Advanced Antenna Technology for a Broadband Ka-Band Communication Satellite

Advanced Antenna Technology for a Broadband Ka-Band Communication Satellite Charles W. Chandler, Leonard A. Hoey, Ann L. Peebles, and Makkalon Em TRW Space & Electronics, Engineering The needs of the Ka-band broadband market have been assessed by numerous antenna trade studies. Wide-coverage, wide-bandwidth, low-noise communication systems with high effective isotropic radiated power (EIRP) must have configurable spot beams to meet the flexible distribution demands of bandwidth and power into high-traffic areas. The trend is toward larger effective apertures, a significantly higher number of smaller beams, higher EIRP, a higher gain-totemperature ratio, more complex switching/combining functions, and onboard processing functions. Satisfying those demands will require an antenna technology significantly more advanced than that employed by current wide-areacoverage transponder systems. TRW has developed a new generation of broadband communication satellite antennas for Gen*Star, a TRW-built advanced space-based broadband digital communication system for the emerging Kaband market. The Gen*Star family of precision high-gain satellite antennas addresses the future needs of the Ka-band market. Performance results exceed those previously shown for other systems. Since future markets may develop in unforeseen ways, the Gen*Star family of antennas has design features flexible enough to meet future market demands. Introduction In response to the demand for broadband satellite systems and services, TRW has developed Gen*Star, an advanced space-based broadband digital communication system for the emerging Ka-band market. With dynamic communication links and sophisticated onboard signal and data processing, Gen*Star provides broadband connectivity with seamless interfaces to a terrestrial infrastructure, using technologies designed to operate in space for years. In addition, key design features make the system flexible and robust enough to meet future market needs. The development and capabilities of Gen*Star s processing payload were detailed in a previous Technology Review Journal article [1]. Here, however, we describe the key design trades of Gen*Star s multiple-beam antenna (MBA) system. To meet a steadily increasing demand for satellite capacity, MBAs have become common in satellite communication systems. MBA systems enable frequency reuse by maximizing capacity, while minimizing required frequency allocation. Service providers can use spot beams to concentrate coverage in high-demand areas, rather than supplying wide-area coverage that may include areas with little or no demand. Gen*Star, for example, provides a full-earth field of view (FOV) from a single satellite in geosynchronous Earth orbit (Figure 1). Technology Review Journal Spring/Summer 2002 37

Figure 1. Gen*Star s full-earth FOV enabled by its MBA system optics Another benefit of higher-frequency MBA systems is their ability to operate with broader bandwidths in the Ka- and V-band frequency regions; the spacecraft is thus able to accommodate smaller antennas. Many new MBA systems now under construction will operate in the Ka-band. Future systems being planned for the V-band, which permits significantly smaller antennas than even the Ka-band, should be operational by about 2010. TRW s Gen*Star antennas are some of the first to be designed for the Ka-band. Table 1 details 11 major Ka- and V-band satellite systems planned by various service providers for operation in the near future. Key MBA System Performance Parameters MBA system design involves trades in several key performance parameters: Antenna gain. Affects DC power, capacity, and ground terminal size. High-gain antennas minimize power consumption and terminal size, while maximizing capacity. Number of beams. Determines the percentage of the desired coverage area available. In addition, their dwell times drive the demand for bandwidth. The available spacecraft power also determines the number of simultaneous beams. Carrier-to-interference (C/I) ratio. Measures the signal-to- noise performance, where the equivalent noise is interference from adjacent beams. A high C/I ratio enables maximal frequency reuse, thereby maximizing capacity. Figure 2 shows the representative sources and levels of interference in a two-dimensional cut of a hypothetical typical beam set. Typical requirements include a four- or sevenfold reuse spacing in densely populated areas. MBA systems must meet stringent crosspolarization and side-lobe-level requirements, because of a high degree of frequency reuse and tight beam spacing. For many MBA systems, however, performance is limited by composite interference from surrounding beams, rather than noise. In those cases, the coverage area must be limited to that in which low cross-polarization and side-lobe levels are achieved, resulting in decreased capacity or penalties on the 38 Technology Review Journal Spring/Summer 2002

Table 1. Major planned Ka- and V-band MBA satellite constellations using multiplespot-beam coverage System Astrolink GEO 5 Population centers anywhere Cyberstar Euroskyway East b WEST SPACEWAY GEO/MEO Celestri Aster GESN c V-Stream CyberPath Satellite a Orbit GEO GEO GEO GEO/MEO GEO/MEO GEO GEO/MEO GEO GEO Number 3 5 12 9 16 36 5 25 19 12 10 Coverage North America, Europe, Asia Europe, Africa, Middle East Europe/Africa Europe, Africa, Middle East Population centers anywhere Freq. Band Ka Ka Ka Ka Ka Ka Ka/V V V V V Beam Size (deg) 0.8 1 1 0.6 0.6 1 Beam Number 96 72 32 64 24 58 Antenna Horn-fed Horn-fed Horn-fed Horn-fed Market Multimedia Multimedia Multimedia Horn-fed Infrastructure Horn-fed Multimedia Infrastructure Infrastructure Infrastructure Infrastructure Onboard Processing Full Baseband Baseband Baseband Baseband Baseband a GEO = geosynchronous Earth orbit. MEO = medium Earth orbit. b WEST = Wide-Band European Satellite Telecommunication. c GESN = Global Extremely High-Frequency Satellite Network (licensed to TRW). terminal design. MBA gain and C/I performance typically degrade as the angle off boresight (scan angle) increases, limiting most MBA systems to regional or national coverage areas and thus also limiting the system global capacity. Coverage flexibility. Defines the ability of the antenna to provide high-performance coverage across a wide FOV. Antennas with excellent coverage capability give the satellite service provider greater flexibility in deployment, sparing, and recovery planning. The optimal selection will also minimize the number of satellites. Spacecraft accommodation. Specifies the compatibility of the antenna system with the spacecraft bus. An antenna with excellent accommodation characteristics enables multiple antennaspacecraft bus combinations. Spacecraft accommodation issues may arise from restrictions on either the spacecraft bus or the launch vehicle, or from other spacecraft functions. With any of those limitations, the system implementation may adversely affect antenna gain and C/I performance. Any performance restrictions ultimately affect the system s profit-generating potential through reduced capacity and increased satellite and terminal costs. Gen*Star Goals TRW s Gen*Star line of antennas was developed to surmount all current limitations of older MBA designs. The Gen*Star antenna is a new MBA design that enables service providers to supply the highest gain and highest C/I coverage anywhere in the full-earth FOV. The Gen*Star antenna design is based on design and development that began in 1995 (Figure 3). Over the past six years, TRW has developed the innovative Gen*Star antenna concept into a mature, proven technology. A major focus was our evaluation of alternative antenna approaches suitable for the densely tiled narrow-spot-beam architectures needed by emerging Ka-band systems [25]. The Gen*Star antenna goal, now Technology Review Journal Spring/Summer 2002 39

Figure 2. Representative patterns show relative sources and levels of interference Figure 3. Gen*Star antenna development timeline 40 Technology Review Journal Spring/Summer 2002

realized, was to provide uniform beam performance (similar peak gain, pattern shape, side lobes, and cross-polarization) over the entire Earth in a single satellite [69]. No current systems, not even MBA, can match that performance, as they can provide only A smaller coverage area with a single satellite Significantly degraded performance for the full-earth FOV, using a single satellite Full-Earth-FOV coverage using multiple satellites In contrast, various trade studies have shown Gen*Star s coverage to be limited only by the number of beams supported by the available spacecraft power. Gen*Star Antenna System Design and Performance The Gen*Star antenna system includes multiple reflector assemblies in which beams are multiplexed among the reflectors, typically according to operating frequency band assignment, in a four-reflector, four-color reuse factor. Figure 4 shows a typical group of interleaved beams and their mapping to a set of four reflector assemblies. The frequency and polarization mapping is usually either a fourfold frequency-reuse factor (higher-traffic areas) or a sevenfold frequency-reuse factor (lower-traffic areas), selected to minimize interference. Color-coding of the beams identifies which beams belong to which frequency and polarization combination. In Figure 4, a classic frequency and polarization selection, defined as seven-color, is mapped with the beam distribution among the four reflectors. The Gen*Star antenna system s uniqueness and major benefits stem from its ability to cover the entire earth from geosynchronous orbit with the same performance that previous systems provided in only a regional area. Yet the Gen*Star antenna is small enough to stow for launch in a very compact space. We have conducted several trade studies to identify the optimal reflector geometry, rating those benefits highest in our selection criteria. 5 3 4 5 6 7 6 7 1 2 3 1 2 3 4 3 4 4 5 6 7 1 2 3 4 3 4 5 6 7 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 4 5 6 7 1 2 3 4 5 6 7 5 1 2 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 1 5 6 2 3 4 5 6 7 1 2 3 4 5 1 2 3 5 6 7 4 5 6 7 3 4 5 6 2 3 4 5 7 1 2 3 6 7 Reflector 1 Reflector 2 7 3 4 6 7 Reflector 3 Reflector 4 1 Figure 4. Beam and frequency mapping to multiple reflector assemblies: Colors map to reflectors and numbers map to frequencies Technology Review Journal Spring/Summer 2002 41

The four best candidate reflector geometries, detailed in Figure 5, were selected and analyzed for performance: a single-offset reflector, a single-offset reflector with a splash plate, and both top-fed and side-fed Cassegrain reflectors. The single-offset reflector the simplest candidate can be easily stowed but required a very long focal length to achieve low scan loss. The single-offset reflector with a splash plate is a folded equivalent to the single-offset. It packages into a smaller volume but still delivers inadequate performance. The preferred designs are the remaining two candidates, top-fed and side-fed with multiple reflectors, which have excellent scan loss characteristics due to high magnification factors. Another trade study, focused on spacecraft packaging, examined five candidate reflector geometries (Figure 6): a single-offset, an offset Cassegrain, an offset Gregorian, a top-fed Cassegrain, and a side-fed Cassegrain. Overall, the performance comparisons show the scan loss improvement possible with top-fed/side-fed reflector geometries when all designs are constrained to fit in a common packaging volume. Again, the single-offset reflector can be easily stowed but has serious scan limitations, owing to its constrained focal length. The offset Cassegrain and Gregorian reflectors proved marginally better but still inadequate for a full-earth FOV. The remaining two candidates with folded optic reflectors again show superior scan loss because they can achieve large focal-length-todiameter (F/D) ratios in a small volume. The top-fed and side-fed geometries both deliver outstanding performance. However, the side-fed option proved superior because it Stows more compactly Offers the added benefit of low-profile stowage characteristics Maintains low side lobes and low cross-polarization Delivers wide-angle scanning with consistent high gain across the entire Earth (because of its large F/D ratio) Previous MBA systems produced beams with gain diminishing and patterns broadening as the scan angles increased beyond 4 deg; the Cassegrain curve shows main beam distortion starting around 3 deg (Figure 7). Such spreading results in higher side lobes, asymmetric beam shape, and higher interference to neighboring cells. Yet the Gen*Star antenna design provides high gain, along with stable low side-lobe and low cross-polarization patterns little affected by changes in frequency at scan angles beyond 8 deg (Figure 8). To validate the selection of the side-fed dual-reflector option for Gen*Star, a developmental reflector assembly was built and tested in TRW s near-field scanner (Figure 9). Precision range measurements were taken for the Gen*Star preproduction unit. The measured patterns correlated to the analytic predictions and did indeed show excellent performance: uniform gain and negligible change in beam shape over the full-earth FOV. Gen*Star Antenna Flexibility The Gen*Star antenna architecture is highly flexible. The configuration can be easily customized for a specific mission requirement. The foremost enablers of Gen*Star s flexibility are Standardized components. Feed assemblies, hinges, launch locks, reflectors, deployment booms, etc. Ability to use any polarization or combination of polarizations. Right-hand and lefthand circular polarization (RHCP, LHCP), horizontal (H), vertical (V), elliptical 42 Technology Review Journal Spring/Summer 2002

Figure 5. Performance comparison of four reflector geometries with size unconstrained: Top-fed and side-fed with multiple reflectors are preferred Frequency insensitivity. Multiple frequency bands accommodated in the same system: C-band, X-band, Ku-band, V-band, etc. Compact stowed system. Packaging and configuration options are significantly increased on various spacecraft whose antenna is virtually independent of the bus or reduces occupied spacecraft real estate on the nadir deck Switched beam. Enables bandwidth-on-demand to be achieved for higher-traffic areas, yet flexibility allows coverage of lower-demand areas Technology Review Journal Spring/Summer 2002 43

Figure 6. Performance comparison of five reflector geometries with size constrained: Top-fed and side-fed are again preferred 44 Technology Review Journal Spring/Summer 2002

Figure 7. Gain variation of Gen*Star antenna aperture superior to that of Cassegrain/Gregorian designs Figure 8. Gen*Star antenna s side-lobe and cross-polarization patterns showing low sensitivity to frequency and scan angle Gen*Star s flexible architecture maximizes reuse of component designs. Besides lowering development costs, standardization of components allows the same horn to be used in any position, whereas other architectures require design of a different horn for every position. Gen*Star thus uses coverage changes to reduce hardware changes. In fact, Gen*Star s uplink assemblies are scaled versions of its downlink assemblies. The only nonstandard elements in the antenna system for different customers are the feed clusters, which are unique to given coverage areas. Another Gen*Star innovation is the ability to configure feed clusters for a superset of beam locations early in the production schedule, so that customers can specify the final configured coverage pattern late in the program cycle. Technology Review Journal Spring/Summer 2002 45

Figure 9. Developmental Gen*Star antenna aperture in near-field range testing Both linear (H and V) and circular (RHCP and LHCP) polarizations have been measured to confirm flexibility in polarization. Circular polarization showed nearly 30-dB crosspolarization response, and linear showed in excess of 35-dB. For either type of polarization, the system produces very low interference to or from neighboring cells. In fact, any polarization or combination of polarizations per ground cell location is possible. Another key feature is the antenna system s ability to support other frequency bands. Its long focal length allows multiplexed-frequency-band feeds to be integrated. Configurations have been developed that provide outstanding spot-beam performance at Ka- and Ku-bands simultaneously. The Gen*Star antenna also has excellent stowage features. The side-fed, dual-reflector system stows naturally in a compact configuration, using a patented double-deployment scheme. Such compactness in stowage enables many mounting options on various spacecraft buses. Two primary configuration options are available: A top-mounted antenna suite with easy accommodation to the top of the spacecraft bus the configuration currently in flight production. A side-mounted configuration, which reduces waveguide runs and thus increases effective isotropic radiated power (EIRP). The use of a dual-frequency feed to reduce the number of apertures, along with side-mounting to the spacecraft bus, may benefit customers with challenging spacecraft or launch vehicle accommodations. The top-mounted Gen*Star antenna (Figure 10) has eight dual-reflector multiple-beam apertures (four uplink and four downlink) that multiplex spot beams into contiguous ground coverage areas. The top-mounted configuration enables very simple integration onto the nadir-facing surface of the spacecraft bus. Four apertures for each frequency 46 Technology Review Journal Spring/Summer 2002

band permit optimal performance and coverage in a region of densely packed cells. Each reflector assembly is independent and individually stows into the compact space of a 4-m fairing. The top-mounted antenna system was in flight production for the Astrolink program. To validate assembly and integration techniques for the top-mounted Gen*Star antenna, we used flight components and processes to develop the Antenna Integration Simulator (Figure 11), a single quadrant of a full-up antenna system. Some satellites have limited space available on the nadir face of the spacecraft bus. In those cases, the folded-optics design, which is very compact, naturally accommodates mounting on the side of the spacecraft. That configuration allows staggering of the feed trays, which opens many more routing options from traveling-wave-tube amplifiers. The result is minimal waveguide length, minimal waveguide loss, and maximal EIRP. Replacing the transmit feed clusters with dual-frequency feeds produces only slightly degraded coverage performance, even when just four reflector assemblies are used (Figure 12). The dual-frequency apertures can mitigate the risk of uplink-to-downlink (UL-to-DL) coverage misalignment. Additional benefits of the side-mounted antenna are its lower satellite center of mass, lower volume, and easier accommodation of the antenna on the spacecraft bus. The increased bus compatibility and low antenna volume enable more flexibility in launch vehicle, allowing the service provider more freedom to select the launch vehicle best suited to a given program. Alternatively, a larger reflector system can be employed in either system to produce increased gain in each beam area. In fact, either system can be configured with fewer apertures, with some tradeoff in performance (Figure 12). Studies reveal many configurations are possible (Table 2), each with advantages and disadvantages with respect to size, weight, complexity, and performance. In an eightaperture configuration, the radio frequency (RF) components are very simple, each beam is independent of all others, and no downlink power couples directly into the uplink receive channels. Seven apertures would enable larger feeds, but that configuration would require all DL-sized apertures and combined UL/DL frequencies to be in the same feed. With six apertures (three UL, three DL), the reflectors grow in size because of reduced feed size and degraded side-lobe performance. With four apertures (four combined UL/ DL), coupling between frequency bands becomes an issue for the feed assembly that supports both bands. With three apertures (three combined UL/DL), aperture size must be Stowed Deployed Figure 10. Gen*Star top-mounted spacecraft configuration Technology Review Journal Spring/Summer 2002 47

UL and DL Feed Clusters Antenna Integration Simulator: Tooling Provides 0-Gravity Aperture Locations Figure 11. Gen*Star Antenna Integration Simulator used to validate assembly and integration techniques Staggered antenna layout for maximal EIRP Dual-frequency feeds enable common apertures for both transmit and receive Side-mounted for lower mass and lower satellite center of mass Optics, scaled dimensions, materials, and fabrication processes identical to those of top-mounted antenna Figure 12. Side-mounted Gen*Star antenna configuration 48 Technology Review Journal Spring/Summer 2002

Table 2. Aperture selection affects aperture size and feed sizes Number of Single/Dual Apertures Aperture Size Frequency Feed Size Description 8 Small Single 7 6 4 3 2 1 Small Medium Medium+ Medium+ Large Large Dual Single Dual Dual Single Dual Large Large Medium+ Medium Medium+ Small+ Small 4 UL and 4 DL apertures 7 DL apertures 3 UL and 3 DL larger apertures 4 DL slightly larger apertures 3 DL large apertures 1 UL and 1 DL oversized apertures 1 DL oversized aperture increased significantly, frequencies are combined, and performance is reduced. With two apertures (one UL, one DL), aperture size approaches twice the original, and multiple elements must be combined to control the illumination. Finally, a single-aperture configuration would face all of those issues. A key study result showed that weight does not increase in direct proportion to the number of apertures. Pointing is a coverage performance issue. For equivalent performance, beamwidth must increase with the pointing error. If desired, closed-loop tracking, based on a UL beacon signal in each aperture, can improve on-orbit pointing. System Advantages of Gen*Star Antenna The Gen*Star antenna is designed to deliver the high performance necessary to support multibeam Ka-band systems. The result is the first antenna to offer excellent gain and C/I performance anywhere in the full-earth FOV. Excellent C/I Performance. A significant advantage of the Gen*Star antenna is its excellent C/I performance, which permits maximal capacity. In many MBA systems, capacity is limited by interference rather than noise. To minimize interference, coverage patterns must be designed to reduce interference to acceptable levels. Typically, optimizing the coverage pattern to reduce the C/I ratio increases the separation between coverage cells and reduces the number of copolarization-interfering channels. The net result is a decrease in system capacity. With the Gen*Star design, service providers can both space coverage cells densely and optimize the coverage pattern for maximal capacity. Maximizing capacity translates directly into service revenue and profit for the satellite service provider. Uniform High EIRP and High G/T Ratio. The excellent scan performance of the Gen*Star antenna translates into uniform high EIRP and a high gain-to-temperature (G/T) ratio for all coverage cells. That uniformity enables standard antenna terminal design, which in turn minimizes terminal cost and thus increases the affordability of the system to the end user. Technology Review Journal Spring/Summer 2002 49

Full-Earth FOV. A full-earth FOV minimizes time to global coverage. The ability of the Gen*Star antenna to provide high-performance coverage over the full-earth FOV reduces the number of satellites required for global coverage, allowing the service provider to reach global coverage with fewer launches in less time. The improved time to market and reduced launch costs may translate into higher revenue and profit for the service provider. Coverage Flexibility. Coverage flexibility offers the service provider high-value approaches to service rollout, sparing, and service restoration. Homogeneous gain and side-lobe performance over the full-earth FOV translate into high levels of coverage flexibility. The Gen*Star antenna uses that flexibility to provide multiregion and multislot coverage. The multiregion antenna system has beam coverage designed for operation from one orbital slot that can cover multiple regions. The multislot antenna system has beam coverage designed for two or more orbital slots that can cover the same or multiple regions [10,11,12]. After launch and deployment, the beams selected for the initial coverage rollout are activated, while the remaining feeds stay dark until the service provider desires to change or redistribute the activated beams to another preconfigured coverage area. With the addition of beam-switching networks, the ultimate goal of bandwidth-on-demand can be realized. Selected beams can be multiplexed to provide the longest dwell in the highest-traffic area, yet retain accessibility to lower-demand regions. Multiregion/multislot coverage capabilities give service providers the option of highvalue approaches to service rollout and sparing. With the ability to cover multiple regions and service multiple slots, the provider has much greater flexibility in deployment. Rather than customizing the satellite for a specific coverage area, the provider can select multiple coverage options and postpone the final selection until launch. That additional flexibility allows the service rollout to be based on the latest market data. Multiregion/multislot coverage capabilities also permit high-value sparing and service restoration approaches [11,12]. Rather than expensive one-for-one sparing, the service provider can configure spares to support multiple regions. For example, a spare can fill in for a failed spacecraft, providing the same coverage. Sparing requirements can be reduced dramatically, depending on the coverage requirements and available orbital slots. In addition, the spare satellite can be either dark or configured to supply additional capacity. If another spacecraft fails, capacity can be reallocated as necessary. Low-Risk Design. The Gen*Star antenna is a mature design that offers high performance with very low levels of risk to the satellite service provider. Satellite coverage has been expanded from national to regional and global markets (Figure 13) with high-quality service to all. The Gen*Star design has been verified, with all manufacturing processes having been proved with the Antenna Integration Simulator. It is now qualified for flight. Flight Performance The first-flight configuration (Figure 14) has been built and tested. Performance measurements (Figure 15) verify the excellent performance in side-lobe and cross-polarization levels that enables Gen*Star to provide high C/I performance in dense-coverage areas. Finally, the pointing error achieved through the alignment process has delivered unprecedented accuracies (Figure 15). 50 Technology Review Journal Spring/Summer 2002

Scan Loss (db) 1 Global 0 1 2 Regional 3 4 National 5 8.8 7.2 5.6 4.0 2.4 0.8 0.8 2.4 4.0 5.6 7.2 8.8 Earth Field of View (deg) Gen*Star Coverage Gain Cassegrain/Gregorian Coverage Gain Figure 13. Gen*Star expands previous national satellite coverage to full-earth FOV Flight Hardware Being Aligned in Near-Field Range Satellite with All Apertures Aligned to Same Reference Figure 14. Protoflight configuration: Gen*Star top-mounted flight unit in range measurement Technology Review Journal Spring/Summer 2002 51

Figure 15. Gen*Star flight antenna performance surpassed expectations Summary TRW s Gen*Star family of precision high-gain satellite antennas offers the expanding coverage required in the Ka-band market. Providing superior performance, flexibility, and capacity, along with a full-earth FOV, the Gen*Star antenna is the clear choice for highcapacity applications. Performance results of the protoflight model exceed those previously shown for other designs. This family of antennas has many flexible design features, so it can meet future market demands. In addition, TRW s long experience in the design, integration, and testing of Ka-band antenna products for government customers enables it to offer a mature but high-performance design with very low levels of risk to the satellite service provider. The authors salute the tremendous efforts of Louis Wilson, whose constant vigilance in the pursuit of perfection enabled the antenna system to perform beyond anyone s expectations. Shady Suleiman s key contributions to the feed development likewise enabled the 52 Technology Review Journal Spring/Summer 2002

outstanding system performance. The diligence and hard work of the mechanical team and integration and test team members resulted in an extraordinary piece of hardware. References 1. M.E. Bever et al., Advanced Broadband Satellite Digital Communication System for the Emerging Ka-Band Market, TRW s Technology Review Journal, Vol. 9, No. 2, Fall/Winter 2001, pp. 118. 2. S. Nguyen et al., Deployment of Dual Reflector Systems, U.S. Patent 6,124,835, September 26, 2000. 3. A.L. Peebles et al., Compact Side-fed Dual Reflector Antenna System for Providing Adjacent, High Gain Antenna Beams, U.S. Patent 6,211,835, April 3, 2001. 4. C.W. Chandler et al., Compact Offset Gregorian Antenna System for Providing Adjacent, High Gain, Antenna Beams, U.S. Patent 6,236,375, May 22, 2001. 5. C.W. Chandler et al., Compact Front-fed Dual Reflector Antenna System for Providing Adjacent, High Gain Antenna Beams, U.S. Patent 6,215,452, April 10, 2001. 6. J.A. Hudson, Off-Axis Performance of Shaped Antennas at Millimeter Wavelengths, Radio Science, Vol. 24, No. 4, July/August 1989, pp. 417426. 7. C. Dragone, Unique Reflector Arrangement with Very Wide Field of View for Multibeam Antennas, Electronic Letters, Vol. 19, 1983, pp. 10621063. 8. R. Jorgensen, P.P. Baling, and W.J. English, Dual Offset Reflector for Multibeam Antenna for International Communications Satellite Applications, IEEE Trans. Antennas Propag., Vol. AP-33, 1985, pp. 13041312. 9. G.W. Collins, Shaping of Subreflectors in Cassegrain Antennas for Maximum Aperture Efficiency, IEEE Trans. Antennas Propag., Vol. AP-21, 1973, pp. 309 313. 10. C.W. Chandler et al., A New Generation of Broadband Communications Satellite Antennas, American Institute of Aeronautics and Astronautics, 20th International Communications Satellite Systems Conference, Montreal, Canada, May 2002. 11. C.W. Chandler et al., Broadband Satellite Communications Antenna Technology for the Emerging Ka-Band Market, 7th Ka-Band Utilization Conference, Santa Margherita, Liguria, Italy, September 2001. 12. C.W. Chandler et al., Advanced Satellite Antenna Technology for the Emerging Ka- Band Market, International Astronautical Federation Conference, Toulouse, France, October 2001. Technology Review Journal Spring/Summer 2002 53

Charles W. Chandler, a senior staff antenna engineer in TRW Space & Electronics Engineering, Antenna RF Engineering Department, currently heads Independent Research and Development (IR&D) projects devoted to the design and development of antennas. He was the Astrolink payload antenna system engineer lead at TRW, responsible for developing, prototyping, and producing commercial antenna systems that meet the requirements of the global broadband processed payload market. Previously, at the National Aeronautics and Space Administration s (NASA s) Jet Propulsion Laboratory, he was the SeaWinds antenna system engineer lead, responsible for developing and producing an antenna for active scatterometry. Before that, he characterized and analyzed antennas for deep space missions. He has over 22 years of experience in the development of advanced antenna systems. He holds 14 U.S. patents. He received a BS in physics from Florida Institute of Technology. chuck.chandler@trw.com Leonard A. Hoey, a TRW Space & Electronics Six Sigma Black Belt, is currently working on an engineering process control and improvement project. During the past five years, in Engineering s Antenna Product Center, he has focused on the Astrolink antenna, the Gen*Star development project, and various IR&D and new business activities. He most recently served as the deputy lead for the Astrolink antenna integrated product team. Previously, he held project management and design lead positions on a variety of commercial communication satellite projects. He holds one U.S. patent. He received a BS in mechanical engineering and material science engineering from the University of California, Berkeley. leonard.hoey@trw.com 54 Technology Review Journal Spring/Summer 2002

Ann L. Peebles, a senior staff antenna engineer in TRW Space & Electronics Engineering, Antenna RF Engineering Department, is currently focused on antenna design and development for the Advanced Extremely High Frequency antenna project. Previously, she was the responsible design engineer for the Astrolink uplink antenna system. She designed and patented the Astrolink Dual Reflector Antenna System and was the test leader of the Astrolink Development Verification Model. She has also been involved in a variety of IR&D projects. Before joining TRW in 1995, she cofounded Innovative Research & Development Company, where she served as a senior scientist, developing millimeter-wave and far-infrared test equipment. Previously, she focused on antenna development for a variety of commercial satellite systems. She holds five U.S. patents. She received a BS, MS, and PhD, all in electrical engineering and all from the University of California, Los Angeles. ann.peebles@trw.com Makkalon Em, a hardware engineer in TRW Space & Electronics Engineering, Antenna RF Engineering Department, focuses on the design, analysis, and simulation of antenna systems for the Astrolink Ka-band satellite communication system. His responsibilities have included the development of software analysis tools and microwave hardware. Currently, he is designing radiating elements for phased-array antenna applications. Before joining TRW in 1997, he studied energy and electromagnetic systems, with a focus on backscattering radiation from photonic band-gap structures. He holds three U.S. patents. He received both a BS and an MS in engineering from the Massachusetts Institute of Technology. makkalon.em@trw.com Technology Review Journal Spring/Summer 2002 55