Spatially Waveform Diverse Radar: Perspectives for High Frequency OTHR

The application of multi-input multi-output (MIMO) radar concepts to HF over-the-horizon radar is considered to improve radar timeline management flexibility and to permit adaptivity on transmit. MIMO radar concepts in the literature are inconsistent and in this paper the taxonomy of MIMO radar is clarified and distinctions between different MIMO radar types drawn. The term "spatially waveform diverse radar" is introduced, and performance equivalences between element-space and beamspace orthogonality discussed. Finally, we outline significant constraints on the design of waveform sets for the case of transmit arrays where (at least for some part of the operational regime) the array inter-element spacing is less than one half wavelength.