This paper presents an analytic closed form expression for shielding effectiveness (SE) estimation of an enclosure with an aperture. The derived expression, which is based on S-parameter analysis and circuit theory forms a new method for SE evaluation and measurement. An experimental test setup is proposed to validate the analytical approach and to confirm the practicality of the proposed measurement method. This approach can be applied to enclosures with any kinds of materials and aperture shapes (i.e. it is not limited to rectangular apertures). The experimental results show excellent agreement with those of the new analytic approach and are in good consistency with the previous literature. In comparison with the previous analytic approaches, the calculated results using the new method have a better agreement with the measured results due to our more accurate theory. One application of this method is to introduce a new figure of merit, S11 of a two port microstrip line (MSL) over the aperture, to estimate the quality of the shielding. Using such a figure of merit, shielding design, optimization and measurement can be performed through a simpler and more convenient process.

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