The impedance of free space / air is said to be 377 ohms. Impedance is ratio
of E/H. The feedpoint impedance of an antenna is usually 50 or 75 ohms.

Can an antenna ever be regarded as a transducer that transforms a radio wave
from 50 ohms to 377 ohms i.e. provides an impedance transformation? With a
long tapered antenna, the feedpoint is at 50 ohms. Is the end of the antenna
at 377 ohms to launch the wave easily into free space? In this case, antenna
is a travelling wave antenna e.g. broad bandwidth biconical. Does the
impedance gradually change from 50 ohms to 377 ohms over the length of the
antenna?

The impedance of the end of an antenna (open circuit), where it is a high
voltage point, is usually 5K or 10K ohms.