206 lines
7.1 KiB
Matlab
206 lines
7.1 KiB
Matlab
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% EXAMPLE / antennas / inverted-f antenna (ifa) 2.4GHz
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%
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% This example demonstrates how to:
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% - calculate the reflection coefficient of an ifa
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% - calculate farfield of an ifa
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%
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% Tested with
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% - Octave 3.7.5
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% - openEMS v0.0.30+ (git 10.07.2013)
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%
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% (C) 2013 Stefan Mahr <dac922@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-3; % all length in mm
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% substrate.width
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% _______________________________________________ __ substrate.
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% | A ifa.l |\ __ thickness
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% | |ifa.e __________________________ | |
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% | | | ___ _________________| w2 | |
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% | | ifa.h | | || | |
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% |_V_____________|___|___||______________________| |
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% | .w1 .wf\ | |
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% | |.fp| \ | |
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% | | feed point | |
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% | | | | substrate.length
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% |<- substrate.width/2 ->| | |
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% | | |
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% |_______________________________________________| |
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% \_______________________________________________\|
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%
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% Note: It's not checked whether your settings make sense, so check
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% graphical output carefully.
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%
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substrate.width = 80; % width of substrate
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substrate.length = 80; % length of substrate
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substrate.thickness = 1.5; % thickness of substrate
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substrate.cells = 4; % use 4 cells for meshing substrate
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ifa.h = 8; % height of short circuit stub
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ifa.l = 22.5; % length of radiating element
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ifa.w1 = 4; % width of short circuit stub
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ifa.w2 = 2.5; % width of radiating element
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ifa.wf = 1; % width of feed element
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ifa.fp = 4; % position of feed element relative to short
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% circuit stub
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ifa.e = 10; % distance to edge
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% substrate setup
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substrate.epsR = 4.3;
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substrate.kappa = 1e-3 * 2*pi*2.45e9 * EPS0*substrate.epsR;
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%setup feeding
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feed.R = 50; %feed resistance
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%open AppCSXCAD and show ifa
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show = 1;
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% size of the simulation box
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SimBox = [substrate.width*2 substrate.length*2 150];
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%% setup FDTD parameter & excitation function
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f0 = 2.5e9; % center frequency
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fc = 1e9; % 20 dB corner frequency
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FDTD = InitFDTD('NrTS', 60000 );
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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)/2 SimBox(3)/2];
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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', 1, 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 plane
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CSX = AddMetal( CSX, 'groundplane' ); % create a perfect electric conductor (PEC)
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start = [-substrate.width/2 -substrate.length/2 substrate.thickness];
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stop = [ substrate.width/2 substrate.length/2-ifa.e substrate.thickness];
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CSX = AddBox(CSX, 'groundplane', 10, start,stop);
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%% create ifa
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CSX = AddMetal( CSX, 'ifa' ); % create a perfect electric conductor (PEC)
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tl = [0,substrate.length/2-ifa.e,substrate.thickness]; % translate
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start = [0 0.5 0] + tl;
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stop = start + [ifa.wf ifa.h-0.5 0];
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CSX = AddBox( CSX, 'ifa', 10, start, stop); % feed element
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start = [-ifa.fp 0 0] + tl;
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stop = start + [-ifa.w1 ifa.h 0];
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CSX = AddBox( CSX, 'ifa', 10, start, stop); % short circuit stub
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start = [(-ifa.fp-ifa.w1) ifa.h 0] + tl;
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stop = start + [ifa.l -ifa.w2 0];
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CSX = AddBox( CSX, 'ifa', 10, start, stop); % radiating element
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ifa_mesh = DetectEdges(CSX, [], 'SetProperty','ifa');
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mesh.x = [mesh.x SmoothMeshLines(ifa_mesh.x, 0.5)];
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mesh.y = [mesh.y SmoothMeshLines(ifa_mesh.y, 0.5)];
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%% apply the excitation & resist as a current source
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start = [0 0 0] + tl;
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stop = start + [ifa.wf 0.5 0];
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[CSX port] = AddLumpedPort(CSX, 5 ,1 ,feed.R, start, stop, [0 1 0], 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_IFA';
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Sim_CSX = 'IFA.xml';
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try confirm_recursive_rmdir(false,'local'); end
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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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if (show == 1)
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CSXGeomPlot( [Sim_Path '/' Sim_CSX] );
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end
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%% run openEMS
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RunOpenEMS( Sim_Path, Sim_CSX); %RunOpenEMS( Sim_Path, Sim_CSX, '--debug-PEC -v');
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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 = real(0.5 * 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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%% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%find resonance frequency 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( '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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plotFF3D(nf2ff)
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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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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,1e-3);
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