openEMS/matlab/Tutorials/Rect_Waveguide.m

%
% Tutorials / Rect_Waveguide
%
% Describtion at:
% http://openems.de/index.php/Tutorial:_Rectangular_Waveguide
%
% Tested with
%  - Matlab 2011a / Octave 3.4.3
%  - openEMS v0.0.31
%
% (C) 2010-2013 Thorsten Liebig <thorsten.liebig@gmx.de>

close all
clear
clc

%% setup the simulation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
physical_constants;
unit = 1e-3; %drawing unit in mm

% waveguide dimensions
length = 5000;
a = 1000;   %waveguide width
b = 1000;    %waveguide heigth

% frequency range of interest
f_start =  300e6;
f_stop  =  500e6;

%waveguide TE-mode definition
TE_mode = 'TE11';

mesh_res = [10 10 10]; %targeted mesh resolution

%% setup FDTD parameter & excitation function %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FDTD = InitFDTD();
FDTD = SetGaussExcite(FDTD,0.5*(f_start+f_stop),0.5*(f_stop-f_start));

% boundary conditions
BC = [0 0 0 0 3 3]; %pml in pos. and neg. z-direction
FDTD = SetBoundaryCond(FDTD,BC);

%% setup CSXCAD mesh %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CSX = InitCSX();
mesh.x = SmoothMeshLines([0 a], mesh_res(1));
mesh.y = SmoothMeshLines([0 b], mesh_res(2));
mesh.z = SmoothMeshLines([0 length], mesh_res(3));
CSX = DefineRectGrid(CSX, unit,mesh);

%% apply the waveguide port %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
start=[mesh.x(1)   mesh.y(1)   mesh.z(8)];
stop =[mesh.x(end) mesh.y(end) mesh.z(15)];
[CSX, port{1}] = AddRectWaveGuidePort( CSX, 0, 1, start, stop, 2, a*unit, b*unit, TE_mode, 1);

start=[mesh.x(1)   mesh.y(1)   mesh.z(end-13)];
stop =[mesh.x(end) mesh.y(end) mesh.z(end-14)];
[CSX, port{2}] = AddRectWaveGuidePort( CSX, 0, 2, start, stop, 2, a*unit, b*unit, TE_mode);

%% define dump box... %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CSX = AddDump(CSX,'Et','FileType',1,'SubSampling','4,4,4');
start = [mesh.x(1)   mesh.y(1)   mesh.z(1)];
stop  = [mesh.x(end) mesh.y(end) mesh.z(end)];
CSX = AddBox(CSX,'Et',0 , start,stop);

%% Write openEMS compatoble xml-file %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Sim_Path = 'tmp_mod';
Sim_CSX = 'rect_wg.xml';

[status, message, messageid] = rmdir(Sim_Path,'s');
[status, message, messageid] = mkdir(Sim_Path);

WriteOpenEMS([Sim_Path '/' Sim_CSX],FDTD,CSX);

RunOpenEMS(Sim_Path, Sim_CSX)

%% postproc %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
freq = linspace(f_start,f_stop,201);
port = calcPort( port, Sim_Path, freq);

s11 = port{1}.uf.ref./ port{1}.uf.inc;
s21 = port{2}.uf.ref./ port{1}.uf.inc;
ZL = port{1}.uf.tot./port{1}.if.tot;
ZL_a = port{1}.ZL; % analytic waveguide impedance

%% plot s-parameter %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure
plot(freq*1e-6,20*log10(abs(s11)),'k-','Linewidth',2);
xlim([freq(1) freq(end)]*1e-6);
grid on;
hold on;
plot(freq*1e-6,20*log10(abs(s21)),'r--','Linewidth',2);
l = legend('S_{11}','S_{21}','Location','Best');
set(l,'FontSize',12);
ylabel('S-Parameter (dB)','FontSize',12);
xlabel('frequency (MHz) \rightarrow','FontSize',12);

%% compare analytic and numerical wave-impedance %%%%%%%%%%%%%%%%%%%%%%%%%%
figure
plot(freq*1e-6,real(ZL),'Linewidth',2);
hold on;
grid on;
plot(freq*1e-6,imag(ZL),'r--','Linewidth',2);
plot(freq*1e-6,ZL_a,'g-.','Linewidth',2);
ylabel('ZL (\Omega)','FontSize',12);
xlabel('frequency (MHz) \rightarrow','FontSize',12);
xlim([freq(1) freq(end)]*1e-6);
l = legend('\Re(Z_L)','\Im(Z_L)','Z_L analytic','Location','Best');
set(l,'FontSize',12);

%% Plot the field dumps %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure
dump_file = [Sim_Path '/Et.h5'];
PlotArgs.slice = {a/2*unit b/2*unit 0};
PlotArgs.pauseTime=0.01;
PlotArgs.component=0;
PlotArgs.Limit = 'auto';
PlotHDF5FieldData(dump_file, PlotArgs)