Near-field Antenna Factor: An Oxymoron?

North Dakota State University Fargo, Fargo ND

Investigators

Abstract

0126412 Nelson The use of high-speed electronics has provided many beneficial effects to society. Unfortunately, one of the potentially adverse effects is that electromagnetic interference (EMJ) can cause malfunction in electronic devices. In particular, circuits made from high-speed devices can become a source of EMI in other devices, or they can be susceptible to malfunction from EMI. In order to design products that are less susceptible to EMI. equipment designers need to know the "electromagnetic environment" of their product. This is obtained via antenna measurements. However, if the devices are in "complex environments" (i.e., close to the radiating, source, or to other metal objects) measuring these fields can be a real challenge. For these cases the antenna factor (e.g., the parameter that allows one to convert a measured antenna voltage to the desired electric field) is ill-defined. Three questions are addressed in this work: oCan antenna factors be determined for frequency-selective (i.e.. narrow-band) measurements of the electric field when the measurement antenna is in the near field of the radiating source, and in close proximity to other metal objects? if so, how is it appropriately defined? oWhat parameters (e.g., distance from the radiating source, distance from the scatterers, etc.) significantly affect the antenna factor for such measurement situations? oWhat guidelines can be offered regarding the validity of using "far-field" antenna factors in terms of the measurement parameters identified above? A three-fold method including analytical expressions, numerical modeling, and experimental measurements will be used to determine answers to these questions. Analytical expressions will be evaluated to determine the AF for two specific near-field situations when source and receiving antennas are in free space, and when they are over a ground plane. Numerical models of near-field measurement environments will be constructed and a method-of-moments software code will be used to numerically determine the AF for several near-field scenarios. Matching funds from TUV Product Services, Inc. will provide access to world-class test facilities, making it possible to gather experimental data which will be used to verify computational and analytical results. Lastly, parameters that significantly affect the near-field antenna factors will be identified and characterized, and guidelines will be developed to determine the conditions for which far-field antenna factors can be used with reasonable accuracy. This work will answer the question of whether or not antenna factors can be determined for "complex" measurement environments for the specific case of a dipole antenna. If the study shows that the concept of a "near-field antenna factor" is indeed valid, and that the AF can be simulated via computational methods, the way will be paved for further work with many types of antennas. If the study shows that the concept is not valid for a dipole antenna, it is doubtful that it will be valid for any other type of antenna typically used in the EMC community. As a result, many investigators will be warned that it is not worth their precious time trying to simulate such an entity. In either case, positive results are expected. Additionally, if the results indicate that the "near-field antenna factor" is a reasonable concept, suggestions will also be presented regarding which measurement parameters most significantly affect the AF, along with guidelines regarding when the far-field AF can be used to provide reasonably accurate results.