Daniel Onori

A fully photonics-based coherent radar system

The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today’s digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.

In-Field Experiments of the First Photonics-Based Software-Defined Coherent Radar

The complete scheme of the first photonics-based fully digital coherent radar system demonstrator is presented. The proposed architecture relies on a novel flexible photonic transceiver, based on the software-defined radio paradigm, capable of generating and receiving signals with arbitrary waveform and carrier frequency. The system core is a single mode-locked laser, whose inherent phase and amplitude stability allows generating high-quality carriers over an extremely broad frequency range, as well as directly digitizing high-frequency signals with unprecedented precision. The implementation of the field trial demonstrator is presented in detail, focusing on both the photonic transceiver and the antennas front-end, as well as on the employed digital signal processing. The excellent performance is proved by the results of the in-field experiments carried out with noncooperative targets in real scenarios. The outcomes from the aerial and naval target detections are here presented and discussed.

Photonics for Radars Operating on Multiple Coherent Bands

The introduction of photonics in microwave systems is setting new paradigms in radar architectures, providing new features potentially improving the surveillance effectiveness. In particular, photonics is enabling a new generation of the multiband radars able to manage multiple coherent radar signals at different frequencies simultaneously, with high and frequency-independent quality, enabling multispectral imaging for advanced surveillance systems. In fact, thanks to its high stability and huge bandwidth, photonics matches the urgent requirements of the performance and flexibility of the next-generation software-defined radar architectures, and it guarantees system compactness, thanks to the use of a single shared transceiver for multiband operations and to the potentials for photonic integration, which also promises reduced power consumption. In this paper, we present the first field trial, in a maritime scenario, of a fully coherent multiband radar enabled by the use of photonics. The paper reviews the basic concepts exploited for the photonic generation and the detection of the radar signals, and describes the extension to the multiband operation. We present details on the implementation and testing of a dual-band coherent radar system, discussing the potentials for a software-defined radio approach. Moreover, the results obtained after a simple digital data fusion are discussed, highlighting the capability of the coherent photonics-based multiband radars in exploiting the extended observation bandwidth for improving the system detection resolution with minimum computational costs.

Coherent Interferometric Dual-Frequency Laser Radar for Precise Range/Doppler Measurement

A novel coherent interferometric dual frequency laser radar that merges the concept of laser and radio detection and ranging (ladar and radar, respectively), for both range and velocity measurement, is presented and experimentally demonstrated. The innovative architecture combines the broadband tunability of dual-wavelength optical sources, enabling a dynamic trade-off between precision and robustness in Doppler estimation, with the high stability of low frequency RF sources for the interferometric measure of the target range with extreme accuracy. The possibility to easily reconfigure the employed frequencies, allows to change the Doppler resolution, as well as the range ambiguity and precision, to dynamically adapt the system to reliably operate in different environments. Moreover, the coherent detection allows to enhance the signal to noise ratio reaching excellent performances also with low level of received power. The laboratory characterization provides an estimation of the system performances, in terms of resolution and sensitivity, as well as the indoor demonstration with targets of opportunity proves the effectiveness of the proposed architecture to operate in real scenarios.

Field trial of the first photonic-based radar for maritime border security and harbor protection

The field trial results of the first photonics-based radar system in a real maritime environment are presented in this paper. The exploited prototype is the final outcome of the ERC-funded project PHODIR (PHOtonics-based fully DIgital Radar). The system exploits photonic technologies for both the generation and the detection of radar RF signals, allowing increased performance and an unprecedented potential flexibility. This paper details the system capabilities and presents the field trial campaign conducted at the port of Livorno (Italy), detecting naval targets on both long range and harbor maneuvering. The results prove the effectiveness of the proposed scheme and the benefits of photonics highlighting the excellent performance and promising improvements.

A photonics-based ultra wideband scanning RF receiver with high sensitivity and dynamic range

This paper presents an innovative photonics-based ultra wideband RF receiver for spectrum sensing applications. The scheme scans the RF spectrum at discrete steps, down-converting at baseband single portions of the detected spectrum, where they can be precisely acquired. The down-conversion is performed modulating a tunable optical carrier with the RF signal, and beating it with an optical local oscillator. The selection of the desired spectrum portion is achieved tuning the wavelength of the optical carrier, avoiding tunable optical filters and allowing a fast scanning of the detected spectrum. The phase locking between the carrier and the local oscillator by means of a coherent optical comb generator ensures very low phase noise. An experimental validation shows an RF input range of 0.5÷9.5 GHz, with high sensitivity and dynamic range. Increasing the number of comb lines by enhancing the comb generation, the architecture has the potential to detect RF signals up to 100GHz. Moreover, implementing the scheme through integrated photonics technologies will ensure high environmental stability and reduced size weight and power consumption, meeting the increasingly stringent requirements of RF spectrum sensing applications.

Fully Coherent S- and X-Band Photonics-Aided Radar System Demonstration

A fully coherent dual band radar system based on a single photonic-assisted transceiver is presented. Photonic technologies have been used for simultaneous generation and detection of radar signals in the S- and X-band. The sharing of a single transceiver for both the frequency bands allows for a perfect coherence among the generated waveforms. The system has been tested in an operative aerial scenario, and the presented target detections demonstrate the effectiveness of the proposed architecture.

A direct-conversion RF scanning receiver based on photonics

A photonics-based direct-conversion RF receiver has been realized and characterized. The innovative architecture uses coherent optical techniques to perform a fast and wideband scan of the RF spectrum avoiding bulky multiple crystal oscillators. The direct-conversion approach based on photonics enables filtering the input signal spectrum by means of a simple electrical low pass filter, and provide total immunity to local oscillator self-mixing and to RF-to-baseband feedthrough, which are typical drawbacks of conventional direct-conversion receivers. The experimental validation shows an operating bandwidth of 0.5÷10.5 GHz and instantaneous bandwidth of 1 GHz, with linear dynamic range of 141 dB/Hz and spurious-free dynamic range of 107 dB/Hz2/3. Further system developments will enhance the operating bandwidth up to 40 GHz. Implementing the scheme through integrated photonics technologies will also ensure high environmental stability and reduced size weight and power consumption.

Tracking of a naval target with a dual-band photonic-based coherent radar system

Results from a field trial campaign of a fully coherent dual band radar system based on a single photonic-assisted transceiver are presented and discussed. The proposed architecture allows independent and simultaneous generation of radar signals in the S- and X-band, and their detection exploiting a single low sample rate analog to digital converter. Moreover the sharing of a single transceiver for both the frequency bands reduce the system cost and complexity and provides a perfect coherence among the generated waveforms. The tracking of a small vessel in an operative maritime scenario, compared wit reference data from a GPS, confirms the effectiveness of the developed system. The performance in the two bands are also discussed and compared with the theoretical model.

Fully photonics-based radar demonstrator: Concept and field trials

This work shows the concept, performance, and field-trials of the first photonics-based radar. The comparative in-field experiments in aerial and naval scenarios against a state-of-the-art commercial system show the photonics potentials in enabling software-defined radars.