194 lines
6.1 KiB
Matlab
194 lines
6.1 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 v0.0.26
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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.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 = [200 200 100];
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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( 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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% currently, openEMS cannot automatically generate a mesh
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max_res = c0 / (f0+fc) / unit / 20; % cell size: lambda/20
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CSX = InitCSX();
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%create fixed lines for the simulation box, substrate and port
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mesh.x = [-SimBox(1)/2 SimBox(1)/2 -substrate.width/2 substrate.width/2 -patch.width/2 patch.width/2 feed.pos];
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mesh.x = SmoothMeshLines( mesh.x, max_res, 1.4); % create a smooth mesh between specified fixed mesh lines
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mesh.y = [-SimBox(2)/2 SimBox(2)/2 -substrate.length/2 substrate.length/2 -feed.width/2 feed.width/2 -patch.length/2 patch.length/2];
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mesh.y = SmoothMeshLines( mesh.y, max_res, 1.4 );
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%create fixed lines for the simulation box and given number of lines inside the substrate
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mesh.z = [-SimBox(3)/2 linspace(0,substrate.thickness,substrate.cells) SimBox(3)/2 ];
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mesh.z = SmoothMeshLines( mesh.z, max_res, 1.4 );
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CSX = DefineRectGrid( CSX, unit, mesh );
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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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%% 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-.1 -feed.width/2 0];
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stop = [feed.pos+.1 +feed.width/2 substrate.thickness];
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[CSX] = AddLumpedPort(CSX, 5 ,1 ,feed.R, start, stop, [0 0 1], 'excite');
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%%nf2ff calc
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SimBox = SimBox - max_res * 4; %reduced SimBox size for nf2ff box
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[CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', -SimBox/2, SimBox/2);
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%% prepare simulation folder
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Sim_Path = 'tmp';
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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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U = ReadUI( {'port_ut1','et'}, 'tmp/', freq ); % time domain/freq domain voltage
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I = ReadUI( 'port_it1', 'tmp/', freq ); % time domain/freq domain current (half time step is corrected)
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% plot feed point impedance
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figure
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Zin = U.FD{1}.val ./ I.FD{1}.val;
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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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uf_inc = 0.5*(U.FD{1}.val + I.FD{1}.val * 50);
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if_inc = 0.5*(I.FD{1}.val + U.FD{1}.val / 50);
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uf_ref = U.FD{1}.val - uf_inc;
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if_ref = if_inc - I.FD{1}.val;
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s11 = uf_ref ./ uf_inc;
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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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P_in = 0.5*U.FD{1}.val .* conj( I.FD{1}.val ); % antenna feed power
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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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thetaRange = (0:2:359) - 180;
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r = 1; % evaluate fields at radius r
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disp( 'calculating far field at phi=[0 90] deg...' );
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[E_far_theta,E_far_phi,Prad,Dmax] = AnalyzeNF2FF( Sim_Path, nf2ff, f_res, thetaRange, [0 90], r );
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Dlog=10*log10(Dmax);
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% display power and directivity
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disp( ['radiated power: Prad = ' num2str(Prad) ' Watt']);
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disp( ['directivity: Dmax = ' num2str(Dlog) ' dBi'] );
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disp( ['efficiency: nu_rad = ' num2str(100*Prad./real(P_in(f_res_ind))) ' %']);
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% calculate the e-field magnitude for phi = 0 deg
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E_phi0_far = zeros(1,numel(thetaRange));
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for n=1:numel(thetaRange)
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E_phi0_far(n) = norm( [E_far_theta(n,1) E_far_phi(n,1)] );
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end
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E_phi0_far_log = 20*log10(abs(E_phi0_far)/max(abs(E_phi0_far)));
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E_phi0_far_log = E_phi0_far_log + Dlog;
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% display polar plot
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figure
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plot( thetaRange, E_phi0_far_log ,'k-' );
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xlabel( 'theta (deg)' );
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ylabel( 'directivity (dBi)');
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grid on;
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hold on;
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% calculate the e-field magnitude for phi = 90 deg
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E_phi90_far = zeros(1,numel(thetaRange));
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for n=1:numel(thetaRange)
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E_phi90_far(n) = norm([E_far_theta(n,2) E_far_phi(n,2)]);
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end
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E_phi90_far_log = 20*log10(abs(E_phi90_far)/max(abs(E_phi90_far)));
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E_phi90_far_log = E_phi90_far_log + Dlog;
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% display polar plot
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plot( thetaRange, E_phi90_far_log ,'r-' );
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legend('phi=0','phi=90')
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