Re: NEC-LIST: Time-harmonic electromagnetic field

Dang Xiaojie wrote:
> The time-harmonic electromagnetic field is the field whose time t is
> from infinity to infinity.Does there exist that field?How we can
> apply the field to time-domain?

Xiajie,

A time-harmonic field of finite duration contains spectral components
immediately on either side of the carrier frequency.

That is, multiplying a complex exponential signal of infinite duration
by a rectangular pulse of finite duration is equivalent to convolving
the Fourier transform of the complex exponential signal (a single delta
function at the carrier frequency) with the Fourier transform of the
rectangular pulse (a sinc function).

This is of practical interest when computing the spectrum of a pulse
radar signal.

I hope this clarifies things.

-- 
Dave Michelson
davem_at_ece.ubc.ca
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