Near-Field Scan Immunity is a powerful technique to identify the root-cause of failures produced during radiated immunity tests at the integrated circuit (IC) and printed circuit board (PCB) levels. However, a prediction method of the radiated immunity level from near-field scan immunity results is still lacking. This type of method would help board designers to anticipate risks of radiated immunity non-compliance related to PCB directly after a near-field scan campaign. This two-part paper addresses this issue. In the first part, the equivalence between far-field and near-field coupling on a microstrip line is discussed in order to derive an estimator of the far-field induced voltage from near-field scan results.