Multiple-In-One Photonic Integrated Transceiver for Multi-Chirp-Rate & Multi-Band ISAR System and Coherent Fusion Processing

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High resolution is the decisive factor for detecting, recognizing, and tracking tiny objects in radars. However, high resolution usually requires large instantaneous bandwidth, imposing critical challenges on device bandwidth and available spectrum resources. An emerging approach is the coherent fusion processing over multiple narrow bandwidths, to obtain a large equivalent bandwidth and thus an enhanced spectral efficiency. Nevertheless, multiple receivers are necessary to separate multiple identical-frequency intermediate-frequency (IF) de-chirped signals in conventional multi-band linear frequency modulation (LFM) radars, leading to complex hardware and scale limitations. In this paper, a novel compact multi-chirp-rate & multi-band inverse synthetic aperture radar (ISAR) is proposed and experimentally demonstrated. Here a “Multiple in One” photonic integrated transceiver is designed to simultaneously process multiple IF signals resulting from multi-chirp-rate & multi-band scheme in only one channel, which greatly simplifies the system. In the integrated transceiver, two cascaded Mach-Zehnder modulators (MZMs) are fabricated via lithium-niobate-on-insulator platform. The first MZM with a half-wave voltage as low as 1.3V, is capable of generating the multi-chirp-rate & multi-band signal under a large modulation index, while the second one targets for photonic de-chirping the echo signal. In experiments, a multi-chirp-rate & multi-band signal covering 3.6 GHz to 16.0 GHz is generated by applying a seed LFM signal with a 0.4-GHz bandwidth, consisting of four bands (0.4, 0.8, 1.2 and 1.6-GHz bandwidth) and four chirp rates (0.8 × 1014, 1.6 × 1014, 2.4 × 1014, and 3.2 × 1014s−2). Then a range resolution of 1.26 cm is obtained for target detection by coherent fusion processing, corresponding to a 12.4-GHz equivalent bandwidth arising from only 0.4 GHz seed bandwidth. Moreover, three reflectors are well recognized in ISAR turntable imaging, indicating high range resolution, compact structure, and high spectral efficiency.