The complete scheme of the first photonics-based fully digital coherent radar system demonstrator is presented. The proposed architecture relies on a novel flexible photonic transceiver, based on the software-defined radio paradigm, capable of generating and receiving signals with arbitrary waveform and carrier frequency. The system core is a single mode-locked laser, whose inherent phase and amplitude stability allows generating high-quality carriers over an extremely broad frequency range, as well as directly digitizing high-frequency signals with unprecedented precision. The implementation of the field trial demonstrator is presented in detail, focusing on both the photonic transceiver and the antenna's front-end, as well as on the employed digital signal processing. The excellent performance is proved by the results of the in-field experiments carried out with noncooperative targets in real scenarios. The outcomes from the aerial and naval target detections are here presented and discussed.