blc.m

Branch line coupler design using Matlab

% Lab Assignment 2... 
% Aim of the Assignment -> Quadrature Hybrid
% Submitted by:
              % Akhilesh Kumar Misra (991202) 
              % Gaurav Singh (991210)



k=input('Enter the length to lambda ratio  ');

Z0=input('Enter the value of Zo :  ');
Za=input('Enter the value of Za :  ');
Zb=input('Enter the value of Zb :  ');


% f->the frequency in Ghz
 
 f=.3*k;                             % f is taken into Ghz
 f=f/2:1/5000:3*f/2;
 Ya=1/Za; Yb=1/Zb; Y0=1/Z0;       
 c=.3; lambda=c./f;                  % c is speed of light   

 x=cos(2*pi./lambda); y=sin(2*pi./lambda);

Toue=j*(Y0*Za*y-Z0*Yb*x-Z0*Ya*y+Z0*Za*Yb*Yb*y-Z0*Yb*x)./((2*x-2*Za*Yb*y)+j*(Y0*Za*y+Z0*Yb*x+Z0*Ya*y-Z0*Za*Yb*Yb*y+Z0*Yb*x));

Touo=j*(Y0*Za*y+Z0*Yb*x-Z0*Ya*y+Z0*Za*Yb*Yb*y+Z0*Yb*x)./((2*x+2*Za*Yb*y)+j*(Y0*Za*y-Z0*Yb*x+Z0*Ya*y-Z0*Za*Yb*Yb*y-Z0*Yb*x));

Transe=2./((2*x-2*Za*Yb*y)+j*(Y0*Za*y+Z0*Yb*x+Z0*Ya*y-Z0*Za*Yb*Yb*y+Z0*Yb*x));

Transo=2./((2*x+2*Za*Yb*y)+j*(Y0*Za*y-Z0*Yb*x+Z0*Ya*y-Z0*Za*Yb*Yb*y-Z0*Yb*x));


% so the S parameters of the scattering matrix

s11=(Toue+Touo)/2;

s12=(Transe+Transo)/2;

s13=(Transe-Transo)/2;

s14=(Toue-Touo)/2;



figure;
plot(f,10*log10(abs(s11)),'r');

hold on;

plot(f,20*log10(abs(s12)),'b');
plot(f,20*log10(abs(s13)),'k');
plot(f,20*log10(abs(s14)),'m');
xlabel('frequency')
ylabel('parameters (in db)')