domingo, 27 de junio de 2010

New Report: Mobile Patents and Intellectual Property Rights

Femtocells and Wi-Fi oriented fixed/mobile solutions are both important for improving wireless services in rural areas, but they rely on availability of decent quality DSL or cable lines for backhaul. But many parts of the world, including regions of Europe and north America plus emerging economies, remain underserved by wired infrastructure. A UK start-up today launches a response to that challenge, a self-installed wireless router backhauled by the cellular network and using innovative antenna technology to optimize the signal.

The WiBE (Wireless Broadband Enabler) from Deltenna is targeted mainly at rural areas with little or poor quality DSL, though it could also be used to improve indoor reception for urban users. Its supplier, a specialist in antennas and their integration with radio systems, promises a reliable 2Mbps connection for users far from the DSL exchange. It also pledges sustained data throughput at 30 times the rate, and five times the range, of a 3G dongle in areas where signal quality is poor. These USB modems have been widely touted as a solution to rural broadband, and are marketed by some cellcos, even in well-served regions, as a lower cost alternative to a DSL line, but remain less reliable than a wired option.

The WiBE is designed to be plug-and-play, and once installed, creates a 2Mbps Wi-Fi hotspot within the home or office, backhauled by 3G. The directional antenna technology achieves average download speed of 2.8Mbps over the HSPA network when a conventional handset or dongle can scarcely register a signal, the company claims after tests in rural UK. Deltenna has patented antenna technology and alignment algorithms, which enable the WiBE to identify the cell that will support the best available download speed, and configure itself automatically to focus on that cell.

The WiBE will be sold to OEMs and operators, targeting rural and emerging economy carriers. An LTE version is in development and will be announced next year, promising rural broadband speeds of 50Mbps.

Andrew Fox, CEO of Deltenna, said: "There are still millions of people throughout Europe and the US for whom fast broadband is a myth."

Iain Wood, of broadband benchmarking organization Epitiro, commented: "Rural broadband consumers in Europe and the US suffer low speeds over copper wiring as a result of being a long distance from the exchange. This challenge of achieving higher speeds lies with the implementation of new technologies to the last mile, be they wired or wireless." However, Eptiro finds that phones and dongles typically achieve only 1Mbps in rural HSPA networks.

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MTI Wireless Edge picks up major order for military antennas

Mti Wireless Edge (LON:MWE), the AIM listed technology group that makes flat panel antennas for fixed wireless broadband, has picked up a US$2.2m order from an existing client to develop and manufacture military antennas. Deliveries of the new units will span two years and approximately US$0.5m is expected to be recognised as revenue in 2010.

Dov Feiner, MTI's chief executive, said: "We are delighted with this order for military antennas. It provides an important revenue stream for us, as well as involvement in the forefront of antenna technology. As leaders in our field, we are the only company with the technical expertise and capability to provide high specification products for military application as well as industry leading antennas for the commercial, high volume market."

Israel-based MTI makes industry-unique, flat panel antennas for commercial applications, fixed wireless and RFID readers as well as military antenna solutions spanning the entire radio frequency range (2MHz-40GHz). The company disappointed investors in May by announcing a 17% fall in revenues to US$2.8m in the three months to March and an operating loss of US$0.5m. At the time it blamed a late influx of late orders during the quarter and said the revenue had simply been delayed rather than lost. In the year to December 2009, revenues fell by 25% to US$13.5m and the company hit breakeven after posting a US$1m profit the year before. It claimed that market shrinkage and increasing competition during 2009 had created a more difficult trading environment.

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URI physics employee invents new antenna technology

KINGSTON, R.I. -- June 2, 2004 -- Rob Vincent, an employee in the University of Rhode Island's Physics Department, proves the adage that necessity is the mother of invention.

An amateur radio operator since he was 14, Vincent has always lived in houses situated on small lots. Because he couldn't erect a large antenna on a confined property, he has been continually challenged over the years to find a way to get better reception.

"I was always tinkering in the basement. Thank goodness, my parents were tolerant. I can still remember my poor father driving up our driveway after a hard day's work to see wires wrapped around the house," Vincent recalls.

"The Holy Grail of antenna technology is to create a small antenna with high efficiency and wide bandwidth," explains Vincent. "According to current theory, you have to give up one of the three—size, efficiency, or bandwidth—to achieve the other two."

After decades of experimentation, combined with a 30-year engineering career and Yankee ingenuity, Vincent has invented a revolutionary antenna technology. The distributed- load, monopole antennas are smaller, produce high efficiency, and retain good to excellent bandwidth. And they have multiple applications.

With this technology it will be possible to double, at minimum, the range of walkie-talkies used by police, fire, and other municipal personnel. Naval ships, baby monitors, and portable antennas for military use are other applications. An antenna could be mounted on a chip in a cell phone and be applied to wireless local area networks. Another application deals with radio frequency identification, which is expected someday to replace the barcode system.

"It could even make the Dick Tracy wrist radio with all the features, such as Internet access, a possibility," Vincent says.

The inventor pursued his quest to build a better antenna in earnest eight years ago when he and his significant other moved into a house situated on a 50-foot by 100-foot lot in Warwick. There was nothing on the commercial market that could fit the lot that would provide the performance Vincent needed to be heard in distant lands and that would be acceptable to his neighbors. All the small antennas being sold were inefficient and lacked bandwidth, which resulted in low performance and high frustration.

Vincent looked at the techniques that were currently used to reduce antenna size and realized something was missing in the way everyone was approaching the problem.

He began to model various combinations into a computer program called MathCad. His first attempt produced a 21 MHz band antenna that was 18 inches high. Normally, antennas for this band are 12 to 24 feet high.

Vincent installed the antenna in his back yard. The legal limit that amateurs can operate is 1,000 watts with the norm being 100 watts. The amateur radio operator experimented with 5 to 10 watts. He reached a station in Chile and made contacts in various European countries. Meanwhile he kept adding power until it reached 100 watts. That's when things suddenly went bad. Walking outside in the backyard, he understood why. The antenna had melted.

After examining the molten matter, Vincent wasn't discouraged. This was only a small model and not designed to handle much power. The part of the antenna that failed proved to be the key to the design. After analyzing the failure, Vincent realized that he was able to transform a lot of current along the antenna with even relatively low power.

"Antennas radiate by setting up large amounts of current flow through various parts of their structure," he says. "The larger the current the more radiation and the better the output of the antenna."

Vincent went back to the drawing board and continued to improve the technology. Relying on his nearly 30 years at Raytheon Co. and at KVH Industries in Middletown R.I., which provided him with a diversified background in electronics and electronic systems, Vincent overcame a myriad of problems and succeeded.

He established three test sites for various prototypes. Antennas were placed in Westport, Mass. in a salt marsh, the best ground for transmission and reception. Another set of antennas was placed on rocky ground in Cumberland, R.I., the worst kind of site, and at a Warwick site which is in between the two in terms of grounding. The antennas, which resemble flagpoles, worked well at all locations.

Tests confirmed that Vincent has created antennas at one third to one ninth of their full size counterparts. Normally smaller antennas are only 8 to 15 percent efficient. Vincent's antennas achieved 80 to 100 percent efficiency as compared to the larger antennas.

A patent is pending on Vincent's technology. The inventor has made the University of Rhode Island and its Physics Department partners that will benefit from any revenue his invention earns. "The University and its Physics Department has been very supportive and given me time and space to work on this project," says Vincent who was recently presented the 2004 Outstanding Intellectual Property Award by URI's Research Office. "I couldn't have done this without the University's support. It's only fair that it share in the profits."

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Antenas inteligentes o “smart antennas”

Son antenas que combinan múltiples elementos con un procesador de señal capaz de optimizar automáticamente la radiación o el patrón de recepción. Las hay de dos tipos:

  • Las de haz conmutado, con un número finito de patrones predefinidos o estrategias de combinación (Antenas sectoriales) o

  • Las de arrays adaptativos o configuración de haz, más avanzadas, que cuentan con un número infinito de patrones de iluminación (dependiendo del escenario) y ajustan el diagrama radiante y los nulos en tiempo real.
Antena sectorial (izquierda) versus antena inteligente de configuración de haz (derecha)

Las antenas de arrays adaptativos mejoran la recepción de la señal y minimizan las interferencias, dando una ganancia mejor que las antenas convencionales. Este tipo de antenas permiten direccionar el haz principal, y/o configurar múltiples haces, así como generar nulos del diagrama de radiación en determinadas direcciones que se consideran interferentes.Con ello se aumenta la calidad de la señal y se mejora la capacidad por la reutilización de frecuencias. Son aplicables a casi todos los protocolos y estándares inalámbricos (comunicaciones móviles, WLL, WLAN, satélite, etc.).

Es una tecnología con un excelente potencial para aumentar la eficacia del uso del espectro en comparación con los sistemas radiantes tradicionales. Con un control inteligente de la iluminación de la antena se puede ampliar la capacidad y la cobertura de las redes móviles.

Antenas Adaptativas: Analogía con el oído y cerebro humano

El siguiente ejemplo le ayudará a entender cómo funciona una antena adaptativa. Cierre los ojos e inicie una conversación con alguien que se mueva por la habitación donde están ustedes dos. A pesar de tener los ojos cerrados, le resultará sencillo saber por donde se mueve el otro interlocutor, por lo siguiente:

  • Vd. está oyéndole por medio de dos oídos que son sus sensores acústicos.

  • La voz llega a cada oído por distinto camino (diversidad de espacio), por tanto los sonidos no llegan a los dos oídos a la vez. Casi siempre habrá una pequeña diferencia.

  • Su cerebro es un procesador de señal muy especial, sin que Vd. se de cuenta está realizando una gran cantidad de cálculos para determinar la posición de la otra persona.

  • Su cerebro, además, suma las señales de los dos oídos, de modo que el sonido que le llega de la orientación del interlocutor es el doble de intenso del que le llega de otras zonas.
Las antenas adaptativas hacen lo mismo, con antenas en vez de oidos. Incluso pueden tener 8, 10 o 12 oídos para ser más precisas. Y como además de recibir sirven para emitir, un sistema adaptativo puede ajustar el patrón de emisión para que ilumine hacia la misma dirección de donde recibe. Por tanto, ese sistema además de "recibir" 8, 10 o 12 veces más fuerte también puede "emitir" más fuerte y con mayor directividad.

Demos un paso más con este ejemplo; si entrasen más personas a la habitación, su procesador de señal (su cerebro) ignoraría el ruido producido por las otras conversaciones, las que no quiere escuchar (las interferencias), para enfocar su antención en la conversación deseada. De manera similar un sistema adaptativo con un procesador adecuado puede diferenciar entre las señales deseadas y las no deseadas.

Multiplexación en código: Analogía con el oído y cerebro humano

Al hilo del ejemplo anterior, aprovecharemos para presentar otro caso que está indirectamente relacionado con las antenas inteligentes: imagine ahora que está en el extranjero en un local lleno de gente, bastante ruidoso por cierto, donde la mayoría de las personas están hablando en el idioma local.

¿No cree le resultará bastante fácil percatarse de alguna conversación que se esté manteniendo en medio de aquel ruido en el idioma de su país, en su idioma materno?

Podríamos decir que las conversaciones de ese local está multiplexadas en código, y que Vd., su cerebro, tiene un procesador de señal con la clave adecuada para distinguir las de su idioma.

Concepto MIMO

Multiple-Input Multiple-Output o MIMO (en castellano « entradas múltiples, salidas múltiples ») es una tecnología de antenas inteligentes de arrays adaptativos empleada en algunas redes inalámbricas como, por ejemplo, en femtoceldas y en WiMAX que aprovecha el fenómeno de multipropagación y radiocomunicaciones en diversidad de espacio para conseguir una mayor velocidad y un mejor alcance del que se consigue con las antenas tradicionales.

La tecnología MIMO emplea varias antenas tanto en el transmisor como en el receptor, y para un mismo ancho de banda y potencia transmitida consigue mejores resultados que los sistemas SISO (single-input single-output). La capacidad de un sistema MIMO en un entorno de dispersión por multipropagación, cuando las señales recibidas no están correlacionadas entre sí, es proporcional al número de antenas empleadas. El diseño de las antenas y el proceso de la señal recibida necesita técnicas especializadas.

El diseño de las antenas MIMO buscar reducir la correlación entre las señales recibidas, para ello utiliza los diferentes modos de diversidad que se pueden dar en la recepción, como la diversidad de espacio (al estar las antenas separadas), la diversidad de ganancia (por emplear antenas con diferentes patrones de radiación, ortogonales u otros) y la diversidad de polarización (antenas con distinta polarización) etc. Estas tres formas de diversidad se muestran el la figura siguiente.

Variantes de la tecnología MIMO

MIMO: Multiple input multiple output; este es el caso en el que tanto transmisor como receptor tienen varias antenas.

MISO: Multiple input Single output; en el caso de que haya varias antenas de emisión pero solamente una en el receptor.

SIMO: Single input multiple output; en el caso de una sola antena de emisión y varias antenas en el receptor.

En función de las tres variantes citadas se empleará una u otra de las siguientes tecnologías:

  • Configuración de Haz (Beamforming): Consiste en la formación de un patrón de iluminación bien determinado, fruto del desfase de la señal en las distintas antenas. Sus principales ventajas son una mayor ganancia de señal además de una menor atenuación con la distancia. Gracias a la ausencia de dispersión el beamforming consigue un patrón bien definido y direccional. En este tipo de transmisiones se hace necesario el uso de dominios de configuración de haz, sobre todo en el caso de múltiples antenas de transmisión. Hay que tener en cuenta que esta técnica precisa un conocimiento previo del canal a utilizar en el transmisor.

  • Multiplexación espacial (Spatial multiplexing): Consiste en la multiplexación de una señal de mayor ancho de banda en señales de menor ancho de banda iguales transmitidas desde distintas antenas. Si estas señales llegan con la suficiente separación en el tiempo al receptor este es capaz de procesarlas y distinguirlas creando así múltiples canales en anchos de banda mínimos. Esta técnica es eficaz para aumentar la tasa de transmisión, sobre todo en entornos difíciles en cuanto a la relación señal ruido. Únicamente está limitado por el número de antenas disponibles tanto en receptor como en transmisor. No requiere el conocimiento previo del canal en el transmisor o receptor. Para este tipo de transmisiones es obligatoria una configuración de antenas MIMO.

  • Diversidad de código (Code-division multiple access): Son una serie de técnicas que se emplean en medios en los que por alguna razón solo se puede emplear un único canal, codificando la transmisión mediante espaciado en el tiempo y la diversidad de señales disponibles dando lugar al código espacio-tiempo. Para aumentar la diversidad de la señal se recurre a una emisión desde varias antenas basándose en principios de ortogonalidad.
La multiplexación de espacio puede ser combinada con la configuración de haz cuando el canal es conocido en el transmisor o combinado con la diversidad de código cuando no es así. La distancia física entre las antenas ha de ser múltiples longitudes de onda en la estación base. Para poder distinguir las señales con claridad, la separación de las antenas en el receptor tiene que ser de al menos 0,3 λ.

Aprovechamiento de la diversidad de espacio

En un sistema de comunicaciones es básico poder distinguir los usuarios. Los sistemas de acceso múltiple más usuales son la multiplexación en frecuencia (frequency division multiple access, FDMA), la multiplexación en tiempo (time-division multiple access, TDMA) y la la multiplexación en código (code-division multiple access, CDMA). Estás técnicas separan los usuarios según la frecuencia, el tiempo y el código, respectivamente, y proporcionan tres tipos de diversidad.
Figura 1 TDMA (izda.), FDMA (centro), CDMA (dcha.)

Una antena inteligente puede reducir las interferencias empleando diversidad de espacio (que se suele denominar en inglés como spatial diversity o SDMA) y en consecuencia aumentar la capacidad de comunicación adaptando dinámicamente las características del sistema radiante. Concretamente, concentra y dirige el haz al usuario, consiguiendo mayor eficacia que una antena sectorial y mejorando el comportamiento ante interferencias.

Patrones de iluminación – Configuración de haz

Un sistema radiante con elementos en fase está formado por un conjunto de elementos radiantes cuyas señales se suman y forman un determinado patrón de radiación o iluminación. Cambiando la amplitud y fase de los elementos individuales se puede modificar la forma del patrón de iluminación, fenómeno que se conoce como "confifuración de haz" (o beamforming process en inglés).

En este tipo de sistemas radiantes se busca tener el máximo de señal en la dirección deseada, y simultáneamente conseguir "nulos" en la dirección de las emisiones indeseadas. Por tanto, la antena se puede ajustar para que tenga una alta sensibilidad a las señales de un determinado usuario y que tenga menos a las de otros usuarios.

Las antenas inteligentes que estamos tratando en este artículo incorporan unos procesadores para poder de variar dinámicamente el patron radiante.

Una de los entidades reguladoras nacionales (ANR) que más esfuerzos de investigación y pruebas ha dedicado a estas técnicas es Ofcom, que ya en 2003 construyó un prototipo de sistema WiFi, IEE 802.11a con antena inteligente, que se muestra en la imagen siguiente.

Prototipo de punto de acceso 802.11a con antena adaptativa semi-inteligente y procesador

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Phased array

Un phased array ("agrupación de antenas controladas por fase") es un conjunto de antenas (array) en el cual las fases relativas de las señales con que se alimenta cada antena se varían intencionadamente con objeto de alterar el diagrama de radiación del conjunto. Lo normal es reforzar la radiación en una dirección concreta y suprimirla en direcciones indeseadas.

Esta tecnología fue desarrollada originalmente por el futuro Premio Nobel Luis Walter Álvarez durante la Segunda Guerra Mundial, para funcionar en radares de respuesta rápida destinados a aplicaciones de Ground-Controlled Approach (GCA), es decir, de ayuda al aterrizaje de aeronaves. Más tarde se adaptó para usos en radioastronomía, valiéndole el Premio Nobel de Física a Anthony Hewish y Martin Ryle, tras desarrollar phased arrays de gran tamaño en la Universidad de Cambridge. El diseño se usa por tanto en radar y es de uso habitual en antenas de radio interferométricas.

PAVE PAWS phased array radar in Alaska.

Si todos los elementos del array están contenidos en el mismo plano y la señal con que se alimentan es de la misma fase, entonces se estará reforzando la dirección perpendicular a ese plano. Si se altera la fase relativa de las señales se podrá "mover" el haz (en realidad lo que se está haciendo es cambiar la dirección en la cual las interferencias son constructivas). Se consigue de este modo hacer barridos sin necesidad de movimiento físico, con la ventaja añadida de que se pueden escanear ángulos del orden de miles de grados por segundo. Esto permite utilizar la antena para compaginar simultáneamente funciones de detección y de seguimiento muchos blancos individuales. Apagando y encendiendo algunos de los elementos radiantes se puede variar el haz de radiación, ensanchándolo para mejorar las funciones de búsqueda o estrechándolo para hacer un seguimiento preciso de un objetivo.

Modelo de phased array de la segunda guerra mundial.

El punto débil de los phased arrays es la imposibilidad de dirigirlo correctamente en ángulos cercanos al plano en el que están los elementos radiantes. Para hacer una cobertura de 360º se suelen disponer 3 arrays en las paredes de una superficie piramidal (ver foto).

Base en Alaska de Cobra Dane

El uso de los phased arrays se remonta a la Segunda Guerra Mundial, pero las limitaciones de la electrónica hacían que fueran poco precisos. Su aplicación original era la defensa antimisiles. En la actualidad son parte imprescindible del sistema AEGIS y el sistema balístico MIM-104 Patriot. Su uso se va extendiendo debido a la fiabilidad derivada del hecho de que no tienen partes móviles. Casi todos los radares militares modernos se basan en phased arrays, relegando los sistemas basados en antenas rotatorias a aplicaciones donde el costo es un factor determinante (tráfico aéreo, meteorología,...) Su uso está también extendido en aeronaves militares debido a su capacidad de seguir múltiples objetivos. El primer avión en usar uno fue el B-1B Lancer, y el primer caza, el MiG-31 ruso. El sistema radar de dicho avión está considerado como el más potente de entre todos los cazas.

En radioastronomía también se emplean los phased arrays para, por medio de técnicas de apertura sintética, obtener haces de radiación muy estrechos. La apertura sintética se usa también en radares de aviones.

Uso de los phased array

Broadcasting (difusión)

En ingeniería de difusión (broadcast),los phased arrays se usan en muchas estaciones de difusión AM por radio para mejorar la potencia de la señal y por lo tanto mejorar la cobertura ofrecida dentro del área establecida para la difusión, minimizando así las interferencias en otras áreas colindantes. Debido a la diferencia entre el día y la noche para la propagación de las ondas por la ionosfera a frecuencias medias, es muy común que las estaciones AM cambien de patrones de radiación utilizando unos para el día y otros para la noche mediante cambios en la fase y la potencia suministrados a los elementos radiantes de cada antena individual.

En VHF, los phased arrays se usan por extensión para la difusión FM. De esta forma se consigue aumentar en gran medida la ganancia de la antena maximizando la energía de radiofrecuencia emitida hacia el horizonte lo que en consecuencia aumenta considerablemente el rango de difusión de la estación.

Uso Naval

Los sistemas de radar basados en phased array se usan en los barcos de guerra de diversas armadas como las de China, Noruega, Estados Unidos, España, etc . Los radares basados en phased arrays permiten a los barcos de guerra usar un radar para detección y búsqueda superficial (encontrando barcos), aérea (detectando misiles y aviones). Antes de usar estos sistemas, cada misil tierra-aire en vuelo necesitaba un radar de control dedicado, lo que significaba que los barcos podían únicamente tener localizados un pequeño número de objetivos. Dado que el haz del radar está dirigido electrónicamente, estos sistemas pueden dirigir las radiaciones del radar lo suficientemente rápido como para mantaner simultáneamente controlados numerosos objetivos, y a la vez, seguir controlando misiles en vuelo. Por ejemplo el radar AN/SPY-1, que pertenece al sistema Aegis combat system de los cruceros y destructores estadounidenses, "es capaz de realizar tareas de búsqueda, localización y guía de misiles simultáneamente de unos 100 objetivos"

Paneles octogonales del radar phased array: AN/SPY-1D, del "USS Mason (DDG-87)".

Pruebas de comunicaciones espaciales

La nave espacial MESSENGER , con misión hacia el planeta Mercurio, tiene prevista su llegada el 18 de marzo de 2011. Esta nave es la primera en ir a una misión al espacio lejano usando phased-array para telecomunicaciones.

Usos en climatología

El Laboratorio Nacional de tormentas severas ha estado usando una antena basada en phased array tipo SPY-1A procedente de la Armada de Estados Unidos para estudios climatológicos desde el 23 de abril de 2003. Mediante este tipo de estudios se logra una mejor comprensión de los tornados y tormentas, pudiendo así predecirlos con mayor margen de tiempo para tomar las precauciones pertinentes.

Instalando el AN/SPY-1A en Norman, OK.

Comunicaciones ópticas

Es posible construir Phased arrays ópticos que emitan en las bandas visibles o infrarrojas. Estos phased arrays se usan en multiplexadores de longitud de onda , filtros para telecomunicaciones, direccionamiento de rayos láser, y holografía.

Identificaciones de radiofrecuencia

Las antenas basadas en phased array han sido incluidas recientemente en sistemas RFID para mejorar de forma significativa la capacidad lectora de las tarjetas pasivas de UHF que pasen de 20 a 600 pies.

Tipos de Phased Array

Hay numerosos tipos de Phased arrays. Básicamente:
  • Phased arrays en el dominio temporal.
  • Phased arrays en el de la frecuencia

Un Phased arrays en el dominio del tiempo funciona mediante operaciones temporales. La operación básica se denomina "retarda y suma" (delay and sum). Funciona retardando la señal de entrada de cada array una cierta cantidad de tiempo, y después las suma todas. En ocasiones se multiplica el array por una ventana para incrementar el radio del lóbulo principal o de los laterales del diagrama de radiación, y para insertar ceros en las características.

Hay muchos tipos de phased arrays en el dominio de la frecuencia. El primer tipo separa componentes frecuenciales presentes en la señal recibida en diferentes haces usando filtros y FFT. Cuando se le aplican a cada componente frecuencial los diferentes retardos y sumas, es posible apuntar el lóbulo principal hacia diferentes direcciones para diferentes frecuencias, lo que es una gran ventaja para enlaces de comunicaciones.

Otro tipo de phased array hace uso de las denominadas frecuancias espaciales. Esto significa que se realiza una FFT entre los diferentes elementos del array, pero no al mismo tiempo. La salida de la FFT de N puntos son N canales que son divididos en espacio. Esta aproximación hace muy simple la implementación de diferentes phased array en el mismo tiempo, pero no es muy flexible porque sus direcciones de radiación son fijas.

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Manufacturer: Hollandse Signaalapparaten BV, Niederlande,

SMART-S (Signaal Multibeam Acquisition Radar for Targeting) is an all-weather 3-D target indication and surveillance radar system intended for all types of naval vessels from fast patrol boats upwards. Its prime application is as the main sensor for data handling and weapon system control, and it has a very high performance in the presence of heavy clutter and electronic countermeasures. The equipment has been designed to cope with small high-speed anti-ship missiles with radar cross-sections down to 0.1 m2 and approach speeds of Mach 3+, which can be either sea skimmers or arriving from high angles of 70° or more.

Figure 1: SMART-S antenna (Source: Jane's Information Group)

The SMART system operates in F-Band (the traditional of this frequency band name was S-Band, the designator is SMART-S therefore), where it offers an optimum balance between range, clutter rejection and antenna dimensions. It provides automatic detection, track initiation and track maintenance of both air and surface threats, with gapless coverage over a complete hemisphere from the sea surface upwards. It incorporates anti-clutter and electronic counter-countermeasures features such as multiple reception beams with ultra-low sidelobes in elevation and azimuth, a clutter analysis sensor, broadband transmission, pulse repetition frequency and radio frequency agility per burst and a jamming analysis sensor. SMART is designed to track 160 air targets and 40 surface targets simultaneously.

The system comprises an antenna and three main below-decks units. The hydraulically stabilised antenna consists of a single-element wideband transmitting array, and a multi-element stripline receiving array. The ultra-low sidelobe phased array allows the formation of multiple receive beams in elevation. To ensure high sensitivity, preprocessing of the received signals takes place in the antenna unit itself. The output of the 16 antennas is fed to a digital beam forming network in which the 12 independent elevation beams are produced, after which Doppler Fast Fourier Transform processing and automatic tracking is carried out. The transmitter is based on a high power, pulse-to-pulse coherent Traveling Wave Tube. Integral identification friend-or-foe can be provided.


Frequency: F-Band
Peak power: 145 kilowatts
Displayed range: 55 nautical miles
Range resolution: 0.5 nautical miles
Beamwidth: 2 degrees
Antenna rotation: 2.22 seconds (27 rpm.)

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AEW&C - Phased Array Technology. Part 1

Australian Aviation, 1994
by Carlo Kopp
© 1996, 2005 Carlo Kopp

The technology of Airborne Early Warning (AEW&C) systems is at a generational junction point at this time. We are now witnessing the next step in the lengthy evolution of this key technology, that being the transition from mechanically scanned antenna technology to electronically scanned phased array technology.

Phased array antenna technology has been in use for some decades, but most applications have been confined to ground based systems, due significant weight and size penalties associated with older families of electronic devices. The ongoing march of miniaturisation combined with significant improvements in microwave power transistor device technology has now allowed its wider use in airborne applications.

Conventional Antenna Systems

The purpose of a radar antenna is to focus a beam of electromagnetic energy into a desired shape and direction, and due some of the nicer properties of electromagnetism, the shape of the transmitted beam is identical to the shape of the antenna's sensitivity pattern when receiving. In an AEW&C application, and typically most airborne surveillance applications, the shape of the beam is designed to maximise the chances of detecting a distant and small target.

But this is not the only requirement which exists, as an AEW&C platform must also have the ability to track targets, find their altitude and resist the effects of jamming by inbound hostiles. These are often contradictory requirements in terms of what the antenna must do, as the search and detect function typically requires a broader beam to cover as large a possible volume of airspace in a single sweep, whereas the tracking function requires as tight a beam as is possible to provide the ability to resolve multiple closely spaced targets, and determine their position as accurately as possible.

A key issue in the design of such antennas is sidelobe performance, sidelobes being spurious and unwanted beams produced by the antenna in directions other than that of the principal beam, the mainlobe. Sidelobes have typically unhealthy effects on a radar system, which by its nature cannot tell whether the energy which it is receiving originated in the mainlobe or the sidelobe. In airborne lookdown radars, which are typically MTIs (Moving Target Indicators) in lower band systems, or pulse Doppler in the microwave bands, sidelobes can inject energy reflected off the airframe and underlying terrain with Doppler shifts which are very different from the Doppler being used as a reference by the electronics which sift through the mainlobe return searching for targets. This can degrade performance if appropriate measures are not taken.

There is another insidious side effect of sidelobes, and that is that they render the radar vulnerable to hostile jamming and anti radiation missiles (ARM). False target generator jammers will typically exploit sidelobing, injecting false target returns into the system via a sidelobe, thus creating the illusion of targets in the mainlobe, where none exist. ARMs will home in on the stray sidelobe emissions, which enable them to track the radar even if it is pointing elsewhere.

As is clearly evident, designing an antenna system for an AEW&C platform is not a trivial task, even for the experts, and many differing solutions have been devised over the last five decades.

The oldest and least effective approach was to produce one of a variety of rotating concave (dish shape) sections, typically based on paraboloid shapes, producing a narrow beam by using a horizontally wider section (ie horizontal orange peel shape), height finding being implemented by switching the beam via several mechanically offset antenna feeds. This meant that one of several beams was active at any time, and each of these beams covered a different range of altitudes. While this is a cumbersome arrangement, it is easy to build, and many systems in the fifties and early sixties used this arrangement. Its principal weakness is poor sidelobe performance, and slow response when height finding.

The venerable Lockheed E/RC-121 and WV-2 Warning Star (Connie) and Avro Shackleton AEW&C.2 used this class of antenna, albeit without height finding capability.

The next step in the evolution of AEW&C antennas was the use of fixed arrays. The idea of an antenna array is very simple and elegant. Instead of designing a single complex antenna shape, the array uses a group of much simpler antenna shapes, and combines their individual signals together. In the fashion, all the mainlobes are added together, and if this is done correctly, a much tighter single mainlobe is produced.

One of the key constraints was that of beamwidth, and the basic rule which applies is that for a given radar wavelength (frequency), the wider the antenna or antenna array, the tighter (narrower) the beam. Typically, the tighter the beam mainlobe, the weaker the sidelobes. This of course introduces a problem in airborne applications, as the bigger the antenna, the bigger the airframe required to carry it, and hence the cost will increase dramatically.

The use of arrays allowed the design of much more compact antennas, and the sixties E-2C AEW&C and seventies E-3 AWACS both capitalised upon this technology to maximise the performance of their antenna designs.

The E-2C uses a family of radars, the APS-125/138/139/145, all of which employ derivatives of the APA-171 antenna assembly in a dorsal radome (saucer shaped). The antenna arrangement hidden under the plastic is a horizontal array of UHF band Yagi antennas.

The bigger E-3A/B/C/D/F uses the larger and more sophisticated APY-1 or 2 pulse Doppler radar, which uses an E/F band microwave slotted planar array. The slotted planar array is a microwave antenna, which uses hundreds or thousands of tiny slots, each slot acting as a very simple antenna element. A complex network of waveguides and delay elements hidden behind the antenna array times the arrival of the microwave signals in such a fashion, that the antenna produces a very tight mainlobe beam, and very small sidelobes. As with a conventional radar, the transmitter uses a large Travelling Wave Tube (TWT) microwave amplifier (usually dual redundant in the E-3) which pumps the very powerful microwave signal into the antenna. In the opposite direction, the slots/waveguides/delay elements feed into a redundant receiver which then in turn feeds a conventional pulse Doppler signal processing chain. The antenna scans in azimuth by the whole antenna assembly being rotated upon its pedestal at 6 RPM, through 360 degrees.

Both the E-2C and the E-3 integrate a primary and secondary radar capability, the secondary/IFF antennas are mounted back to back with the primary radar antenna.

This family of microwave antennas was the first to see a limited application of of the phased array principles to be discussed, and this is typically used for the height finding function.

Phased Arrays - An Introduction

The phased array is extension of the idea of the planar array. In the planar array, the beam is fixed in direction and shape, because the timing of the microwaves fed into the array is fixed. However, if the timing can be varied, then both the shape of the beam and its direction can be changed. If this is done electronically, the shape and direction of the beam can be changed in a very small fraction of a second.

Needless to say, this can be as daunting a task as it appears to be, because several hundred or thousand array elements must be retimed simultaneously. The key elements in building such an array are the programmable phase shifter (or more colloquially, "shifter"), a device which can change the phase (ie time delay or timing) of the microwaves passing through it under electronic control, and the ubiquitous digital computer. Using the computer to control the shifters, the whole array becomes in effect an antenna with software programmable beam shape and direction.

Until the late eighties, building such a system involved a substantial volume of hardware, which meant that fully electronically steerable phased arrays were mainly used in surface based applications, such as the massive BMEWS ballistic missile warning radars and the somewhat smaller US Navy SPY-1 Aegis air defence radar, carried on the Ticonderoga class cruisers and more recently, the Arleigh Burke destroyer. The only known airborne applications were the large Flash Dance radar fitted to the gargantuan Soviet Foxhound air defence interceptor, and the attack radar in the Rockwell B-1B Lancer.

Airborne applications suffered mostly from the penalty of weight, as the first generation of phased array technology used a substantially conventional radar architecture. While the antenna changed, all else remained as was, but additional computer hardware was added to control the antenna shifters. This translated into a heavier antenna, an extra computer, and extra power loading on the electrical system resulting in bigger accessory generators.

The performance benefits of the phased array however justified the extra cost. The phased array could in a single antenna do the jobs of several purpose built antennas, almost simultaneously. Wide beams could be used for searching, narrow beams for tracking, flat fan shaped beams for height finding and narrow pencil beams for terrain following (B-1B). In a hostile jamming environment the benefits were even greater, as phased arrays allow the system to place a "null", an area of zero receiver sensitivity, over a jammer and thus in effect block it from entering the receiver chain. Another benefit, although minor in non-surveillance applications, is that there is no longer the need to mechanically point the antenna in the direction of the target. Typically a multiple sided antenna arrangement could provide 360 coverage, with fixed antennas covering all directions at once.

Less obvious benefits also flowed from this technology. One was the ability to rapidly scan a small sector of sky to increase the likelihood of detecting a small and fleeting target, unlike a slowly rotating antenna which can only scan a particular sector once per rotation, typically seconds apart. A small target like a low flying cruise missile may be almost impossible to track under such conditions. The phased array's ability to almost instantaneously change beam direction and shape in fact adds a whole new dimension to tracking, as multiple targets may be tracked by multiple beams, all of which are interleaved in time with a periodically scanning search beam. As an instance, a search beam may sweep 360 degrees periodically, while tracking beams can follow individual targets regardless of where the search beam is looking at, at the time.

Significant as these gains may have been, the first generation of this technology was simply too physically cumbersome to penetrate into the AEW&C environment. The E-3 uses a limited phased array capability, in that the APY-1/2 can height find through vertical beam steering, this was implementable at modest cost as the antenna slots could be controlled in horizontal "stripes" to achieve this functionality. A shifter is thus only required for each stripe, thus cutting their number down to something modest, rather than thousands.

Phased arrays do have their limitations, as all designs have. The principal limitation is the range of angles through which the beam can be steered. In practice, the limit is about 45 to 60 degrees off the vertical to the plane of the antenna, steering the beam to shallower angles degrades antenna performance significantly. Two effects are at play here. The first of these is that the effective length (width) of the antenna is reduced with increasing beam deflection angle (for technical readers the effective length L' becomes L'=L.cos(A), where L is the physical array length and A the angle off the antenna axis, at the array boresight L'=L, falling to 0.5L at 60 degrees and zero at 90 degrees), reducing array length in turn diminishes its ability to resolve targets at a distance, while also reducing antenna gain, a measure of its efficiency. The second effect is less apparent, but derives from the radiation pattern of the constituent elements, the slots, which radiate less with increasing angle off the vertical, thus reducing the power transmitted and the sensitivity. In effect, at extreme angles the mainlobe is both substantially weakened and defocussed (technical readers are directed to Eli Brookner's item in Scientific American Feb 1985, pp 76 for a more detailed discussion). So substantial is this reduction, that a typical situation would see antenna gain, and hence power radiated and sensitivity, cut down to 25% at 60 degrees off the vertical.

The application of phased arrays to AEW&C technology had to wait for another technological development, that being the active phased array. In an active phased array, each array element or group of elements has its own miniature microwave transmitter, dispensing with the single large transmitter tube of the older passive array technology. In an active phased array, each element is comprised of a module which contains the antenna slot, phase shifter, transmitter, and often also a receiver. In a conventional passive array, a single transmitter of several hundred kiloWatts of power feeds several thousand elements, each of which emits only tens of Watts of power each. A modern microwave transistor amplifier can, however, also produce tens of Watts, and in an active phased array design, several thousand modules each producing tens of Watts of power add up to an equally powerful mainlobe of hundreds of kiloWatts.

While the final effect is identical, the active array is far more reliable, as the failure of any array element merely degrades antenna performance by a fraction of a percent. This is graceful degradation, as the catastrophic transmitter tube failures which plague conventional radar simply cannot occur. A side benefit is the weight saving incurred by dispensing with the bulky high power tube, its associated cooling system and its large high voltage power supply.

Another powerful feature which may be exploited only in active arrays, is the ability to control the gain of the individual transmit/receive/shifter modules. If this can be done, the range of angles through which the beam can be swept is increased substantially, and thus many of the array geometry constraints which plague the conventional phased array may be circumvented. Such arrays are termed supergain arrays. From published literature it is unclear whether any existing or development designs use this technique, and the coverage limits indicated for some existing designs suggest that this is not the case as yet.

In summary it is fair to say that the active phased array outclasses conventional radar designs in almost all respects, providing superior performance, tracking capability and reliability, albeit at some penalty in complexity and possibly cost.

The venerable Hawkeye is the mainstay of US Navy AEW squadrons, as well as being used by Israel and Singapore. The APS-125/138/145 systems carried by subtypes of this aircraft are based on sixties UHF antenna technology, using the APA-171 radome which contains an array of Yagi antennas. Its strength is maturity and simplicity, and it delivers very good performance in its maritime environment (AEWA).

The AWACS is the flagship of US AEW technology, based on evolved versions of the 1970s APY-1 radar. The APY-1 and 2 radars are microwave E/F band systems, with mechanical rotodome scan in azimuth and phased array techniques in heightfinding. The system delivers superlative long range detection and tracking performance, but is penalised by size and weight, which impose the need for a large airframe (C-137/B-707 or widebody) and this reflects in high acquisition and support cost (AEWA).
The Hawkeye's UHF radar has been integrated with both the Lockheed P-3 and C-130 airframes, providing a mid range system with substantially better range and endurance performance than the E-2C. These derivative systems exploit the additional airframe volume available and use larger and newer computer and display technology, in comparison with the cramped E-2C airframe.

The best known phased array radar in use today is the US Navy's SPY-1 Aegis, a large passive array system fitted to Ticonderoga class cruisers. The large SPY-1 has four 3.65 x 3.65 m arrays, each with 4100 elements, and can concurrently track several hundred targets at a range of altitudes. Designed to counter saturation attacks by several hundred anti-ship cruise missiles, the radar relies heavily on its ability to flexibly allocate its system computing power to best advantage, and vividly illustrates the potential of modern phased array technology (LM Photo).

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AEW&C - Phased Array Technology. Part 2

Active phased array antenna technology promises significant improvements in AEW&C platform performance. While the technology base has yet to mature, the first designs using this technology are beginning to appear.

AEW&C using Active Phased Arrays

While the application of active arrays to AEW&C systems has been under discussion for many years, only two designs have been built to date and the technology has yet to reach full scale operational deployment. Applying the active array to an AEW&C platform introduces some interesting problems with antenna placement.

Conventional AEW&C systems have traditionally employed a rotodome, the characteristic saucer shaped radome which covers a conventional antenna, the rotodome rotating in order to scan 360 degrees about the platform. The placement of the rotodome on pylons, elevated well above the aircraft's fuselage, ensured that the antenna had an unobstructed field of view about the aircraft. This was achieved at considerable cost in weight, as the fuselage required strengthening to carry the structure, which itself wasn't featherweight. In typical designs, the rotodome is designed with an aerodynamic profile which produces, under cruise conditions, lift equal to the weight of the rotodome assembly, thus alleviating structural loading in cruise, but not necessarily in other configurations, unless the rotodome is built to tilt and thus change the AoA of its aerodynamic section.

The rotodome arrangement is readily applicable to active array systems, as a four or three sided array may be fixed in the same position as the rotodome, providing 360 degree coverage and good clearance from the aircraft's structure. Lockheed have proposed a three sided array in this configuration, fitted to either a new airframe or the existing S-3 Viking airframe, to meet USN E-2C replacement requirements. The three or four sided array arrangement may be applied to any airframe able to accommodate a rotodome, and may well become the standard in years to come. Its only significant failing is that it retains much of the cost and weight penalties of the rotating rotodome.

Another configuration derived from this idea is that of the Swedish Ericsson Erieye, which uses a two sided array in a beam shaped structure, carried above the fuselage of a twin engined commuter airframe. The two sided array used in this arrangement is almost as long as the APY-2 antenna of the AWACS, potentially providing similar angular resolution performance at range, on a very small airframe.

This arrangement however suffers from an obvious and significant operational limitation, as it cannot provide 360 degree coverage, using conventional active phased array technology. With each array scanning a 120 degree sector, the two sided array has a 60 degree blind sector over the nose and the tail of the aircraft, and degraded antenna performance beyond 45 degrees off the beam of the aircraft. With Sweden's compact geography this would probably not be an issue, as multiple platforms would cover a single area, and operating in pairs, the aircraft could patrol in two racetrack orbits set 90 degrees apart to provide overlapping coverage. The success of this scheme then devolves down to the capability of the computer datalink networking which links the platforms to each other or the ground air defence centre, to ensure that a comprehensive picture of the air situation exists at whatever is the central command post.

In a heavy ECM environment, where platform to platform or platform to ground datalink function is interfered with, the two sided array has thus a major limitation. Producing a three or four sided array with similar array length results in a structure with a size comparable to an E-3 AWACS radome, which in turn requires at least a 737 sized aircraft to carry it, thereby largely defeating the apparent cost advantage of the linear array concept.

A possible resolution would be the use of a supergain array, where the ultimate size of the blind sector would be determined by the array's module parameters and array length.

Another alternative which exists is the use of a rhombic four sided array geometry, with a 60-120-60-120 degree arrangement of arrays. While the rhombic arrangement will provide full 360 degree coverage, its effective antenna length is halved in the nose and tail sectors. The result is a compromise between the bulky but excellent four or three sided array, and the compact but partially blind two sided array. No publicly discussed proposals to date have involved the rhombic arrangement.

An idea which has created some excitement in the engineering community is the concept of conformal active arrays or "smart skins", where active arrays are embedded in the skin of the aircraft, thus avoiding the structural, aerodynamic and weight penalties of an external radome. However, close examination of most existing airframe designs suggests they may not always accommodate this concept without some other penalties, such as coverage limitations like those suffered by the two sided array concept.

The Israeli Phalcon system, which uses a B-707 airframe, was reported initially to have been the first implementation of this scheme. The aircraft's public debut has however shown this not to be true, as the aircraft uses fuselage mounted boxes for its main sidelooking arrays, and a nose mounted radome for a smaller forward looking array.

The fuselage mounted linear arrays provide for excellent coverage over the beam aspect 120 degree sectors, but the nose and (reported optional) tail mounted arrays which "plug" the holes in beam array coverage are much shorter due fuselage diameter and thus would suffer a major loss in resolution performance fore and aft. Again the use of supergain array techniques could alleviate this problem.

As with two sided and rhombic array configurations, the Phalcon arrangement may or may not be suitable for a given operational environment. Where the threat axis is defined unambiguously and the aircraft's patrol racetrack can be aligned appropriately, the coverage limitations may not be of significant importance. Where the threat can approach from multiple axes concurrently, full 360 degree coverage is almost mandatory.

Westinghouse's MESA system which is currently in development, uses a podded arrangement of sidelooking linear arrays carried by a C-130, with some reports suggesting that supplementary nose and tail arrays could be fitted to plug nose and tail coverage.

Other alternatives do exist. An arrangement publicised by Boeing for the now defunct USN E-X program involved the use of an airframe with a trapezoidal (diamond shaped) wing, with arrays embedded in the wing surfaces to provide 360 degree coverage. The S-3 sized aircraft had been proposed to replace the E-2C. Recent budget cuts have put its future very much in doubt.

The dilemma faced by designers is simple: active arrays provide the potential for a small airframe to have E-3 AWACS class antenna performance, however antenna coverage requirements will force the use of a either a mast mounted radome or a new airframe geometry, both negating the potential cost advantage offered by the antenna technology.

Other alternatives may yet exist, but investigating their suitability will require some effort by airframe manufacturers. Most modern airliner airframes have a wing sweep of about 60 degrees, which suggests that the leading edges of the wings have the almost ideal geometry to accommodate conformal arrays. A six to eight metre conformal array embedded in the leading edge, inboard, would automatically provide two sides of the three sided array configuration. The problem is that this would preclude the use of leading edge lift devices over at least 30% of the span, and also preclude the use of wing mounted engines, which would obstruct the array's field of view. The unresolved issue is the third side of the array, which could only be implemented by placing an array on the tail of the aircraft. A six to eight metre array length will require, by default, a beam structure of similar size.

Closer examination of available airframes suggests that those with aft mounted engines (B-727, MD-80) would be geometrically most suited to leading edge array placement, but the positioning of the powerplants would cause difficulties in positioning the tail array. The optimal geometry would see engine pods mounted above the wings (cf VFW-614), and the tail array beam structure fitted to the end of the fuselage, or at the top of the vertical stabiliser. The scale of change would again force a new airframe design, or substantial rework of an existing design.

The application of supergain array techniques could of course alleviate many of these difficulties, and it remains to be seen how soon this technology becomes adapted to an AEW&C application. Clearly as the technology of active phased arrays matures, designers will settle upon the most suitable configurations, but as is often the case, the simple and orthodox solutions may ultimately prevail simply because they were a good idea in the first place. The pylon mounted radome may be with us for some time to come.

The Australian Perspective

Australia has some unique problems in acquiring its future AEW&C capability. These revolve primarily about the operational requirements associated with the range of missions to be performed, further complicated by the geography of our landmass. Projected RAAF AEW&C operations can be basically divided into the support of air defence (DCA or Defensive Counter-Air), and the support of maritime operations and OCA (Offensive Counter Air). Existing doctrine is focussed on DCA (AAP1000-Ch.5).

Local air defence of point targets can at a minimum, be performed by a smaller aircraft with lesser radar range, the requirement being centred on the ability to quickly get an aircraft aloft to a station within 200 NM of the runway in use, and to provide 2-4 hours of time on station. Given the concentration of potential targets in the North into specific areas and potential threat axes, 360 degree coverage may not be a mandatory requirement. Supported by long range threat warning from Jindalee, this mission can be performed readily by a smaller twin engined aircraft. The proximity to a land base means that the requirements imposed insofar as Command/Control/Communications go are modest, because land based facilities may be used to support the mission. Wider coverage of the large expanses of the North would however preclude this approach.

Providing AEW&C support for DCA in the air-sea gap, maritime operations and OCA becomes a more demanding affair, as the area of operations may be several hundred nautical miles from the operating base, over the ocean, out of the reach of land based UHF comms and exposed to enemy air attack from many axes. These conditions impose the requirement for considerable range and endurance, to ensure that the AEW&C aircraft can remain on station for a substantial time, and also demand comprehensive C3 capability and 360 degree radar, IFF and ESM coverage. Good radar range is also to an advantage, as is transit speed to station and inflight refuelling capability.

All AEW&C systems in use today reflect these operational requirements. The E-3 has superb radius, endurance, radar coverage and a comprehensive C3 suite, which allows for wholly autonomous operation as an airborne command post. The former Soviet Mainstay was designed to a similar requirement. The E-2C, optimised for local air defence in the maritime carrier environment, has limited range, endurance, C3 capability and radar performance, although it does provide the necessary 360 degree coverage. The SAAB-2000/Erieye has endurance and range in the class of the E-2C, limited C3 capability, and limited coverage, reflecting the local air defence requirements of the congested airspace of the Baltic, and predictable threat axes.

In the Australian context, the question is whether we can effectively capitalise upon the emerging technology of active arrays. The RAAF in defining its AEW&C requirement will ultimately have to decide whether to opt for a twin engined system limited to localised DCA operations, closely coupled to ground C3 facilities and hence depart from established doctrine, or whether to opt for an extended AEW&C umbrella satisfying existing DCA doctrine and encompassing RAAF OCA and RAN operations, and hence select a longer ranging four engined aircraft capable of performing as a self contained command post. Existing RAAF DCA doctrine (AAP1000-5.41,5.42) stresses the latter approach.

The central question in this matter is whether the RAAF will define its requirement in the context of recent doctrine, opting for a longer ranging platform, or whether it will yield to the inevitable financial pressure from the government to select a smaller and less capable aircraft. The selection of off-the-shelf candidates which meet stated doctrine and obvious requirements is both limited and split between older conventional technology and newer array technology. The alternative would then be a custom integration exercise, combining active array radar with a platform and array geometry not necessarily used at this time by the radar vendor.

What is significant in this context is that judicious choice of airframe and array geometry could minimise integration costs, while providing scope for domestic integration work which would in turn bolster our domestic defence industry, and ease longer term support costs for the design once in service. It is central in this debate that the government recognise that short term acquisition cost advantages may not translate into a cost or operational advantage over the whole life cycle of the AEW&C system, and hence that the government does not pressure the RAAF in the direction of short term expediency.

Active array technology promises major gains in the capability of both medium sized and smaller AEW&C systems, but to capitalise fully on these gains will require further integration effort. Australia has in many senses a unique operational environment and it would not be wise to bend requirements to fit established and very much development systems. We can hope the government will recognise this when it eventually proceeds with the AEW&C acquisition.

The Boeing E-3 AWACS was the first AEW&C platform to use a limited amount of phased array technology in its APY-1/2 surveillance radar. The APY-1/2 utilises a slotted planar array which scans azimuth mechanically and height electronically. With the closure of 707 airframe production, Boeing will integrate the system with a newer widebody airframe.

The Ericsson Erieye system uses an active phased array radar mounted in a two sided array geometry. The whole array is contained in a large beam shaped structure carried above the fuselage of a commuter twin airframe. The limitation of the two sided array is that it can only cover two 120 degree sectors abeam of the aircraft, leaving 60 degree blind sectors over the nose and tail of the aircraft, and reduced antenna performance from 45 degrees off the beam aspect. Another limitation stems from the use of an airframe too small to accommodate a comprehensive self contained command, control and communications system, and other sensors such as a capable ESM and track association system.

Pic.3 (Phalcon - not enclosed)

The Israeli Phalcon is the first full scale application of phased array technology, using arrays along the fuselage and under the nose and tail. While providing full 360 degree coverage, the smaller size of the nose and tail arrays will limit angular resolution in the nose and tail sectors, thus degrading system performance in these areas. While cheaper than external pylon mounted radomes in terms of structural modifications, conformal arrays require suitable airframe geometry if they are to be used to full advantage.

This AMSS Lockheed proposal for an E-2C replacement depicts a three sided array geometry. Three sided and four sided arrays offer 360 degree coverage without significant degradation in angular resolution against azimuth, but incur the cost, weight and drag penalties of the radome structures. At the time of writing no design using this geometry has been flown.

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Phased Array technology: concepts, probes and applications


Over the last few years, piezocomposite materials have enabled a new ultrasound probe technology to be developed for the Non-Destructive Testing of materials: Phased Array probes.

These probes, made up of a large number of simple probes organized in linear, annular, circular or matrix arrays, allow electronic scanning, focusing and deflection to be carried out. These different concepts will be presented, as well as their associated benefits in terms of performance, flexibility, speed and feasibility of certain inspections.

Different applications that have implemented this technology will also be presented, with details about the particular probes used. Through these applications, the benefits of phased array technology for many fields will be highlighted, including the nuclear, aeronautical and in-line testing industries.


A certain number of industries requiring advanced means of Non-Destructive Testing, such as the nuclear, aeronautic or in-line testing industries, constantly seek improvements in the performance of their monitoring systems.

The most common requests concern an increase in productivity, reduction in the size of untested areas and improvements in detection and sizing performance.

For the last ten years, Imasonic has responded to these needs by designing and developing transducers based on Phased Array technology.

The Phased Array concept

The Phased Array concept is based on the use of transducers made up of individual elements that can each be independently driven. These probes are connected to specially-adapted drive units enabling independent, simultaneous emission and reception along each channel. These units should also be able to effect, during both emission and reception, the different electronic time delays for each channel.

For some applications implementing electronic scanning, not all the elements of the probe are used simultaneously. In this case, the drive unit uses dynamic multiplexing to distribute the active elements among the elements of the transducer.

Electronic scanning

Electronic scanning, illustrated in figure 6, consists of moving a beam in space by activating different active apertures in turn, each one made up of several elements of a phased array probe.

It allows a mechanical scanning axis to be replaced electronically.

In general, this concept is used for in-line testing of plates, bars or tubes, and can also be used for inspecting welds.

Electronic focusing

Electronic focusing, shown in figure 7, is based on the use of electronic delays applied during emission and reception along each of the channels of the probe. These delays have an effect similar to that of a focusing lens and enables focusing to different depths.

Electronic focusing allows only one phased array probe to be used where several single-element probes with different focal distances would be necessary. The most common applications are heavy plates inspection.

Electronic deflection

Electronic deflection, illustrated in figure 8, uses delay laws for electronic focusing. In this case, they are calculated to give the emitted beam an angle of incidence which can be varied simply by modifying the delay law (all the delays applied to each of the concerned channels).

Electronic focusing enables only one probe to be used for inspections traditionally requiring several probes working at different angles. In addition, it allows the beam to be deflected without using a wedge, allowing parts to be inspected from very small spaces.(3)

Electronic scanning, focusing and deflection can be combined to resolve applications such as the inspection of welds or tubes. Examples will be dealt with in the paragraph "Examples of applications" below.

Fig 6: Diagrammatic view of electronic scanning: groups of elements are successively activated to move the beam along the transducer.
Fig 7: Diagrammatic view of electronic focusing: electronic delay laws are applied (left) to focus the beam.
Fig 8: Diagrammatic view of electronic deflection: electronic delay laws are applied (left) to deflect the beam.

Phased array probes

Phased array technology requires the use of multi-element probes with variable geometry, but must also meet certain criteria:

  • Elements must be able to be driven individually and independently, without generating vibration in nearby elements due to acoustic or electrical coupling.

  • The performance of every element must be as close as possible in order to ensure the construction of a homogeneous beam.
Imasonic, thanks to its Piezocomposite 1-3 technology (1) and to its multi-element probe construction technology, designs and manufactures probes that meet these two criteria (2).

Figure 2 shows the different possible geometries of the multi-element probes described below.

Fig 2: Examples of geometries of phased array transducer elements:
1. Linear array
2. Annular array with uniform pitch (non constant surfaces)
3. Matrix arrays (checkerboard and sectored rings)
4. Circular array

Linear array probes

These probes are made up of a set of elements juxtaposed and aligned along an axis. They enable a beam to be moved, focused, and deflected along a plane.

Annular array probes

Annular array probes are made up of a set of concentric rings. They allow the beam to be focused to different depths along an axis. The surface of the rings is in most cases constant, which implies a different width for each ring.

Circular array probes

These probes are made up of a set of elements arranged in a circle. These elements can be directed either towards the interior, or towards the exterior, or along the axis of symmetry of the circle. In the latter case, a mirror is generally used to give the beam the required angle of incidence (see figures 3 and 4).

Fig 3: Principle of tube inspection from the outside with a 10MHz 128-element flat circular array and a mirror.

Fig 4: Principle of a tube inspection from the inside with a 10MHz 128-element flat circular array and a mirror.

Matrix array probes

These probes have an active area divided in two dimensions in different elements. This division can, for example, be in the form of a checkerboard, or sectored rings. These probes allow the ultrasonic beam to be driven in 3D by combining electronic focusing and deflection.

Main characteristics

Beyond their geometry, Phased Array probes offer the same flexibility of use as single-element probes. They can be used in immersion or in contact, their active area can be flat or focused, and they can also take into account the strong constraints of the industrial environment, such as temperature, pressure, vibration and radiation.

Examples of applications

Inspection of blade roots and rotor steeples

This inspection, carried out using various miniaturized phased array probes, one of which is shown in figure 1.3, has enabled many previously untested areas to be inspected.

The use of phased array technology has enabled the use of beam-deflecting wedges to be avoided, and thus inspections to be carried out from restricted spaces inaccessible with other techniques. In addition, the probes' electroacoustic performances have enabled the depth of detection and the accuracy of sizing to be increased (3).
Fig 1: Examples of the use of phased array technology
1. Inspection of plate using a 10MHz 128-channel linear array transducer implementing electronic scanning and focusing
2. Tube inspection from the inside using a 10MHz 80-channel focused circular array implementing electronic scanning and focusing
3. Inspection of blade roots using 10MHz 32-channel linear array contact transducers implementing electronic focusing and deflection.
4. Inspection of heavy forgings using a 5MHz 16- channel annular array implementing electronic focusing.
5. Inspection of welds with a 5MHz 32-channel linear array implementing electronic focusing and deflection.
6. In-line tube inspection from the outside with a 10MHz 256-channel circular array combining electronic scanning, focusing and deflection.

Inspection of tubes

Several phased array techniques can be used for inspecting tubes. In-line testing of tubes is generally done from the outside with encircling probes, as illustrated in figure 1.4.

Inspection of heat exchanger tubes is generally done from the inside for reasons of accessibility. The generator tubes of the Superphœnix nuclear power plant were inspected from the inside using the phased array circular probes illustrated in figures 1.2 and 8. Here, phased array technology enabled the required testing speed to be achieved. In addition, the active area, made up of 80 elements, was focused by shaping to obtain the required beam characteristics (4).

This inspection can also be carried out from the inside and from the outside by using a flat circular array associated with a mirror, as illustrated in figures 3 and 4.

Inspection of titanium billets

Titanium billets are traditionally inspected with sets of single-element probes, where each probe is dedicated to the inspection of a specific zone (depth range), for a specific diameter of billet. Although efficient in detecting defects, this solution has the major disadvantage of requiring many probes, and several shots to inspect a single billet.

An alternative consists in using a matrix array. The cutting of the elements, such as shown in figure 5, and the electronic focusing and deflection enable the probes to be adapted to different diameters of billets and to different working depths.

It is also possible to use the time reversal mirror technique (5), which has enabled flat-bottomed holes of a diameter of 0.4mm to be detected at a depth of 140mm, with a signal / noise ratio superior by at least 6dB to that obtained using any other technique

Fig 5: FERMAT matrix probe for inspecting titanium billets using the time reversal mirror technique (M.Fink ESPCI).


The advantages of using Phased Array technology are the technical and economic benefits gained:

  • Traditional mechanical scanning is replaced by the much faster electronic scanning.

  • Electronic focusing allows the use of a single probe for working at different depths.

  • Electronic deflection allows the angles of incidence to be varied with only one probe.
Costs are thus significantly reduced because of the inspection and adjustment time saved.

In addition, phased array technology has made some applications possible that could not be resolved by traditional solutions, for example, when beam deflection is necessary without enough space to use a wedge (rotor steeple and blade root inspection) or when scanning is necessary without enough space for the corresponding mechanics (inspection of bent small-diameter tubes from the inside).

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Materia: CRF