The SOLE coherent MIMO radar  demonstrator

The SOLE concept will be validated through the implementation of a demonstrator of a coherent constellation of MIMO radars, including the photonic core inside and three dual-band (S, X) sensor peripherals (SPs), connected through optical fibres. The demonstrator implementation will exploit an extension of an already available dual band radar prototype. The rest of the networked system will be based on discrete commercially available components.

The SOLE coherent MIMO radar system will be deployed and tested in the Livorno Harbour. Fig. 1 shows the possible spatial distribution of the SPs, that has been defined considering the influence of sensors distribution geometry on some design parameters, such as the radar maximum range, the covered area, the signal distribution, the communication with the SPs for control and so on. These parameters, on their turn, affect the antennas orientation and radiation patterns, the maximum transmitted power, the cross-talk level, the pulse repetition frequency.

Fig. 1: Satellite view of Livorno harbour. The possible radar beams from the horn antennas are reported in yellow, showing the antennas positions and the region where they overlap.

One of the advantages of the SOLE MIMO radar system is that SPs will be equipped with fixed horn antennas, instead of rotating parabolic antennas. The antennas are orientated to avoid as much as possible anyone of them pointing directly to any other. The residual cross-talk between the SPs will be further mitigated by some absorbing panels. The positioning of the antennas has been set also by the optical fibre deployment in the harbour area, and the selected points to locate the antennas allow the access to optical fibre.

The demonstrator will be validated through experiments of detection, tracking and imaging in a controlled and relevant maritime environment with cooperating and non-cooperating targets. These trials will be performed at the facilities and with the support of the Port Authority of Livorno, within an already existing agreement with CNIT.

Fig. X. Demonstrator functionalities block scheme.

At the Livorno Port, a network of already installed optical fiber will be exploited for connecting the sensor peripherals to the photonic core.

A quantitative evaluation of the improvements associated to multistatic imaging, as well as to interferometric applications due to the use of multiple frequency, is complex because of the highly non-linear behaviour of the target response and of the processing chain going from the raw data to the final output. One of the main objectives of SOLE will therefore be the investigation of the improvements achievable with the different acquisition configurations.

The complete architecture of the radar network is reported in Fig… . The photonic core (light-pink block on the left) and the 3 SPs (light-green, boxes on the right) are highlighted, and their internal structure is sketched.

Fig. 2: Architecture of the distributed radar network. DAC: Digital-to-Analog Converter; ADC: Analog-to-Digital Converter; MLL: Mode-locked laser; AWG: Arrayed-Waveguide Grating; MZM: Mach-Zehnder Modulator; EDFA: Erbium-Doped Fibre Amplifier; CTRL: Control.

The SOLE demonstrator of a MIMO photonic radar network will operate on two bands (S and X), leaving open the possibility of extending the architecture to operation in the Ku band. Every frequency band at every SP takes advantage of the full available modulation bandwidth, which is limited to half of the MLL repetition rate. In the RF domain, transmission and reception orthogonality between the SPs will be obtained thanks to time division multiplexing (TDM), i.e. a single SP will transmit both S- and X-band signal, and all three the SPs will wait for backscattered echoes for a time given by the pulse repetition interval (PRI). Afterwards, a different SP will transmit, and the same operation is repeated in a round-robin fashion by all SPs. This will simplify for the system the operation of discriminating between the echoes related to the transmission of different SPs.