% % Tutorials / simple patch antenna % % Describtion at: % http://openems.de/index.php/Tutorial:_Simple_Patch_Antenna % % Tested with % - Matlab 2013a / Octave 4.0 % - openEMS v0.0.33 % % (C) 2010-2015 Thorsten Liebig close all clear clc %% setup the simulation physical_constants; unit = 1e-3; % all length in mm % patch width in x-direction patch.width = 32; % resonant length % patch length in y-direction patch.length = 40; %substrate setup substrate.epsR = 3.38; substrate.kappa = 1e-3 * 2*pi*2.45e9 * EPS0*substrate.epsR; substrate.width = 60; substrate.length = 60; substrate.thickness = 1.524; substrate.cells = 4; %setup feeding feed.pos = -6; %feeding position in x-direction feed.R = 50; %feed resistance % size of the simulation box SimBox = [200 200 150]; %% setup FDTD parameter & excitation function f0 = 2e9; % center frequency fc = 1e9; % 20 dB corner frequency FDTD = InitFDTD( 'NrTs', 30000 ); FDTD = SetGaussExcite( FDTD, f0, fc ); BC = {'MUR' 'MUR' 'MUR' 'MUR' 'MUR' 'MUR'}; % boundary conditions FDTD = SetBoundaryCond( FDTD, BC ); %% setup CSXCAD geometry & mesh CSX = InitCSX(); %initialize the mesh with the "air-box" dimensions mesh.x = [-SimBox(1)/2 SimBox(1)/2]; mesh.y = [-SimBox(2)/2 SimBox(2)/2]; mesh.z = [-SimBox(3)/3 SimBox(3)*2/3]; %% create patch CSX = AddMetal( CSX, 'patch' ); % create a perfect electric conductor (PEC) start = [-patch.width/2 -patch.length/2 substrate.thickness]; stop = [ patch.width/2 patch.length/2 substrate.thickness]; 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 = [-substrate.width/2 -substrate.length/2 0]; stop = [ substrate.width/2 substrate.length/2 substrate.thickness]; CSX = AddBox( CSX, 'substrate', 0, start, stop ); % add extra cells to discretize the substrate thickness mesh.z = [linspace(0,substrate.thickness,substrate.cells+1) mesh.z]; %% create ground (same size as substrate) CSX = AddMetal( CSX, 'gnd' ); % create a perfect electric conductor (PEC) start(3)=0; stop(3) =0; CSX = AddBox(CSX,'gnd',10,start,stop); %% apply the excitation & resist as a current source start = [feed.pos 0 0]; stop = [feed.pos 0 substrate.thickness]; [CSX port] = AddLumpedPort(CSX, 5 ,1 ,feed.R, start, stop, [0 0 1], true); %% finalize the mesh % detect all edges except of the patch mesh = DetectEdges(CSX, mesh,'ExcludeProperty','patch'); % detect and set a special 2D metal edge mesh for the patch mesh = DetectEdges(CSX, mesh,'SetProperty','patch','2D_Metal_Edge_Res', c0/(f0+fc)/unit/50); % generate a smooth mesh with max. cell size: lambda_min / 20 mesh = SmoothMesh(mesh, c0/(f0+fc)/unit/20); CSX = DefineRectGrid(CSX, unit, mesh); %% add a nf2ff calc box; size is 3 cells away from MUR boundary condition start = [mesh.x(4) mesh.y(4) mesh.z(4)]; stop = [mesh.x(end-3) mesh.y(end-3) mesh.z(end-3)]; [CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', start, stop); %% prepare simulation folder Sim_Path = 'tmp_Patch_Ant'; Sim_CSX = 'patch_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( 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; % 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 %% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %find resonance frequncy from s11 f_res_ind = find(s11==min(s11)); f_res = freq(f_res_ind); % calculate the far field at phi=0 degrees and at phi=90 degrees disp( 'calculating far field at phi=[0 90] deg...' ); nf2ff = CalcNF2FF(nf2ff, Sim_Path, f_res, [-180:2:180]*pi/180, [0 90]*pi/180); % 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./port.P_inc(f_res_ind)) ' %']); % normalized directivity as polar plot figure polarFF(nf2ff,'xaxis','theta','param',[1 2],'normalize',1) % log-scale directivity plot figure plotFFdB(nf2ff,'xaxis','theta','param',[1 2]) % conventional plot approach % plot( nf2ff.theta*180/pi, 20*log10(nf2ff.E_norm{1}/max(nf2ff.E_norm{1}(:)))+10*log10(nf2ff.Dmax)); 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'); figure plotFF3D(nf2ff,'logscale',-20); E_far_normalized = nf2ff.E_norm{1} / max(nf2ff.E_norm{1}(:)) * nf2ff.Dmax; DumpFF2VTK([Sim_Path '/3D_Pattern.vtk'],E_far_normalized,thetaRange,phiRange,'scale',1e-3);