David wrote:
Is the current sinewave on the feeder a standing wave?

Standing wave current is usually drawn as an envelope
using maximum absolute values. If the current is drawn
as a sine wave, it may be a snapshot of a traveling wave.
A snapshot of the traveling wave on 50 ohm coax feeding
a 50 ohm antenna would be a sine wave.

The Balanis diagram is definitely standing waves
as it is NOT a sine wave but rather an envelope
of maximum absolute values. And it also is not
100% accurate as the current envelope is a
perfect half circle.
--
73, Cecil http://www.w5dxp.com