Angles Estimation for mmWave MIMO Radar Using Coupled Coarrays

It is known that with collocated uniform linear arrays (ULA), say $N_t$ transmit antennas and $N_{r}$ receive antennas, we can obtain a virtual array of size $O\left(N_t N_r\right)$. It is also known that with a sparse nonuniformly spaced receive array of $N_{r}$ antennas, we can construct a virtual array of size $O\left(N_r^2\right)$ using coarrays and second-order statistics. In this work, we consider angle estimation for a millimeter wave (mmWave) MIMO radar system with collocated arrays. An mmWave system usually has a large number of antennas but few radio frequency (RF) chains, which indirectly restricts the effective antenna size as the number of RF chains is the number of signals available for digital processing. For an mmWave radar with collocated arrays, we show it is possible have the combined advantage of sparse arrays and collocated arrays based on the so-called couple coarrays and second-order statistics. When there are $\bar{N}_t$ RF chains at the transmitter and $\bar{N}_{r}$ RF chains at the receiver, we show that a virtual ULA in the order of $\bar{N}_t^2 \bar{N}_r^2$ can be constructed.