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This paper deals with the distortion effects in a TEM cell resulting from loading by the object under test. To insure that higher order modes are ruled out as contributing factors, a brief discussion of the cutoff frequencies of these modes is presented. The paper then proceeds to a theoretical and experimental analysis of the loading effects. In the theoretical analysis for the loading effects, i.e., the electromagnetic-field distortion caused by an object under test in a TEM cell, the frequency-domain integral equation for the magnetic field, or equivalently, the current density on the surface of a perfectly conducting cylinder in a parallel-plate waveguide, is solved by the method of moments to predict the degree of magnetic-field distortion. The experimental investigations are performed by mounting a number of electrically small half loops on the surface of the conducting cylinder in a TEM cell. The loading effects in terms of magnetic-field distortion are analyzed as the ratio of one of the object dimensions (height) to the separation distance between the inner conductor and the ground plane of the TEM cell. Also, the response of an electrically small loop to both the magnetic and electric components of the electromagnetic field is used to measure the phase relation between the magnetic and electric fields, which in turn can be used to determine the degree of degradation of the TEM mode due to the presence of the conducting cylinder. These theoretical and experimental results are compared with the available quasi-electrostatic results.