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Photonic Radars for Drones, Fighter jets, Satellites and Airships provide software-defined operation and Anti-Stealth functions

Radar, an electromagnetic sensor used for detecting, locating, tracking, and recognizing objects of various kinds at considerable distances. It operates by transmitting electromagnetic energy toward objects, commonly referred to as targets, and observing the echoes returned from them.  Energy is emitted in various frequencies and wavelengths from large wavelength radio waves to shorter wavelength gamma rays.

 

Radar is an “active” sensing device in that it has its own source of illumination (a transmitter) for locating targets. It typically operates in the microwave region of the electromagnetic spectrum—measured in hertz (cycles per second), at frequencies extending from about 400 megahertz (MHz) to 40 gigahertz (GHz).

 

In typical conventional radars, the radar signals and radar beams are formed by a variety of complex electronic techniques. All signals are produced and processed by electrical processes, i.e. using electronic components and techniques. Mainly there are two types of radars, continuous wave (CW) radar with continuous electromagnetic wave transmission and pulsed radar which transmits a sequence of finite pulsed waveforms.   The CW is more appropriate for Doppler measurement, it detects the velocity by processing the Doppler frequency shift. While the pulsed radar is for both range and Doppler.

 

Different types of radar use different frequency ranges – from radio to microwaves. In the microwaves range, the transmission of the signal is usually carried out through strip lines or waveguides, such as metal pipes of rectangular cross-sections. The properties of microwaves make it necessary to select the dimensions of the waveguide strictly matched to the range of microwaves used and must be maintained during operation.

 

The next generation of radar systems needs to have much higher resolutions, smaller sizes, lighter antennas, consume less energy, and above all, be very versatile. Therefore they should be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. High range and cross-range resolution profiles or equivalently higher Bandwidths are required for many functions including the identification and Anti-Stealth functions.

 

The pressure of growing expectations and needs to ensure that unmanned aerial vehicles, autonomous vehicles and even mobile navigation devices can also be reliably navigated requires the miniaturisation of radars as well. This means that radars must be transformed into much lighter and smaller devices that consume less power and have a much higher resolution than today

 

The current Radars are made from electronics components including synthesizers and analogue-to-digital converters which 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 down conversions are necessary for higher frequencies. Transporting the signals also require expensive, heavy cabling – and this creates noise in the system.

 

Photonic Radar

The term “photonic radar” originated in the idea of replacing all radar systems using electronic technology with photonic systems. The photonic system consists of subsystems and elements transforming modulated signals from the electrical field into electromagnetic (optical) signals and vice versa.

 

Photonic radar can overcome some of the limitations of current electronic systems. A laser produces a finely-tuned digital signature, which is converted into a radio frequency wave and transmitted from the radar antenna. The returning wave is also converted via laser into a digital signal free from “jitter”. The cables are replaced with fibre optics – it is cheaper, lighter and crucially – it has less interference.

 

It’s very accurate.” “Because the light is very precise, so is the radio frequency signal,” said Prof David Stupples, an expert on radar systems at City University in London. “Currently we produce the carrier wave using electronics.

 

Photonics can 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.

 

Photonics-enabled multiband radar structure has the ability to operate multiple coherent radar signals simultaneously. It can do accurate target detection and high-quality radar imaging for progressive surveillance.

 

Photonic Radar Technology

Photonic radar technology requires many technologies such as Optical sources of sufficient performance (e.g. mode-locked lasers), Optical signal modulators (e.g. optical fibre, electro-optical modulators), and High-speed photodetectors (e.g. PIN or MSM diodes (GaAsN/GaAs)).

 

Mode-locked lasers (MLL), distributed feedback lasers (DFB)

These devices produce laser radiation called the optical frequency comb. It assumes the form of a spectrum consisting of a sequence of stable, evenly distributed and ultra-short femtosecond laser pulses.  MLL lasers provide compensation of the chromatic dispersion of laser radiation, i.e. compensation of the effects resulting from the interaction of light with electrons of the medium in which this light is being propagated, as well as a compensation of interference or geometric effects, which affect the changes in the phase and group speed of pulses of the light propagating in this medium depending on the optical frequency of light.

 

Systems converting the electromagnetic radiation frequency. These systems are based on the so-called optical heterodyne. Optical heterodyne is a process using the effects of summing up the signals of modulated laser beams. The conversion systems are parts of systems that produce optical signals, e.g., in systems that convert these signals into electrical microwave signals.

 

Other elements needed include the pin and MSM photodiodes, optical fibres, optical modulators, optical phase shifters, and beam dividers through which the signals are processed and then the required waveforms are formed to produce the radar microwave beams and to receive the echoes, and finally obtain the electrical target information signals.

 

Fibre optic microwave signal transmission can be done simultaneously in both directions and at different wavelengths. In comparison to traditional transmission lines, the photonic networks are characterized by smaller sizes, lower weight and costs, as well as very high resistance to electromagnetic interference, and also very low attenuation, low dispersion and high capacity. Photonic networks permit two-way and duplex microwave signal transmission.

 

The modulator

In the photonic systems, microwave signals, as well as internal control signals, are transmitted through optical beams. Modulated optical beams are produced by direct laser modulation or by external modulation. The electro-optical modulators based on the Pockels effect are used in the range of very high modulation speeds and frequencies (e.g. in materials such as LiNbO3 or organic polymers). The disadvantage of the modulators of this type – despite the fact that they reach a band of several dozen GHz – is that they require control signals from several hundred volts to even several dozen kilovolts.

 

In terms of convenience, the electro-absorption modulators based on the Franz-Keldysh effect are much easier to use. For a similar modulation band, there is a need for only a few volts of amplitude per signal. Modulated beams are also produced with the application of Mach-Zehnder’s interferometers

 

Photonic Radar Demonstrations

The world’s first photonic radar was tested at Pisa Airport in Italy and achieved “world-class” performance, according to an independent expert.

 

 

Italian Researchers develop “PHODIR” , fully photonics-based radar system

A team of researchers from Italy, including from the National Laboratory of Photonic Networks has reported in Nature about the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR (‘Photonics-based fully digital radar’). The new PhoDiR (Photonics-based fully digital radar) system is a working prototype for next-generation radars – designed to let pilots and air traffic control exchange far more information in a single signal.

 

The new PhoDiR (Photonics-based fully digital radar) system is a working prototype for next-generation radars – designed to let pilots and air traffic control exchange far more information in a single signal.

 

The compact system could potentially be installed on aircraft, and has a very large bandwidth – allowing pilots to transmit detailed information directly to ground stations within range. “In future, we imagine a system on an airplane that can scan objects around but also communicate what’s happening in the cockpit – what has been said, movements in the airplane, everything,” Dr Ghelfi told BBC News. “One could imagine transmitting live streaming video, together with the radar surveillance data. The advantage would be that a single system can do the entire job, instead of multiple systems.”

 

Photonic systems promise:
• Higher precision – less noise (interference) in the radar transmission
• Higher bandwidth – able to transmit cockpit data (eg critical flight systems) as well as location data, simultaneously
• Greater flexibility – more frequencies available
• Smaller antennas – cheaper, lighter and more portable

 

The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radiofrequency 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

 

The radar system, is an effort to improve the tracking and speed calculation abilities of current electronic signal based systems. It’s well understood that making improvements in such a system will require higher frequency signals, something that can’t be done with current systems due to an increase in noise that creates more uncertainty in the signals received.

 

For that reason, scientists have been looking to use lasers—such signals are much more stable. Building a radar system using a laser requires an optical mode of oscillation that is able to maintain a highly stable phase relationship—that’s the hurdle the researchers had to overcome.

 

PhoDIR system is characterized by excellent parameters in relation to analogous systems implemented in the traditional electronic technology. It has more than 10 times less phase noise (better than 140 dBc/Hz)

 

They used a mode-locked laser, it allowed for establishing a periodic sequence of laser pulses that exhibited low timing jitter. Using it, in conjunction with a computer running software they wrote, they were able to produce an RF signal with low phase noise by adding an optical filter located past the laser, which was sent to a photo diode, allowing for two optical modes to be selected.

 

The team tested its abilities by monitoring real aircraft taking off at a nearby airport and then comparing what they observed with data from traditional electronic signal based systems. They report that the systems matched very closely. That of course is just an initial test, as McKinney notes, much more research and testing will need to be done before the researchers will know if such a system could provide better results than conventional systems. Also, another area of concern is range, which could impact jitter, and thus the accuracy of the system.

 

By eliminating the need to convert the frequency of signals (up or down), a significant reduction in undesirable components has been achieved and, in addition, we have gained a much higher capacity and efficiency at a level unattainable for electronic systems and at carrier frequencies significantly above 2 GHz.

 

 

Russian Airships shall employ photonics based radar for Missile Defence in 2018

In the early 2020s, the Russian fifth generation fighter PAK FA could get a photonics-based radar system using active radio-optical phased array technology (known by its Russian acronym ROFAR). It should be able to view stealth aircraft at distances beyond the range of air-to-air missiles.

 

KRET, the developer of ROFAR technology, believes that radio-photonic technology will pave the way for both military and civilian electronics of the future, as the tech will be applied in radio astronomy, radio detection and ranging, optical fiber and mobile communications and other practical fields. Such systems also have application in helping high-speed trains instantly detect obstacles on the tracks.

 

“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,” say Paolo Ghelfi and others. 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.

 

Another major advantage of ROFAR is the stability of the radar to the action of electronic warfare (electronic warfare). To suppress the operation of devices with ROFAR, a generator is required, which is at least 2,5-3 times higher than the functionality of existing generators for electronic warfare systems. So far, such a generator (at least in the version of placement on an airplane, helicopter or UAV) does not exist even in the version of promising developments. If we draw any analogies, considering the potential actions of modern electronic warfare against systems with ROFAR, then this could resemble an attempt to keep water in the sieve.

 

Russia  is developing a photonics-based radar system using active radio-optical phased array technology (known by its Russian acronym ROFAR) for its fifth-generation PAK FA fighter jet.  The radio-photonic radar system will be based on active radio-optical phased array (Russian abbreviation: ROFAR) technology being developed now by Radio-Electronic Technologies Concern (KRET), an integral part of the Rostech state corporation.

 

The transmission frequency of a modern radar system is at most 10 GHz, and with ROFAR it can reach 100 GHz. According to developer KRET, the future radio-optical phased array antenna known as ROFAR will be half the weight of the conventional radar system. At the same time, its resolution will be 10 times better.

 

It is expected to open a new era of light and precise radar electronics for systems where weight is critical, such as drones and satellites. In the future, he said, the antenna system based on the principles of radio-photons can be mounted on airships and used as part of the missile defense system. “There is no need to build a huge antenna on the ground when you can simply raise the antenna to the necessary height and look beyond the horizon,” said Vladimir Mikheev.

 

“We are planning to begin production of the radar based on the principles of radio-photons,” said Vladimir Mikheev, adviser to the first deputy CEO of KRET, as reported by TASS. As previously reported, state investment in the project for developing an active phased array radar based on radio-photons will amount to 680 million rubles.

 

Radio-photons are an analog of electronics, though photons, unlike electrons, have neither mass nor charge. The new concept will reduce the weight of the equipment by 1.5-3 times, increase its reliability and efficiency by 2-3 times, and increase the scanning speed and resolution dozens of times over. This will help create broadband radars whose resolution and speed enable what is called radar sight.

 

KRET announced that radio-photonic antennas will have “unique stability” regards electromagnetic-frequency impulses, such as those caused by close-range lightning strikes, solar magnetic storms and EMP effects caused by nuclear explosions.

 

ROFAR works in the USA, China, South Korea. In this regard, it can be stated that the correspondence struggle for the possession of the ROFAR technology has now developed into a serious one. For Russia, obtaining the latest radars would enable them to equip fifth-generation Su-57 fighters, transferring them to at least generation 5+. The same can happen with the appearance of aviation radars with ROFAR in relation to the American F-35 and Chinese J-20

 

 Researchers at the University of Sydney developed the photonic wideband stepped-frequency (P-WSF) radar system, reported in feb 2022

The use of photonics enabled the system to generate high-resolution images in a format that is simpler and potentially less expensive than conventional electronic radar systems, the researchers said. The system uses analog photonic generation and processes ultrawideband signals using only megahertz (MHz)-level electronics for detection and imaging. It synthesizes stepped-frequency (SF), continuous-wave radar signals using a frequency-shifted optical modulation that is driven by a low-frequency electronic oscillator.

 

The optical mixing of a broadband radar signal and its echoes at the receiver produces a demodulated signal with a bandwidth that is much smaller than the frequency step. This signal could be processed by low-bandwidth devices with high precision to enable real-time radar ranging and imaging.

 

Because the bandwidth of the radar is driven and processed by MHz-level-electronics-based, acoustic-optic modulation, the need for high-speed, complex electronics for wideband radar signal generation and processing is eliminated. The radar’s signal bandwidth is more than 11 GHz and can exceed 20 GHz without radio frequency (RF) antenna bandwidth limitations.

 

The P-WSF radar provides high spatial resolution at the centimeter level and a real-time imaging rate of 200 frames/s−1. It combines high resolution and rapid response, which enables it to detect rapidly moving objects, like the blades of an unmanned aerial vehicle (UAV), at high resolution. The researchers demonstrated the use of the P-WSF radar system for high-resolution range detection and 2D radar imaging. They achieved high spatial resolution down to 1.3 cm and an ultralarge time-bandwidth product exceeding 5 × 105.

 

One such application for the technology could be to monitor vital signs; it could unobtrusively monitor respiratory rate in a patient with sensitive skin, or in an infant by continuously detecting the rise and fall of the patient’s chest. Respiratory rate is typically monitored by a strap around the person’s chest. Unlike traditional health surveillance methods, which use cameras to monitor patients, a radar system would automatically protect the patient’s privacy.

 

The P-WSF radar could lead to next-generation broadband radars with reduced system complexity — a necessity for ubiquitous sensing applications such as autonomous driving, environmental surveillance, and vital sign detection.

The research was published in Laser & Photonics Review (www.doi.org/10.1002/lpor.202100549).

 

Microwave Photonic Enhances Radar Performance

Researchers from Israel have developed a technique that draws upon optical imaging to enhance  the spatial resolution of a radar system. Radar spatial resolution is essential when trying to identify more than one radar target simultaneously. The new method provides improved radar spatial resolution through frequency coding—various parts of the radar target are illuminated with different microwave frequencies using a transmission antenna array.

 

In the approach by Moshe Mizrahi of the Department of Electrical and Computer Engineering, BarIlan University, RamatGan, Israel, and the Department of Electrical and Electronic Engineering, Ariel University, Israel, and fellow researchers based in Israel ,  the size of the optical imaging lens is the same as the aperture of the radar antenna.

 

The array transmits the full frequency spectrum of interest, but portions of the frequency spectrum are used to illuminate different parts of the radar target. The received signals are processed to identify the different parts of the illuminated target with improved spatial resolution. The optical sensor works in collaboration with the frequency techniques, with the number of pixels in the optical sensor equivalent to the number of different frequency channels used for the radar detection.

 

Modeling performed with commercial electromagnetic (EM) simulation software showed the effectiveness of the new approach in detecting and differentiating four separate metallic targets in an experimental test setup as reported by  Jack Browne in Microwaves and RF. It was compared against a standard radar, which had difficulty in simultaneously detecting three different targets over the same test range. For radar experiments performed over a bandwidth of 4 GHz, the frequency selective,optically aided process shows great promise as a means of improving the spatial resolution of radar systems for both onedimensional (1D) and twodimensional (2D) radar target data.

 

Phased Array Antenna Architecture via Integrated Photonics

The U.S. Army Research Laboratory (ARL) has developed and patented next-generation phased array radar based upon photonic integrated circuits.

Electronic based phased array antenna systems are bulky, power- hungry and focus on low frequency bandwidth, but they are still widely used in both military and commercial radio-frequency (RF) systems. ARL’s new RF-photonic based architecture overcomes size, weight, power and other known technical disadvantages of previous scanning antennas and is cost competitive thanks to the continual drop in the cost of commercial photonic devices.

ARL has built a fiber-based true time delay (TTD) system as a proof- of-concept demonstration of a proposed optical circuit architecture. The ultimate goal is to develop a chip-scale semiconductor based optical TTD beamforming/steering system. The optical circuit architecture would be employed in a large phased array antenna system that can perform two-dimensional beam scanning for both transmit and receive mode. Further, this will enable a miniaturized optically controlled phase array antenna system that can be used in numerous applications where reduced form factor and power consumption are a primary concern.

The First-available architecture for true-time-delay phased array radar based upon photonic integrated circuits has many benefits like not frequency-band limited can target wideband and high frequency applications; It has reduced size, weight, and power requirement for compact chip-based systems. It can have diverse military, commercial applications such as UAV, broadcasting, radar, space communication, weather research, RFID, optics, human-machine interface, and more.

 

GAIA (PHOTONICS FRONT-END FOR NEXT-GENERATION SAR APPLICATIONS)

As part of the European Space strategy in GMES (Global Monitoring for Environment and Security), the development of state-of-the-art SAR (Synthetic Aperture Radar) instruments has become one of the key enablers for the success of the European leading position, fostering the competitiveness of the European Space industry. Example of the state of the art SAR instruments are the SENTINEL family, ENVISAT, TERA-SAR or COSMO-SkyMed.

A SAR, principally, produces a virtual long linear array antenna by means of computer technique moving a smaller real antenna along a straight line and collecting and storing all signals with respect to amplitude, phase, frequency, polarization, and running time for gaining desired information with special processing algorithms. The most essential SAR system component, however, is the real SAR antenna itself; it is, for example, the greatest weight driver for space borne SAR.

The evolution of SAR has shown a clear trend towards higher performance at lower cost, less mass, size and power consumption imposing strong requirements in the today’s antenna technology since larger antennas means complex, bulky, difficult to route RF harness, and strong mechanical and thermal requirements for in-orbit deployable antennas. Larger bandwidths associated with larger antennas and scanning angles requires True-Time-Delay (TTD) beamforming, resulting in bulky and complex solutions.

The use of photonic integrated circuits (PIC) technology in the beamforming is a clear key enabling technology due to TTD can be implemented by using integrated photonics achieving order-of-magnitude improvements in size and mass, antenna system integration and reduction of the risks associated to the in-orbit antenna deployment.

Europe seventh framework programme (FP7) established a project named GAIA (Photonics front-end for next-generation SAR applications, Oct. 2012—Oct. 2015), to develop the photonic technologies required in future array antenna systems for the implementation of the next generation synthetic-aperture radar (SAR) applications for future Earth observation missions.

The aim of GAIA is the development of the photonic technology required in future array antenna systems for SAR applications, covering from the optical signal distribution to the antenna, the true-time-delay control of the signal for each antenna element by using integrated photonics (PICs) both in transmission and reception, with broadband characteristics and covering up to Ka band, the design of the optical harness suitable for large, deployable antennas and the development of an antenna array module in X band (which imposes strong requirement in the optical delay implementation).

GAIA main achievements have been:

– Design, fabrication, packaging, integration and test of a Photonic Integrated Circuit (PIC) as main element of an Optical Beamforming Network (OBFN).

– Development of design, fabrication and test procedures for optimised PIC performance, considering propagation losses (< 0.1 dB/cm), crosstalk, light coupling, etc.

– Development and functional demonstration of OBFN building blocks (CSDU, FoDS, APFE and AES) confirming the suitability of a TTD Photonic Beamformer for SAR Applications.

 

 

The article sources also include:

 

 

Cite This Article

 
International Defense Security & Technology (October 5, 2022) Photonic Radars for Drones, Fighter jets, Satellites and Airships provide software-defined operation and Anti-Stealth functions. Retrieved from https://idstch.com/technology/electronics/photonic-radars-for-drones-fighter-jets-satellites-and-airships-provide-software-defined-operation-and-anti-stealth-functions/.
"Photonic Radars for Drones, Fighter jets, Satellites and Airships provide software-defined operation and Anti-Stealth functions." International Defense Security & Technology - October 5, 2022, https://idstch.com/technology/electronics/photonic-radars-for-drones-fighter-jets-satellites-and-airships-provide-software-defined-operation-and-anti-stealth-functions/
International Defense Security & Technology August 26, 2022 Photonic Radars for Drones, Fighter jets, Satellites and Airships provide software-defined operation and Anti-Stealth functions., viewed October 5, 2022,<https://idstch.com/technology/electronics/photonic-radars-for-drones-fighter-jets-satellites-and-airships-provide-software-defined-operation-and-anti-stealth-functions/>
International Defense Security & Technology - Photonic Radars for Drones, Fighter jets, Satellites and Airships provide software-defined operation and Anti-Stealth functions. [Internet]. [Accessed October 5, 2022]. Available from: https://idstch.com/technology/electronics/photonic-radars-for-drones-fighter-jets-satellites-and-airships-provide-software-defined-operation-and-anti-stealth-functions/
"Photonic Radars for Drones, Fighter jets, Satellites and Airships provide software-defined operation and Anti-Stealth functions." International Defense Security & Technology - Accessed October 5, 2022. https://idstch.com/technology/electronics/photonic-radars-for-drones-fighter-jets-satellites-and-airships-provide-software-defined-operation-and-anti-stealth-functions/
"Photonic Radars for Drones, Fighter jets, Satellites and Airships provide software-defined operation and Anti-Stealth functions." International Defense Security & Technology [Online]. Available: https://idstch.com/technology/electronics/photonic-radars-for-drones-fighter-jets-satellites-and-airships-provide-software-defined-operation-and-anti-stealth-functions/. [Accessed: October 5, 2022]

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