A primer on antenna near-field and far-field for the practical engineer
For conformance and compliance, electromagnetic compatibility (EMC) and antenna performance testing, it is crucial to know the nuances of electromagnetic (EM) radiation from an antenna at given distances from the antenna aperture. This is important because the EM signal from an antenna behaves differently at various distances from the antenna, and if not properly accounted for, can result in substantial measurement errors. This is because there are three main regions where the EM radiation behaves differently as a function of distances away from an antenna: the reactive near-field (RNF), the radiating near-field/Fresnel Region and the far-field/Fraunhofer Region.
The majority of specifications are designed and written for testing an antenna in the far field, which requires a test engineer to know how far away from a given antenna the test antenna must be placed. Additionally, the different antenna types and sizes require different calculations to determine the boundary between these regions. Different applications present different methods of calculating when the far-field begins.
This paper aims to educate those new to the concepts of antenna field regions and help readers to understand the calculations involved in determining the boundaries between the various regions.