Szczepan Białek wrote:


"Richard Fry" wrote
...
On Sep 14, 12:41 pm, Szczepan Białek wrote:

In which parts of antenna the charges acclerate?

Parts with r-f-current flow, the greatest radiation occurring from
locations along the radiator where current is greatest.

Your words: "Only the change in current and charge, over time, produces
EM radiation."
At oscillations the current start from zero, accelerate to max speed and
deccelerate to zero.
At the max speed no acceleration at all.

Current flow is near zero at the ends of any unloaded dipole, and at
the top of any unloaded vertical monopole (even those in directional
arrays).

At the ends are the max accelerations and the max radiation.
S*

Your problem is not understanding the motion of charges in the antenna.

Sure, the derivative of a sine wave is 0 at the peak, but this does
not directly translate to the motion of the electrons
at specific locations in the antenna.

Look at the antenna current as an electron oscillating
back and forth between the ends. The position over time is described
by a function. Throughout the entire length, the electron is
changing velocity (accelerating).

Hint: the _voltage_ at the feed point may be described by a sine wave.
Your challenge is to determine how the electrons move in response
to that sine wave.

Part of understanding this is knowing the difference between what is
happing as time progresses at the different parts of the antenna.

The trick to understanding this is to carefully do and understand
the mathematics that are involved.