Microwave Photonics: Empowering Next-Generation Military Communications, Radars, and Electronic Warfare Systems for Spectrum Dominance

Rajesh Uppal July 25, 2023 Electronics & EW, Photonics Comments Off on Microwave Photonics: Empowering Next-Generation Military Communications, Radars, and Electronic Warfare Systems for Spectrum Dominance 3,146 Views

Introduction:

Microwave Photonics, the fusion of microwave and optical technologies, is revolutionizing the field of military communications, radars, and electronic warfare systems. With its unique capabilities and versatility, Microwave Photonics offers the potential for spectrum dominance, providing the armed forces with advanced capabilities for communication, surveillance, and electronic countermeasures. In this article, we explore how Microwave Photonics is enabling the next generation of military technologies, empowering armed forces with enhanced situational awareness, communication resilience, and electronic warfare capabilities.

Understanding Microwave Photonics

Microwave photonics refers to the application of photonic technologies in the microwave frequency range (typically above 1 GHz). It involves the use of optical technologies to generate, modulate, process, and detect microwave signals. The aim of microwave photonics is to use photonic devices to achieve microwave functions that are difficult or impossible for electronic techniques.

Microwave photonics offers several advantages over traditional microwave electronics, including, low loss (and, more importantly, independent of radiofrequency), high bandwidth, low noise, and immunity to electromagnetic interference. These benefits make microwave photonics particularly useful in applications where high-quality microwave signals are required, such as in radio astronomy, communication systems, and military radar systems.

In addition, it enables key processing features, such as fast tunability and reconfigurability, which are very complex or even impossible to achieve using conventional electronic approaches. These attractive properties are behind the increasing interest, from both the research community and the industry, over the last two decades in various application areas.

Bringing together the worlds of radiofrequency and optics engineering, Microwave photonics (MWP) is an emerging interdisciplinary area that investigates the interaction between microwave and optical waves for the generation, processing, control, distribution, and measurement of microwave, millimeter-wave, and THz-frequency signals.

In microwave photonics, optical technologies are used to manipulate microwave signals in a number of ways, such as frequency generation, signal modulation, filtering, and amplification. For example, microwave photonics can be used to generate microwave signals through the use of optical frequency combs, which can produce a large number of evenly spaced optical frequencies.

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Microwave photonics applications

The integration of microwave photonics with traditional microwave electronics is expected to lead to new and innovative applications in the coming years, such as high-speed communication systems, advanced radar systems, and more efficient microwave signal processing.

Another area where microwave photonics is being used is in the field of sensing, where it can be used to detect and measure physical parameters, such as temperature, pressure, and strain, with high accuracy and sensitivity. For example, microwave photonics can be used in remote sensing applications, such as weather monitoring and environmental monitoring, where real-time data is critical.

MWP is being applied in applications ranging from defense applications, such as radar and electronic warfare systems, to civil applications, such as wireless and satellite communications, imaging and instrumentation. In telecommunication networks, MWP enables distributed antenna and radio-over-fiber systems, where broadband microwave and millimeter-wave signals are delivered from/to a central office to/from a variety of base stations with limited distortion, as well as very low frequency-independent losses.

Apart from the considerable added value that MWP brings to traditional microwave and radiofrequency systems, this interdisciplinary field holds a promising future in a myriad of emerging areas, such as the Internet of Things, converged fiber-wireless and in-home networks, medical imaging systems using terahertz waves, optical coherence tomography, distributed sensing, wireless and body personal area networks, as well as converged fiber-wireless broadband access networks for 5G communications

Microwave photonics is also finding applications in the field of quantum technology, where it is being used to develop quantum communication systems, quantum computing, and quantum cryptography. Photonic technologies provide a secure and robust platform for the generation, manipulation, and detection of quantum states, which is essential for the development of these advanced technologies.

Enhanced Military Communications:

Microwave Photonics enables military communications systems with unparalleled capabilities. Through the integration of microwave and optical technologies, it offers high-speed, secure, and reliable communication networks that can withstand jamming and provide seamless connectivity in challenging environments. We delve into how Microwave Photonics enables the development of advanced military communication systems, including satellite networks, secure point-to-point links, and resilient battlefield communication.

Advanced Radar Systems:

Radar systems are critical for military operations, providing crucial surveillance and target detection capabilities. Microwave Photonics revolutionizes radar systems by enhancing their performance and capabilities. We discuss how Microwave Photonics enables the development of high-resolution imaging, phased array radar systems, and synthetic aperture radar (SAR) technology. These advancements provide the military with enhanced situational awareness, target identification, and tracking capabilities.

Electronic Warfare and Spectrum Dominance:

Microwave Photonics plays a pivotal role in electronic warfare, enabling the military to dominate the electromagnetic spectrum. We explore how Microwave Photonics enhances electronic warfare systems by providing agile and robust microwave signal generation, modulation, and detection capabilities. With Microwave Photonics, the military gains the upper hand in electronic countermeasures, signal intelligence, and spectrum monitoring, ensuring information superiority and operational advantage.

Microwave photonics for 5G Communications

Microwave photonics is also being investigated for use in 5G communications systems, where high bandwidth and low latency are essential for providing fast and reliable data transmission. By using photonics technologies, it is possible to achieve faster data transmission rates, higher spectral efficiency, and improved reliability compared to traditional microwave electronics.

Since the first radio transmission, the size of the radio spectrum has doubled every 30 months, following an exponential increase in data transfer rates in wireless communications. The next generation 5G systems would require an increase in wireless data transfer rates to above 100Gb/s that may be achieved by using millimeter-wave (30–300GHz) and terahertz (300–3000GHz) frequency ranges as carriers. Microwave photonics by combining photonics and high-frequency electronics at the chip level can provide a cost-effective method of achieving the increased bandwidth required for 5G networks.

One key application of MWP is the transport and distribution of radio or wireless signals over optical fiber. Currently, researchers are working on defining the next generation of wireless communication, i.e., 5G. 5G communications require a multi Gb/s data transmission in its small cells. For this purpose millimeter-wave (mm-wave) RF signals are the best solutions to be utilized for high-speed data transmission. Wireless access network (WAN) at millimeter-wave bands (30–300 GHz) has large bandwidth which offers an alternative for high speed indoor/hotspot communication to be utilized for 5G. For generating the high-frequency mm-wave electrical signals, using conventional electronics becomes less financially attractive, therefore, there is a high concern to directly generate mm-wave signals in the optical domain.

In a typical configuration, distributed and remote antennas gather various wireless-based services (mobile units or wireless sensor nodes, for example) and transmit their radio frequency (RF) signals to the central office through optical fiber links. The researchers are developing microwave photonics-based generation, modulation, and distribution of 60 GHz frequency band signals to be applied in 5G. The generation of photonics-based millimeter-based source is based on the principle of mixing two or more coherent longitudinal modes of the laser beam with frequency spacing equal to the wanted mm-wave. As the longitudinal modes beat with each other in the photodiode, the required electrical mm-wave could be generated.

Radar

Microwave photonics is one of the most promising directions in modern radar engineering. Application of microwave photonics components provides a significant improvement in certain characteristics of radar, such as dramatically improving informational content and resolution range of radar; increasing range of target detection; high noise immunity; performance stability under changing climate, primarily, temperature conditions; lessened weight and size parameters of antenna systems and lessened cost.

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. However, it is very difficult for the state of the art electronic technologies to operate the microwave components in multiple frequency bands without sacrificing performance. In addition, the calibration of the system would be a critical issue because the electrical devices always have different insertion losses, phase shifts and reflection coefficients in different frequency bands.

Today’s digital microwave components (synthesizers and analog-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 analog up-and-down conversions are necessary for higher frequencies. In contrast, Photonics provides high precision and ultrawide bandwidth allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimeter waves, and the detection of such signals and their precise direct digitization without downconversion. The U.S. Army Research Laboratory (ARL) has developed and patented next-generation phased array radar-based upon photonic integrated circuits.

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’). 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.

Electronic Warfare

MIT Lincoln Laboratory has been developing several MWP subsystems that leverage its technology to realize next-generation wideband EW receivers and simultaneous transmit and receive (STAR) systems. They have recently achieved and reported a compact wideband channelized electronic intelligence (ELINT) receiver architecture that leverages high-Q silicon-photonic filter PIC, low-noise lasers, and high-saturation photodetectors.

The Laboratory demonstrated a prototype system for a two-channel ELINT receiver; the system performed both channelization and photonic frequency down-conversion from X band to baseband (IF ~1.5 GHz) with image rejection >85 dB using advanced photonic filtering. This level of performance is necessary for ELINT receivers operating in dense signal environments.

The Lincoln is also developing Simultaneous transmit and receive (STAR), a critical system need in electronic attack and electronic protection systems, The Laboratory’s RF system architecture for STAR operation utilizes an adaptive RF canceller. The function of the RF canceller is to adaptively replicate the response of the surrounding environment, adjusting the transfer function, to match an inverted version of the mutual coupling between the transmitter and receiver. At Lincoln, a photonic tapped-delay-line RF canceller architecture for STAR is being developed. In this effort, low-loss photonic taps are achieved through a fiber Bragg grating (FBG) written into the core of a low-loss optical fiber.

They are also focusing on Integration of multiple photonic components on a common substrate that is highly desired not only to reduce the cost, size, weight and power (SWaP) of photonic subsystems, but also to improve the optical system performance through reduction of parasitic losses and physical delay lengths. The most basic photonic integrated circuit (PIC) for an optical communication link would include lasers, modulators, filters, amplifiers, and photodetectors.

Microwave photonics technology

The growth of MWP is driven by the availability of cost-effective telecom-based components such as lasers, modulators, and photodiodes and the ability to use optical fibers to transmit RF signals over long distances to remote antenna units.

Despite its potential, the widespread adoption of MWP has been hindered by the high cost, bulkiness, complexity, and power consumption of existing systems. Typical commercial MWP systems exhibit significant Space, Weight, and Power (SWAP) figures, rendering them unsuitable for mass production and widespread deployment required by emerging applications.

DARPA has been investigating the development of microwave photonic technology that has the potential to dramatically reduce all of the SWAP-C parameters of a traditional RF telecommunications link. DARPA has identified three dominant components that could enable a photonic link: low-noise/high-power laser diodes, low-loss/low-drive-voltage electro-optic modulators, and high-power/highly linear photodiodes. DARPA-funded research efforts have led to many discoveries and advancements in microwave-photonic components, such as electro-optic modulators, high-power photodiodes, low-noise laser diodes, and microwave photonic link configurations.

Integrated microwave photonics (IMWP)

Spain Researchers Daniel Pérez, Ivana Gasulla and José Capmany, in their paper, describe the two salient approaches that are available for the implementation of IMWP chips from a functional point of view. On one hand, there is Application-Specific Photonic Integrated Circuits (ASPICs), where a particular circuit and chip configuration is designed to optimally perform a particular MWP functionality. Examples on different functionalities recently reported will be presented, including tunable filtering, optoelectronic oscillation, instantaneous frequency measurement, frequency up and down conversion, etc.

On another hand, in a radically different approach, the universal MWP signal processor architecture that can be integrated on a chip and is capable of performing all the main functionalities by suitable software programming of its control signals. This last approach is inspired by the flexibility of digital signal processors, where a common hardware is shared by multiple functionalities through a software-defined approach (or programmability), leading to significant cost reduction in the hardware fabrication.

In such concept, the central element is a reconfigurable optical core included after external modulation (represented as an E/O device) and prior to detection (represented as an O/E device). The role of the optical core is to provide the required routing/switching functionalities and also the implementation of reconfigurable processing elements such as FIR/IIR filtering, delay lines and phase shifting operations either in standalone or in cascade configuration.

Future Trends and Innovations:

We discuss the future trends and potential innovations in Microwave Photonics for military applications. This includes advancements in integrated microwave photonic circuits, cognitive radio systems, quantum microwave photonics for secure communication, and the development of compact, lightweight systems for military deployment. These advancements will shape the future of military technologies, ensuring enhanced capabilities and resilience in the ever-evolving battlefield.

Conclusion:

Microwave Photonics is set to transform the landscape of military communications, radars, and electronic warfare systems. By leveraging the integration of microwave and optical technologies, armed forces gain enhanced communication resilience, improved surveillance capabilities, and electronic warfare dominance. The potential for spectrum dominance becomes a reality, empowering the military to maintain information superiority and achieve mission success. With ongoing research and technological advancements, Microwave Photonics will continue to play a pivotal role in shaping the future of military operations.