So now I am refreshing my balcony antenna. Previously (see the above figure) it was a full length dipole for the 40 m band with the far end of each element folded artistically. With an ATU (ICOM AH-4), the VSWR values were well below 1.2 for all the bands from 80 m to 6 m.
My first trial is to fold the element more compactly so that the antenna does not hinder the utility of the balcony.
The result is:
It seems that how you fold the elements is something critical even with an ATU. I wonder what happens if I simply cut off the elements so that there is only a straight part.
Note that the low VSWR is merely a necessary condition, and it may not be a sufficient condition in many cases.