Abstract
As the only method for all-weather, all-time and long-distance target detection and recognition, radar has been intensively studied since it was invented, and is considered as an essential sensor for future intelligent society. In the past few decades, great efforts were devoted to improving radar's functionality, precision, and response time, of which the key is to generate, control and process a wideband signal with high speed. Thanks to the broad bandwidth, flat response, low loss transmission, multidimensional multiplexing, ultrafast analog signal processing and electromagnetic interference immunity provided by modern photonics, implementation of the radar in the optical domain can achieve better performance in terms of resolution, coverage, and speed which would be difficult (if not impossible) to implement using traditional, even state-of-the-art electronics. In this tutorial, we overview the distinct features of microwave photonics and some key microwave photonic technologies that are currently known to be attractive for radars. System architectures and their performance that may interest the radar society are emphasized. Emerging technologies in this area and possible future research directions are discussed.
Highlights
R ADAR, the acronym of RAdio Detection And Ranging, is regarded as the primary and popular method for allweather, all-time and long-distance target detection, imaging, classification and recognition [1]
Thanks to the fast development of the optoelectronic devices, the relative intensity noise (RIN) of the laser diode (LD), which affects the noise floor of the microwave photonic system, has been improved from −135 dB/Hz in the 1980s to the current −168 dB/Hz [16], [17]; the linewidth, which could be converted into microwave amplitude, phase, or frequency noises in different microwave photonic systems, has been declined from 7.5 GHz to 0.01 Hz [14], [18]; and the output power, which is associated with the gain of the system, has been boosted from several mW to 2 W [19], [20]
A linearized analog optical link with the third-order intermodulation distortion (IMD3) component suppressed by 40 dB was built in [142]; an image-reject mixer with an image-rejection ratio of 25 dB for a 1.2-GHz instantaneous bandwidth linearly frequency-modulated (LFM) signal was realized in [150]; a 30-dB co-site interference cancellation ratio over 9.5 GHz frequency range was obtained in [156]; and an optical link with the common-mode noise suppressed by 15 dB over an 18-GHz frequency range was implemented in [164]
Summary
R ADAR, the acronym of RAdio Detection And Ranging, is regarded as the primary and popular method for allweather, all-time and long-distance target detection, imaging, classification and recognition [1]. To deal with these issues, photonics-based technologies were introduced to radars thanks to the distinct features of modern photonics, such as broad bandwidth, flat response, low loss transmission, multidimensional multiplexing, fast analog signal processing, highly coherent pulse source and electromagnetic interference (EMI) immunity [2]–[7]. Different architectures of microwave photonic radars were proposed recently, which demonstrated the exceptional reconfigurability, multiple functionalities, wide area distribution, and high-resolution imaging capability enabled by the photonics
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