MIMO radars demystified — and their conventional equivalents

This paper is given in tutorial form using a simple explanation starting from basics of phased arrays and how they work. Physical insight into MIMO is then given. No heavy math used. It has been shown in the literature that MIMO thin/full array radars can provide orders of magnitude better resolution and accuracy than conventional radars. The thin/full array consisted of two co-linear arrays of N elements each. The full and thin arrays have spacings respectively of λ /2 and N 2 /2 with the thin one used for transmit and the full for receive. We show how to use the same thin/full arrays in conventional radars to do as well and also without grating lobes. The monostatic MIMO full array radar and two conventional equivalents are detailed: the Skolnik ubiquitous equivalent and the machine gunning equivalent. A simple physical explanation is given of why the Cramer-Rao bound provides a V2 better angle accuracy for the MIMO monostatic full array than the conventional ubiquitous array equivalent and why this result does not apply for the machine gunning equivalent. It has been also shown in the literature that a MIMO thin/full array airborne GMTI radar can provide a better minimum detectable velocity (MDV) than a conventional one. Here again we show how same MIMO thin/full array can be used in a conventional GMTI radar system to provide the same advantages as the MIMO system re coherence dwell time and aperture size and thus should provide the same MDV. The operation, waveforms, detection sensitivities, use of maximum likelihood estimation (MLE) for angle estimation and detection, and resolutions of these systems are detailed. We show that conventional equivalents to MIMO radar systems can do just as well as the MIMO systems in rejecting barrage-noise jammers, repeater jammers, hot-clutter jammers (jammer signals reflected from the ground) and mainlobe jammers. We show that the signal processing load for the MIMO radar system can typically be much larger than for its conventional equivalents. There is also often a more difficult waveform design problem with MIMO. Finally we present potential practical applications of the MIMO radar.