A new function is addressed to describe the radio footprint of air showers using physical reasoning. The air shower induced by a cosmic-ray primary particle emits radio emission due to the Geomagnetic effect and the Askaryan effect. The function describes these two mechanisms separately. CoREAS simulations of LOFAR events are used to parameterize the function in order describe as a function of the shower characteristics: the shower maximum and the primary particle energy. The parameterization is applied to simulations and measured LOFAR data. This contribution shows the resolution to determine the shower energy and the shower maximum and compares the results with previous outcomes.