In this letter, the prediction of the radiation of wideband HF antennas is investigated. The ground upon which they are placed mainly influences the sky wave and the surface wave mode radiated by these antennas. Classical methods of simulations or measurement applied to microwave radiating structures are not suitable for this kind of antenna. Thus, this letter proposes a method to perform a near field to far field transformation, adapted to the problem of interest, and based on a power criterion. This criterion requires both the electric and magnetic near fields, but by using an appropriate approximation, it is possible to assert that only the measurement of the electric near field is required. Far field radiation has been computed at two different frequencies within a bandwidth of 1.3:1 (28.5 %).