TABLE OF CONTENTS If electric field strength E, and magnetic strength H, are known, the power density (the power density flux) is explicitly (as to its magnitude, phase and direction) determined by the Poynting vector S. The averaged value of the vector S a, which expresses the power flow from a source, is the subject of our interest. The quantity is given by:
In far-field conditions it is enough to have (calculated, measured) one of the field components as their mutual relationship is known and the relation is expressed by formulas in the form of (2.13) and (2.14). The power density is the sum of the electric power density S E, and the magnetic one S H, that may be expressed (changing vector notation to scalar) in the form:
In the near-field, the mutual relationship of the E and H fields is unknown beforehand and is a function of the structure of a radiation source as well as the distance between the source and the point of observation. Thus, the power density evaluation based on only one component measurement is flawed because of methodology error. This error is of remarkable interest (and it creates a very important limitation in the use of the method and measuring equipment) because the method is widely applied in measuring devices available on the market. However, nowhere is it explained as to what are acceptable (i.e., to assure required measurement accuracy) conditions of equipment use. We may add here that,...
