Fig. 1. Architecture of the proposed photonics-enabled distributed MIMO radar. E/O, electro-optical converter; O/E, opto-electrical converter; ADC, analog-to-digital converter; DSP, digital signal processor; Ref., reference signal.

Fig. 2. (a) Schematic diagram of the proposed photonics-enabled distributed MIMO radar. (b) Instantaneous frequency–time diagram of the reference signal, echoes, and de-chirped signals, in the case of a 2×2 array. LNA, low-noise amplifier; PA, power amplifier; LD, laser diode; WDM, wavelength-division multiplexer; f0, B, and Tp, center frequency, bandwidth, and pulse width of the reference signal, respectively; Tr and TR, pulse repetition periods of the reference signal and emission signal, respectively.

Fig. 3. Flowchart of 3D imaging based on the proposed system.

Fig. 4. Test results of a static TCR. (a) Spectrum of one period de-chirped signal relative to one TX and four RXs. (b) Phase drift of RX1 (blue line) and phase difference drift between RX1 and RX4 (red line).

Fig. 5. Test results of a pair of rotating TCRs. (a) Single-channel ISAR image. (b) Range slice of one TCR.

Fig. 6. (a) Overhead topology of distributed MIMO radar on a bridge and the flight path passing by. (b) Photograph of distributed MIMO radar, including a CO, four TXs, and four RXs. (c) Layout of distributed MIMO radar and corresponding APCs.

Fig. 7. Photograph and single-channel ISAR image of the imaged airplane.

Fig. 8. Comparison of reconstructed 3D images obtained by conventional MIMO radar and established MIMO radar: (a) the former including two TXs and four RXs with a maximum baseline of 1.3 m [28]; (b) the latter including two TXs and four RXs with a maximum baseline of 4.2 m; (c) the latter including four TXs and four RXs with a maximum baseline of 9 m.