Abstract
A photonics-based radar with generation and de-chirp processing of broadband linear frequency modulated continuous-wave (LFMCW) signal in optical domain is proposed for high-resolution and real-time inverse synthetic aperture radar (ISAR) imaging. In the proposed system, a broadband LFMCW signal is generated by a photonic frequency quadrupler based on a single integrated electro-optical modulator, and the echoes reflected from the targets are de-chirped to a low frequency signal by a microwave photonic frequency mixer. The proposed radar can operate at a high frequency with a large bandwidth, and thus achieve an ultra-high range resolution for ISAR imaging. Thanks to the wideband photonic de-chirp technique, the radar receiver could apply low-speed analog-to-digital conversion and mature digital signal processing, which makes real-time ISAR imaging possible. A K-band photonics-based radar with an instantaneous bandwidth of 8 GHz (18-26 GHz) is established and its performance for ISAR imaging is experimentally investigated. Results show that a recorded two-dimensional imaging resolution of ~2 cm × ~2 cm is achieved with a sampling rate of 100 MSa/s in the receiver. Besides, fast ISAR imaging with 100 frames per second is verified. The proposed radar is an effective solution to overcome the limitations on operation bandwidth and processing speed of current radar imaging technologies, which may enable applications where high-resolution and real-time radar imaging is required.
Highlights
In order to identify, classify targets efficiently, and take actions timely, high-resolution and real-time radar imaging is highly desired in many applications, such as pilotless automobiles, unmanned aerial vehicles and quick security checks [1,2,3]
To down-convert the high-frequency RF signals, many microwave photonic frequency conversion techniques have been proposed [19,20,21], but it is hard for a traditional radar receiver to process the down-converted baseband or intermediate frequency (IF)-band signals when a very large operation bandwidth is adopted
The echoes reflected from the targets are collected by a receive antenna, which are properly amplified by another electrical amplifier (EA2) before applied to an electro-optical phase modulator (PM) to modulate the reference optical signal from the dual-parallel MachZehnder modulator (DPMZM)
Summary
Classify targets efficiently, and take actions timely, high-resolution and real-time radar imaging is highly desired in many applications, such as pilotless automobiles, unmanned aerial vehicles and quick security checks [1,2,3]. To down-convert the high-frequency RF signals, many microwave photonic frequency conversion techniques have been proposed [19,20,21], but it is hard for a traditional radar receiver to process the down-converted baseband or intermediate frequency (IF)-band signals when a very large operation bandwidth is adopted. The received LFMCW signal is dechirped to a low-frequency signal based on phase modulation of a reference optical signal followed by optical filtering This photonic de-chirp technique can directly process highfrequency and large bandwidth signals without frequency conversion, and the de-chirped signal can be sampled by a low-speed analog-to-digital converter (ADC) and processed in real time. High-resolution and real-time ISAR imaging can be achieved One such photonics-based imaging radar at K band with an instantaneous bandwidth of 8 GHz is established. To the best of our knowledge, this is the first experimental demonstration of high-resolution and real-time ISAR imaging at centimeterwave band
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