Distortion of radiation patterns for leakage power transmitted through attenuating cover panels and shielding gaskets-need for reverberation chamber measurement of total leakage power

Testing of microwave shielding gaskets and cover panels-recent work at Rome Laboratories

“…Therefore, if A/2 is equal to (2% VOL)/(kQ), the opening radiation loss is equal to the wall loss, and the Q is reduced by a factor of two [5]. On the other hand, if A is much smaller than this value,…”

“…(4) and (5). Thus, the estimated error in power and ETA in decibels is Estimated E m = 10 Log (3Ey2/EMAGAVE2) Thus, a particular REVCH can be characterized by the set of values of Ex, Ey, and Ez measured with N1 three-dimensional Efield probes distributed randomly throughout the volume [4, 61. Equation (6) can then provide a rough estimate of the range of errors that can be expected in estimating the total leakage power radiated into the REVCH.…”

“…(4) represents the average power density inside the REVCH [l, 2, 31, this factor can also be interpreted as the effective aperture for wall losses inside the REVCH [5]. Thus the net power that enters the REVCH and is dissipated internally is equal to the effective wall area, (2x VOL/(kQ) times the equivalent "Poynting vector magnitude", EMAGAVE2/qo.…”

“…Inequality (7) , represents the first condition required for the Black-Hole Principle [5], [6] to be valid. In this case, power radiated back out of the opening and the resulting reduction in Q are small, and Q appearing in the above equations can be set equal to the Q without the opening, Condition (7) applies for an open (uncovered) aperture.…”

“…The effect of the image was much more pronounced in preliminary measurements with ten hole positions spaced by 1.0", in which case, the edges of the 0.750"-diameter end holes were only 0.375" from the flanges. The estimated leakage power can vary significantly in an unknown way from point-to-point over the area of an attenuating cover panel, or along the length of a gasketed seam, as a result of' non-uniformities in matc:rial composition and cross-sectional dimensions [5]. This can result in local regions of high or low leakage which can vary by as much as +-10 dB or more about typical average values of say 30 to 80 dB.…”