Wireless electronic systems have been relying on dish antennas to send and receive signals. These systems have been widely used where directivity is important and many of those systems work well at a relatively low cost after years of optimization. These dish antennas having a mechanical arm to rotate the direction of radiation does have some drawbacks, which include being slow to steer, physically large, having poorer long-term reliability, and having only one desired radiation pattern or data stream.
The demands on Wireless communications and radar systems have been continuingly increasing as the need for accuracy, efficiency, and more advanced metrics become increasingly important. Many new applications will only be possible with antennas that consume less power in a lower profile than traditional mechanically steered dish antennas. For example, the ongoing New Space revolution which has planned up to 50,000 active satellites to be in orbit over the next 10 years. All these satellites have complex and variegated sets of orbits and waveforms that satellite communication (SATCOM) networks need to support. This drives the need for SATCOM operators to create flexible and adaptable networks capable of operating on a myriad of different waveforms, orbits, and constellations—while simultaneously maintaining service quality and profitability.
These requirements are in addition to the desire to reposition quickly to a new threat or user, transmit multiple data streams, and operate over longer lifetimes at aggressive cost targets. In some applications, there is a need to null an incoming blocking signal and have a low probability of intercept.
As a result, engineers have pushed toward advanced antenna architecture such as phased array antenna technology to improve these features and add new functionality. Phased array antennas include multiple emitters and are used for beamforming in high-frequency RF applications. A phased array antenna enables beamforming by adjusting the phase difference between the driving signal sent to each emitter in the array. This allows the radiation pattern to be controlled and directed to a target without requiring any physical movement of the antenna. Phased array antennas are a type of antenna array that comes with the feature of electronic steering to change the direction and shape of radiated signals, without any physical movement of the antenna. The phase difference between the radiated signals from each antenna in the array is responsible for this electronic steering.
Phased Array antenna principle
A phased array antenna is a collection of antenna elements assembled together such that the power from the transmitter is fed to the antennas through devices called phase shifters, controlled by a computer system. The fundamental principle of the phased array antenna is the phase-dependent superposition of two or more radiated signals. When the signals are in-phase, they combine together to form a signal of additive amplitude. When the signals are counter-phase, they cancel each other.
Each antenna in the array has an independent phase and amplitude setting to form the desired radiation pattern. This phase shift will introduce interference between the signals transmitted. which can alter the phase electronically, thus steering the beam of radio waves to a different direction. The radiofrequency current from the transmitter is fed to the individual antennas with the correct phase relationship so that the radio waves from the separate antennas add together to increase the radiation in the desired direction while canceling to suppress radiation in undesired directions. The direction of radiation can be manipulated by changing the phase of the signal fed into each antenna element.
The phase shift is controlled by placing a slight time delay between signals sent to successive emitters in the array. Outside of the main beam emission direction, the beam intensity decreases. There are also sidelobes in the beam pattern because signals are periodic, but you do get a very strong beam along a specific direction.
The radiation pattern of each individual element constructively combines with neighboring antennas to form an effective radiation pattern called the main lobe. The main lobe transmits radiated energy in the desired location while the antenna is designed to destructively interfere with signals in undesired directions, forming nulls and side lobes. The antenna array is designed to maximize the energy radiated in the main lobe while reducing the energy radiated in the side lobes to an acceptable level.
Phased array antennas are electrically steered and offer numerous benefits compared to traditional mechanically steered antennas such as low profile/less volume, improved long-term reliability, fast steering, and multiple beams.
Power—the power of the collective signal is the summation of the individual signal powers, therefore, the strength is increased.
Beamforming—the shape of the beam can be controlled by the phase difference of the individual signals and the radiation pattern of the phased array antenna is narrow compared to single antennas.
Beam Steering—the elimination of mechanical repositioning makes the beam steering or beam positioning flexible. The beam steering is established using electronically variable phase shifters.
Multi-Beams—with the help of phase shifters, hundreds of beams can be synthesized in phased array antennas.
Digital or Mixer Option—phase shifting can be achieved either in an analog or digital way. The analog phase shifters rely on down-conversion and time-shifting of signals. The digital approach is to shift the phase of the Intermediate Frequency (IF) mixer or Local Oscillator (LO) signal.
Weight—the weight of phased array antennas is less than the mechanically-steered single antenna.
Cost—a mechanically-steered antenna can be replaced by a less expensive phased array antenna, keeping the resolution the same.
Reliability—the reliability of phased array antennas is much greater than single antennas. If one array antenna becomes impaired, the remaining antennas in the array will continue to function with a slight modification of the radiation pattern.
Phased Array Applications
Phased arrays were invented for use in military radar systems, to steer a beam of radio waves quickly across the sky to detect planes and missiles. With above benefits, the industry is seeing adoption in military applications, satellite communications (satcom), and 5G telecommunications including connected automobiles.
The future of 5G communication requires key technologies such as multiple accesses, multi-beams, high gain, and ultra-dense networking. Antenna designers are prepared to meet the requirements of upcoming wireless communication systems with phased array antennas.
In particular, phased array technology offering electronic steering is an asset in RF wireless communication systems. With phased array antennas, you can electronically enhance the direction, strength, and shape of the transmitted or received beams without loss of resolution.
Phased array antennas are also important for applications such as SATCOM On-The-Move (SOTM) which offers a means for Beyond-Line-Of-Sight satellite communications. Satcom on the Move (SOTM), or satellite communications on the move, is a phrase used in the context of mobile satellite technology, specifically relating to military ground vehicles, Maritime and Airborne platforms. The basic principle behind Satcom On The Move is that a vehicle equipped with a satellite antenna is able to establish communication with a satellite and maintain that communication while the vehicle is moving. Ubiquitous SOTM requires mobile-based tactical ground terminals with reduced cost, size, weight and power (CSWaP). Phased-array beamforming antenna technology enables fast electronic beam steering without moving antenna apertures and is a key technology enabler for SOTM. However, phased arrays have yet to be widely deployed mainly because of high implementation cost.
Today, satcom applications consist of active electronically scanned arrays (AESAs) that use multiple transmit/receive modules (TRMs) to electronically steer beams independently. In the past, AESAs were quite large as they used a 3D brick configuration made up of boards placed side by side and attached using multiple connectors and cables.
Instead of this bulky configuration, designs are now using 2D planar arrays that are built like a PCB using surface-mount (SM) attachment of components (Figure 1, right). A planar configuration removes the need for most connectors and cables, which not only improves SWaP-C but also increases reliability and simplifies manufacturing.
Phased array radar systems are used by warships of many navies. Because of the rapidity with which the beam can be steered, phased array radars allow a warship to use one radar system for surface detection and tracking (finding ships), air detection and tracking (finding aircraft and missiles) and missile uplink capabilities. Before using these systems, each surface-to-air missile in flight required a dedicated fire-control radar, which meant that radar-guided weapons could only engage a small number of simultaneous targets. Phased array systems can be used to control missiles during the mid-course phase of the missile’s flight. During the terminal portion of the flight, continuous-wave fire control directors provide the final guidance to the target. Because the antenna pattern is electronically steered, phased array systems can direct radar beams fast enough to maintain a fire control quality track on many targets simultaneously while also controlling several in-flight missiles.
The AN/SPY-1 phased array radar, part of the Aegis Combat System deployed on modern U.S. cruisers and destroyers, “is able to perform search, track and missile guidance functions simultaneously with a capability of over 100 targets.” Likewise, the Thales Herakles phased array multi-function radar used in service with France, Russia and Singapore has a track capacity of 200 targets and is able to achieve automatic target detection, confirmation and track initiation in a single scan, while simultaneously providing mid-course guidance updates to the MBDA Aster missiles launched from the ship. The German Navy and the Royal Dutch Navy have developed the Active Phased Array Radar System (APAR). The MIM-104 Patriot and other ground-based antiaircraft systems use phased array radar for similar benefits.
Phased Array Technology
The three types of phased array antennas are 1) linear array, 2) planar array, and 3) frequency scanning array.
Linear Array: The array elements are placed in a straight line with a single-phase shifter. Even though the antenna arrangement is simple, the beam steering is limited to a single plane. The vertical arrangement of several linear arrays forms the flat antenna.
Planar Array: For each antenna in a planar array, there is a phase shifter. The matrix arrangement of the individual antennas form the planar arrangement. The beam can be deflected in two planes. The disadvantage of planar array antennas is the large number of phase shifters required.
Frequency Scanning Array: If the beam steering control is a function of the frequency of the transmitter, then phased array antennas utilizing such technology are called frequency scanning array antennas. No phase shifters are present in frequency scanning array antennas, and the beam steering is controlled by the transmitter’s frequency.
Phased arrays take multiple forms. However, the four most common are the passive phased array (PESA), active electronically scanned array (AESA), hybrid beam forming phased array, and digital beam forming (DBF) array. A passive phased array or passive electronically scanned array (PESA) is a phased array in which the antenna elements are connected to a single transmitter and/or receiver, as shown in the animation. PESAs are the most common type of phased array. Generally speaking, a PESA uses one receiver/exciter for the entire array.
An active phased array or active electronically scanned array (AESA) is a phased array in which each antenna element has an analog transmitter/receiver (T/R) module which creates the phase shifting required to electronically steer the antenna beam. Active arrays are a more advanced, second-generation phased-array technology which are used in military applications; unlike PESAs they can radiate several beams of radio waves at multiple frequencies in different directions simultaneously. However, the number of simultaneous beams is limited by practical reasons of electronic packaging of the beam former(s) to approximately three simultaneous beams for an AESA. Each beam former has a receiver/exciter connected to it.
Most phased array antennas that have been designed in past years have used analog beamforming where the phase adjustment is done at RF or IF frequencies and there is one set of data converters for the entire antenna. There is increased interest in digital beamforming where there is one set of data converters per antenna element and the phase adjustment is done digitally in the FPGA or some data converters. A digital beam forming (DBF) phased array has a digital receiver/exciter at each element in the array. The signal at each element is digitized by the receiver/exciter. This means that antenna beams can be formed digitally in a field programmable gate array (FPGA) or the array computer. This approach allows for multiple simultaneous antenna beams to be formed.
There are many benefits to digital beamforming starting with the ability to transmit many beams easily or even change the number of beams almost instantly. This remarkable flexibility is attractive in many applications and is driving its adoption. Continuous improvements in the data converters are lowering power dissipation and expanding to higher frequencies where RF sampling at the L-band and S-band are making this technology a reality in radar systems.
Semiconductor IC-based phase adjustments can be made in nanoseconds such that we can change the direction of the radiation pattern to respond to new threats or users quickly. Similarly, it is possible to change from a radiated beam to an effective null to absorb an interferer, making the object appear invisible, such as in stealth aircraft. These changes in repositioning the radiation patterns or changing to effective nulls can be done almost instantaneously because we can change the phase settings electrically with IC-based devices rather than mechanical parts. An additional benefit of a phased array antenna over a mechanical antenna is the ability to radiate multiple beams simultaneously, which could track multiple targets or manage multiple data streams of user data. This is accomplished by digital signal processing of the multiple data streams at baseband frequencies.
Conformal Phased array
One possible physical implementation of a phased array is called a conformal antenna. It is a phased array in which the individual antennas, instead of being arranged in a flat plane, are mounted on a curved surface. The phase shifters compensate for the different path lengths of the waves due to the antenna elements’ varying position on the surface, allowing the array to radiate a plane wave. Conformal antennas are used in aircraft and missiles, to integrate the antenna into the curving surface of the aircraft to reduce aerodynamic drag.
There are multiple considerations to make when considering analog vs. digital beamforming, but the analysis usually is driven by the number of beams required, power dissipation, and cost targets. The digital beamforming approach typically has higher power dissipation with a data converter per element but offers a lot of flexibility in the ease of creating multiple beams. The data converters also require higher dynamic range since the beamforming that rejects blockers is only done after the digitization.
Analog beamforming can support multiple beams but requires an additional phase adjustment channel per beam. For example, to create a 100 beam system would multiply the number of RF phase shifters for a 1 beam system by 100, so the cost consideration of data converters vs. phase adjustment ICs can change depending on the number of beams. Similarly, the power dissipation is usually lower for an analog beamforming approach that can utilize passive phase shifters but as the number of beams increases, the power dissipation will increase as well if additional gain stages are needed to drive the distribution network. A common compromise is a hybrid beamforming approach where there are subarrays of analog beamforming followed by some digital combination of the subarray signals. This is an area of growing interest in the industry and will continue to evolve in the years to come.
A hybrid beam forming phased array can be thought of as a combination of an AESA and a digital beam forming phased array. It uses subarrays that are active phased arrays (for instance, a subarry may be 64, 128 or 256 elements and the number of elements depends upon system requirements). The subarrays are combined together to form the full array. Each subarray has its own digital receiver/exciter. This approach allows clusters of simultaneous beams to be created.
The phased array antenna is a complex solution that needs a careful designing of antenna elements and distribution of network to meet the requirements on bandwidth and low losses. The proposed concept aims to create a new SatCom product with low production and maintenance costs that will deliver high data rates in areas, where mobile cellular infrastructure is not available. There are design trade-offs to consider with the size of the array vs. the power of each radiating element that impacts the directivity of the beam and effective radiated power.
Another key aspect of phased array antenna design is the spacing of the antenna elements. Once we have determined the system goals by setting the number of elements, the physical array diameter is largely driven by limits to each unit cell being less than approximately one-half wavelength, which prevents grating lobes. Grating lobes amount to energy radiated in undesired directions. This puts strict requirements on the electronics that go into the array to be small, low power, and low weight. The half-wavelength spacing creates particularly challenging designs at higher frequencies where the length of each unit cell becomes smaller. This drives the ICs at higher frequencies to be increasingly integrated, packaging solutions to become more advanced, and thermal management techniques to be simplified in spite of becoming increasingly challenging.
As we construct the entire antenna, there are many challenges of the array design, including the routing of control lines, power supply management, pulsed circuitry, thermal management, environmental considerations, etc. There is a major push in the industry toward low profile arrays that consume less volume and weight. The traditional plank architecture uses small PCB planks with electronics on them perpendicularly fed into the backside of the antenna PCB. This approach has been improved over the past 20 years to continually reduce the size of the plank thereby reducing the depth of the antenna. Next-generation designs move from this plank architecture to a flat panel approach where there is enough integration in each IC to fit them simply on the backside of the antenna board, significantly reducing the depth of the antenna and making them easier to fit into portable or airborne applications.
Phased Array technology
Since the array must consist of many small antennas (sometimes thousands) to achieve high gain, phased arrays are mainly practical at the high frequency end of the radio spectrum, in the UHF and microwave bands, in which the antenna elements are conveniently small.
Numerous designs and structures for low-cost mm-wave electronic scanning antennas have been assessed. They contain active or passive-array structures, printed planar arrays, reflect arrays, or lens arrays. Each design may consist of different radiating elements with various properties, such as narrowband or wideband, linear or circularly polarized, digital or analog phase shifters, as well as various kinds of array feeding structures. The more integrated ICs significantly reduce the challenges in the antenna design and, as the antennas become smaller with more electronics packed into a reduced footprint, the antenna design demands new semiconductor technology to help make the solutions viable.
The last two decades have seen significant reduction in the costs associated with front-end monolithic microwave integrated circuit (MMIC) technologies. This is enabled not only by continuous improvement in widely used III-V semiconductor technologies (GaAs, GaN, and InP), but also new development of low cost, high performance RFICs based on Si CMOS and SiGe BiCMOS technologies.
In particular, the use of Silicon technologies could result in a ten-fold reduction in the cost for phased array antennas and enable largescale phased arrays with a very large number of radiating elements. On-Chip mixed signal processing capabilities such as built-in selftest and calibration, amplifier linearization, etc., can also be easily incorporated, even at individual element level, because of the high level of integration and mixed signal capabilities offered by CMOS.
In the past several years, Si based phased array demonstrators have been built for emerging applications such as SATCOM and upcoming 5G systems, covering frequencies ranging from microwave (3-30 GHz) to EHF (30-300 GHz). In spite of these encouraging developments, many technical challenges, such as packaging, thermal management, reliability, noise performance, and linearity, etc., still need to be addressed before IC based phased array systems can be widely deployed. The goal of this topic is to develop deployable low cost phased array antennas based on IC technologies for AEHF SATCOM applications by addressing these technical challenges.
The recent proliferation of phased array antennas has been aided by semiconductor technology. The advanced nodes in SiGe BiCMOS, SOI (silicon-on-insulator), and bulk CMOS have combined digital circuitry to control the steering in the array, as well as the RF signal path to achieve the phase, and amplitude adjustment into a single IC. It’s possible today to achieve multichannel beamforming ICs that adjust gain and phase in a 4-channel configuration with up to 32 channels aimed at millimeter wave designs.
In some lower power examples, a silicon-based IC could be a monolithic solution for all functions above. In high power applications, gallium nitride-based power amplifiers have significantly increased the power density to fit into the unit cell of phased array antennas that would have been traditionally served by traveling wave tube (TWT)-based PAs or relatively low power GaAs-based PAs.
In airborne applications, we are seeing a trend to flat panel architectures with the power added efficiency (PAE) benefits of GaN technology. GaN has also enabled large ground-based radars to move to phased array-based antenna technology from a dish antenna driven by a TWT. We are now able to have monolithic GaN ICs capable of delivering over 100 watts of power with over 50% PAE. Combining this level of PAE with the low duty cycle of radar applications allows for surface-mount solutions to be possible, greatly reducing the size, weight, and cost of the antenna array. The additional benefit beyond the pure power capability of GaN is the size reduction compared to existing GaAs IC solutions. Comparing a 6 W to 8 W GaAs power amplifier at X-band to a GaN-based solution reduces the footprint by 50% or more. This footprint reduction is significant when trying to fit these electronics into the unit cell of a phased array antenna.
First digital single-chip millimeter-wave beamformer will exploit 5G capabilities
The first fully integrated single-chip digital millimeter-wave (MMW) beamformer, created by electrical and computer engineers at the University of Michigan, opens up new possibilities in high-frequency 5G communications. The technology could be used to improve vehicle-to-vehicle communication, autonomous driving, satellite internet, and national defense, to name a few.
Beamforming allows a device that is transmitting signals to point them in a particular direction, as opposed to having the signals radiate out in all directions—which can lead to significant interference and loss of efficiency. It is an essential technique for MMW communication, which occurs at a relatively high frequency (typically between 24GHz and 100GHz). This high frequency communication allows for high-speed data transfer, one of the key advantages of 5G.
Analog beamforming has been a standard approach for researchers, but Prof. Michael Flynn has been investigating a digital approach to exploit advantages such as large-scale beamforming, highly accurate beam-patterns, flexibility, and the ability to generate multiple beams simultaneously. “With analog beamforming, you can only listen to one thing at a time,” said Flynn. “But there are a number of new applications where you want to listen to multiple things at the same time, and switch quickly between them.”
Flynn and his group built a 28GHz MMW digital beamformer, with a custom-designed antenna array consisting of 16 antennas in single integrated circuit. It is the first known single-chip system to do MMW digital beamforming. In part because it’s a single chip, the power and size are better than current digital systems by an order of magnitude. And because it’s digital, the signal can both be pointed in any direction, and can “listen” in from four different directions at once. That means, for example, the device could track four airplanes or communicate with four satellites at the same time.
For example, Flynn can imagine using digital beamforming on drones sent into disaster areas to provide emergency internet to people in trouble. Similarly, there are plans to launch satellites in space in order to provide internet to people who live outside cities, where access to the internet can be spotty or non-existent. Having phones with digital wireless beamforming capability would provide individuals with more reliable access to the Internet.
Phased Array Radar (APAR) Market
The electronically scanned arrays market is projected to grow from USD 6.24 Billion in 2016 to USD 8.43 Billion by 2021, at a CAGR of 6.20% during the forecast period. The base year considered for the study is 2015, and the forecast period is from 2016 to 2021. Factors such as replacement of traditional electronically scanned array systems and integration of active electronically scanned arrays with traditional radar system components are expected to drive the growth of the electronically scanned arrays market.
Active electronically scanned arrays (AESA) also known as active phased array radars (APAR) are equipped with transmitters and receivers, which are composed of numerous small solid-state transmitter/receiver modules. These radars are considered to be highly effective for radar resource management. Active electronically scanned arrays are capable of spreading emissions across a wide range of frequencies, and thus, are widely utilized for land and sea surveillance.
The APAR radar system can spread signal emissions across a wider range of frequencies, which makes them more difficult to detect over background noise, allowing ships and aircraft to radiate powerful radar signals while still remaining stealthy. APAR’s missile guidance capability supports the Evolved Sea Sparrow Missile (ESSM) and the SM-2 Block IIIA missile. Most of the radar systems used in modern combat aircraft are using APAR (radar by application of AESA systems). Hence, the APAR market is majorly driven by the defense sector.
The primary application area of Active Phased Array Radar (APAR) is in the defense sector. Governments across various economies are focusing on increasing investment in their military sector, in order to strengthen their defense system, which will allow them to better defend in times of war.
The medium range segment of the electronically scanned arrays market is anticipated to grow at the highest CAGR from 2016 to 2021. Frequency bands such as X, K, Ku, and Ka are considered under the medium range. Medium-range electronically scanned arrays function within the frequency range of 8 GHz to 40 GHz. These radars are used to detect targets typically between 50 km and 150 km range. Medium-range electronically scanned arrays are utilized in air traffic management, maritime activities, warships, and naval activities.
Based on platform, the naval segment of the electronically scanned arrays market is projected to grow at the highest CAGR during the forecast period. Naval radars are used for detection and tracking of naval activities. Detection of warships, submarine, offshore patrol vessels (OPV), and other naval vessels is the prime function of naval-based radar systems. These systems are also utilized for the detection of anti-ship missiles and other ammunitions.
APAR is the first naval AESA radar that gives a hemispheric coverage of out to 150 km. It is capable of searching, tracking and supporting of Evolved SeaSparrow Missiles (ESSM) and Standard Missiles SM-2, simultaneously. During a missile testing held in March 2005 by the Royal Netherlands Navy (RNLN), APAR radar system was successful in guiding two ESSM and two SM-2 simultaneously to various targets. RNLN carried out three tests scenarios on board of “De Zeven Provinciën”. APAR engaged two drones by guiding four missiles simultaneously to the targets, using only one of its four faces. This advanced technology radar system is currently only operational in the naval defense of European countries and also is developed and manufactured by Thales Nederland, which is a Europe-based company. Thus, this makes Europe the largest market for APAR.
Europe held the largest market share in the global Active Phased Array Radar (APAR) in 2017. APAR is an advanced and effective radar system used in the naval defense sector. The technology is already adapted and implemented by the navy, in countries in the Europe region. APAR is operational in the four Royal Netherlands Navy (RNLN) LCF De Zeven Provinciën class frigates, three German Navy F124 Sachsen class frigates, and three Royal Danish Navy Ivar Huitfeldt class frigates, since late 2000s.
The electronically scanned arrays market in the Asia-Pacific region is anticipated to grow at the highest CAGR during the forecast period, owing to increasing terror threats in this region, which have propelled the demand for upgrading surveillance capabilities. Territorial disputes among countries in the Asia-Pacific region have grown considerably over the past decade. This has further led to rise in military budgets to enhance anti-missile capacities, thereby contributing to the increasing demand for electronically scanned arrays in the Asia-Pacific region.
Key players in the electronically scanned arrays market include Lockheed Martin Corporation (U.S.), Saab AB (Sweden), Northrop Grumman Corporation (U.S.), The Raytheon Company (U.S.), and Thales Group (France), Mitsubishi Electric, Israel Aerospace Industries, Japan Radio, China Electronics Technology Group Corporation (CETGC), Selex Es S.P.A, Thales Raytheon Systems Company, Kelvin Hughes, Terma A/S, Furuno Electric, and Reutech Radar Systems.
The C-COM Company is investing heavily into the R&D of next generation antenna systems and has aggressive plans to be a disruptive force in the antenna design market. C-COM is in late-stage development of a potentially revolutionary Ka-band, electronically steerable, modular, conformal, flat panel phased array antenna. In cooperation with the University of Waterloo, (CIARS), C-COM is engaged in the design of this unique antenna with the intent of providing low-cost, high-throughput mobility applications over GEO, LEO and MEO satellite constellations for land, airborne and maritime verticals.
The Company has received Government funding for the project and owns all the intellectual properties relating to the design and development of this technology. The Company has already received two patents relating to the design of this new antenna system and additional patents are pending. This project should provide C-COM with new revolutionary patentable Ka-band and higher frequency (5G+/6G) antenna technology. The antenna is going to be able to track multiple satellites in GEO/LEO and MEO orbits and could also be deployed on spacecraft and other airborne vehicles like HAPS and drones.
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