Technology Today Volumn 3 Issue 1 - Raytheon

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SATELLITE Sensors Space-borne Microwave Remote Sensing Microwave remote sensing has evolved into an important all-weather tool for monitoring the atmosphere and planetary object surfaces, which emphasizes the characterization of the earth phenomenology. This type of sensing encompasses the physics of radio wave propagation and interaction with material media, including surface and volume scattering and emissions. “Active” remote sensors include scatterometers, Synthetic Aperture Radar (SAR) and altimeters, whereas “passive” sensors are known as microwave radiometers. Raytheon has a 30-plus-year history in space Satellite Communications (SATCOM) and within the last decade, has added remote sensing payloads to our repertoire of outstanding orbital performances. The SeaWinds remote sensor has a specialized Ku-band radar (scatterometer), designed to accurately measure the amplitude scattering return from the ocean and convert the data into global ocean surface wind speeds and directions. A normalized radar backscatter coefficient of the ocean surface is measured at the same point on the ocean surface at four different incident angles, and is a function of the angle of incidence and the sea state. Receive power is determined by measuring the power in narrow- and wide-band filters, then solving two simultaneous equations from the received power and the ubiquitous receiver noise. The science community experimentally and analytically established a geophysical model of wind vectors and wind geometry over the last two decades to achieve this complex indirect measurement from space. The Scatterometer Electronic Subsystem (SES) was designed and developed by Raytheon St. Petersberg for the NASA/JPL program, and is currently on orbit and fully operational. Examples of previous wind vector maps of the Atlantic and Pacific oceans and newly acquired data from QuikScat’s SeaWinds are shown in the figure (center column). The radar operates at a carrier frequency of 13.402 GHz with a 10 nominal peak power of 110 watts, pulse rate of 192 Hz and pulse width of 1.5 m/sec. The highly stable receiver measures the return echo power from the ocean to a precision of 0.15 dB. Key measurements are a 1,800 km swath during each orbit providing 90 percent coverage of the Earth’s oceans every day, with wind speed measurement range from 3 to 30 m/sec with a 2 m/sec accuracy and wind direction accuracy of 20 degrees at a vector resolution of 25 km. Fifteen times a day, the satellite beams collected science data to NASA ground stations, which relay the data to scientists and weather forecasters. Winds play a major role in weather systems and directly affect the turbulent exchanges of heat, moisture and greenhouse gases between the Earth’s atmosphere and the ocean. They also play a crucial part in the scientific equation for determining long-term climate change. Data from SeaWinds’ two-year mission will greatly improve meteorologists’ ability to forecast weather and understand longerterm climate change. SeaWinds provides ocean wind coverage to an international team of climate specialists, oceanographers and meteorologists interested in discovering the secrets of climate patterns and improving the speed with which emergency preparedness agencies can respond to fastmoving weather fronts, floods, hurricanes, tsunamis and other natural disasters. Operating as NASA’s next El Nino watcher, QuikScat will be used to better understand global El Nino and La Nina weather abnormalities. A recent example of the advantages of spaceborne sensing was demonstrated when an iceberg the size of Rhode Island had elluded ship-borne and airborne surveillance devices and was drifting undetected off Antarctica until Quikscat located it and mapped its location (see figure above). Another on-orbit remote sensor is the US Navy GeoSAT Follow-On Ku-Band Radar Altimeter, designed to maintain continuous ocean observation from the GFO Exact Repeat Orbit. This satellite includes all the capabilities necessary for precise measurement of both mesoscale and basin-scale oceanography. Data retrieved from this satellite is useful for ocean research, offshore energy production, ocean circulation patterns and environmental change. GFO was launched aboard a TAURUS launch vehicle on Feb. 10, 1998, from Vandenberg Air Force Base in California and still provides valuable data sets for the U.S. Navy today. The radar uses co-boresighted radiometers, a Raytheon design, for water vapor correction. Radiometer calibration has become a niche area of research, and Raytheon holds several patents in calibrating radiometers using variable Cold Noise Sources based on MHEMT technology that have been validated at NIST. Space-borne SATCOM Payloads From Iridium to MILSTAR to FLTSATCOM, Raytheon has played a key role in the development of commercial military space satellite communications. Raytheon is the major supplier of UHF SATCOM products and services to the warfighter, including space and ground hardware, software, Continued on page 30
ELECTRONIC WARFARE and Signal Intelligence Historically, Electronic Warfare (EW) has been referred to as Electronic Countermeasures (ECM) — jamming, pure and simple. As the electronic battlefield became more sophisticated, EW has included Electronic Attack (EA), Electronic Protect (EP) and Electronic Support (ES). Technological advances have contributed to larger roles for EW, for example, Situational Awareness, Passive Counter Targeting and Precision Emitter Identification. Since EW has come to be used universally, it has become a necessary and integral part of both mission planning and campaign strategy. Radar and Electronic Countermeasures have similarly evolved together over the years as another facet of the arms and armament race. By today’s standards, the early radars were quite unsophisticated. Operation could be disrupted simply by transmitting more noise within the radar bandwidth than was returned from the target echo. Jamming was relatively easy to carry out, because substantial losses were sustained in the bidirectional path from radar to target and back, compared to the one-way transmission associated with the jamming method. Radar designers responded with transmitters having more and more power and antennas having higher gain in order to increase the radar’s Effective Radiated Power (ERP). In addition, jammers also became more powerful. The measure of performance of EW systems was based almost entirely upon the Jam-to-Signal Ratio (J/S). Radars got the task of not only detecting threats, but also tracking and targeting them. Chaff, bunched as bundles of tinfoil strips which were cut to the resonant length of the radar, burst into clouds when dispensed from an aircraft, with the result that alternative targets were offered to the enemy radar to track. Tracking algorithms for the radars improved from conical scan to scan-on-receive-only to obscure scanning from EW jammers. Jammers could jam scanning radars generating false scanning signals by slowly varying scanning modulation through a range of potential values. The base measure of performance for EW systems continued to be J/S. Radars having a monopulse tracking capability were soon invented. By having several, independent receive channels, detection, ranging and tracking could all be done using a single received pulse. Since only a single pulse was needed for tracking, jamming modulations became ineffective. A number of new jamming techniques were devised to defeat monopulse tracking radars. For example, during the Cold War, war plans included having aircraft enter and exit the target area at very low altitudes, allowing the aircraft to hide in the radar clutter. Raytheon EW invented the Terrain Bounce technique in case an interceptor acquired target lock. The Terrain Bounce technique simply received the radar signal, amplified it and retransmitted it in a narrow beam in front of the entering aircraft. The bounce off the ground technique, while experiencing a degree of signal loss, nevertheless provided a true false angle that the monopulse-tracking radar would follow. Other techniques, such as cross-polarization and cross-eye, provided false angle information to monopulsetracking radars at the expense of severe loss of coupling into the radar information bandwidth. As a result, jammers continued to have a high power requirement. Raytheon EW has produced a number of high-power radar jammers over the years. For example, Raytheon has supplied almost all the transmitters for the EF-111 and EA-6B standoff jammers. The very high-powered SLQ-32 provided protection for the Navy’s Cruisers, Battleships and Carriers. The ALQ-184 jamming pod provided self-protection for tactical aircraft like the A-10 and F-16. The SLQ-32 and ALQ-184 produced high ERP using novel Rotman Lenses. The ALE-50 Rotman lens enabled high gain retrodirective jamming on a pulse-by-pulse basis, without the need of computing an angle of arrival of the radar signal. Radars have basically won the RF Power arms race against jammers, because it became increasingly difficult to provide high power jammers with robust techniques that would be effective against a wide variety of radars. Not only could radars generate high ERP efficiently, but digital technology vastly improved their processing gain by using post-detection integration, pulse coding and Doppler filtering. EW has continued to exploit radar vulnerabilities throughout the kill chain of weapons systems. For example, Raytheon’s ALE-50 is a small repeater/transmitter towed behind the protected aircraft. The ALE-50 transmits a stronger signal than the echo bounced off the protected aircraft Continued on page 12 11
Page 1 and 2: technology today HIGHLIGHTING RAYTH
Page 3 and 4: TECHNOLOGY TODAY technology today i
Page 5 and 6: (less than 20 KHz) to visible light
Page 7 and 8: Radars aboard the F-15, F-14, F/A-1
Page 9: and target discrimination, which ar
Page 13 and 14: RF Communications Radios, Data Link
Page 15 and 16: emote battlefield sensors to sense
Page 17 and 18: Leadership Perspective Dr. PETER PA
Page 19 and 20: Pioneering Phased Array Systems & T
Page 21 and 22: separate receive elements, employin
Page 23 and 24: AESAs use the brick package. Brick
Page 25 and 26: Capability Maturity Model Integrati
Page 27 and 28: Figure 2. The deployment infrastruc
Page 29 and 30: New Global Headquarters Showcases T
Page 31 and 32: DAVID K. BARTON ROBERT E. MILLETT C

Technology Today Volumn 3 Issue 1 - Raytheon

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