140 lines
3.7 KiB
Matlab
140 lines
3.7 KiB
Matlab
%
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% Tutorials / bi-quad antenna
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%
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% Tested with
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% - Octave 3.8.1
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% - openEMS v0.0.32
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%
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% (C) 2011-2014 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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quad_size = 110;
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port_length = 10;
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quad_mesh = 5;
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Feed_R = 75;
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% size of the simulation box
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SimBox = [800 800 400];
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% frequency range of interest
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f_start = 400e6;
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f_stop = 1000e6;
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% frequency of interest
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f0 = 700e6;
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freq = linspace(f_start,f_stop,201);
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%% setup FDTD parameter & excitation function
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FDTD = InitFDTD( 'endCriteria', 1e-4 );
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FDTD = SetGaussExcite(FDTD,0.5*(f_start+f_stop),0.5*(f_stop-f_start));
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BC = {'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8'}; % 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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%create fixed lines for the antenna outline and port
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mesh.x = [-quad_size*sqrt(2) -quad_size/sqrt(2) 0 quad_size/sqrt(2) quad_size*sqrt(2)];
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mesh.y = [-quad_size/sqrt(2) -port_length/2 0 port_length/2 quad_size/sqrt(2)];
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mesh.z = [0];
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mesh = SmoothMesh(mesh, quad_mesh, 1.3);
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% add air box
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mesh.x = [mesh.x -SimBox(1)/2 SimBox(1)/2];
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mesh.y = [mesh.y -SimBox(2)/2 SimBox(2)/2];
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mesh.z = [-SimBox(3)/2 0 SimBox(3)/2];
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max_res = c0 / (f_stop) / unit / 20; % cell size: lambda/20
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mesh = SmoothMesh(mesh, max_res, 1.4);
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CSX = DefineRectGrid( CSX, unit, mesh );
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%% create bi-quad
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points(1,1) = 0;
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points(2,1) = port_length/2;
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points(3,1) = 0;
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points(1,end+1) = quad_size/sqrt(2);
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points(2,end) = quad_size/sqrt(2);
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points(1,end+1) = quad_size*sqrt(2);
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points(2,end) = 0;
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points(1,end+1) = quad_size/sqrt(2);
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points(2,end) = -quad_size/sqrt(2);
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points(1,end+1) = 0;
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points(2,end) = -port_length/2;
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points(1,end+1) = -quad_size/sqrt(2);
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points(2,end) = -quad_size/sqrt(2);
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points(1,end+1) = -quad_size*sqrt(2);
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points(2,end) = 0;
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points(1,end+1) = -quad_size/sqrt(2);
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points(2,end) = quad_size/sqrt(2);
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points(1,end+1) = 0;
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points(2,end) = port_length/2;
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% create a thin metal wire...
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CSX = AddMetal(CSX,'metal'); %create PEC with propName 'metal'
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CSX = AddCurve(CSX,'metal',10, points);
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%% apply the excitation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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start = [0 -port_length/2 0];
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stop = [0 port_length/2 0];
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[CSX port] = AddLumpedPort(CSX,10,0,Feed_R,start,stop,[0 1 0], true);
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%% nf2ff calc
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start = [mesh.x(9) mesh.y(9) mesh.z(9)];
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stop = [mesh.x(end-8) mesh.y(end-8) mesh.z(end-8)];
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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';
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Sim_CSX = 'bi_quad_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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port = calcPort(port, Sim_Path, freq);
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s11 = port.uf.ref ./ port.uf.inc;
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% plot reflection coefficient S11
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figure
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plot( freq/1e9, 20*log10(abs(s11)), 'k-', 'Linewidth', 2 );
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ylim([-30 0]);
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grid on
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title( 'reflection coefficient S_{11}' );
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xlabel( 'frequency f / GHz' );
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ylabel( 'reflection coefficient |S_{11}|' );
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%% calculate 3D far field pattern
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phiRange = -180:2.5:180;
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thetaRange = 0:2.5:180;
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nf2ff = CalcNF2FF(nf2ff, Sim_Path, f0, thetaRange*pi/180, phiRange*pi/180);
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disp( ['directivity: Dmax = ' num2str(10*log10(nf2ff.Dmax)) ' dBi'] );
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% plot far-field pattern with Matlab
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figure
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plotFF3D(nf2ff, 'logscale', -20)
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%%
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disp( 'Dumping far-field pattern to vtk (use Paraview to visualize)...' );
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DumpFF2VTK('Bi_Quad_Pattern.vtk', nf2ff.E_norm{1} / max(nf2ff.E_norm{1}(:)) * nf2ff.Dmax, thetaRange, phiRange, 'scale', 0.05);
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