"Richard Harrison" wrote in message
...
Chris wrote:
"The formulae for all the field strengths can be found in reliable books
such as Kraus "Antennas"."

I agree.

On page 40 of Kraus` 3rd edition of "Antennas" is found:
"For a 1/2-wave dipole antenna, the energy is stored at one instant of
time in the electric field, mainly near the ends of the antenna or
maximum charge regions, while a 1/2-period later the energy is stored in
the magnetic field mainly near the center of the antenna or maximum
current region."

My preceding statement was before reading Kraus:
"A standing wave antenna stores energy in the magnetic field near its
center during one half of the cycle and in the electric fields near its
ends during the other half cycle."

My statement lacks clarity and precision. I am a poor engineer who has
never worked as an educator. Chris` point? Close but no cigar? OK, I
deserve the critism.

Best regards, Richard Harrison, KB5WZI


I hardly dare to say it but, actually that's incorrect for the radiation
field (which is what I wrote about). The radiation resistance of an antenna
accounts for its ability to radiate power into the surrounding space and,
like all other resistances, the peak of current co-insides with the peak of
applied voltage - so one doesn't occur '1/2-period later' at all. What's
described in the passage above is the situation in respect of the temporary
storage of energy in the 'reactive near fields' corresponding to a reactive
component of the terminal impedance, not the radiation resistance. I would
expect the latter to be of greater importance to those interested in
communication.

I wouldn't disagree with the statement that stored energy is concentrated in
the regions near the 'maximum charge regions' but if you plot the equipotent
lines around a dipole and equate the amount of energy stored to the electric
field strength it illustrates that the spatial distribution of energy in the
electric field is similar to that in the magnetic field ... as one might
expect.

Chris