This is a wire, the positive goes into the negative and stays out, now disconnect the wire,
This becomes a dipole antenna, don’t you think? ok straighten the wire
The magnetic fields at both ends point to infinity, which is a dipole
What? Dual frequency dipole?
Don’t wait long
As for the length, the theory: lambda=c/f, generally take 2×1/4λ
It depends on what frequency band you want, dielectric loss, etc.