< The reference antenna is a so-called an isotropic radiator, a non
existing antenna that will equally radiate in all
directions. Any 'real world' antenna will have a certain directivity....>

A toroidal coil placed between two aluminium discs,  fed between one end of
the toroid and the lower disc and with the other end of the toroid
connected to the upper plate, can be adjusted to radiate equally in all
directions,  the phase varies with time but not with space.   One can also
achieve this property with configurations of contra-wound toroids.
73,
Roger, G2AJV.