Antennas are our electronic eyes and ears on the world. They play a very important role in mobile network architecture, satellite communications system, military communications, radars and electronic warfare by transforming a Radiofrequency ( RF) signal, traveling on a conductor, into an electromagnetic wave in free space and vice versa.
The first radio antennas were built by Heinrich Hertz, a professor at the Technical institute in Karlsruhe, Germany. Since then many varieties of antennas have proliferated including dipoles/monopoles, loop antennas, slot/horn antennas, reflector antennas, microstrip antennas, log periodic antennas, helical antennas, dielectric/lens antennas and frequency-independent antennas have been . Each category possesses inherent benefits that make them more or less suitable for particular applications.
Antennas for cellular phones and all types of wireless devices link us to everyone and everything.The main objective in designing antenna system for mobile devices is that that can operate for all existing band of mobile phone from 2G to 4G, and also for extension band planned for 5G communications.
The size of the antenna has to miniaturized as much as possible while preserving the efficiency. The numerous advantages of planar or microstrip antenna, such as its low weight, small volume, and ease of fabrication using printed circuit technology, led to the design of several configurations for various personal and mobile applications.
The miniaturization is also needed because it will enable to integrate multiple antennas in a device to support MIMO schemes. Multiple transmit and multiple receive (MIMO) antennas has emerged as one of the most significant technical breakthroughs in next generation wireless communications. MIMO is the use of multiple antennas at both the transmitter and receiver to improve communication performance.
Wearable applications require antennas and electronic devices to be embedded into clothing. Generally they need to be small, lightweight, conformal, and reliable. A widely studied approach to meet these requirements is fabrication of antennas from electrically conductive textiles (e-textiles).
Military Requirements of Antennas
Military Antennas encompasses a wide range of highly sensitive active and passive, omnidirectional and directional, and broadband antennas for mobile and stationary use, covering wide spectrum from the 100 Hz to 40 GHz frequency range. Wideband antennas are essential for military systems requiring spectrum-agility or multi-functionality.
The antenna are required for land-based, naval, and airborne communications, as well as communications intelligence (COM- INT) and electronic warfare (EW) systems for communications electronic support measures (CESM) and communications electronic countermeasures (CECM). Aperture size is constrained by the dimensions of the host platform (e.g. aircraft or naval ship).
Military and aerospace users are keenly interested in developing antennas for SATCOM-on-the-move (SOTM) technology for land, sea, and airborne applications. “Going forward, the parabolic- designed antenna will continue to be the mainstay for SOTM terminals because of its efficiency,” Marvin Shoemake, vice president of business development, General Dynamics SATCOM Technologies in Duluth, Ga. predicts.
Military applications combine the need for high performance and reliability with some of the hardest environmental conditions, explains Klaus Fischer, product manager, Antennas, Rhode & Schwarz in Munich, Germany. “This especially applies to antenna products, as they are generally the most exposed equipment of any system.
The need for supporting extremely high data transfer rate capable military communication systems in diverse communication environments is also driving the development of novel compact antennas and arrays. Experts predict that antennas of tomorrow will likely be smaller than today yet provide superior performance, and metamaterial technology will play an important role in new antenna development.
Modern antenna systems in mobile devices and transmission towers are increasingly being set up as arrays of antenna elements to increase performance, directionality, bandwidth and safety. For example, by adjusting the phase of individual antenna elements, the radiation pattern from an antenna array in a mobile phone can be directed away from the user for safety, while the radiation pattern from a transmission tower can be concentrated on a specific area for improved coverage. There is a demand for high-performance antenna array systems in numerous applications, such as radar surveillance, biomedical imaging, remote sensing, radio astronomy and satellite communications.
The goal of DARPA Arrays at Commercial Timescales (ACT) program is to develop a common technology base for Electronically Scanned Array (ESA) systems. Historically, most fielded ESA systems have been comprised of highly tailored, application-specific layers.
Bluewater Defense, Inc. and Vorbeck Materials Corp. have introduced of next generation, high performance wearable antennas for military, tactical and commercial use in apparel and equipment featuring multiple communication bands including LTE capabilities at AUSA 2016. They offered robust, high-gain, low-cost, and discrete conformal printed graphene antennas embedded in military apparel and backpacks. Benefits include: Increase existing cell phone coverage by up to 200%, Significant improvements of upload and download speeds, Omni-directional coverage through the deployment of an array of antennas, Supports wide frequency range from 800-3000 Mhz, Durable, flexible, washable and non-corrosive — environmentally friendly and Increased battery life by reducing operating power.
Massive MIMO Antennas for 5G
Samsung Electronics, has announced the development of breakthrough 5G-ready case-integrated antenna, which incorporates dozens of antenna elements in a module that is less than 1mm thick – a critical step towards engineering both compact small cell base stations and user devices. The new technologies are intended to be applied to both 5G base stations and end-user devices using 28GHz millimeter wave (mmWave) spectrum. mmWave frequencies are widely expected to be one of the primary enablers of next-generation networks.
Size is particularly critical for 5G devices, as the peak and average throughputs of next-generation networks are expected to be on the gigabit-scale, where radio signal processing and power consumption can be very high without appropriately efficient technologies. Also, due to the naturally short range of the high frequency mmWave spectrum, network coverage strategies will likely require dense deployments of 5G small cells mounted in inconspicuous locations on walls and utility poles. These small cells thus need to be as small, light and efficient as possible.
Massive (or Very Large) MIMO techniques use more than 100 antennas. This technique has a big potential. A massive MIMO technique can increase 10 times or more channel capacity and improve 100 times or more energy efficiency. MIMO technique is well matched at a high frequency technique such as millimeter wave (mmWAVE) techniques.
Multiple Input Multiple Output (MIMO) techniques are one of key technologies in 5G systems. The main idea is to use the multiple antennas at a transmitter and receiver to improve the performance of wireless communication systems. Namely, a higher number of MIMO antennas mean a higher spectral efficiency.
Researchers at Utah State University are developing smarter antenna to improve cell phone service and data streaming that can dynamically change its properties like frequency, polarization, and radiation pattern. A circuit board allows the antenna to morph its dimensions to better function with the varying signals. The goal of the research is to be able to maintain optimum performance at all times on all wireless devices. U.S. Air Force recently gave USU a grant for $1 million to expand the research.
Adaptive antenna systems can steer the main beam in a desired direction and spatial nulls in undesired directions to avoid interference. Adaptive antenna systems represent a significant element of design for enhanced small‐cell deployment. These kinds of adaptive antenna systems can enable extension of transmission range, increase of data throughput, enhance spectrum reuse, and substantially reduce co-channel interference which is one critical issue in future heterogeneous wireless communications systems where classical macro networks and more advanced small cell systems are coexisting.
Active steering Antennas
Ethertronics has unveiled a new chip that will bring its active steering algorithms to Wi-Fi antennas, increasing their range and boosting their throughput in less than optimal conditions. Active steering essentially creates multiple radiation patterns around the same antenna and then selects the ideal pattern to hit its targeted device with best signal. Ethertronics has demonstrated in its tests, a 20 percent to 45 percent increase in throughput between access points and devices living on the fringes of a network.
UT Austin Engineers Design Next-Generation Non-Reciprocal Antenna
Andrea Alù, associate professor in the Department of Electrical and Computer Engineering, along with postdoctoral fellows Yakir Hadad and Jason Soric, have designed a non-reciprocal antenna, as reported in the Proceedings of the National Academy of Sciences.“Our achievement is that we break the symmetry between transmission and reception signals, so we are able to prevent the antenna from having to listen to reflections and echoes that affect the source,” Alù said.
“We show that it is possible to efficiently overcome these constraints using temporally modulated traveling-wave antennas.” This enables faster data rates and improved connections while requiring less bulky antenna systems.Beyond telecommunications, the new antenna technology may be applied to sensors used in applications as diverse as health care and weather tracking, allowing the sensors to pick up stronger signals for more accurate data collection.
Conventional antennas are subject to reciprocity, or the natural symmetry in radiation characteristics while transmission or reception, because of which they unavoidably transmit and receive signals with the same efficiency. As it happens, this property is not always a beneficial feature because transmitting antennas are prone to absorb surrounding reflections or echoes that bounce back from nearby obstacles. This noise deteriorates the quality of the transmission signals.
In the team’s experiments, the researchers fed the antenna with two signals simultaneously: the radio-frequency signal that they want to transmit or receive, and a weak low-frequency modulation signal that slowly changes the properties of the antenna as the radio-frequency signal travels along it. This modulation breaks the inherent symmetry of the antenna in transmission and reception, overcoming the reciprocity constraints. Presently in the telecommunications field, magnet-based isolators are commonly used as part of antenna systems to prevent received signals from traveling into the transmission amplifier. The researchers believe their new antenna may be an efficient solution to significantly reduce the need of isolators and reduce the size and cost of telecommunication systems.
Tunable Liquid Metal Antennas
Researchers have held tremendous interest in liquid metal electronics for many years, but a significant and unfortunate drawback slowing the advance of such devices is that they tend to require external pumps that can’t be easily integrated into electronic systems.
Team of North Carolina State University (NCSU) researchers have created a reconfigurable liquid metal antenna controlled by voltage only by using electrochemical reactions to shorten and elongate a filament of liquid metal and change the antenna’s operating frequency. Applying a small positive voltage causes the metal to flow into a capillary, while applying a small negative voltage makes the metal withdraw from the capillary.
The shape and length of the conducting paths that form an antenna determine its critical properties such as operating frequency and radiation pattern. “Using a liquid metal—such as eutectic gallium and indium—that can change its shape allows us to modify antenna properties more dramatically than is possible with a fixed conductor,” explained Jacob Adams, coauthor and an assistant professor in the Department of Electrical and Computer Engineering at NCSU.
The positive voltage “electrochemically deposits an oxide on the surface of the metal that lowers the surface tension, while a negative potential removes the oxide to increase the surface tension,” Adams said. These differences in surface tension dictate which direction the metal will flow.
This advance makes it possible to “remove or regenerate enough of the ‘oxide skin’ with an applied voltage to make the liquid metal flow into or out of the capillary. We call this ‘electrochemically controlled capillarity,’ which is much like an electrochemical pump for the liquid metal,” Adams noted.
Myriads of potential applications await within the realm of mobile devices. “Mobile device sizes are continuing to shrink and the burgeoning Internet of Things will likely create an enormous demand for small wireless systems,” Adams said. “And as the number of services that a device must be capable of supporting grows, so too will the number of frequency bands over which the antenna and RF front-end must operate. This combination will create a real antenna design challenge for mobile systems because antenna size and operating bandwidth tend to be conflicting tradeoffs.”
This is why tunable antennas are highly desirable: they can be miniaturized and adapted to correct for near-field loading problems such as the iPhone 4’s well-publicized “death grip” issue of dropped calls when by holding it by the bottom. Liquid metal systems “yield a larger range of tuning than conventional reconfigurable antennas, and the same approach can be applied to other components such as tunable filters,” Adams said.
In the long term, Adams and colleagues hope to gain greater control of the shape of the liquid metal — not only in one-dimensional capillaries but perhaps even two-dimensional surfaces to obtain nearly any desired antenna shape. “This would enable enormous flexibility in the electromagnetic properties of the antenna and allow a single adaptive antenna to perform many functions,” he added.
Inflatable satellite antennas
US and coalition forces are using lightweight, easily transportable Ground Antenna Transmit & Receive or GATR Inflatable satellite antennas, enabling them to achieve high-bandwidth network connectivity anywhere in the world from small deployable packages. Fitting in just two transit cases, the GATR antenna provides the same robust data links as conventional rigid satellite dishes, but weighs up to 80 percent less. The spherical shape greatly reduces the effect of wind, and a unique cable anchoring system assures stability in winds exceeding 40 mph, and survivability up to 60 mph–wind speeds that can interrupt connectivity in all other terminals.
Distributed Aperture satellite Antenna
US Army is poised for a breakthrough in Antenna that would make command armored vehicles less detectable to enemies and safer to operate. The current SATCOM dish antennas are too bulky and cumbersome to fit inside heavy vehicles like the Bradley or the Abrams tank that have turreted weapon systems. The Army’s communications technology lab has identified distributed aperture terminals technology, wherein small antennas can be inserted on the exterior of the vehicle, to help shrink SATCOM systems. The Army Communications Electronics Research & Development Engineering Center (CERDEC) has awarded Harris Corp. a 29-month, $10 million fixed-price contract to build a distributed aperture satellite communications system in a Bradley infantry personnel carrier.
Low profile antennas
DARPA has awarded Kerby-Patel applied electromagnetics researcher the 2015 Young Faculty Award (YFA) for research into flatter low profile antennas that can be employed on both manned and unmanned aerial vehicles for navigation and communications.
“I’m working on a new way to design low-profile antennas backed by high impedance surfaces,” says Kerby-Patel. “High impedance surfaces are a promising new material for antennas, but right now there is a lot of trial and error in the design process. We’re trying to eliminate that trial and error.”
Her research involves three components: First, she will develop a model that simplifies the physics of the antenna into an equivalent circuit. Second, she’ll compare the behavior of the actual antenna to the model using electromagnetic simulation software and real-world experiments. Finally, she’ll use the new physical detail captured by the model to create novel methods for designing low-profile antennas.
The Best Radio Antenna Is One That’s a Tank, according to University of Wisconsin engineers
Troops in the field communicate using relatively low frequency radio signals like HF band. The upside is that they don’t require much power and can travel long distances. But to operate efficiently, antennas need to be at least one-quarter the length of the radio waves ( that can range from 10 to 100 yards at HF band) they transmit . University of Wisconsin–Madison engineers are seeking to effectively enlarge antenna size by using the vehicle itself as an antenna as part of a project supported by the Office of Naval Research (ONR).
“We’re basically looking at using the ‘antennas’ traditionally mounted on military vehicles as a means of exciting the platform itself,” says Nader Behdad, associate professor of electrical and computer engineering at UW–Madison. “If a large metallic structure is there, why not take advantage of it?”
The team aims to design “coupling structures” that, when strategically placed on a vehicle, allow it to transmit or receive signals at low frequencies. The structures act as electric or magnetic dipoles “exciting” the main structure—that is, making it resonate at frequencies comparable to its size and shape. They can “tune” the vehicle to work as an antenna across a range of frequencies.
“Think of an armored personnel carrier for example,” Behdad says. “The dimensions are generally about 10 meters long. Some natural resonate modes of the structure resonate very efficiently at HF frequencies with different [stimulative] current distributions and radiation patterns. With the scale model we used, we showed that this works.”
The team’s goal is to achieve a bandwidth of 25 KHz at 2 MHz and a larger range at 10 MHz. Such bandwidth could allow for data transmission rates up to 100 Kbps, sufficient for voice and text data if not video or images
Engineering professor brings antenna capabilities to military armor
Villanova University Electrical and Computer Engineering Professor Ahmad Hoorfar, recently announced the development and successful testing of armor panels in providing multi-channel communications and advanced active protection for vehicles, ships and buildings. He has been working on wideband low-profile antennas that provide electronic warfare, jamming and communication capabilities for fiberglass ballistic and blast-resistant armor panels.
According to the company’s news release, “The multi-function armor eliminates the need for multiple high-profile communications antenna structures on military vehicles and ships, making them less visible and identifiable in hostile situations. The armor-encased antennas also have jamming capability to block radio signals, such as those used to remotely trigger explosives, including improvised explosive devices (IEDs).”
“One of the problems that many military communications systems have is that they use low frequencies — anywhere from 2 MHz to below 1 GHz,” says Nader Behdad, an assistant professor of electrical and computer engineering at the University of Wisconsin-Madison. “As a result, very often you see huge antennas sticking off of their vehicles.”
Behdad thinks that those enormous antennas could be scrapped for low-profile, broadband antennas — thanks to a different approach to antenna design that replaces large dipole antennas with a more compact and conformal multi-mode radiator.
With traditional dipole antennas, the lower the operating frequency of an antenna, the larger it needs to be. Rather than fighting the laws of physics and trying to lower the operating frequency of a single antenna, Behdad’s concept involves tuning multiple parts of the same antenna structure to radiate at different frequencies, using synthetic “metamaterials” to shape their radiation patterns so that they won’t interfere with one another. Composed of metals, dielectrics and other materials, metamaterials react to electromagnetic waves differently, based on their index of refraction, making it possible to manipulate two competing radiation patterns and make them work in tandem within one antenna.
The research was supported by a federal Small Business Technology Transfers program sponsored by the Office of Naval Research.
US ARL exploring 3D printing antennas
Larry Holmes, the principal investigator for materials and technology development in additive manufacturing at the U.S. Army Research Laboratory (ARL), is exploring potential uses for additive manufacturing of 3D printed plastic antennas. Unlike conventional antennas that are made of conductive material University of Texas at El Paso is exploring the use of plastic or even ceramic.
Holmes explains that the 3D printed antenna would work “by the dielectrics that are internal to the structure, solely because of the shapes you can make through 3D printing.” That is, the antenna would function electronically through its geometric composition, meticulously designed with 3D technology, rather than through its material, plastic being a non-conductive material.
The benefits of having an additively manufactured antenna include being able to manufacture them on the spot rather than having parts and equipment imported, as Holmes puts it, the antenna would “help us reduce logistics and the logistics trail but also help with signature management.
DARPA’s Arrays at Commercial Timescales (ACT) program
Phased radio frequency (RF) arrays use numerous small antennas to steer RF beams without mechanical movement. Today’s electromagnetic (EM) systems use antenna arrays to provide unique capabilities, such as multiple beam forming and electronic steering, which are important for a wide variety of applications such as communications, signal intelligence (SIGINT), radar, and electronic warfare. However current phased array programs need to customize the array to a specific defense application every time a new system is needed due to which current DoD array development programs can take more than a decade and cost tens of billions of dollars.
DARPA’s Arrays at Commercial Timescales (ACT) program seeks to build rapidly upgradable and widely deployable array architecture that will be scalable and customizable for each application, without requiring a full redesign for each application space.
The ACT program has three thrusts: Digitally- interconnected common building module for insertion into a wide range of applications; Reconfigurable and tunable RF interface from S-band to X-band frequencies (and points between) and over-the-air coherent array aggregation. The third technological area of ACT aims to reduce the space requirements for defense electronics by developing distributed phased arrays that can communicate with each other to function as a single larger array.
For more information on DARPA ACT: http://idstch.com/home5/international-defence-security-and-technology/technology/electronics/darpas-act-program-speedier-development-rf-phased-array-antennas-communications-radar-electronic-warfare-ew/
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