Is antenna a transducer to 377 ohms?
Roy Lewallen wrote:
377 ohms does not describe the E and H fields in the near field. 377
ohms is the ratio of E to H in the *far field* when the medium is free
space or, for practical purposes, air. In the near field, the ratio of E
to H can be not only far from 377 ohms, but it's commonly also complex
(that is, E and H not in time phase). For an illustration, model a short
dipole or small loop with EZNEC or NEC-2, and use the near field
analysis to find E and H at some point close to the antenna (within a
fraction of a wavelength). When you divide E by H, you'll get a wide
variety of results(*) depending on the type of antenna and the
observation point. But as you get farther and farther from *any*
antenna, you'll find that the ratio always converges to 377 ohms, purely
real (that is, the E and H fields in time phase).
Yes, I agree with that completely Roy. I apologize for simplifying my
response so much as to not mention this. I was trying to answer the
question at the same level as was asked. I did not mean to offend the
more mathematically astute members of this group.
I will stand by my comment that radiation from antennas, no matter how
well predicted mathematically, is not well understood at a subatomic
level. I personally prefer a model that assumes photons result from
electron acceleration (or deceleration or energy level decrease).
There are obviously competing models.
Gary
N0GW
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