TechnologyToday

Raytheon’s Sensing Technologies Featuring innovative electro-optical and radio frequency systems

2008 Issue 1

HIGHLIGHTING RAYTHEON’S TECHNOLOGY

RAYTHEON TECHNOLOGY TODAY 2008 ISSUE 1 17

Feature

Today’s weather forecasting and warning infrastructure uses data from high-power radars that have

helped meteorologists improve forecastssignificantly in the past 20-plus years.Despite having substantial capability tomeasure wind and rainfall and to diagnosestorms, these long-range radars have limit-ed ability to observe the lowest and mostcritical part of the atmosphere owing to theEarth’s curvature. This prevents the radarsfrom observing the behavior of tornadoesand other hazards at or near ground level.As a result, one in five tornadoes goesundetected by current technology, and 80 percent of all tornado warnings turn out to be false alarms.

Raytheon Integrated Defense Systems (IDS),in partnership with a team of academic1,government and industrial collaborators,has formed a National Science FoundationEngineering Research Center (ERC) calledthe Center for Collaborative AdaptiveSensing of the Atmosphere (CASA) toaddress this problem. CASA is researching a new weather hazard forecasting andwarning technology based on low-cost,dense networks of radars that operate atshort range, communicate with one another, and adjust their sensing strategiesin direct response to the evolving weatherand to changing end-user needs. In con-trast to today’s large weather radars with 10-meter-diameter antennas, the antennasin CASA networks are expected to be one-meter in diameter with electronics that areabout the size of a personal computer. Thissmall size allows these radars to be placedon existing cellular towers and rooftops,enabling them to comprehensively mapdamaging winds and heavy rainfall fromthe top of storms down to the criticalboundary layer region beneath the view of current technology.

This approach can achieve breakthroughimprovements in resolution and update

times, leading to significant reductions intornado false alarms; quantitative precipita-tion estimation for more accurate flood prediction; fine-scale wind field imaging;and the estimation of thermodynamic statevariables for use in short-term numericalforecasting and other applications such asairborne hazard dispersion forecasting. Inaddition to the radars and their associatedhardware and data communication infra-structure, a new generation of meteorologi-cal software is being developed to targetthe resources in these radars in order tosimultaneously support emergency man-agers and government and private industryorganizations that need weather data formaking critical decisions.

Field tests reveal that this technology offersobserving capabilities fundamentallybeyond today’s state of the art. The back-ground image in Figure 1 shows a thunder-storm observed using a 4-radar test networkdeployed in “Tornado Alley.” At 500-meterspatial resolution, the system is capable ofresolving critical substructure within thestorm cell that cannot be resolved with thecoarser resolution, more distant WSR-88Dradars deployed operationally today.

At a typical spacing of 30 km, 10,000 ofthese radars would be required to blanketthe contiguous United States. Such radars

would require only 10’s of W of averagetransmitter power, yet they would be capa-ble of fine-scale storm mapping throughoutthe entire troposphere — from the criticallow troposphere “gap” region below 3 km,up to the tops of storms. Such networksthus have the potential to supplement — orperhaps replace — the large networks inuse today.

Blanket deployment of thousands of smallradar nodes across an entire nation is butone of several possible future deploymentstrategies for this technology. Additionalstrategies would include selective deploy-ment of smaller networks in heavy popula-tion areas, geographic regions particularlyprone to wind hazards or flash floods, valleys within mountainous regions, or specific regions where it is particularlyimportant to improve observation of low-level meteorological phenomena. Cost,maintenance and reliability issues, as well as aesthetics, motivate the use of small(approximately 1-meter diameter, 2-degreebeamwidth) antennas that could beinstalled on either low-cost towers or existing infrastructure elements (such asrooftops or cellular communication towers).The cost to deploy and operate such a network will include the upfront cost ofthe radars and their associated communica-tion and computation infrastructure, alongwith the recurring costs to maintain the systems; buy or rent land and space ontowers/rooftops; and provide for data communication between the radars, operations and control centers, and users.These costs, in addition to numerous technological and system-level tradeoffs,need to be balanced to ultimately developan effective system design.

Phased arrays are a key enabling technologyin many production radars today and adesirable technology for use in dense networks since they do not require

Continued on page 18

Figure 1. CASA test network data

Active Panel Array TechnologyEnables Affordable Weather Radar

18 2008 ISSUE 1 RAYTHEON TECHNOLOGY TODAY

FeatureContinued from page 17

maintenance of moving parts and they permit flexibility in beam steering. A partic-ular challenge in realizing cost-effectivedense networks composed of thousands ofradars will be to achieve a design that canbe volume-manufactured for approximately$10,000 per array (current dollars). Severalthousand transmit/receive (T/R) channels areneeded to realize a phased array capable ofelectronically steering a 2-degree beam intwo dimensions over the desired scan rangeof these radars. The realization of such anantenna will benefit from leveraging com-modity silicon RF semiconductors to achieveT/R functions, in combination with verylow-cost packaging, fabrication and assembly techniques. Below, we describe apromising architecture and prototype of aphased array that can be manufacturedusing processes similar to those for makinglow-cost computer boards.

System Performance/Cost Objective andActive Panel Array ApproachThe air-cooled panel array is the “buildingblock” for a larger, active phased array. Thestrategy for reducing cost is based on thefollowing four objectives:

1. Significant reduction in printed wiringboard (PWB) fabrication and assemblyprocess steps

• Fabrication: One image and etch, onelamination, one drill and plate

• Assembly: One solder reflow operationto attach all components

2. Significant reduction in components

• Surface mount “flip-chip” MMICs andcomponents

• Modular: Highly integrated RF, DC andlogic PWB manifold

• Environmental coatings/protection tailored to application

3. Reliance on established technology

• Incorporation of mature and advancedtechnologies as required

• Low-power designs (<1W per element)leverages mature RF CMOS, SiGe, orGaAs MMICs

• Higher power designs leverage emerging GaN

• Scalable from L-Band to Ka-band

4. Design for manufacturing • Common material set • Common fabrication and

assembly process • Panel DC and RF test on factory floor

The constraint of minimizing PWB fabrication steps resulted in the followingmixed-signal design approach:

• RF. RF Isolation Cage: All RF, DC andlogic vias are drilled in one step through

the entire PWB laminate. A square pattern subset of plated vias, connectingall RF ground planes, defines an “RF isolation cage” for each unit cell andsuppresses cross-talk between transmit/receive channels.

RF Via “Stub” Tuning: The RF via “stub”extending beyond the RF transmissionline junction is tuned for an impedancematch over the required bandwidth.

Figure 2. 128 T/R channel panel array: radiator side

Figure 3. 128 T/R channel panel array: active component side

Affordable Weather Radar

Angelo PuzellaProgram Manager, Low-Cost Active ArraysRaytheon Integrated Defense Systems

Advanced Technology Program Manager Angelo Puzella

believes it’s important for engineers to think outside the

numbers, facts and figures that are central to their jobs.

By doing this, he said, they can spark their creativity. “If

you’re looking around you at other things, you might see

something that triggers an idea,” he said.

Puzella himself has found many opportunities to apply

this approach to his own 25-year Raytheon career. An

annual visitor to Italy (his wife is from Milan), Puzella

has acquired an appreciation for classical architecture

among the Roman ruins and renaissance architecture

of Florence. From looking at temples, amphitheaters,

aqueducts and churches, he said, you can see the

underlying building block: the simple arch. “This

common engineering building block served to raise

huge vaulted domes and span great ravines, built civic

and religious institutions, and provided the necessary

infrastructure for ancient civilizations.”

As part of IDS’ Advanced Technology, Puzella has carried

the idea of a common building block to active phased

arrays: a panel array composed of the same materials;

fabricated and assembled in the same fashion; and used

to assemble a larger, active phased array for various

applications. The active panel array is similar to a com-

puter board and the key is to leverage commercial manu-

facturing to incorporate mature or advanced semicon-

ductor technologies as needed. The potential applications

for panel arrays range from weather radars to battlefield

radars and terrestrial and satellite communications.

“The ultimate goal for panel array technology,” Puzella

said, “would to be as ubiquitous and useful as the arch

has been throughout the past 2,000 years.”

To achieve this, Puzella believes, it’s important to take

risks. “The commercial world is full of examples of peo-

ple taking risks, of using trial and error and inspiration.

If you can push something forward like this panel, other

applications come up for it.”

ENGINEERING PROFILE

RAYTHEON TECHNOLOGY TODAY 2008 ISSUE 1 19

FeatureSlot Coupling to Radiator: A slot coupledfeed to stacked patches simplifies PWBfabrication while providing excellent RFperformance.

Beamformer Circuits: Untrimmed inkresistors are used because of lower fabrication cost. The tolerance of the ink resistor has been incorporated intothe design.

• DC. High-current power plane is locatedon the layer directly below the surfacemount MMIC layer.

• Logic. Logic lines are routed betweeneach unit cell’s RF isolation cage.

Modeled dual-linear polarized performance,including a radome, is summarized:

• VSWR < 2:1 for maximum scan angle of 65 degrees

• Ohmic loss < 1dB

• Minimum/Maximum cross-polarization: -29dB/ -11dB

ProgressA prototype active T/R channel panel array,the building block for a 1m2 weather radar,

was assembled with “flip-chip” MMICs andtested. Figure 4 shows active receive, linear-horizontal polarized patterns of the T/Rchannel panel array at 9.5GHz; the dottedline is cross-polarization.

Future PlansIn 2008, Raytheon will assemble a panelarray. It will be integrated and tested with aDC/DC converter panel (using COTS con-verters) and a receiver-exciter (REX) panel

(also using COTS components) in the prototype 1m2 array frame with radome.The first fully populated 1m2 weather radarwill be field-tested in 2009. •

Angelo Puzellaangelo_puzella@raytheon.com

Co-author: David J. McLaughlin

1The core academic partners of the CASA team are the Universityof Massachusetts Amherst (lead university), University ofOklahoma, Colorado State University, and University of PuertoRico at Mayaguez.

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Figure 4. 128 T/R channel panel array: active component side

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