Application Note

Application Note: Antenna Far Field Distances

Source: AR
ARwp

By Jason Smith, Manager Applications Engineering and Pat Malloy, Sr. Applications Engineer

Antenna specifications can seem confusing or worse yet, can be misinterpreted. Of all the salient antenna specifications, antenna gain seems to present the biggest problem. The antenna gain provided in data sheets is generally understood to be valid in the so-called "far-field" region. In this region the field energy primarily consists of radiated RF with an angular field distribution that tends to be independent of distance from the antenna and a field level that is inversely proportional to the separation between the antenna and EUT. As the EUT is moved closer to the antenna a point is reached where the induction field begins to affect energy level and standard equations are no longer valid. This is referred to as the "near-field" region. The key element here is the point where the transition from near-field to far-field takes place. While the precise point is generally unknown, two commonly used criteria suffice for most applications.