203 lines
6.4 KiB
Matlab
203 lines
6.4 KiB
Matlab
%
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% Tutorials / horn antenna
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%
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% Describtion at:
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% http://openems.de/index.php/Tutorial:_Horn_Antenna
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%
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% Tested with
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% - Matlab 2011a / Octave 3.6.4
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% - openEMS v0.0.31
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%
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% (C) 2011,2012,2013 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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% horn width in x-direction
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horn.width = 20;
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% horn height in y-direction
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horn.height = 30;
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% horn length in z-direction
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horn.length = 50;
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horn.feed_length = 50;
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horn.thickness = 2;
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% horn opening angle in x, y
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horn.angle = [20 20]*pi/180;
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% size of the simulation box
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SimBox = [200 200 200];
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% frequency range of interest
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f_start = 10e9;
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f_stop = 20e9;
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% frequency of interest
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f0 = 15e9;
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%waveguide TE-mode definition
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TE_mode = 'TE10';
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a = horn.width;
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b = horn.height;
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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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% currently, openEMS cannot automatically generate a mesh
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max_res = c0 / (f_stop) / unit / 15; % 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 -a/2 a/2 SimBox(1)/2];
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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 -b/2 b/2 SimBox(2)/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 = [-horn.feed_length 0 SimBox(3)-horn.feed_length ];
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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 horn
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% horn feed rect waveguide
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CSX = AddMetal(CSX, 'horn');
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start = [-a/2-horn.thickness -b/2 mesh.z(1)];
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stop = [-a/2 b/2 0];
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CSX = AddBox(CSX,'horn',10,start,stop);
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start = [a/2+horn.thickness -b/2 mesh.z(1)];
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stop = [a/2 b/2 0];
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CSX = AddBox(CSX,'horn',10,start,stop);
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start = [-a/2-horn.thickness b/2+horn.thickness mesh.z(1)];
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stop = [ a/2+horn.thickness b/2 0];
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CSX = AddBox(CSX,'horn',10,start,stop);
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start = [-a/2-horn.thickness -b/2-horn.thickness mesh.z(1)];
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stop = [ a/2+horn.thickness -b/2 0];
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CSX = AddBox(CSX,'horn',10,start,stop);
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% horn opening
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p(2,1) = a/2;
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p(1,1) = 0;
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p(2,2) = a/2 + sin(horn.angle(1))*horn.length;
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p(1,2) = horn.length;
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p(2,3) = -a/2 - sin(horn.angle(1))*horn.length;
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p(1,3) = horn.length;
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p(2,4) = -a/2;
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p(1,4) = 0;
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CSX = AddLinPoly( CSX, 'horn', 10, 1, -horn.thickness/2, p, horn.thickness, 'Transform', {'Rotate_X',horn.angle(2),'Translate',['0,' num2str(-b/2-horn.thickness/2) ',0']});
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CSX = AddLinPoly( CSX, 'horn', 10, 1, -horn.thickness/2, p, horn.thickness, 'Transform', {'Rotate_X',-horn.angle(2),'Translate',['0,' num2str(b/2+horn.thickness/2) ',0']});
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p(1,1) = b/2+horn.thickness;
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p(2,1) = 0;
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p(1,2) = b/2+horn.thickness + sin(horn.angle(2))*horn.length;
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p(2,2) = horn.length;
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p(1,3) = -b/2-horn.thickness - sin(horn.angle(2))*horn.length;
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p(2,3) = horn.length;
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p(1,4) = -b/2-horn.thickness;
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p(2,4) = 0;
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CSX = AddLinPoly( CSX, 'horn', 10, 0, -horn.thickness/2, p, horn.thickness, 'Transform', {'Rotate_Y',-horn.angle(2),'Translate',[ num2str(-a/2-horn.thickness/2) ',0,0']});
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CSX = AddLinPoly( CSX, 'horn', 10, 0, -horn.thickness/2, p, horn.thickness, 'Transform', {'Rotate_Y',+horn.angle(2),'Translate',[ num2str(a/2+horn.thickness/2) ',0,0']});
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% horn aperture
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A = (a + 2*sin(horn.angle(1))*horn.length)*unit * (b + 2*sin(horn.angle(2))*horn.length)*unit;
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%% apply the excitation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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start=[-a/2 -b/2 mesh.z(8) ];
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stop =[ a/2 b/2 mesh.z(1)+horn.feed_length/2 ];
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[CSX, port] = AddRectWaveGuidePort( CSX, 0, 1, start, stop, 2, a*unit, b*unit, TE_mode, 1);
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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, 'Directions', [1 1 1 1 0 1]);
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%% prepare simulation folder
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Sim_Path = 'tmp_Horn_Antenna';
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Sim_CSX = 'horn_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(f_start,f_stop,201);
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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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plot( freq/1e9, 20*log10(abs(s11)), 'k-', 'Linewidth', 2 );
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ylim([-60 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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drawnow
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%% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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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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disp( 'calculating far field at phi=[0 90] deg...' );
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nf2ff = CalcNF2FF(nf2ff, Sim_Path, f0, thetaRange*pi/180, [0 90]*pi/180);
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Dlog=10*log10(nf2ff.Dmax);
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G_a = 4*pi*A/(c0/f0)^2;
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e_a = nf2ff.Dmax/G_a;
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% display some antenna parameter
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disp( ['radiated power: Prad = ' num2str(nf2ff.Prad) ' Watt']);
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disp( ['directivity: Dmax = ' num2str(Dlog) ' dBi'] );
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disp( ['aperture efficiency: e_a = ' num2str(e_a*100) '%'] );
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%%
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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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drawnow
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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-', nf2ff.theta, D_log(:,2) ,'r-' );
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% polar plot
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figure
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polarFF(nf2ff,'xaxis','theta','param',[1 2],'logscale',[-40 20], 'xtics', 12);
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drawnow
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% polar( nf2ff.theta, nf2ff.E_norm{1}(:,1) )
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%% calculate 3D pattern
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phiRange = sort( unique( [-180:5:-100 -100:2.5:-50 -50:1:50 50:2.5:100 100:5:180] ) );
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thetaRange = sort( unique([ 0:1:50 50:2.:100 100:5:180 ]));
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disp( 'calculating 3D far field...' );
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nf2ff = CalcNF2FF(nf2ff, Sim_Path, f0, thetaRange*pi/180, phiRange*pi/180, 'Verbose',2,'Outfile','nf2ff_3D.h5');
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figure
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plotFF3D(nf2ff);
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%%
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E_far_normalized = nf2ff.E_norm{1}/max(nf2ff.E_norm{1}(:));
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DumpFF2VTK([Sim_Path '/Horn_Pattern.vtk'],E_far_normalized,thetaRange,phiRange,'scale',1e-3);
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