openEMS/matlab/Tutorials/Rect_Waveguide.m

%
% Tutorials / Rect_Waveguide
%
% Description at:
% http://openems.de/index.php/Tutorial:_Rectangular_Waveguide
%
% Tested with
%  - Octave 4.0.0
%  - openEMS v0.0.33
%
% (C) 2010-2015 Thorsten Liebig <thorsten.liebig@gmx.de>

close all
clear
clc

%% setup the simulation %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
physical_constants;
unit = 1e-6; %drawing unit in um

% waveguide dimensions
% WR42
a = 10700;   %waveguide width
b = 4300;    %waveguide height
length = 50000;

% frequency range of interest
f_start = 20e9;
f_0     = 24e9;
f_stop  = 26e9;
lambda0 = c0/f_0/unit;

%waveguide TE-mode definition
TE_mode = 'TE10';

%targeted mesh resolution
mesh_res = lambda0./[30 30 30];

%% setup FDTD parameter & excitation function %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FDTD = InitFDTD('NrTS',1e4, 'OverSampling', 5);
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(11)];
stop =[mesh.x(end) mesh.y(end) mesh.z(15)];
[CSX, port{1}] = AddRectWaveGuidePort( CSX, 0, 1, start, stop, 'z', 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, 'z', a*unit, b*unit, TE_mode);

%% define dump box... %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CSX = AddDump(CSX,'Et','FileType',1,'SubSampling','2,2,2');
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)