  This paper presents a novel microwave photonic (MWP) radar scheme that is
capable of optically generating and processing broadband linear
frequency-modulated (LFM) microwave signals without using any radio-frequency
(RF) sources. In the transmitter, a broadband LFM microwave signal is generated
by controlling the period-one (P1) oscillation of an optically injected
semiconductor laser. After targets reflection, photonic de-chirping is
implemented based on a dual-drive Mach-Zehnder modulator (DMZM), which is
followed by a low-speed analog-to-digital converter (ADC) and digital signal
processer (DSP) to reconstruct target information. Without the limitations of
external RF sources, the proposed radar has an ultra-flexible tunability, and
the main operating parameters are adjustable, including central frequency,
bandwidth, frequency band, and temporal period. In the experiment, a fully
photonics-based Ku-band radar with a bandwidth of 4 GHz is established for
high-resolution detection and inverse synthetic aperture radar (ISAR) imaging.
Results show that a high range resolution reaching ~1.88 cm, and a
two-dimensional (2D) imaging resolution as high as ~1.88 cm x ~2.00 cm are
achieved with a sampling rate of 100 MSa/s in the receiver. The flexible
tunability of the radar is also experimentally investigated. The proposed radar
scheme features low cost, simple structure, and high reconfigurability, which,
hopefully, is to be used in future multifunction adaptive and miniaturized
radars.
