% STUB Provides VSWR, reflection coefficient and input impedance
% for a terminated transmission line with a shunt stub at
% the input terminals.
%
% [VSWR, RHO, ZIN] = STUB(ZL,ZO,ZD,L,LT,ST,BW)
%
% ZL, ZO and ZD are the load, characteristic and desired
% impedances, respectively. L is the line length, LT is the
% stub length whereas BW is the bandwidth. Values of L and
% LT must be normalized in terms of wavelength and BW
% should be given in percentage.
%
% ST=10 means short-circuit stub near the generator;
% ST=11 means open-circuit stub near the generator;
% ST=20 means short-circuit stub near the load;
% ST=21 means open-circuit stub near the load.
% RFWave - The Radio Frequency Wave Toolbox
% Versions: 1.0 22-May-1997, 1.1 18-Aug-1999,
% 1.2 16-Jul-2002
% Developed by A. C. de C. Lima
% E-mail: acdcl@ufba.br
% Electrical Engineering Department
% Federal University of Bahia (UFBA)
% Brazil
function [vswr, rho, zin] = stub(zl,zo,zd,l,lt,st,bw)
if nargin < 7
fn=1;
else
if bw==0
fn=1;
else
bw=bw/100;
bw2=bw/2;
fn=1-bw2:bw/100:1+bw2;
end
end;
yl=zo/zl;
yd=zo/zd;
beta=2*pi*fn;
tgblt=tan(beta.*lt);
if st == 11 | st == 21
yt=j*tgblt;
else
yt=-j./(tgblt+eps);
end;
tgbl=tan(beta*l);
if st == 11 | st == 10
yeq=(yl+j*tgbl)./(1+j*yl*tgbl);
y=yeq+yt;
elseif st == 21 | st == 20
yeq=yl+yt;
y=(yeq+j*tgbl)./(1+j*yeq*tgbl);
else
error('ST must be 10, 11, 20 or 21.');
end
rho=(yd-y)./(conj(yd)+y)*yd/conj(yd);
mrho=abs(rho);
vswr=(1+mrho)./(1-mrho);
zin=zo./y;
