Broadband multibeam phased array antennas play a crucial role in wireless communication, satellite communication, and radar systems. Microwave photonics and photonic integration circuit technologies offer the benefits of ultralow transmission loss, extensive operating bandwidth, electromagnetic immunity, and various multiplexing schemes, thereby providing robust technical support for broadband multibeamforming networks. In this letter, a broadband optical multi-beamforming network architecture combining both transmission and reception using optical true time delay is proposed and demonstrated by simulation. A 3×3 broadband multibeamformer based on the architecture is designed and fabricated on an 8mm × 3mm silicon-on-insulator chip.
A multi-functional microwave photonic circuit with meshed architecture is designed and demonstrated on thin film lithium niobate platform. Taking the advantages of the fast response of the Pockels effect and optimized device design, the operation bandwidth of the chip exceeds 60GHz. By controlling the transmission paths of the photon at each node, the on-chip device resources are configurated as a variety of microwave links, corresponding to different signal processing functions. The capabilities of signal generation, down-conversion mixing with high dynamic range and self-interference cancellation with high suppression ratio are experimentally demonstrated. For signal generation, the chip can be regarded as a frequency doubler, and both linear and nonlinear frequency modulated waveforms are obtained with a time-bandwidth product of 2×105 and an in-band spurious suppression ratio higher than 40dB. When configurated as a mixer, the chip achieves a spurious free dynamic range of 105 dB/Hz2/3 and a down-conversion efficiency of -7.4dB. The lithium niobate avoids the nonlinear carrier transportation and absorption existing in traditional silicon photonics, breaking the limitation of linearity and efficiency. As self-interference cancellation mode is set, the interference is suppressed by 50dB over 1.1GHz span. The uniformity of microfabrication in combination with the precise adjustment of the amplitude and phase of the optical field guarantees the high cancellation ratio. To the best of our knowledge, this photonic chip possesses the largest bandwidth and excellent comprehensive performance in terms of active signal processing among integrated multifunctional microwave photonic circuits.
With the rapid development of microwave photonic technology in recent years, microwave photonic radar can generate and process signals far beyond the relative bandwidth of traditional radar, and can achieve centimeter-level resolution when imaging. However, the echo characteristics of microwave photonic radar are quite different from those of traditional radar, which degrades the performance of traditional imaging algorithms. Therefore, it is crucial to propose an imaging algorithm that is compatible with the characteristics of microwave photonic imaging radars. This paper first summarizes the development of microwave photonic imaging radar. Then analyzes the typical problems in the imaging process of microwave photonic radar, and proposes corresponding solutions to these problems. Finally the processing results of some measured data of microwave photonic imaging radar are shown.
A wideband programmable linearly frequency modulated (LFM) signal is highly desired in modern radar systems to adapt to variable environments and achieve high detection resolution. However, conventional digital microwave generation has restrictions on operation band and bandwidth. Current optical microwave generation has provided solutions to the dilemma of electronic devices, meanwhile arising new problems like insufficient time-bandwidth product and dependence on high-frequency or high-rate RF sources. Here, utilizing heterodyne-beating two phase-locked lasers, we present a new LFM signal generation method with no aid of high-frequency or high-rate electronics, featuring simple structure, large bandwidth and adjustable parameters. A frequency-swept laser (FSL) and a frequency-fixed laser (FFL) combined with a voltage-controlled oscillator are phase locked to the same oscillator to reduce phase fluctuations and employed for heterodyne-beating. An LFM waveform with an instantaneous bandwidth of 7.3 GHz cross X and Ku band is developed. The reconfigurable capability is also investigated, the bandwidth, central frequency and pulse width of the LFM signal are programmed by merely adjusting the central frequency of the FFL, voltage amplitude and the period of a low-frequency driving voltage signal driving the FSL. Measured results validate the effectiveness and prospect of the approach.
We demonstrated a photonics-based X-band radar system, in which the transmitter generates a linear frequency modulated signal centered at 10GHz with 2GHz bandwidth based on photonic arbitrary waveform generator (PAWG), and the receiver is based on photonic de-chirping. We conducted a field experiment on this radar system and achieved inverse synthetic aperture radar (ISAR) imaging of non-cooperative targets (airplane), verified the possibility of its application in future radar applications.
A photonic-assisted dual-band coherent radar transmitter system with a large frequency tunable range is proposed and demonstrated. This dual-band transmitter is composed of a triple-loop optoelectronic oscillator (OEO) link, a low frequency band subsystem (LFBS) and a high frequency band subsystem (HFBS). The triple-loop OEO link is developed for the generation of an ultralow phase noise microwave signal with a large tunable range, microwave photonic down-converting is used in the LFBS to change band range, microwave photonic frequency multiplying is applied in the HFBS to achieve the bandwidth extension. The band ranges of the proposed dual-band transmitter can cover from S to Ka six bands in all. Performances in the time and the frequency domains of the dual-band microwave signals are also investigated.
A novel photonics channelization spectrum stitching technique in a dual-OFC-based photonic channelizer for receiving a wide-band signal is proposed. By studying the slow and rapid variant characteristics of the channel differences separately, all the channels’ responses are precisely estimated and stitched in the frequency domain. A proof-of-concept experiment is performed and signals with 3 GHz bandwidth are recovered with an SNR loss of 1.01 dB.
KEYWORDS: Radar, Receivers, Ku band, Digital signal processing, Signal processing, Signal detection, Modulators, Microwave photonics, Transmitters, Modulation
In this paper, a microwave photonic dual band radar based on a photonic-assisted de-chirp processing receiver is proposed. The dual band operation is realized independently and simultaneously with a single set of hardware. At a transmitter end, two linear frequency-modulated signals separately located in C-band and Ku-band are transmitted, echoes are collected and sent to a receiver to implement photonic-assisted de-chirp processing. At the receiver end, a main modulator with a special structure, which consists of four parallel sub-modulators, is employed. The echoes and reference signals of C-band and Ku-band are applied to two pairs of sub-modulators of the main modulator, which are biased at the peak points for C-band and biased at the null points for Ku-band. In this case, the intermediate frequency signals of C-band and Ku-band produced by de-chirp processing locate at two different frequencies. Thus operation in different bands based on a unified system is achieved. An experiment operating in C-band and Ku-band with a bandwidth of 700 MHz and 3600 MHz is conducted. The results verify the concept of the dual band radar and show the potential of photonic technology to improve the performance of modern radar system.
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