(0,substrate.thickness,substrate.cells)];
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% generate a smooth mesh with max. cell size: lambda_min / 20
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max_res = c0 / (f0+fc) / unit / 20;
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max_ang = max_res/(SimBox.rad+patch.radius); % max res in radiant
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mesh = SmoothMesh(mesh, [max_res max_ang max_res], 1.4);
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disp(['Num of cells: ' num2str(numel(mesh.r)*numel(mesh.a)*numel(mesh.z))]);
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CSX = DefineRectGrid( CSX, unit, mesh );
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%% create nf2ff, keep some distance to the boundary conditions, e.g. 8 cells pml
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start = [mesh.r(4) mesh.a(8) mesh.z(8)];
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stop = [mesh.r(end-9) mesh.a(end-9) mesh.z(end-9)];
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[CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', start, stop, 'Directions',[1 1 1 1 1 1]);
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%% prepare simulation folder & run
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Sim_Path = ['tmp_' mfilename];
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Sim_CSX = [mfilename '.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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% write openEMS compatible xml-file
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WriteOpenEMS( [Sim_Path '/' Sim_CSX], FDTD, CSX );
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% show the structure
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CSXGeomPlot( [Sim_Path '/' Sim_CSX] );
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% run openEMS
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RunOpenEMS( Sim_Path, Sim_CSX);
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%% postprocessing & do the plots
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freq = linspace( max([1e9,f0-fc]), f0+fc, 501 );
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port = calcPort(port, Sim_Path, freq);
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Zin = port.uf.tot ./ port.if.tot;
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s11 = port.uf.ref ./ port.uf.inc;
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P_in = 0.5*real(port.uf.tot .* conj(port.if.tot)); % antenna feed power
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% plot feed point impedance
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figure
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plot( freq/1e6, real(Zin), 'k-', 'Linewidth', 2 );
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hold on
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grid on
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plot( freq/1e6, imag(Zin), 'r--', 'Linewidth', 2 );
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title( 'feed point impedance' );
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xlabel( 'frequency f / MHz' );
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ylabel( 'impedance Z_{in} / Ohm' );
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legend( 'real', 'imag' );
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% plot reflection coefficient S11
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figure
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plot( freq/1e6, 20*log10(abs(s11)), 'k-', 'Linewidth', 2 );
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grid on
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title( 'reflection coefficient S_{11}' );
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xlabel( 'frequency f / MHz' );
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ylabel( 'reflection coefficient |S_{11}|' );
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drawnow
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%find resonance frequncy from s11
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f_res_ind = find(s11==min(s11));
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f_res = freq(f_res_ind);
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%%
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disp('dumping resonant current distribution to vtk file, use Paraview to visualize');
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ConvertHDF5_VTK([Sim_Path '/Jt_patch.h5'],[Sim_Path '/Jf_patch'],'Frequency',f_res,'FieldName','J-Field');
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%% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% calculate the far field at phi=0 degree
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nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, [-180:2:180]*pi/180, 0,'Center',[patch.radius+substrate.thickness 0 0]*unit, 'Outfile','pattern_phi_0.h5');
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% normalized directivity as polar plot
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figure
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polarFF(nf2ff,'xaxis','theta','param',1,'normalize',1)
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% calculate the far field at phi=0 degree
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nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, pi/2, (-180:2:180)*pi/180,'Center',[patch.radius+substrate.thickness 0 0]*unit, 'Outfile','pattern_theta_90.h5');
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% normalized directivity as polar plot
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figure
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polarFF(nf2ff,'xaxis','phi','param',1,'normalize',1)
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% display power and directivity
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disp( ['radiated power: Prad = ' num2str(nf2ff.Prad) ' Watt']);
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disp( ['directivity: Dmax = ' num2str(nf2ff.Dmax) ' (' num2str(10*log10(nf2ff.Dmax)) ' dBi)'] );
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disp( ['efficiency: nu_rad = ' num2str(100*nf2ff.Prad./real(P_in(f_res_ind))) ' %']);
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drawnow
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%%
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disp( 'calculating 3D far field pattern and dumping to vtk (use Paraview to visualize)...' );
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thetaRange = (0:2:180);
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phiRange = (0:2:360) - 180;
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nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, thetaRange*pi/180, phiRange*pi/180,'Verbose',1,'Outfile','3D_Pattern.h5','Center',[patch.radius+substrate.thickness 0 0]*unit);
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figure
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plotFF3D(nf2ff,'logscale',-20);
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