Multiple-input multiple-output (MIMO) radars offer significant advantages over conventional standalone radars in terms of target detection and localization capabilities. However, to fully exploit ...their potential, such systems require excellent time and phase synchronization among the central unit and the radar heads. Only recently, thanks to microwave photonics (MWP) techniques, it has been possible to develop the first coherent MIMO radar demonstrators. In this paper, a simulation tool in MATLAB programming language is proposed to model coherent MIMO radars based on MWP techniques in maritime surveillance applications. Moreover, a novel approach for estimating the radar cross section of extended maritime targets is presented. The system performance in co-located and distributed MIMO configuration, as well as in single- and multi-band operations, is evaluated by means of relevant key performance indicators (KPIs). Simulations are carried out in two close-to-reality scenarios. In the first, a co-located MIMO radar is mounted on top of a patrolling vessel. In the second, a distributed MIMO radar is deployed inside a port. The proposed KPIs are analyzed in terms of both geometric and frequency diversities of the system, laying the foundations for general system optimization criteria valid in any given surveillance application.
This paper describes algorithms used to retrieve high-resolution wind fields in tropical cyclone conditions from synthetic aperture radar (SAR) data acquired at C-band with either co-polarization or ...cross-polarization. Wind directions are estimated from the orientation of wind-induced streaks visible in SAR images using a simple tropical cyclone flow field. Wind speeds are retrieved from the normalized radar cross section taking into account imaging geometry and SAR-retrieved wind direction using a geophysical model function. The algorithms are validated by comparing outputs to a set of SAR images acquired under tropical cyclone conditions. The simulated wind fields are compared to co-located results from the QuikSCAT scatterometer as well as to wind speeds measured by the Stepped Frequency Microwave Radiometer (SFMR) during reconnaissance flights through individual storms. Comparison of QuikSCAT winds to SAR co-polarization data shows that winds can be retrieved with a root mean square error of 17.6° for wind directions and 4.6 m s⁻¹ for wind speeds. Comparison of SAR wind speeds to SFMR data result in a root mean square error of 5.7 m s⁻¹ for co-polarization data and 3.8 m s⁻¹ for cross-polarization data. SAR cross-polarization data are significantly better suited for SAR wind retrieval under tropical cyclone conditions at wind speeds above approximately 20 m s⁻¹.
In the last decades, great interest has been directed toward low-power high-frequency (HF) surface-wave radars as long-range early warning tools in maritime-situational-awareness applications. These ...sensors, developed for ocean remote sensing, provide an additional source of information for ship detection and tracking, by virtue of their over-the-horizon coverage capability and continuous-time mode of operation. Unfortunately, they exhibit many shortcomings that need to be taken into account, such as poor range and azimuth resolution, high nonlinearity, and significant presence of clutter. In this paper, radar detection, multitarget tracking, and data fusion (DF) techniques are applied to experimental data collected during an HF-radar experiment, which took place between May and December 2009 on the Ligurian coast of the Mediterranean Sea. The system performance is defined in terms of time on target (ToT), false alarm rate (FAR), track fragmentation, and accuracy. A full statistical characterization is provided using one month of data. The effectiveness of the tracking and DF procedures is shown in comparison to the radar detection algorithm. In particular, the detector's FAR is reduced by one order of magnitude. Improvements, using the DF of the two radars, are also reported in terms of ToT as well as accuracy.
This paper reviews on the latest advances in microwave photonics applied to radar systems, tracing the evolutions of functionalities in the photonic radar toward a new generation of ...enhanced-performance systems. Photonics is demonstrated to enable a new generation of miniaturized, heterogeneous, and distributed radars, i.e., future radars on chip with different features, working in different radio spectral regions, and organized in spatially distributed sensors for the enhanced detection of a wider range of target properties. In these systems, the use of photonics assures benefits in terms of frequency flexibility, accuracy, and computational load reduction. Innovative capabilities supported by the photonic approach are presented, such as the use of coherent sparse bands for the synthesis of ultrawide bands, the use of distributed sensors for multiple-input multiple-output detections, and the use of an ultrawide band photonics-based receiver for radio frequency spectrum scanning. The presented novel concepts will open the way to new research activities both in photonic technology and radar systems, contributing to the development of a new generation of remote sensing systems. This expanding cross fertilization will lead to exciting and challenging research activities in the years to come.
In the last decades, photonic technologies have been increasingly proposed for microwave and millimeter-wave applications, opening the way to the development of a new field of research known as ...Microwave Photonics. The hybridization of the microwave world with photonics has demonstrated a beneficial impact on both communications and remote sensing. 5G radio access networks, as well as the next-coming generation of distributed, multistatic radars, are expected to massively leverage on photonic techniques for the generation, distribution, processing, and acquisition of microwave signals. This is due to the advantages brought about by photonics in terms of system transparency to the employed frequency or waveform, low losses, electromagnetic interference immunity, high signal stability. In particular, the inherent coherence guaranteed by photonics will enable next-future multiple input-multiple output radars with enhanced performance. In this paper, we expose in detail some of the most widely employed functions on RF signals obtained with photonic techniques, highlighting the achievable performance that help overcoming some limitations of classical electronic technologies. Finally, two recently implemented microwave photonics systems are described, i.e., a multiple input-multiple output radar and a RF spectrum scanner, showing with practical examples all the potential of microwave photonics systems.
Today, the advent of radar sensing in applications requiring ever higher precision, such as automotive and industrial monitoring, needs the development of systems with superior resolution, stability ...and accuracy on 2D/3D spaces. Multiple-input-multiple-output (MIMO) radar systems have been studied for more than twenty years, proving to achieve excellent resolutions by merging simultaneous observations from sparse multiple radars. In addition, long-term frequency/phase coherence among distributed signals to and from remote and widely distributed radar frontends, enables a centralized architecture where, in a common base station (BS) site, all the received signals can be coherently processed in synergy, allowing to further improve detection, localization, and imaging capabilities. Radio-over-fiber (RoF) solutions represent an enabling technology for guaranteeing coherence among all radar signals coherently generated in the BS and distributed/collected to/from the radar heads by means of optical fiber links. Despite the unprecedented frequency-agility provided by photonics-based radiofrequency (RF) up-/down-conversion in the optical domain, for applications requiring massive low-cost production and power efficiency, such as advanced driver-assistance systems, it might be convenient to transmit and receive conventionally generated RF signals, and to limit the use of photonics, as in RoF, to RF signal distribution through cheap high-capacity optical links, in order to avoid EM interference, minimize loss, signal distortion and link encumbrance, still keeping the coherence among distributed signals. In this work, we present a MIMO radar-over-fiber (RaoF) network, where a common BS transmits and receives RF signals through optical standard single-mode fiber (SSMF), to and from two remote radar transmitters (TXs) and four receivers (RXs), all remote with respect to the BS and distributed on a 3 m-long baseline, and employing cheap patch antennas. Electro-optic conversion is achieved through direct modulation (DM) of low-cost, power-effective, and high-speed vertical-cavity surface-emitting lasers (VCSELs) working in the 1.3 µm-wavelength regime. Such a wavelength ensures propagation over SSMF with negligible distortions up to the km-range. The system is tested in a down-scaled indoor scenario and an RF carrier of 8.5 GHz is used, due to the limited frequency response of the employed VCSELs. System performance is evaluated with 1.4 GHz-bandwidth signals, comparing non-coherent and coherent signal elaboration. In addition, dual-band operation in the same RF region is tested, confirming that VCSEL-based optical links are a viable way to guarantee phase coherence among the distributed signals and among multiple frequency bands. Coherent MIMO processing also confirm the potential to achieve superior range and cross-range resolution than non-coherent data fusion.
Soon after its introduction in the communications domain, the novel concept of multiple input-multiple output (MIMO) has been making its way also into the radar world. A new generation of multistatic ...netted systems with unprecedented capabilities has been fully theorised, unveiling its potential advantages over its classical stand-alone, monostatic counterparts. However, MIMO radars mainly remained the object of abstract modeling, since electronic technology could hardly support the practical implementation of this new class of systems. With the development of microwave photonics, the realization of MIMO radar networks at the best of their capabilities has become a reality, thanks to the inherent coherence of photonics systems, and to the broad-band, low-distortion, and interference-immune optical signal distribution. This paper presents the results of a microwave photonics widely-distributed, dual-band MIMO radar network, deployed in a real freight port for maritime traffic monitoring, with inverse synthetic aperture radar imaging capabilities. It employs a central unit connected to multiple widely distributed remote radar peripherals thanks to optical fiber. The possibility to operate in dual-band mode, and the coherent management of the transmitted and received signals are demonstrated, exploiting geometric and frequency diversity in target detection. The system exhibits a spurious-free dynamic range of <inline-formula><tex-math notation="LaTeX">\boldsymbol{\sim 82}\,{\mathbf{d}\mathbf{B}\cdot \mathbf{\mathbf{Hz}}^{\mathbf{2/3}}}</tex-math></inline-formula> and a sensitivity of <inline-formula><tex-math notation="LaTeX">\mathbf{-110}\,\mathbf{dBm}</tex-math></inline-formula>. Under these premises, a small boat of <inline-formula><tex-math notation="LaTeX">\mathbf \sim\! 1\,{\mathrm{\mathrm{m}}^{\mathrm{2}}}</tex-math></inline-formula> radar cross section has been detected at more than <inline-formula><tex-math notation="LaTeX">\mathbf {800}\,{\mathbf{m}}</tex-math></inline-formula>, achieving a probability of detection of about <inline-formula><tex-math notation="LaTeX">\mathbf {0.85}</tex-math></inline-formula>, for a false alarm rate of <inline-formula><tex-math notation="LaTeX">\mathbf {7.7\times 10^{-4}}</tex-math></inline-formula>.
The Internet-of-Things paradigm is pushing the current fully-automated industry to Industry 4.0, laying on a high degree of end-to-end digitization of all physical assets and their integration into ...data-based services. A significant contribution to recent advances of digital technologies comes from microwave photonics, whose benefits for RF systems in terms of performance and flexibility have been largely demonstrated. In the radar domain, the high degree of coherence granted by photonics makes possible multiple input-multiple output systems, enabling an enhancement of surveillance and monitoring capabilities, thanks to the possibility of performing centralized processing and raw-data fusion. The advantages offered by photonics for surveillance converge with the Industry 4.0 revolution, helping in the actualization of the "Port of the Future" paradigm, to monitor the freight traffic inside ports, increasing goods distribution efficiency, at the same time reducing carbon footprint. Here, we present the first photonics-based widely distributed multiple input-multiple output dual-band radar network, designed to operate in a real port, showing the achieved enhanced potential detection and imaging capabilities. The integration of the targets radar tracks within the monitoring and control platform of the port is reported, enabling the fusion with other data managed by the multiservice monitoring platform.
This paper presents a geophysical model function (GMF) that has been developed to describe the relation of the ocean surface wind with the normalized radar cross section (NRCS) at C-band cross ...polarization (cross-pol). Synthetic aperture radar (SAR) images have been simultaneously collected at copolarization (co-pol) and cross-pol at moderate to high wind speeds. Using the SAR co-pol retrieved wind fields and an uncertainty estimate of the retrieved wind speeds, the cross-pol dependencies of the NRCS are investigated with respect to wind, incidence angle, and polarization pairs. For wind speeds above 10 m/s, there is a significant dependence of the NRCS on wind speed. However, the SAR cross-pol data are also significantly affected by the noise floor and crosstalk between the channels. Estimates of the noise floor are determined and removed from the NRCS. Three GMFs are developed: the first is for transmission at horizontal (H) polarization and the second at vertical (V) polarization. A third GMF accounts for wind direction dependence. Validation of the GMFs is conducted by comparison with collocated Stepped Frequency Microwave Radiometer (SFMR) data. The resulting bias of -0.7 m/s and standard deviation of 3.7 m/s demonstrate the excellent performance for these GMFs for wind speed retrieval between 10 and 35 m/s. Furthermore, comparisons show that SAR cross-pol retrieved wind speeds are of similar quality as those of SFMR and are significantly better in the moderate to high wind speed regime than SAR co-pol retrieved winds.
While automotive radars are driving the development of high-performance technologies for remote sensing, pushing radiofrequency systems to higher frequencies, photonics is gradually changing the ...approach to micro- and millimetre wave RF generation and distribution. With its unique features, photonics can extend the potential of radars, in particular for ground-based traffic surveillance and on-board automotive applications, enhancing traffic safety and enabling the deployment of smart driver-less vehicles. In fact, microwave photonics offers unprecedented flexibility and stability, such as −113 dBc/Hz (at 100 kHz offset frequency) at 80 GHz, with the capability of generating an extremely broad range of carrier frequencies. Moreover, it can employ signals which span up to several GHz of bandwidth, thus allowing higher precision in target detection and discrimination. This study compares photonic and electronic technologies, and it demonstrates, through simulation results, the benefits of a multiple input, multiple output photonic radar when applied to automotive case-study scenarios.
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