Orthogonal waveform support in MIMO HF OTH radars

HF skywave radar performance and flexibility can benefit from transmission of multiple orthogonal waveforms in a multiple-input, multiple-output (MIMO) radar architecture. Several practical limitations need to be considered in such a design. One issue is that many HF radar transmit arrays are over-sampled spatially to allow for operation over a significant portion of the HF band. Transmission of orthogonal waveforms in this case can result in large reactive power and consequent equipment damage. Another issue is the ability to generate orthogonal waveform sets with sufficient cardinality at the low time-bandwidth products typical of aircraft surveillance operation. There are likely to be fewer waveforms than transmit elements and so some form of spatial rank expansion, from waveform to radiated signal, is required. Both of these issues are examined using Maric-Titlebaum frequency-hop codes as one example of an orthogonal waveform set.