% % Tutorials / simple patch antenna % % Describtion at: % http://openems.de/index.php/Tutorial:_Simple_Patch_Antenna % % Tested with % - Matlab 2009b % - openEMS v0.0.23 % % (C) 2010,2011 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 = 30; % 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.width = 2; %feeding port width feed.R = 50; %feed resistance % size of the simulation box SimBox = [200 200 100]; %% setup FDTD parameter & excitation function f0 = 0e9; % center frequency fc = 3e9; % 20 dB corner frequency (in this case 0 Hz - 3e9 Hz) FDTD = InitFDTD( 30000, 1e-5 ); FDTD = SetGaussExcite( FDTD, f0, fc ); BC = {'MUR' 'MUR' 'MUR' 'MUR' 'MUR' 'MUR'}; % boundary conditions FDTD = SetBoundaryCond( FDTD, BC ); %% setup CSXCAD geometry & mesh % currently, openEMS cannot automatically generate a mesh max_res = c0 / (f0+fc) / unit / 20; % cell size: lambda/20 CSX = InitCSX(); %create fixed lines for the simulation box, substrate and port mesh.x = [-SimBox(1)/2 SimBox(1)/2 -substrate.width/2 substrate.width/2 -patch.width/2 patch.width/2 feed.pos]; mesh.x = SmoothMeshLines( mesh.x, max_res, 1.4); % create a smooth mesh between specified fixed mesh lines mesh.y = [-SimBox(2)/2 SimBox(2)/2 -substrate.length/2 substrate.length/2 -feed.width/2 feed.width/2 -patch.length/2 patch.length/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 = [-SimBox(3)/2 linspace(0,substrate.thickness,substrate.cells) SimBox(3)/2 ]; mesh.z = SmoothMeshLines( mesh.z, max_res, 1.4 ); CSX = DefineRectGrid( CSX, unit, mesh ); %% 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 ); %% 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-.1 -feed.width/2 0]; stop = [feed.pos+.1 +feed.width/2 substrate.thickness]; [CSX] = AddLumpedPort(CSX, 5 ,1 ,feed.R, start, stop, [0 0 1], 'excite'); %%nf2ff calc SimBox = SimBox - max_res * 4; %reduced SimBox size for nf2ff box [CSX nf2ff] = CreateNF2FFBox(CSX, 'nf2ff', -SimBox/2, SimBox/2); %% prepare simulation folder Sim_Path = 'tmp'; 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 ); U = ReadUI( {'port_ut1','et'}, 'tmp/', freq ); % time domain/freq domain voltage I = ReadUI( 'port_it1', 'tmp/', freq ); % time domain/freq domain current (half time step is corrected) % plot feed point impedance figure Zin = U.FD{1}.val ./ I.FD{1}.val; 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 uf_inc = 0.5*(U.FD{1}.val + I.FD{1}.val * 50); if_inc = 0.5*(I.FD{1}.val + U.FD{1}.val / 50); uf_ref = U.FD{1}.val - uf_inc; if_ref = if_inc - I.FD{1}.val; s11 = uf_ref ./ uf_inc; 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}|' ); P_in = 0.5*U.FD{1}.val .* conj( I.FD{1}.val ); % antenna feed power %% 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 thetaRange = (0:2:359) - 180; r = 1; % evaluate fields at radius r disp( 'calculating far field at phi=[0 90] deg...' ); [E_far_theta,E_far_phi,Prad,Dmax] = AnalyzeNF2FF( Sim_Path, nf2ff, f_res, thetaRange, [0 90], r ); Dlog=10*log10(Dmax); % display power and directivity disp( ['radiated power: Prad = ' num2str(Prad) ' Watt']); disp( ['directivity: Dmax = ' num2str(Dlog) ' dBi'] ); disp( ['efficiency: nu_rad = ' num2str(100*Prad./real(P_in(f_res_ind))) ' %']); % calculate the e-field magnitude for phi = 0 deg E_phi0_far = zeros(1,numel(thetaRange)); for n=1:numel(thetaRange) E_phi0_far(n) = norm( [E_far_theta(n,1) E_far_phi(n,1)] ); end E_phi0_far_log = 20*log10(abs(E_phi0_far)/max(abs(E_phi0_far))); E_phi0_far_log = E_phi0_far_log + Dlog; % display polar plot figure plot( thetaRange, E_phi0_far_log ,'k-' ); xlabel( 'theta (deg)' ); ylabel( 'directivity (dBi)'); grid on; hold on; % calculate the e-field magnitude for phi = 90 deg E_phi90_far = zeros(1,numel(thetaRange)); for n=1:numel(thetaRange) E_phi90_far(n) = norm([E_far_theta(n,2) E_far_phi(n,2)]); end E_phi90_far_log = 20*log10(abs(E_phi90_far)/max(abs(E_phi90_far))); E_phi90_far_log = E_phi90_far_log + Dlog; % display polar plot plot( thetaRange, E_phi90_far_log ,'r-' ); legend('phi=0','phi=90')