Synthetization of Virtual Transmit Antennas for MIMO OFDM Radar by Space-Time Coding

Recent publications have investigated and demonstrated new digital modulation techniques that allow realization of orthogonal frequency division multiplexing (OFDM) radar with relatively low hardware effort. This is especially interesting as the digitally defined signals offer additional freedom for multiplexing schemes of multiple-input multiple-output (MIMO) radar sensors. MIMO radar sensors rely on strictly orthogonal signals to distinguish between multiple transmitters (TX). To span a virtual array with a maximum number of antenna positions, a novel method that combines orthogonal signals with strongly correlated signals generated by space-time coding (STC) is introduced. This leads to virtual transmit antenna positions that are used to improve the unambiguous angular area of an otherwise ambiguous MIMO antenna array. The proposed method is validated with an integrated OFDM radar at millimeter-wave frequencies.