lähipäätteisiin

Lähisäteisiin, often translated as "near-field radiation" or "near-field effects," refers to the electromagnetic fields that exist in the region of space close to an antenna or radiating element. This region is typically defined as being within one wavelength of the antenna. In the near-field, the electric and magnetic field components are not necessarily in phase with each other, and their relative strengths can vary significantly with distance and angle.

The near-field region is further divided into two sub-regions: the reactive near-field and the radiating near-field. The reactive near-field, closest to the antenna, is dominated by stored energy that is exchanged between the antenna and its surroundings, and it does not propagate as electromagnetic waves. The radiating near-field, further out but still within one wavelength, contains fields that are beginning to propagate as waves, but their characteristics are still strongly influenced by the antenna's geometry and termination.

Beyond the near-field lies the far-field, or Fraunhofer region, where the electromagnetic fields behave as propagating waves, with the electric and magnetic fields in phase and their strengths decreasing as the inverse of the distance. The transition from the near-field to the far-field is gradual. Understanding near-field effects is crucial for antenna design, electromagnetic compatibility (EMC) testing, and the analysis of microwave circuits.