Further thoughts....

In order to be able to both release and then fold up the
antenna, a mechanism based on two tendons, not too
dissimilar to the human knee and elbow joints would be
required.

Consider the flexing effect of each of your fingers - one
tendon at the back and one at the front.

And in order to maintain good RF contact across the joint,
perhaps the use of braid recovered from coax cable?

"Airy R. Bean" wrote in message
...
Could we conceive of an antenna, even possible an HF beam, that
folds away into a single rod-like structure when not in use?