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[References: 23 tit.]

The angular characteristics of millimeter radiation generated by a 6.1-MeV electron beam flying near a multilayer prism target consisting of conducting plates separated by vacuum gaps and near a homogeneous Teflon prism have been studied experimentally. The angular distributions of radiation from both targets have been compared. It has been shown that the angular distribution for the Teflon prism is in good agreement with the classical theory of Cherenkov radiation, whereas the evolution of angular distributions for the multilayer target is inconsistent with known expressions with a fixed effective refractive index. Radiation from the multilayer target (quasi-Cherenkov radiation) should assumingly be described by a tensor refractive index.