Electromagnetic Fields of a Small Helical Toroidal Antenna

A physical realization of this winding is shown on the right above, as perhaps first proposed by Corum [1], where two counter windings of N/2 turns are each driven with current I = 2πaK(ρ = a)e−iωt/N such that the magnetic dipole moment is zero. A complication in this case is that at the N close crossings of the two windings, there is localized, oscillating charge accumulation due to the capacitance between the nearby wires which leads to azimuthal variation of the currents in the windings.