  A photonic-assisted multi-functional radar system for simultaneous distance
and velocity measurement and high-resolution microwave imaging is proposed and
experimentally demonstrated by using a composite transmitted microwave signal
of a single-chirped linearly frequency-modulated (LFM) signal and a single-tone
microwave signal. In the system, the transmitted signal is generated via
photonic frequency up-conversion based on a single integrated dual-polarization
dual-parallel Mach-Zehnder modulator (DPol-DPMZM), whereas the echo signals
scattered from the target are de-chirped to two low-frequency signals using a
microwave photonic frequency mixer. By using the two low-frequency de-chirped
signals, the real-time distance and radial velocity of the moving target can be
measured accurately according to the round-trip time of the echo signal and its
Doppler frequency shift. Compared with the previous reported distance and
velocity measurement methods, where two LFM signals with opposite chirps are
used, these parameters can be obtained using only a single-chirped LFM signal
and a single-tone microwave signal. Meanwhile, high-resolution inverse
synthetic aperture radar (ISAR) imaging can also be realized using ISAR imaging
algorithms. An experiment is performed to verify the proposed multi-functional
microwave photonic radar system. An up-chirped LFM signal from 8.5 to 12.5 GHz
and an 8.0 GHz single-tone microwave signal are used as the transmitted signal.
The results show that the absolute measurement errors of distance and radial
velocity are less than 5.9 cm and 2.8 cm/s, respectively. ISAR imaging results
are also demonstrated, which proves the high-resolution and real-time ISAR
imaging ability of the proposed system.
