Contrary to claims made Multiple Input and Multiple Output (MIMO) radars do not provide an order of magnitude better angle resolution, accuracy and identifiability over conventional radars. What is claimed: MIMO array radar system consisting of a full transmit array and thinned receive array (or vice versa; called here a full/thin array) provides an order of magnitude or more of accuracy, resolution and identifiability, the ability to resolve and identify targets than a conventional array. This claim for MIMO results from making the wrong comparison to a full conventional array rather than to a conventional full/thin array. It is shown here that a conventional full/thin array radar can have the same angle accuracy, resolution and identifiability as a MIMO full/thin array. Moreover the conventional full/thin array example given here can have a better search energy efficiency. Where does the MIMO radar provide a better angle accuracy than a conventional radar? A monostatic MIMO array radar does provide a better angle accuracy than its conventional monostatic equivalent, but it is only about a factor of 1/root 2 (29 percent) better and its resolution is the same. Alternately, a monostatic MIMO array radar can offer the advantage of the same accuracy as a conventional monostatic array radar with a smaller aperture size, one that is 1/root 2 = 0.707 smaller, or equivalently 29 percent smaller. This improved accuracy comes at a heavy computation cost. For a MIMO monostatic linear array of N elements >= N-2 matched filters (MFs) are needed versus just N for its conventional equivalent. The factor >= results from the need for a bank of F >= 1 MFs being needed for the MIMO array. A bank of F MFs are need because the MF for an orthogonal waveform is usually Doppler intolerant. In contrast a conventional array would use a linear FM waveform (chirp waveform) which is Doppler tolerant. An alternate approach for achieving this factor of root 2 advantage is to simply increase the radiated power of a conventional radar by a factor of root 2. This latter approach to getting the root 2 advantage has to be traded off against the cost resulting from the throughput increase required when using MIMO. MIMO radar is best for search not for track, unless track-whilescan. For track, conventional array processing should be used for maximum energy efficiency and to reduce the signal processing requirements. When a MIMO array is used to search a large scan angle, it is best for maximum search energy efficiency to use subarrays of the array as the elements of the MIMO array to form what we call a subarray-MIMO (SAMIMO). When searching a small scan angle, the subarrays should be sized so that the volume of space illuminated by the subarrays of the SA-MIMO array matches, or is smaller than, the volume of space to be searched. Using SA-MIMO reduces the processing throughput requirements. MIMO radar in the near term will be useful for coherent and incoherent combining of existing radars to achieve about a 9 dB better power-aperturegain (PAG).
