The World of the Near Field

摘要

For many EMC test situations, the demarcation between the far field and near field is clear. In these cases, testing is relatively straightforward. Where it's possible to obtain far field conditions, it makes sense to do so. On the other hand, understanding how the reactive and radiated near field and the far field antenna behaviors differ can only help ensure accurate measurements. Should test results appear inconsistent, it may be that near field effects are manifesting themselves. And, in some immunity tests involving extremely high fields, it is intended that the DUT be positioned in the near field. UWB testing is problematic because of the low signal levels and wide bandwidths involved. A narrowband signal of similar amplitude would be relatively easy to work with because the receiver noise within a small bandwidth is much smaller than in the cited 1-MHz example. This is an area that no doubt will see refinements in test methods and equipment as UWB applications are further developed.