175 lines
5.3 KiB
Matlab
175 lines
5.3 KiB
Matlab
%
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% Tutorials / simple patch antenna
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%
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% Describtion at:
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% http://openems.de/index.php/Tutorial:_Simple_Patch_Antenna
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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 v0.0.27
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%
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% (C) 2010-2012 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 x-direction
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patch.width = 30; % resonant length
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% patch length in y-direction
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patch.length = 40;
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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 = 60;
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substrate.length = 60;
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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 = -6; %feeding position in x-direction
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feed.R = 50; %feed resistance
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% size of the simulation box
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SimBox = [200 200 150];
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%% setup FDTD parameter & excitation function
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f0 = 2e9; % center frequency
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fc = 1e9; % 20 dB corner frequency
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FDTD = InitFDTD( 'NrTs', 30000 );
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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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CSX = InitCSX();
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%initialize the mesh with the "air-box" dimensions
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mesh.x = [-SimBox(1)/2 SimBox(1)/2];
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mesh.y = [-SimBox(2)/2 SimBox(2)/2];
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mesh.z = [-SimBox(3)/3 SimBox(3)*2/3];
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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.width/2 -patch.length/2 substrate.thickness];
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stop = [ patch.width/2 patch.length/2 substrate.thickness];
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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 = [-substrate.width/2 -substrate.length/2 0];
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stop = [ substrate.width/2 substrate.length/2 substrate.thickness];
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CSX = AddBox( CSX, 'substrate', 0, start, stop );
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% add extra cells to discretize the substrate thickness
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mesh.z = [linspace(0,substrate.thickness,substrate.cells+1) mesh.z];
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%% create ground (same size as substrate)
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CSX = AddMetal( CSX, 'gnd' ); % create a perfect electric conductor (PEC)
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start(3)=0;
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stop(3) =0;
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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 = [feed.pos 0 0];
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stop = [feed.pos 0 substrate.thickness];
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[CSX port] = AddLumpedPort(CSX, 5 ,1 ,feed.R, start, stop, [0 0 1], true);
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%% finalize the mesh
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% generate a smooth mesh with max. cell size: lambda_min / 20
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mesh = DetectEdges(CSX, mesh);
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mesh = SmoothMesh(mesh, c0 / (f0+fc) / unit / 20);
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CSX = DefineRectGrid(CSX, unit, mesh);
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%% add a nf2ff calc box; size is 3 cells away from MUR boundary condition
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start = [mesh.x(4) mesh.y(4) mesh.z(4)];
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stop = [mesh.x(end-3) mesh.y(end-3) mesh.z(end-3)];
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[CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', start, stop);
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%% prepare simulation folder
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Sim_Path = 'tmp_Patch_Ant';
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Sim_CSX = 'patch_ant.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 * port.uf.inc .* conj( port.if.inc ); % 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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%% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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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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% calculate the far field at phi=0 degrees and at phi=90 degrees
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disp( 'calculating far field at phi=[0 90] deg...' );
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nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, [-180:2:180]*pi/180, [0 90]*pi/180);
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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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% normalized directivity
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figure
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plotFFdB(nf2ff,'xaxis','theta','param',[1 2])
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% D_log = 20*log10(nf2ff.E_norm{1}/max(max(nf2ff.E_norm{1})));
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% D_log = D_log + 10*log10(nf2ff.Dmax);
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% plot( nf2ff.theta, D_log(:,1) ,'k-' );
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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');
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figure
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plotFF3D(nf2ff);
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E_far_normalized = nf2ff.E_norm{1} / max(nf2ff.E_norm{1}(:)) * nf2ff.Dmax;
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DumpFF2VTK([Sim_Path '/3D_Pattern.vtk'],E_far_normalized,thetaRange,phiRange,'scale',1e-3);
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