Characterization and testing of shielding gaskets at microwave frequencies

It is shown that nonuniformities in gasket materials, construction, and installation can cause the leakage transmission through a gasket to vary significantly in both magnitude and phase along its length. This largely determines the approaches that can be used at microwave frequencies to devise meaningful test methods for characterizing the gasket leakage. It is argued that the commonly used characterization in terms of transfer impedance loses its meaning at microwave frequencies if the gasket length exceeds about one wavelength. It is proposed instead that a gasket be characterized in terms of an effective transmission area (per unit length), defined as the total power (watts per unit length) radiated into the region on the output side of the gasket divided by the electromagnetic power density (watt/square-meters) incident on the input side. Two methods for measuring the effective transmission area per unit length are discussed. In both methods, the gasket radiates into a large reverberation chamber