Cecil, W5DXP wrote:
"I wonder if we can agree that if there is no physical impedance
discontinuity, there can be no reflection?"

Terman says on page 118 of his 1955 opus:
"When a wave traveling along a transmission line encounters an isolated
discontinuity, it is partially reflected; i.e., while a portion of the
wave continues to travel down the line, another portion of the wave is
reflected backwards."

On page 119 Terman says:
"A traveling wave passing through such a section (a tapered transmission
line to gradually and continuously change its impedance from one value
to another) will have its ratio of voltage to current transformed in
accordance with the ratio of the characteristic impedances involved."

Abrupt changes in impedance are discontinuities which produce
reflections. These are secondary energy sources.

Total reflection produced the wave distribution diagrammed in Fig. 4-3
on page 91, from an open-circuit on the line.

I see that a virtual short-circuit results 1/4-wave back from the open
circuit and the "short" is repeated 1/2-wave back from the first virtual
short. Through all the virtual shorts and opens, Terman shows the
incident and reflected waves progressing unimpeded.

I believe that if a generator is connected through 1/4-wave of
transmission line to a real short, 360-degrees of phase rotation
presents the generator with a voltage which is almost of the same phase
and magnitude as the generator`s output. Almost no current flows either
into the short or back into the generator. It is similar to connecting
nearly identical transformer windings in parallel.

Hybrid ring isolators are also constructed of 1/4-wave transmission line
sections, and whether a port accepts or rejects energy results from
voltage distributions at the ports, I think.

Best regards, Richard Harrison, KB5WZI