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+%
+% Tutorials / conical horn antenna
+%
+% Describtion at:
+% http://openems.de/index.php/Tutorial:_Conical_Horn_Antenna
+%
+% Tested with
+%  - Matlab 2011a / Octave 4.0
+%  - openEMS v0.0.33
+%
+% (C) 2011-2015 Thorsten Liebig <thorsten.liebig@uni-due.de>
+
+close all
+clear
+clc
+
+%% setup the simulation
+physical_constants;
+unit = 1e-3; % all length in mm
+
+% horn radius
+horn.radius  = 20;
+% horn length in z-direction
+horn.length = 50;
+
+horn.feed_length = 50;
+
+horn.thickness = 2;
+
+% horn opening angle
+horn.angle = 20*pi/180;
+
+% size of the simulation box
+SimBox = [100 100 100]*2;
+
+% frequency range of interest
+f_start =  10e9;
+f_stop  =  20e9;
+
+% frequency of interest
+f0 = 15e9;
+
+%% setup FDTD parameter & excitation function
+FDTD = InitFDTD( 'NrTS', 30000, 'EndCriteria', 1e-4 );
+FDTD = SetGaussExcite(FDTD,0.5*(f_start+f_stop),0.5*(f_stop-f_start));
+BC = {'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8' 'PML_8'}; % boundary conditions
+FDTD = SetBoundaryCond( FDTD, BC );
+
+%% setup CSXCAD geometry & mesh
+% currently, openEMS cannot automatically generate a mesh
+max_res = c0 / (f_stop) / unit / 15; % cell size: lambda/20
+CSX = InitCSX();
+
+%create fixed lines for the simulation box, substrate and port
+mesh.x = [-SimBox(1)/2 -horn.radius 0 horn.radius SimBox(1)/2];
+mesh.x = SmoothMeshLines( mesh.x, max_res, 1.4); % create a smooth mesh between specified fixed mesh lines
+
+mesh.y = mesh.x;
+
+%create fixed lines for the simulation box and given number of lines inside the substrate
+mesh.z = [-horn.feed_length 0 SimBox(3) ];
+mesh.z = SmoothMeshLines( mesh.z, max_res, 1.4 );
+
+CSX = DefineRectGrid( CSX, unit, mesh );
+
+%% create horn
+% horn + waveguide, defined by a rotational polygon
+CSX = AddMetal(CSX, 'Conical_Horn');
+p(1,1) = horn.radius+horn.thickness;   % x-coord point 1
+p(2,1) = -horn.feed_length;     % z-coord point 1
+p(1,end+1) = horn.radius+horn.thickness;   % x-coord point 1
+p(2,end) = 0;     % z-coord point 1
+p(1,end+1) = horn.radius+horn.thickness + sin(horn.angle)*horn.length; % x-coord point 2
+p(2,end) = horn.length; % y-coord point 2
+p(1,end+1) = horn.radius + sin(horn.angle)*horn.length; % x-coord point 2
+p(2,end) = horn.length; % y-coord point 2
+p(1,end+1) = horn.radius;  % x-coord point 1
+p(2,end) = 0;     % z-coord point 1
+p(1,end+1) = horn.radius;   % x-coord point 1
+p(2,end) = -horn.feed_length;     % z-coord point 1
+CSX = AddRotPoly(CSX,'Conical_Horn',10,'x',p,'z');
+
+% horn aperture
+A = pi*((horn.radius + sin(horn.angle)*horn.length)*unit)^2;
+
+%% apply the excitation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+start=[-horn.radius -horn.radius mesh.z(10) ];
+stop =[+horn.radius +horn.radius mesh.z(1)+horn.feed_length/2 ];
+[CSX, port] = AddCircWaveGuidePort( CSX, 0, 1, start, stop, horn.radius*unit, 'TE11', 0, 1);
+
+%%
+CSX = AddDump(CSX,'Exc_dump');
+start=[-horn.radius -horn.radius mesh.z(8)];
+stop =[+horn.radius +horn.radius mesh.z(8)];
+CSX = AddBox(CSX,'Exc_dump',0,start,stop);
+
+%% nf2ff calc
+start = [mesh.x(9) mesh.y(9) mesh.z(9)];
+stop  = [mesh.x(end-8) mesh.y(end-8) mesh.z(end-8)];
+[CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', start, stop, 'Directions', [1 1 1 1 0 1]);
+
+%% prepare simulation folder
+Sim_Path = 'tmp';
+Sim_CSX = 'horn_ant.xml';
+
+[status, message, messageid] = rmdir( Sim_Path, 's' ); % clear previous directory
+[status, message, messageid] = mkdir( Sim_Path ); % create empty simulation folder
+
+%% write openEMS compatible xml-file
+WriteOpenEMS( [Sim_Path '/' Sim_CSX], FDTD, CSX );
+
+%% show the structure
+CSXGeomPlot( [Sim_Path '/' Sim_CSX] );
+
+%% run openEMS
+RunOpenEMS( Sim_Path, Sim_CSX);
+
+%% postprocessing & do the plots
+freq = linspace(f_start,f_stop,201);
+
+port = calcPort(port, Sim_Path, freq);
+
+Zin = port.uf.tot ./ port.if.tot;
+s11 = port.uf.ref ./ port.uf.inc;
+
+% plot reflection coefficient S11
+figure
+plot( freq/1e9, 20*log10(abs(s11)), 'k-', 'Linewidth', 2 );
+ylim([-60 0]);
+grid on
+title( 'reflection coefficient S_{11}' );
+xlabel( 'frequency f / GHz' );
+ylabel( 'reflection coefficient |S_{11}|' );
+
+drawnow
+
+%% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+% calculate the far field at phi=0 degrees and at phi=90 degrees
+thetaRange = (0:2:359) - 180;
+disp( 'calculating far field at phi=[0 90] deg...' );
+nf2ff = CalcNF2FF(nf2ff, Sim_Path, f0, thetaRange*pi/180, [0 90]*pi/180);
+
+Dlog=10*log10(nf2ff.Dmax);
+G_a = 4*pi*A/(c0/f0)^2;
+e_a = nf2ff.Dmax/G_a;
+
+% display some antenna parameter
+disp( ['radiated power: Prad = ' num2str(nf2ff.Prad) ' Watt']);
+disp( ['directivity: Dmax = ' num2str(Dlog) ' dBi'] );
+disp( ['aperture efficiency: e_a = ' num2str(e_a*100) '%'] );
+
+%%
+% normalized directivity
+figure
+plotFFdB(nf2ff,'xaxis','theta','param',[1 2]);
+drawnow
+%   D_log = 20*log10(nf2ff.E_norm{1}/max(max(nf2ff.E_norm{1})));
+%   D_log = D_log + 10*log10(nf2ff.Dmax);
+%   plot( nf2ff.theta, D_log(:,1) ,'k-', nf2ff.theta, D_log(:,2) ,'r-' );
+
+% polar plot
+figure
+polarFF(nf2ff,'xaxis','theta','param',[1 2],'logscale',[-40 20], 'xtics', 12);
+drawnow
+%   polar( nf2ff.theta, nf2ff.E_norm{1}(:,1) )
+
+%% calculate 3D pattern
+phiRange = sort( unique( [-180:5:-100 -100:2.5:-50 -50:1:50 50:2.5:100 100:5:180] ) );
+thetaRange = sort( unique([ 0:1:50 50:2.:100 100:5:180 ]));
+
+disp( 'calculating 3D far field...' );
+nf2ff = CalcNF2FF(nf2ff, Sim_Path, f0, thetaRange*pi/180, phiRange*pi/180, 'Verbose',2,'Outfile','nf2ff_3D.h5');
+
+figure
+plotFF3D(nf2ff);        % plot liear 3D far field
+
+%%
+E_far_normalized = nf2ff.E_norm{1}/max(nf2ff.E_norm{1}(:));
+DumpFF2VTK([Sim_Path '/Conical_Horn_Pattern.vtk'],E_far_normalized,thetaRange,phiRange,'scale',1e-3);