Walter Maxwell wrote:

Jim, try the following on for size:

Let us now determine why open or short circuits are developed by
wave interference. From King,37 we know that voltage and current
traveling along the line can be represented by individual generators
placed at any point along the line. Those generators are called "point
generators." For the purpose of analysis, a point generator is an
impedance-less EMF that can represent or replace the voltage and
current on the line equal to the voltage and current actually
appearing at that point on the line, without disturbing the wave
action on the line.
To simulate and analyze interference between two waves of equal
magnitude and opposite phase traveling in the same direction, such as
the two sets of reflected waves generated by the load mismatch and the
stub mismatch, we can connect two point generators together in either
of two different configurations. Each generator replaces the voltage
and current of each individual wave at the point of interference, the
match point. In the first configuration, the two generators are
connected in phase. Because their voltages are equal and in phase, the
differential voltage is zero, resulting in no current flow. This
connection is equivalent to an open circuit between the generators. In
the second configuration, the generators are connected with their
terminals reversed. Their voltages are now in opposite phase at the
interference point and the resulting voltage is the sum of the
voltages delivered by each generator; i.e., twice the voltage of each
generator. This connection results in a short circuit between the two
generators.
Identical wave-interference phenomena establishing a short
circuit also occur in free space in the same manner as in guided-wave
propagation along transmission lines. For example, when the fields
emanating from two radiators in an array of antennas are of equal
magnitude and 180° out of phase at a point in space, a virtual short
circuit is established by destructive wave interference, resulting in
a null in the radiation pattern at that point. Following Poynting's
Theorem, the energy in the combined fields propagating is reversed in
direction at that point; and with the constructive interference that
follows, that energy adds to that in the fields propagating in the
opposite direction, thus achieving gain in the that direction.

Walt, W2DU

Hi Walt,

I think that is all well and good, Walt - except for your statement
regarding the Poynting theorem. I can find no support in the literature
for a claim that interference changes the direction of the Poynting
vector - or for that matter, is a cause for any other phenomenon to
occur. I once asked you for a reference, but your books weren't handy
at the time. Let me know if it turns up. I am very interested to take
a look at it.

Thanks,

Jim Kelley