DRAFT Recommended Practice for Measurements and ...

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1/29/98 104 C95.3-1991 Revision — 2 nd Draft 10/98 Draft d = Distance from the wire to field point P (m) A6. Bibliography [A1] ANSI C63.2-1987, American National Standard for Specifications for Electromagnetic Noise and Field-Strength Instrumentation, 10 kHz to 40 GHz. [A2] ANSI C63.3-1964 (R1969), American National Standard for Specifications for Radio- Noise and Field-Strength Meters, 20 [E] 1000 Megacycles/Second. [A3] ANSI C63.4-1991, American National Standard for Measurement of Radio-Noise Emissions from Low-Voltage Electrical and Electronic Equipment in the Range of 9 kHz to 40 GHz. [A4] MIL STD-462, Measurement of Electromagnetic Interference Levels, (1986). [A5] SAE Standard ARP-958, Electromagnetic Measurement Antennas; Standard Calibration Requirements and Methods, (1991). Copyright © 1998 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change.
1/29/98 105 C95.3-1991 Revision — 2 nd Draft 10/98 Draft Appendix B Theoretical Calculations of Exposure Fields B1. Technical Considerations of RF Source Characteristics Although the prediction of power-density levels in the vicinity of RF sources is complicated by many factors, useful estimates can be made. The quality of such calculations will depend on the analytical approach used, as well as on the accuracy of the values of the peak power, pulse duration, pulse repetition rate, antenna radiation patterns, antenna placement, and scanning rates that are used in theoretical computations. Corrections for near-field effects may also be appropriate. The operating parameters listed below must be specified adequately so that the true average-radiated power from the antenna, and the resulting power density at a distant point can be calculated. For all sources (pulsed or CW), the antenna type and size, gain, antenna pattern including E and H plane beam widths and sidelobe distribution, antenna height above ground, operating frequency, antenna beam orientation (all possible cases) and the attenuation of the transmission line that connects the RF generator to the antenna should be known or estimated. For the calculation of the expected power density levels of pulse modulated sources, the maximum possible values of peak power, pulse duration, and pulse repetition rate that closely approximate, but do not exceed the maximum rated duty factor of a transmitter should be used. In the case of multiple sources, the contribution of each source should be considered when estimating the combined effect. B2. Antennas -- On Axis The field in front of an antenna can be characterized by the following three regions. (1) Reactive Near-Field Region. This is the region of space immediately surrounding the antenna or leakage source where the reactive (nonradiating) components predominate and energy is stored in the field. The reactive near-field region extends to a distance of approximately one wavelength from the antenna, except for the case of electrically large antennas (whose physical size is greater, in any dimension, than several wavelengths). (2) Radiating Near-Field Region (Fresnel Region). In this region, which starts at a distance from the antenna where the reactive field region has diminished to an insignificant amount, the antenna gain and the angular distribution of the radiated field vary proportionally with distance from the antenna. This is because the phase and amplitude relationships of the various waves arriving at the observation point from different areas of the antenna change with distance. For reflector-type antennas, such as parabolic dishes, the radiation is somewhat more complex in its distribution pattern. (3) Far-field Region (Fraunhofer Region). This region is sufficiently far from the source that the phase and amplitude relationships of the waves arriving from different areas of the antenna do not change appreciably with distance. The antenna gain and angular pattern are essentially independent of distance, and the power density is inversely proportional to the square of the distance from the source. Although Copyright © 1998 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft, subject to change.
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