A comparison between near-field shielding-effectiveness measurements based on coaxial dipoles and electrically small apertures

The near-field shielding effectiveness (SE) of a material can be measured by placing it between two closely spaced dipoles (electric or magnetic) and noting the resulting insertion loss. An alternative approach is to cover an electrically small aperture with the test material and measure the resulting loaded aperture polarizability (electric or magnetic), as is done in a dual TEM (transverse electromagnetic) cell. The author develops approximations leading to simple closed-form SE expressions by developing expressions that relate these two configurations. Small-aperture theory is discussed first, followed by a development of approximate dipole coupling expressions. The results are then compared with an experimental example