MIMO radar - some practical considerations

This paper describes practical constraints on the use of MIMO radars imposed by the need for separable codes on each transmitter waveform, and where long code repetition intervals can degrade performance. This is especially problematic for long range radars with many transmitter elements which require long code repetition intervals. This causes beamforming problems if the scene is not phase stationary over this interval. Shorter codes do not help, as they introduce cross correlation which also degrades the beamforming process. We give examples of two useful orthogonal coding schemes to show how range and transmitter numbers extend the code duration and how target Doppler affects the beamforming. We describe a processing technique which will compensate for Doppler, but only if it is constant over a suitable sequence of code repetition intervals. A novel technique is then presented which virtually eliminates these problems. This uses a perimeter array with phase scanned transmitter sub arrays and a two part orthogonal MIMO code. We also identify the unique ability MIMO has to focus at all distances simultaneously in the near field.