An Investigation of the Validity of Applying MIL-STD-285to EMP Shielding Effectiveness.

摘要

HDL-TR-1636 'EMP Shielding Effectiveness and MIL-STD-285' by R. L. Monroe (AD-771 997) concludes that measurements carried out in the manner prescribed by MIL-STD-285 will give upper and lower bounds for the EMP (Plane Wave) shielding effectiveness of any metallic structure at all frequencies of interest (100 Hz to 100 MHz). Upper and lower bounds to EMP shielding effectiveness are provided by dipole and loop antenna measurements, respectively. We conclude that the assumptions used in HDL-TR 1636 lead to an over-simplification of the problem. A more precise treatment is, therefore, provided which correlates the magnitude of shielding effectiveness exhibited by a planar metallic sheet to these two diverse electromagnetic fields - one being generated many wavelengths from the shield and the other being generated at a fraction of a wavelength away. This technique, termed an 'Angular Spectrum of Plane Waves' makes no simplifying assumptions, but calculates the wave form in the near field of small loop and dipole antennas in the absence of the shield and converts the actual field configuration to an equivalent family of plane waves. The family of plane waves is then transmitted through the shield and shielding effectiveness is computed from considerations of the incident power and the power transmitted through the shield.