Shielding Effectiveness Evaluation of Enclosure on PCB by Nesting Cavities Test Method

This article presents a nesting cavities test method for determining the electromagnetic (EM) shielding effectiveness (SE) of enclosures on a printed circuit board (PCB) and its gaskets. A common fixture of a resonant rectangular cavity with two monopole probing antennas is used as an equivalent to the equipment shell, and the small PCB enclosure under test can be fixed under its cover. The internal dimension of the test fixture is
$100\times 61.8\times38.2$
mm, which can be excited by the monopole antennas on its top cover to generate a minimum resonant frequency of 2.853 GHz corresponding to the TM110 mode, and a minimum operating frequency of 17.118 GHz is considered six times the minimum resonant frequency, corresponding to more than 200 modes in it. The SE is determined by comparing the transfer parameter
$S_{21}$
through the two probing antennas, which correspond with/without the small PCB enclosure under test in the fixture. Three typical enclosures are simulated and measured to verify the test method. The ideal enclosures have an internal dimension of
$40\times 15\times3$
mm, the thickness of the side wall in contact with the test fixture is 5 mm, and the contact surfaces are direct metal contact, 1-mm-high and 1-mm-thick form-in-place (FIP) gasket contact, and the FIP gasket contact with a 5-mm gap. The determined SE is almost more than 30 dB, more than 65 dB, and less than 20 dB, respectively. The results verified that this method is a simple, efficient, accurate, and low-cost PCB SE test method.