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Inspired by recent advances in multiple-input multiple-output (MIMO) communications,this tutorial introduces the widely spread antenna MIMO radar concept.MIMO systems have had great impact on wireless communications.The signal model for MIMO radar with distributed antennas bears similarities to the communications signal model,suggesting the possibility of interesting cross-fertilization of ideas between MIMO communications and MIMO radar.We will demonstrate that complex targets contain a large number of scatterers that result in diverse RCS patterns as a function of aspect angle.We will specify the conditions for decorrelation of the elements of the channel matrix in terms of separation between antennas,target size,target range,and carrier wavelength.We will discuss parallels to MIMO communication,in particular the similar roles that the transmission medium (channel) and target play in respectively,communication and radar.We will show that combining target returns resulting from independent illuminations yields a diversity gain akin to the diversity gain obtained in the communication problem over fading channels when the data is transmitted through independent channels.We will develop the optimal detectors for MIMO radar,and for comparison,for other radar architectures.For very widely spaced antennas,optimal processing combines sensor outputs non-coherently.From the non-coherent combination of sensor outputs,we will switch to MIMO radar with coherent processing of sensor outputs.We will show that MIMO radar can locate targets with high resolution and can resolve between closely spaced targets.The Cramer-Rao lower bound on the achievable accuracy will be discussed,and it will be shown to depend on both the carrier frequency and the sensors locations.