  For usual radiation the integral of the electric field strength over the time
is zero. First time the possibility of unipolar radiation generation has been
considered theoretically in the paper [EG.Bessonov. Preprint No 76 of the
Lebedev Physical Institute of the Academy of Science of the USSR, Moscow,
1990]. According to this work the unipolar radiation is radiation for which the
integral of the electric field strength over the time differs significantly
from zero. Futher a number of theoretical articles have been devoted to this
problem mainly in respect to a synchrotron radiation. However up to now there
are no experimental investigations of this phenomenon. In this paper we present
the results of experimental observation of the unipolar Cherenkov and
diffraction radiation generated by relativistic electrons in millimeter
wavelength region. For this purpose the detector sensitive to the selected
direction of the electric field strength has been elaborated. We observed the
coherent Cherenkov radiation and backward diffraction radiation of bunched
electron beam when the electrons moving near the targets. The partial
unipolarity effect has been registered for the Cherenkov radiation and the
almost full unipolarity has been observed for the backward diffraction
radiation.
