111 lines
4.2 KiB
Matlab
111 lines
4.2 KiB
Matlab
function [S11,beta,ZL,vi] = calcPort( portstruct, SimDir, f, ref_shift )
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%[S11,beta,ZL,vi] = calcPort( portstruct, SimDir, [f], [ref_shift] )
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%
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% Calculate the reflection coefficient S11, the propagation constant beta
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% of the MSL-port and the characteristic impedance ZL of the MSL-port.
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% The port is to be created by AddMSLPort().
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%
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% input:
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% portstruct: return value of AddMSLPort()
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% SimDir: directory, where the simulation files are
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% f: (optional) frequency vector for DFT
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% ref_shift: (optional) reference plane shift measured from start of port (in drawing units)
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%
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% output:
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% S11: reflection coefficient (normalized to ZL)
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% beta: propagation constant
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% ZL: characteristic line impedance
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% vi: structure of voltages and currents
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% vi.TD.v.{val,t}; vi.TD.i.{val,t};
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% vi.FD.v.{val,val_shifted,f}; vi.FD.i.{val,val_shifted,f};
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%
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% reference: W. K. Gwarek, "A Differential Method of Reflection Coefficient Extraction From FDTD Simulations",
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% IEEE Microwave and Guided Wave Letters, Vol. 6, No. 5, May 1996
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%
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% openEMS matlab interface
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% -----------------------
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% (C) 2010 Sebastian Held <sebastian.held@uni-due.de>
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% See also AddMSLPort
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%DEBUG
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% save('/tmp/test.mat', 'portstruct', 'SimDir', 'f', 'nargin' )
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% load('/tmp/test.mat')
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% check
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if portstruct.v_delta(1) ~= portstruct.v_delta(2)
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warning( 'openEMS:calcPort:mesh', 'mesh is not equidistant; expect degraded accuracy' );
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end
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if nargin < 3
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f = [];
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end
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% read time domain data
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filename = ['port_ut' num2str(portstruct.nr)];
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U = ReadUI( {[filename 'A'],[filename 'B'],[filename 'C']}, SimDir, f );
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filename = ['port_it' num2str(portstruct.nr)];
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I = ReadUI( {[filename 'A'],[filename 'B']}, SimDir, f );
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% store the original time domain waveforms
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vi.TD.v = U.TD{2};
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vi.TD.i.t = I.TD{1}.t;
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vi.TD.i.val = (I.TD{1}.val + I.TD{2}.val) / 2; % shift to same position as v
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% store the original frequency domain waveforms
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vi.FD.v = U.FD{2};
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vi.FD.i = I.FD{1};
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vi.FD.i.val = (I.FD{1}.val + I.FD{2}.val) / 2; % shift to same position as v
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f = U.FD{2}.f;
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Et = U.FD{2}.val;
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dEt = (U.FD{3}.val - U.FD{1}.val) / (sum(abs(portstruct.v_delta(1:2))) * portstruct.drawingunit);
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Ht = (I.FD{1}.val + I.FD{2}.val)/2; % space averaging: Ht is now defined at the same pos as Et
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dHt = (I.FD{2}.val - I.FD{1}.val) / (abs(portstruct.i_delta(1)) * portstruct.drawingunit);
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beta = sqrt( - dEt .* dHt ./ (Ht .* Et) );
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beta(real(beta) < 0) = -beta(real(beta) < 0); % determine correct sign (unlike the paper)
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% determine S11
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A = sqrt( Et .* dHt ./ (Ht .* dEt) );
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A(imag(A) > 0) = -A(imag(A) > 0); % determine correct sign (unlike the paper)
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S11 = (A - 1) ./ (A + 1);
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% determine S11_corrected
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delta_e = sum(portstruct.v_delta(1:2))/2 * portstruct.drawingunit;
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delta_h = portstruct.i_delta(1) * portstruct.drawingunit;
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S11_corrected = sqrt( Et .* (dHt ./ (sin(beta.*delta_h*.5)/(beta*delta_h*.5))) ./ ((Ht ./ cos(beta*delta_h*.5)) .* (dEt ./ (sin(beta*delta_e)./(beta*delta_e)))));
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S11_corrected(imag(S11_corrected) > 0) = -S11_corrected(imag(S11_corrected) > 0); % determine correct sign (unlike the paper)
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S11_corrected = (S11_corrected-1) ./ (S11_corrected+1);
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% my own solution...
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temp = sqrt(-dHt .* dEt ./ (Ht .* Et));
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S11 = (-1i * dEt + Et .* temp) ./ (Et .* temp + 1i * dEt); % solution 1
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% S11 = (-1i * dEt - Et .* temp) ./ (-Et .* temp + 1i * dEt); % solution 2
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% % determine ZL
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% Et_forward = Et ./ (1 + S11);
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% Ht_forward = Ht ./ (1 - S11);
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% ZL = Et_forward ./ Ht_forward;
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%
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% % determine ZL_corrected
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% Et_forward_corrected = Et ./ (1 + S11_corrected);
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% Ht_forward_corrected = Ht ./ (1 - S11_corrected);
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% ZL_corrected = Et_forward_corrected ./ Ht_forward_corrected;
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% determine ZL
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ZL = sqrt(Et .* dEt ./ (Ht .* dHt));
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% reference plane shift (lossless)
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if (nargin > 3)
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% renormalize the shift to the measurement plane
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ref_shift = ref_shift - portstruct.measplanepos;
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ref_shift = ref_shift * portstruct.drawingunit;
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S11 = S11 .* exp(2i*real(beta)*ref_shift);
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S11_corrected = S11_corrected .* exp(2i*real(beta)*ref_shift);
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% store the shifted frequency domain waveforms
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phase = real(beta)*ref_shift;
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vi.FD.v.val_shifted = vi.FD.v.val .* cos(-phase) + 1i * vi.FD.i.val.*ZL .* sin(-phase);
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vi.FD.i.val_shifted = vi.FD.i.val .* cos(-phase) + 1i * vi.FD.v.val./ZL .* sin(-phase);
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end
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