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function [port] = calcTLPort( port, SimDir, f, varargin)
% [port] = calcTLPort( port, SimDir, f, varargin)
%
% Calculate voltages and currents, the propagation constant beta
% and the characteristic impedance ZL of the given transmission line port.
%
% The port has to be created by e.g. AddMSLPort().
%
% input:
% port: return value of e.g. AddMSLPort()
% SimDir: directory, where the simulation files are
% f: frequency vector for DFT
%
% variable input:
% 'RefImpedance': - use a given reference impedance to calculate inc and
% ref voltages and currents
% - default is given port or calculated line impedance
% 'RefPlaneShift': - use a given reference plane shift from port beginning
% for a desired phase correction
% - default is the measurement plane
% - the plane shift has to be given in drawing units!
% 'SwitchDirection': 0/1, switch assumed direction of propagation
%
% output:
% % output signals/values in time domain (TD):
% port.ut.tot total voltage (time-domain)
% port.ut.time voltage time vector
% port.it.tot total current (time-domain)
% port.it.time current time vector
%
% % output signals/values in frequency domain (FD):
% port.f the given frequency fector
% port.uf.tot/inc/ref total, incoming and reflected voltage
% port.if.tot/inc/ref total, incoming and reflected current
% port.beta: propagation constant
% port.ZL: characteristic line impedance
% port.ZL_ref used refernce impedance
%
% example:
% port{1} = calcTLPort( port{1}, Sim_Path, f, 'RefImpedance', 50);
%
% reference: W. K. Gwarek, "A Differential Method of Reflection Coefficient Extraction From FDTD Simulations",
% IEEE Microwave and Guided Wave Letters, Vol. 6, No. 5, May 1996
%
% openEMS matlab interface
% -----------------------
% (C) 2010 Sebastian Held <sebastian.held@uni-due.de>
%
% See also AddMSLPort, calcPort
if (iscell(port))
for n=1:numel(port)
port{n}=calcTLPort(port{n}, SimDir, f, varargin{:});
end
return;
end
if ((strcmpi(port.type,'MSL')~=1) && (strcmpi(port.type,'Coaxial')~=1) && (strcmpi(port.type,'StripLine')~=1) && (strcmpi(port.type,'CPW')~=1))
error('openEMS:calcTLPort','error, type is not a transmission line port');
end
% check
if abs((port.v_delta(1) - port.v_delta(2)) / port.v_delta(1))>1e-6
warning( 'openEMS:calcPort:mesh', 'mesh is not equidistant; expect degraded accuracy' );
end
%% read optional arguments %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%set defaults
ref_ZL = -1;
ref_shift = nan;
switch_dir = 1;
UI_args = {};
for n=1:2:numel(varargin)
if (strcmp(varargin{n},'RefPlaneShift')==1);
ref_shift = varargin{n+1};
elseif (strcmp(varargin{n},'RefImpedance')==1);
ref_ZL = varargin{n+1};
elseif (strcmpi(varargin{n},'SwitchDirection')==1);
if (varargin{n+1})
switch_dir = -1;
end
else
UI_args(end+1) = varargin(n);
UI_args(end+1) = varargin(n+1);
end
end
if ((strcmpi(port.type,'StripLine')==1) || (strcmpi(port.type,'CPW')==1))
U1 = ReadUI( port.U_filename(:,1), SimDir, f, UI_args{:} );
U2 = ReadUI( port.U_filename(:,1), SimDir, f, UI_args{:} );
U = U1;
for n=1:3
U.TD{n}.val = U1.TD{n}.val+U2.TD{n}.val;
U.FD{n}.val = U1.FD{n}.val+U2.FD{n}.val;
end
else
U = ReadUI( port.U_filename, SimDir, f, UI_args{:} );
end
% read time domain data (multiples files)
I = ReadUI( port.I_filename, SimDir, f, UI_args{:} );
% time domain signals
port.ut.time = U.TD{2}.t;
port.ut.tot = U.TD{2}.val;
port.it.time = I.TD{1}.t;
port.it.tot = switch_dir*(I.TD{1}.val + I.TD{2}.val) / 2; % interpolate to same position as v
% store the original frequency domain waveforms
u_f = U.FD{2}.val;
i_f = switch_dir*(I.FD{1}.val + I.FD{2}.val) / 2; % shift to same position as v
f = U.FD{2}.f;
Et = U.FD{2}.val;
dEt = (U.FD{3}.val - U.FD{1}.val) / (sum(abs(port.v_delta(1:2))) * port.drawingunit);
Ht = (I.FD{1}.val + I.FD{2}.val)/2; % space averaging: Ht is now defined at the same pos as Et
dHt = (I.FD{2}.val - I.FD{1}.val) / (abs(port.i_delta(1)) * port.drawingunit);
beta = sqrt( - dEt .* dHt ./ (Ht .* Et) );
beta(real(beta) < 0) = -beta(real(beta) < 0); % determine correct sign (unlike the paper)
% determine ZL
ZL = sqrt(Et .* dEt ./ (Ht .* dHt));
% if (strcmpi(port.type,'Coaxial'))
% port.ZL = Z0/2/pi/ref_index*log(port.r_o/port.r_i);
% end
% reference plane shift (lossless)
if ~isnan(ref_shift)
ref_shift = ref_shift * port.LengthScale;
% shift to the beginning of MSL
ref_shift = ref_shift - port.measplanepos;
ref_shift = ref_shift * port.drawingunit;
% store the shifted frequency domain waveforms
phase = real(beta)*ref_shift;
U.FD{1}.val = u_f .* cos(-phase) + 1i * i_f.*ZL .* sin(-phase);
I.FD{1}.val = i_f .* cos(-phase) + 1i * u_f./ZL .* sin(-phase);
u_f = U.FD{1}.val;
i_f = I.FD{1}.val;
end
if (ref_ZL < 0)
ref_ZL = ZL;
end
port.ZL = ZL;
port.beta = beta;
port.ZL_ref = ref_ZL;
port.f = f;
uf_inc = 0.5 * ( u_f + i_f .* ref_ZL );
if_inc = 0.5 * ( i_f + u_f ./ ref_ZL );
uf_ref = u_f - uf_inc;
if_ref = if_inc - i_f;
port.uf.tot = u_f;
port.uf.inc = uf_inc;
port.uf.ref = uf_ref;
port.if.tot = i_f;
port.if.inc = if_inc;
port.if.ref = if_ref;
port.raw.U = U;
port.raw.I = I;
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