Richard Clark wrote:
"Uh-huh, makes a trap an antenna?"

A trap usually isn`t the best radiator.

A 1/4-wave shorted stub is electrically equivalent to a parallel
resonant circuit, so they are interchangeable. You can use a parallel
resonant circuit to replace a 1/4-wave shorted stub or vice versa.

VHF collinear antenna arrays often use 1/4-wave shorted stubs to invert
the phase at 1/2-wave intervals to keep the current going in the same
direction in all elements.

The Franklin antenna is a vertical collinear array used by some medium
wave broadcasters. A 1/4-wave stub would be inconvenient for the medium
wave broadcaster, so he sometimes uses a parallel resonant circuit for
his phase inverter between 1/2-wave collinear elements.

You might think the parallel resonant circuit or 1/4-wave shorted stub
would function as a trap. Traps are used in multiband antennas. But the
parallel resonant circuit does not function as a trap in collinear
arrays. The length of the element beyond the tuned circuit is 1/2-wave
resonant and readily accepts power through and around the tuned circuit.
Not so with a trap. The length of the element beyond the trap is not
resonant and accepts very little power. The trap is an isolator which
keeps power out of the extension beyond the trap. The phase inverter is
a coupler which conveys energy with a phase reversal produced by the
inverter.

Best regards, Richard Harrison, KB5WZI