Richard Clark wrote:
"Perhaps others will join in."

Haven`t read all the postings and don`t propose to contradict anyone.
Radio waves are energy in motion. They continue so long as their supply
does.

The same energy can`t be in two places at once. Energy can be
redirected. Practical antennas are an example. The only non-directional
antenna is the imaginary isotropic radiator which if it were constructed
would by definition produce waves of equal strength in all directions.
Terman says on page 871 of his 1955 opus:
"Thus a gain of 4 (or 6dB) means that the power intensity is 4 times as
great (field intensity twice as great) as would be the case if the
radiator in question were an isotropic antenna radiating the same total
power."

The foregoing tells us power phased-out in some directions is redirected
to a direction of maximum radiation. Constructive interference exactly
equals destructive interference because a fixed amount of power is
available and conservation of erergy must be satisfied.

The same is true on a transmission line whose only possible directions
are forward and reverse.

Best regards, Richard Harrison, KB5WZI