I. Introduction
Multiple-input multiple-output (MIMO) radars has received great attentions in both the academic and the industrial field [1], [2]. There are mainly two important categories of MIMO radars according to the antenna elements relative to the transmitted wavelength. In the first category, different transmit and receive antenna elements are sufficiently close to each other. Parameter identifiability and detection performance can be significantly improved with waveform diversity in this system [3]–[5]. In the second category, distributed MIMO (DMIMO) radars is well-known with widely separated transmit/receive antenna elements. We can improve detection and localization performances, and decrease the radar cross section (RCS) fluctuation effect with DMIMO radars by utilizing space diversity [6]–[9]. The DMIMO radars under the “defocused transmit-defocused receive” (DTDR-DMIMO) operating mode, in which each transmitter forms a completely defocused beam to illuminate the whole surveillance area and each receiver adopts a defocused beam, is a common one with little time consumption [10].