at every section of
∞ length transmission line, looking forward/backward, we see an impedance that is called characteristic impedance of a line .... for a lossless line (inductive and capacitive only):
Z0=jlw+11Z0+jcwjlw+Z01+jcwZ0=Z0j(lw−Z20cw)−lcw2z0=0
for a very short piece of T-line (length approaches zero), we can assume
l×c→0. In this case, equation
(1) results in:
Z0=√lc
Z0 is length independent and is called characteristic impedance of a transmission line.