Technology Today. Raytheon s Sensing Technologies Featuring innovative electro-optical and radio frequency systems HIGHLIGHTING RAYTHEON S TECHNOLOGY

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1 Technology Today HIGHLIGHTING RAYTHEON S TECHNOLOGY 2008 Issue 1 Raytheon s Sensing Technologies Featuring innovative electro-optical and radio frequency systems

2 Active Panel Array Technology Enables Affordable Weather Radar Today s weather forecasting and warning infrastructure uses data from high-power radars that have helped meteorologists improve forecasts significantly in the past 20-plus years. Despite having substantial capability to measure wind and rainfall and to diagnose storms, these long-range radars have limited ability to observe the lowest and most critical part of the atmosphere owing to the Earth s curvature. This prevents the radars from observing the behavior of tornadoes and other hazards at or near ground level. As a result, one in five tornadoes goes undetected 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 academic 1, government and industrial collaborators, has formed a National Science Foundation Engineering Research Center (ERC) called the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) to address this problem. CASA is researching a new weather hazard forecasting and warning technology based on low-cost, dense networks of radars that operate at short range, communicate with one another, and adjust their sensing strategies in direct response to the evolving weather and to changing end-user needs. In contrast to today s large weather radars with 10-meter-diameter antennas, the antennas in CASA networks are expected to be onemeter in diameter with electronics that are about the size of a personal computer. This small size allows these radars to be placed on existing cellular towers and rooftops, enabling them to comprehensively map damaging winds and heavy rainfall from the top of storms down to the critical boundary layer region beneath the view of current technology. This approach can achieve breakthrough improvements in resolution and update Figure 1. CASA test network data times, leading to significant reductions in tornado false alarms; quantitative precipitation estimation for more accurate flood prediction; fine-scale wind field imaging; and the estimation of thermodynamic state variables for use in short-term numerical forecasting and other applications such as airborne hazard dispersion forecasting. In addition to the radars and their associated hardware and data communication infrastructure, a new generation of meteorological software is being developed to target the resources in these radars in order to simultaneously support emergency managers and government and private industry organizations that need weather data for making critical decisions. Field tests reveal that this technology offers observing capabilities fundamentally beyond today s state of the art. The background image in Figure 1 shows a thunderstorm observed using a 4-radar test network deployed in Tornado Alley. At 500-meter spatial resolution, the system is capable of resolving critical substructure within the storm cell that cannot be resolved with the coarser resolution, more distant WSR-88D radars deployed operationally today. At a typical spacing of 30 km, 10,000 of these radars would be required to blanket the contiguous United States. Such radars would require only 10 s of W of average transmitter power, yet they would be capable of fine-scale storm mapping throughout the entire troposphere from the critical low troposphere gap region below 3 km, up to the tops of storms. Such networks thus have the potential to supplement or perhaps replace the large networks in use today. Blanket deployment of thousands of small radar nodes across an entire nation is but one of several possible future deployment strategies for this technology. Additional strategies would include selective deployment of smaller networks in heavy population areas, geographic regions particularly prone to wind hazards or flash floods, valleys within mountainous regions, or specific regions where it is particularly important to improve observation of lowlevel meteorological phenomena. Cost, maintenance and reliability issues, as well as aesthetics, motivate the use of small (approximately 1-meter diameter, 2-degree beamwidth) antennas that could be installed on either low-cost towers or existing infrastructure elements (such as rooftops or cellular communication towers). The cost to deploy and operate such a network will include the upfront cost of the radars and their associated communication and computation infrastructure, along with the recurring costs to maintain the systems; buy or rent land and space on towers/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 develop an effective system design. Phased arrays are a key enabling technology in many production radars today and a desirable technology for use in dense networks since they do not require Continued on page 18 RAYTHEON TECHNOLOGY TODAY 2008 ISSUE 1 17

3 Affordable Weather Radar Continued from page 17 maintenance of moving parts and they permit flexibility in beam steering. A particular challenge in realizing cost-effective dense networks composed of thousands of radars will be to achieve a design that can be volume-manufactured for approximately $10,000 per array (current dollars). Several thousand transmit/receive (T/R) channels are needed to realize a phased array capable of electronically steering a 2-degree beam in two dimensions over the desired scan range of these radars. The realization of such an antenna will benefit from leveraging commodity silicon RF semiconductors to achieve T/R functions, in combination with very low-cost packaging, fabrication and assembly techniques. Below, we describe a promising architecture and prototype of a phased array that can be manufactured using processes similar to those for making low-cost computer boards. Figure T/R channel panel array: radiator side System Performance/Cost Objective and Active Panel Array Approach The air-cooled panel array is the building block for a larger, active phased array. The strategy for reducing cost is based on the following four objectives: 1. Significant reduction in printed wiring board (PWB) fabrication and assembly process steps Fabrication: One image and etch, one lamination, one drill and plate Assembly: One solder reflow operation to attach all components 2. Significant reduction in components Surface mount flip-chip MMICs and components Modular: Highly integrated RF, DC and logic PWB manifold Environmental coatings/protection tailored to application 3. Reliance on established technology Incorporation of mature and advanced technologies as required Low-power designs (<1W per element) leverages mature RF CMOS, SiGe, or GaAs MMICs Higher power designs leverage emerging GaN Scalable from L-Band to Ka-band Figure T/R channel panel array: active component side 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 following mixed-signal design approach: RF. RF Isolation Cage: All RF, DC and logic vias are drilled in one step through the entire PWB laminate. A square pattern subset of plated vias, connecting all RF ground planes, defines an RF isolation cage for each unit cell and suppresses cross-talk between transmit/ receive channels. RF Via Stub Tuning: The RF via stub extending beyond the RF transmission line junction is tuned for an impedance match over the required bandwidth ISSUE 1 RAYTHEON TECHNOLOGY TODAY

4 Slot Coupling to Radiator: A slot coupled feed to stacked patches simplifies PWB fabrication while providing excellent RF performance. Beamformer Circuits: Untrimmed ink resistors are used because of lower fabrication cost. The tolerance of the ink resistor has been incorporated into the design. DC. High-current power plane is located on the layer directly below the surface mount MMIC layer. Logic. Logic lines are routed between each 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 Progress A prototype active T/R channel panel array, the building block for a 1m 2 weather radar, Amplitude (db) Hcut Hcut Azimuth (deg) was assembled with flip-chip MMICs and tested. Figure 4 shows active receive, linearhorizontal polarized patterns of the T/R channel panel array at 9.5GHz; the dotted line is cross-polarization. Future Plans In 2008, Raytheon will assemble a panel array. It will be integrated and tested with a DC/DC converter panel (using COTS converters) and a receiver-exciter (REX) panel Amplitude (db) Vcut Vcut Figure T/R channel panel array: active component side Elevation (deg) (also using COTS components) in the prototype 1m 2 array frame with radome. The first fully populated 1m 2 weather radar will be field-tested in Angelo Puzella angelo_puzella@raytheon.com Co-author: David J. McLaughlin 1 The core academic partners of the CASA team are the University of Massachusetts Amherst (lead university), University of Oklahoma, Colorado State University, and University of Puerto Rico at Mayaguez. ENGINEERING PROFILE Angelo Puzella Program Manager, Low-Cost Active Arrays Raytheon 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 computer board and the key is to leverage commercial manufacturing to incorporate mature or advanced semiconductor 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 people taking risks, of using trial and error and inspiration. If you can push something forward like this panel, other applications come up for it. RAYTHEON TECHNOLOGY TODAY 2008 ISSUE 1 19

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