Frank wrote:
"I have trouble with the concept of "Reflection", how can charges
(electrons) flow in both directions simultaneously."

The wave, or signal flowing in one direction is distinctly different
from that flowing in the opposite direction. Upon reflection, the phase
between current and voiltage prodiuced by the wave is inverted. Only
phase of the volts or amps is inverted by reflection, not both. The
phase relation between volts and amps is the key to the direction the
wave is traveling on the line. It`s the wave which travels. The volts
and amps are generated by the wave traveling on the line. The line is
just guiding the wave.

The traveling forward and reflected waves, traveling in opposite
directions on the same line, produce the familiar standing wave patterns
through superposition of volts and amps. Transmission lines and the
appurtenances used with them have no problem keeping values associated
with the waves straight with proper design. A directional wattmeter can
separate the two directions of travel wery well indeed. It knows one
direction from the other by whether the volts and amps are in-phase or
out-of-phase.

Best regards, Richard Harrison, KB5WZI