Following the discussion of fundamental antenna parameters in the previous chapter, another important topic to consider is the near-field and far-field regions of an antenna.
The radiation intensity measured close to the antenna differs from that measured at a distance. Although the far-field region is located far from the antenna, it is still considered a valid region because the radiation intensity remains relatively high.
Near-Field Region
The region immediately surrounding the antenna is called the near-field region. This region is dominated by inductive effects and is therefore also referred to as the induction field region, although it still contains some radiative components.
Far-Field Region
The region far from the antenna is called the far-field region. It is also known as the radiation field region, as radiative effects dominate here. Many key antenna parameters, such as directivity and radiation pattern, are defined and measured within this region.
Field Pattern
The distribution of the field can be quantified by field strength, and the resulting graphical representation is called the field pattern. Specifically, when the radiated power of an antenna is expressed in terms of electric field intensity E (V/m), the resulting plot is referred to as the field pattern. If quantified in terms of power (W), it is called the power pattern.
The graphical distribution of the radiation field or power depends on:
•In the far-field region, only on the spatial angles (θ,ϕ);
•In the near-field region, on both the spatial angles (θ,ϕ) and the radial distance (r).
The characteristics of the near-field and far-field regions can be more clearly understood with the aid of graphical representations.
Field patterns can be categorized as follows:
•Reactive Near-Field Region and Radiating Near-Field Region — both collectively referred to as the near-field region.
•Radiating Far-Field Region — simply referred to as the far-field region.
The region immediately surrounding the antenna is the reactive near-field region, also known as the non-radiative field region, where radiation effects are not dominant. Adjacent to this is the radiating near-field region, also called the Fresnel region, where radiation becomes dominant and the angular field distribution depends on the physical distance from the antenna.
Beyond this lies the radiating far-field region. In this region, the field distribution is independent of distance, and the effective radiation pattern is established.
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Post time: Apr-01-2026
