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Old December 1st 05, 08:18 PM posted to rec.radio.amateur.antenna
Richard Harrison
 
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Default Antenna reception theory

Roy Lewallen wrote:
"You can find the explanation for why this is in any electromagnetic
text."

I found it in Terman.

As we all know, we place correctly polarized dipoles, for example,
parallel to the wavefront for maximum response. Terman confirms the
electric field in this instance induces no energy in the antenna. It all
comes from the magnetic field.

If antenna current flows, no matter where it comes from, loss resistance
causes a voltge drop. That`s why the wire needs to be perfect. The
electric field produces no voltage in the antenna because the wavefront
has the same voltage across its entire surface. That`s because it all
left the same point at the same time. So, a wire parallel to the front
has no difference of potential induced by the wavefront`s electric
field. It all must come from the mgnetic field.

On page 2 of his 1955 edition, Terman says:
"The strength of the wave measured in terms of microvolts per meter of
stress in space is also exactly the same voltage that the MAGNETIC FLUX
(my emphasis) of the wave induces in a conductor 1 m long when sweeping
across this conductor with the velocity of light."

From the above, it is seen that the electric field is not effective in
inducing current in a receiving antenna parallel to a wavefront. All the
energy intercepted by the antenna is induced by the magnetic field.

Best regards, Richard Harrison, KB5WZI