Compared with classical electromagnetic (EM) waves

the vortex electromagnetic wave carrying orbital angular momentum (OAM) has higher dimensional information-modulation freedom

which paves the way to the OAM's applications in radar target detection and imaging. Firstly

the concept of vortex EM wave and the radiation field in linear polarization are introduced. Subsequently

the principles of the vortex-EM-wave-based radar imaging and detection are presented. The advantages over traditional radar detection technology are analyzed and elaborated. Moreover

the development history and research actuality of the EM vortex imaging and the rotational Doppler frequency detection are overviewed. Especially

the generation technique of vortex EM waves for radar detection purposes is summarized. Finally

by viewing the prospects for the applications of vortex EM waves

some scientific problems in the development of vortex-EM-wave-based radar are proposed.