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%
% Tutorials / horn antenna
%
% Describtion at:
% http://openems.de/index.php/Tutorial:_Horn_Antenna
%
% Tested with
% - Matlab 2011a / Octave 3.6.4
% - openEMS v0.0.31
%
% (C) 2011,2012,2013 Thorsten Liebig <thorsten.liebig@uni-due.de>
close all
clear
clc
%% setup the simulation
physical_constants;
unit = 1e-3; % all length in mm
% horn width in x-direction
horn.width = 20;
% horn height in y-direction
horn.height = 30;
% horn length in z-direction
horn.length = 50;
horn.feed_length = 50;
horn.thickness = 2;
% horn opening angle in x, y
horn.angle = [20 20]*pi/180;
% size of the simulation box
SimBox = [200 200 200];
% frequency range of interest
f_start = 10e9;
f_stop = 20e9;
% frequency of interest
f0 = 15e9;
%waveguide TE-mode definition
TE_mode = 'TE10';
a = horn.width;
b = horn.height;
%% setup FDTD parameter & excitation function
FDTD = InitFDTD('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 -a/2 a/2 SimBox(1)/2];
mesh.x = SmoothMeshLines( mesh.x, max_res, 1.4); % create a smooth mesh between specified fixed mesh lines
mesh.y = [-SimBox(2)/2 -b/2 b/2 SimBox(2)/2];
mesh.y = SmoothMeshLines( mesh.y, max_res, 1.4 );
%create fixed lines for the simulation box and given number of lines inside the substrate
mesh.z = [-horn.feed_length 0 SimBox(3)-horn.feed_length ];
mesh.z = SmoothMeshLines( mesh.z, max_res, 1.4 );
CSX = DefineRectGrid( CSX, unit, mesh );
%% create horn
% horn feed rect waveguide
CSX = AddMetal(CSX, 'horn');
start = [-a/2-horn.thickness -b/2 mesh.z(1)];
stop = [-a/2 b/2 0];
CSX = AddBox(CSX,'horn',10,start,stop);
start = [a/2+horn.thickness -b/2 mesh.z(1)];
stop = [a/2 b/2 0];
CSX = AddBox(CSX,'horn',10,start,stop);
start = [-a/2-horn.thickness b/2+horn.thickness mesh.z(1)];
stop = [ a/2+horn.thickness b/2 0];
CSX = AddBox(CSX,'horn',10,start,stop);
start = [-a/2-horn.thickness -b/2-horn.thickness mesh.z(1)];
stop = [ a/2+horn.thickness -b/2 0];
CSX = AddBox(CSX,'horn',10,start,stop);
% horn opening
p(2,1) = a/2;
p(1,1) = 0;
p(2,2) = a/2 + sin(horn.angle(1))*horn.length;
p(1,2) = horn.length;
p(2,3) = -a/2 - sin(horn.angle(1))*horn.length;
p(1,3) = horn.length;
p(2,4) = -a/2;
p(1,4) = 0;
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']});
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']});
p(1,1) = b/2+horn.thickness;
p(2,1) = 0;
p(1,2) = b/2+horn.thickness + sin(horn.angle(2))*horn.length;
p(2,2) = horn.length;
p(1,3) = -b/2-horn.thickness - sin(horn.angle(2))*horn.length;
p(2,3) = horn.length;
p(1,4) = -b/2-horn.thickness;
p(2,4) = 0;
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']});
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']});
% horn aperture
A = (a + 2*sin(horn.angle(1))*horn.length)*unit * (b + 2*sin(horn.angle(2))*horn.length)*unit;
%% apply the excitation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
start=[-a/2 -b/2 mesh.z(8) ];
stop =[ a/2 b/2 mesh.z(1)+horn.feed_length/2 ];
[CSX, port] = AddRectWaveGuidePort( CSX, 0, 1, start, stop, 2, a*unit, b*unit, TE_mode, 1);
%% 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_Horn_Antenna';
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( 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);
%%
E_far_normalized = nf2ff.E_norm{1}/max(nf2ff.E_norm{1}(:));
DumpFF2VTK([Sim_Path '/Horn_Pattern.vtk'],E_far_normalized,thetaRange,phiRange,'scale',1e-3);
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