At 08:05 PM 3/25/02, Tom Rauch wrote:
>Really?
Really. Is it such a radical concept?
>Please explain how two identical-pattern antennas, each lossless
>or with the same percentage of power loss, can have different
>gains.
Because the two antennas would have to possess different radiative
resistances. Add to that the century and a half of physics subsequent to
James Clerk Maxwell that backs up radiative resistance as a valid concept
in the theory of electromagnetic waves.
As an example, the classical elementary dipole (with length << wavelength)
has a dipolar radiation pattern in the far field; that pattern is
independent of the dipole's length. But an elementary dipole also has a
radiative resistance and therefore a gain that varies with its length
squared. That's an infinite family of identical-pattern antennas possessing
differing gains.
>Better yet, point me to a engineering reference that
>describes that effect.
If one of my students was having a lot of difficulty comprehending this
explanation I'd send him off to review the discussions on radiative
resistance in a basic E&M text:
Bekefi & Barrett, Electromagnetic Vibrations, Waves, and Radiation
Jackson, Classical Electromagnetism
Kong, Electromagnetic Wave Theory
Landau & Lifshitz, The Classical Theory of Fields
Staelin, Morgenthaler & Kong, Electromagnetic Waves
73,
Mike K1MK
Michael Keane, K1MK
k1mk@alum.mit.edu
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