% % EXAMPLE / antennas / inverted-f antenna (ifa) 2.4GHz % % This example demonstrates how to: % - calculate the reflection coefficient of an ifa % - calculate farfield of an ifa % % Tested with % - Octave 3.7.5 % - openEMS v0.0.30+ (git 10.07.2013) % % (C) 2013 Stefan Mahr close all clear clc %% setup the simulation physical_constants; unit = 1e-3; % all length in mm %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % substrate.width % _______________________________________________ __ substrate. % | A ifa.l |\ __ thickness % | |ifa.e __________________________ | | % | | | ___ _________________| w2 | | % | | ifa.h | | || | | % |_V_____________|___|___||______________________| | % | .w1 .wf\ | | % | |.fp| \ | | % | | feed point | | % | | | | substrate.length % |<- substrate.width/2 ->| | | % | | | % |_______________________________________________| | % \_______________________________________________\| % % Note: It's not checked whether your settings make sense, so check % graphical output carefully. % substrate.width = 80; % width of substrate substrate.length = 80; % length of substrate substrate.thickness = 1.5; % thickness of substrate substrate.cells = 4; % use 4 cells for meshing substrate ifa.h = 8; % height of short circuit stub ifa.l = 22.5; % length of radiating element ifa.w1 = 4; % width of short circuit stub ifa.w2 = 2.5; % width of radiating element ifa.wf = 1; % width of feed element ifa.fp = 4; % position of feed element relative to short % circuit stub ifa.e = 10; % distance to edge % substrate setup substrate.epsR = 4.3; substrate.kappa = 1e-3 * 2*pi*2.45e9 * EPS0*substrate.epsR; %setup feeding feed.R = 50; %feed resistance %open AppCSXCAD and show ifa show = 1; %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % size of the simulation box SimBox = [substrate.width*2 substrate.length*2 150]; %% setup FDTD parameter & excitation function f0 = 2.5e9; % center frequency fc = 1e9; % 20 dB corner frequency FDTD = InitFDTD('NrTS', 60000 ); 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)/2 SimBox(3)/2]; %% 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', 1, start, stop ); % add extra cells to discretize the substrate thickness mesh.z = [linspace(0,substrate.thickness,substrate.cells+1) mesh.z]; %% create ground plane CSX = AddMetal( CSX, 'groundplane' ); % create a perfect electric conductor (PEC) start = [-substrate.width/2 -substrate.length/2 substrate.thickness]; stop = [ substrate.width/2 substrate.length/2-ifa.e substrate.thickness]; CSX = AddBox(CSX, 'groundplane', 10, start,stop); %% create ifa CSX = AddMetal( CSX, 'ifa' ); % create a perfect electric conductor (PEC) tl = [0,substrate.length/2-ifa.e,substrate.thickness]; % translate start = [0 0.5 0] + tl; stop = start + [ifa.wf ifa.h-0.5 0]; CSX = AddBox( CSX, 'ifa', 10, start, stop); % feed element start = [-ifa.fp 0 0] + tl; stop = start + [-ifa.w1 ifa.h 0]; CSX = AddBox( CSX, 'ifa', 10, start, stop); % short circuit stub start = [(-ifa.fp-ifa.w1) ifa.h 0] + tl; stop = start + [ifa.l -ifa.w2 0]; CSX = AddBox( CSX, 'ifa', 10, start, stop); % radiating element ifa_mesh = DetectEdges(CSX, [], 'SetProperty','ifa'); mesh.x = [mesh.x SmoothMeshLines(ifa_mesh.x, 0.5)]; mesh.y = [mesh.y SmoothMeshLines(ifa_mesh.y, 0.5)]; %% apply the excitation & resist as a current source start = [0 0 0] + tl; stop = start + [ifa.wf 0.5 0]; [CSX port] = AddLumpedPort(CSX, 5 ,1 ,feed.R, start, stop, [0 1 0], true); %% finalize the mesh % generate a smooth mesh with max. cell size: lambda_min / 20 mesh = DetectEdges(CSX, mesh); 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_IFA'; Sim_CSX = 'IFA.xml'; try confirm_recursive_rmdir(false,'local'); end [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 if (show == 1) CSXGeomPlot( [Sim_Path '/' Sim_CSX] ); end %% run openEMS RunOpenEMS( Sim_Path, Sim_CSX); %RunOpenEMS( Sim_Path, Sim_CSX, '--debug-PEC -v'); %% 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 = real(0.5 * 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 %% NFFF contour plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %find resonance frequency from s11 f_res_ind = find(s11==min(s11)); f_res = freq(f_res_ind); %% 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'); plotFF3D(nf2ff) % 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))) ' %']); 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,1e-3);