The next generation of radar 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. High range and cross-range resolution profiles or equivalently higher Bandwidths are required for many functions including the identification and Anti-Stealth functions.
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.
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.
The world’s first photonic radar was tested at Pisa Airport in Italy and achieved “world-class” performance, according to an independent expert. 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.”
The U.S. Army Research Laboratory (ARL) has developed and patented next-generation phased array radar based upon photonic integrated circuits.
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.
Experts say 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.
“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.
Microwave Photonic Enhances Radar Performance
Researchers fro 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.
Russian Airships shall employ photonics based radar for Missile Defence in 2018
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.
“The antenna will be designed within the next two years. “We are planning to begin production of the radar based on the principles of radio-photons by 2020,” 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.
Earlier this year 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.
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.
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
“Until now, the photonics-based generation and detection of radiofrequency 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 PHODIR27.”
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.
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.
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.
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