% % Tutorials / bent patch antenna % % Describtion at: % http://openems.de/index.php/Tutorial:_Bent_Patch_Antenna % % Tested with % - Matlab 2011a / Octave 3.6.4 % - openEMS v0.0.31 % % (C) 2013 Thorsten Liebig 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);