MIMO radars 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 collocated parallel linear arrays of N elements each. One is a thin array and the other a full array having spacings respectively of Nλ/2 and λ/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 (GLs). Also covered are full/thin array equivalents. Detailed are the monostatic MIMO full array radar and its Skolnik ubiquitous equivalent and a machine gunning equivalent. The performance of these systems against jammers is summarized. 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. We show how the 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 the signal processing load for the MIMO radar system can typically be much larger than for its conventional equivalents. There is also usually a more difficult waveform design problem with MIMO. Finally we present potential practical applications of the MIMO radar.