11.13.3 Fourier Transform
When 
is an isolated pulse, it cannot be converted to a discrete spectrum since it is not periodic. However, let us consider that this interval is extended to infinity. Then the spectra obtained will represent the spectra of the isolated pulse.
Substituting equation (11.15) into equation (11.14), we get
(11.20)
where the frequency 
of the fundamental wave is denoted by 
Here we represent the frequency of the
order by 
and the difference in frequencies between the adjacent components by 
.
If we make 
, we have
(11.21)