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%
% Tutorials / bent patch antenna
%
% Describtion at:
% http://openems.de/index.php/Tutorial:_Bent_Patch_Antenna
%
% Tested with
% - Matlab 2011a / Octave 4.0
% - openEMS v0.0.33
%
% (C) 2013-2015 Thorsten Liebig <thorsten.liebig@uni-due.de>
close all
clear
clc
%% setup the simulation
physical_constants;
unit = 1e-3; % all length in mm
% patch width in alpha-direction
patch.width = 32; % resonant length in alpha-direction
patch.radius = 50; % radius
patch.length = 40; % patch length in z-direction
%substrate setup
substrate.epsR = 3.38;
substrate.kappa = 1e-3 * 2*pi*2.45e9 * EPS0*substrate.epsR;
substrate.width = 80;
substrate.length = 90;
substrate.thickness = 1.524;
substrate.cells = 4;
%setup feeding
feed.pos = -5.5; %feeding position in x-direction
feed.width = 2; %feeding port width
feed.R = 50; %feed resistance
% size of the simulation box
SimBox.rad = 2*100;
SimBox.height = 1.5*200;
%% setup FDTD parameter & excitation function
FDTD = InitFDTD('CoordSystem', 1); % init a cylindrical FDTD
f0 = 2e9; % center frequency
fc = 1e9; % 20 dB corner frequency
FDTD = SetGaussExcite( FDTD, f0, fc );
BC = {'MUR' 'MUR' 'MUR' 'MUR' 'MUR' 'MUR'}; % boundary conditions
FDTD = SetBoundaryCond( FDTD, BC );
%% setup CSXCAD geometry & mesh
% init a cylindrical mesh
CSX = InitCSX('CoordSystem',1);
% calculate some width as an angle in radiant
patch_ang_width = patch.width/(patch.radius+substrate.thickness);
substr_ang_width = substrate.width/patch.radius;
feed_angle = feed.pos/patch.radius;
%% create patch
CSX = AddMetal( CSX, 'patch' ); % create a perfect electric conductor (PEC)
start = [patch.radius+substrate.thickness -patch_ang_width/2 -patch.length/2 ];
stop = [patch.radius+substrate.thickness patch_ang_width/2 patch.length/2 ];
CSX = AddBox(CSX,'patch',10,start,stop); % add a box-primitive to the metal property 'patch'
%% create substrate
CSX = AddMaterial( CSX, 'substrate' );
CSX = SetMaterialProperty( CSX, 'substrate', 'Epsilon', substrate.epsR, 'Kappa', substrate.kappa );
start = [patch.radius -substr_ang_width/2 -substrate.length/2];
stop = [patch.radius+substrate.thickness substr_ang_width/2 substrate.length/2];
CSX = AddBox( CSX, 'substrate', 0, start, stop);
%% save current density oon the patch
CSX = AddDump(CSX, 'Jt_patch','DumpType',3,'FileType',1);
start = [patch.radius+substrate.thickness -substr_ang_width/2 -substrate.length/2];
stop = [patch.radius+substrate.thickness +substr_ang_width/2 substrate.length/2];
CSX = AddBox( CSX, 'Jt_patch', 0, start, stop );
%% create ground (not really necessary, only for esthetic reasons)
CSX = AddMetal( CSX, 'gnd' ); % create a perfect electric conductor (PEC)
start = [patch.radius -substr_ang_width/2 -substrate.length/2];
stop = [patch.radius +substr_ang_width/2 +substrate.length/2];
CSX = AddBox(CSX,'gnd',10,start,stop);
%% apply the excitation & resist as a current source
start = [patch.radius feed_angle 0];
stop = [patch.radius+substrate.thickness feed_angle 0];
[CSX port] = AddLumpedPort(CSX, 50 ,1 ,feed.R, start, stop, [1 0 0], true);
%% finalize the mesh
% detect all edges
mesh = DetectEdges(CSX);
% add the simulation domain size
mesh.r = [mesh.r patch.radius+[-20 SimBox.rad]];
mesh.a = [mesh.a -0.75*pi 0.75*pi];
mesh.z = [mesh.z -SimBox.height/2 SimBox.height/2];
% add some lines for the substrate
mesh.r = [mesh.r patch.radius+linspace(0,substrate.thickness,substrate.cells)];
% generate a smooth mesh with max. cell size: lambda_min / 20
max_res = c0 / (f0+fc) / unit / 20;
max_ang = max_res/(SimBox.rad+patch.radius); % max res in radiant
mesh = SmoothMesh(mesh, [max_res max_ang max_res], 1.4);
disp(['Num of cells: ' num2str(numel(mesh.r)*numel(mesh.a)*numel(mesh.z))]);
CSX = DefineRectGrid( CSX, unit, mesh );
%% create nf2ff, keep some distance to the boundary conditions, e.g. 8 cells pml
start = [mesh.r(4) mesh.a(8) mesh.z(8)];
stop = [mesh.r(end-9) mesh.a(end-9) mesh.z(end-9)];
[CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', start, stop, 'Directions',[1 1 1 1 1 1]);
%% prepare simulation folder & run
Sim_Path = ['tmp_' mfilename];
Sim_CSX = [mfilename '.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( max([1e9,f0-fc]), f0+fc, 501 );
port = calcPort(port, Sim_Path, freq);
Zin = port.uf.tot ./ port.if.tot;
s11 = port.uf.ref ./ port.uf.inc;
P_in = 0.5*real(port.uf.tot .* conj(port.if.tot)); % antenna feed power
% plot feed point impedance
figure
plot( freq/1e6, real(Zin), 'k-', 'Linewidth', 2 );
hold on
grid on
plot( freq/1e6, imag(Zin), 'r--', 'Linewidth', 2 );
title( 'feed point impedance' );
xlabel( 'frequency f / MHz' );
ylabel( 'impedance Z_{in} / Ohm' );
legend( 'real', 'imag' );
% plot reflection coefficient S11
figure
plot( freq/1e6, 20*log10(abs(s11)), 'k-', 'Linewidth', 2 );
grid on
title( 'reflection coefficient S_{11}' );
xlabel( 'frequency f / MHz' );
ylabel( 'reflection coefficient |S_{11}|' );
drawnow
%find resonance frequncy from s11
f_res_ind = find(s11==min(s11));
f_res = freq(f_res_ind);
%%
disp('dumping resonant current distribution to vtk file, use Paraview to visualize');
ConvertHDF5_VTK([Sim_Path '/Jt_patch.h5'],[Sim_Path '/Jf_patch'],'Frequency',f_res,'FieldName','J-Field');
%% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% calculate the far field at phi=0 degree
nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, [-180:2:180]*pi/180, 0,'Center',[patch.radius+substrate.thickness 0 0]*unit, 'Outfile','pattern_phi_0.h5');
% normalized directivity as polar plot
figure
polarFF(nf2ff,'xaxis','theta','param',1,'normalize',1)
% calculate the far field at phi=0 degree
nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, pi/2, (-180:2:180)*pi/180,'Center',[patch.radius+substrate.thickness 0 0]*unit, 'Outfile','pattern_theta_90.h5');
% normalized directivity as polar plot
figure
polarFF(nf2ff,'xaxis','phi','param',1,'normalize',1)
% display power and directivity
disp( ['radiated power: Prad = ' num2str(nf2ff.Prad) ' Watt']);
disp( ['directivity: Dmax = ' num2str(nf2ff.Dmax) ' (' num2str(10*log10(nf2ff.Dmax)) ' dBi)'] );
disp( ['efficiency: nu_rad = ' num2str(100*nf2ff.Prad./real(P_in(f_res_ind))) ' %']);
drawnow
%%
disp( 'calculating 3D far field pattern and dumping to vtk (use Paraview to visualize)...' );
thetaRange = (0:2:180);
phiRange = (0:2:360) - 180;
nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, thetaRange*pi/180, phiRange*pi/180,'Verbose',1,'Outfile','3D_Pattern.h5','Center',[patch.radius+substrate.thickness 0 0]*unit);
figure
plotFF3D(nf2ff,'logscale',-20);
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