Cecil Moore wrote:

snip

Kraus says: "It is generally assumed that the current distribution
of an infinitesimally thin antenna is sinusoidal, and that the phase
is constant over a 1/2WL interval, changing abruptly by 180 degrees
between intervals."

Kraus says something quite similar in the second edition of "Antennas". (I
believe you are quoting from the third edition, which was co-authored by someone
else.)

However, Kraus is merely being careless with terminology. (It is likely that he
did not fully anticipate that he would be quoted out of context.) If one studies
the accompanying diagrams it is clear that Kraus is simply referring to the
standard functional form of a sinusoidal curve. For reasons not clear to me he
decides to call the natural progression from positive to negative as the sine
function passes through zero an abrupt 180 degree phase change. This is
misleading at best.

A true phase change would be, for example, an abrupt transition from +1 to -1 in
the sine function. This sort of phase change is used in numerous communication
schemes, such as PSK31.

snip

Consider something even more bizarre. If the coil is exactly 1/2WL and
each end is located at a current node, assuming the forward current is
equal to the reflected current (Kraus' assumption) then zero net current
is flowing in and out of both ends of the coil even though there is a
current maximum point in the middle of the coil. This is how Kraus'
phase-reversing coil works in his collinear array antenna.

Why is this even the least bit bizarre? Your favorite example of an ideal
transmission line with a perfectly reflecting termination shows exactly the same
thing. Are you suggesting that any node on an ideal standing wave cuts off
everything further downstream? If so, then you might want to consider Tom's
suggestion and head back to school.

73,
Gene
W4SZ