ADVANCED COMMUNICATION SATELLITE TECHNOLOGIES

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1 Paper, presented at: Workshop on Space Borne Antennae Technologies and Measurement Techniques 18. April 2002, ISRO, Ahmedabad, India ADVANCED COMMUNICATION SATELLITE TECHNOLOGIES J. Hartmann, J. Habersack, H.-J. Steiner, M. Lieke Astrium GmbH, EADS Telecommunication and Navigation, Antennas & Tests - TN Munich, Germany Phone: / Fax: / [email protected] Abstract The available frequency spectrum and satellite orbits are both getting more and more crowded. Therefore, the demands on satellite antennas using efficiently these resources are increasing, so that future satellite antennas are illuminating several spots on earth by providing several contoured beams. Shaped reflector and multi-feed antennas instead of formerly used elliptical beam antenna are increasingly used for such applications. Within the paper modern satellite programs with its specific antenna design will be described. 1. Introduction Future communication satellite systems call for higher system capacities and lower costs per channel. Further, a highly efficient illumination of the service areas has to be performed by well contoured antenna beams in order to use the spacecraft power resources economically. Mainly two different antenna designs, depending on the requirements, emerged in the last years, to improve the formerly used elliptical beam antennas. For more regional coverages with shaped beams and with polarisation isolation, the shaped reflector and multi-feed designs were developed. For achieving very stringent isolation requirements between beams which are spatially isolated, multi-feed antennas are used for multi-beam generation. State of the art designs continue to be provided by Astrium GmbH. Further, new design technologies are developed within studies, to meet future space applications. For shaped reflector antennas past and several on-going programmes at Astrium employ this type of design. Among them, the INSAT 2E shaped reflector antenna was delivered to ISRO in early Further, the NAHUEL, SINOSAT and as recent development, the INTELSAT X can be named as examples. For multi-feed antenna developments, the AMOS, INTELSAT VIII, INTELSAT IX and a L- /S-band mobile communication satellite study can be named as examples. In the paper, the feed and reflector design of the mentioned satellite programmes will be described and analysed. 2. Elliptical Beam Antennas TV-SAT was the first German direct broadcasting satellite (DBS), equipped with a transmit antenna in Ku-band. The antenna reflector is an elliptically contoured parabolic offset reflector with 2.7 m x 1.4 m projected aperture, fed by an elliptical corrugated horn [1]. It was designed to illuminate only the area of the former Federal Republic of Germany with a Half-Power-Beam-Width (HPBW) of 0.72 x 1.62 and Left-Hand- Circular (LHC) polarisation from the

2 geostationary orbit in position 19 west. For the second DBS generation the illumination of the whole German Language Zone, including Austria, Germany and Switzerland was envisaged. This service area appears from the 19 west, as well as from the alternative 29 east orbit position as an ellipse. The elliptical form of the coverage area still remains, even if this zone will be extended to a second service area with 6 dbw reduced EIRP-requirements, comprising the preferred German touristical destinations in the Medi-terranean See area, e.g. the Spanish coast from the Costa Brava to the Costa Blanca, the Baleario Islands, Italy with most parts of Sicilia and the whole Yugoslavian coast, and the Eastern European countries Hungary, Czechoslavakia and Poland. Therefore an elliptical beam antenna making use of space-proven TV-SAT technology turned out to be the optimum solution in terms of electrical performance and mass. A Figure of the TV-SAT satellite antenna is shown in Figure 1. isolation requirements, a reflector antenna with a shaped surface, fed by a single feed system is an appropriate solution saving mass and volume compared to the multifeed approach. For linear polarisation, two antennas can be combined in a Polarisation Sensitive Reflector (PSR) system. The INSAT 2E antenna subsystem uses such a concept where one reflector is used for the transmit and the other for the receive case. The INSAT 2E antenna subsystem also includes a shaped reflector antenna with a solid Carbon-Fibre-Reinforced-Plastics (CFRP) reflector, fed by a single feed [2]. The principle sketch of the spacecraft is shown in Figure 2. The shaped reflector of one broadcasting unit with feeding section is shown in Figure 3. Figure 2 INSAT 2E Principle Sketch with Antennas, View from North Figure 1 German TV-SAT Satellite with Elliptical Beam Antenna 3. Shaped Reflector Antennas For applications, which require a contoured beam, but no in-orbit reconfigurability and limited sidelobe The design of the INSAT 2E communication antennas has been performed to achieve optimum electrical performance, i.e. maximum gain over the required coverages, maximum cross-polar discrimination, high power handling capability and extremely low risk of passive intermodulation products (PIMPs) under the given geometrical and thermal constraints of the spacecraft layout and launcher. To reach the mentioned requirements, Dornier Satellitensysteme GmbH (DSS), the former Astrium GmbH, has combined its advanced feed horn technology (axially and radially corrugated horns) with standard surface shaping

3 procedures. Each reflector surface shape has been optimised individually, taken into account the requirements of the corresponding coverage and frequency range. Therefore, the reflector surface synthesis software tools POS (from TICRA, Denmark) has been used. Three representative thermal load cases (hot, cold, gradient), corresponding to the worst case scenarios over the spacecraft orbital life, have been included in the shell optimisation. This results in a slight degradation of the Edge-Of-Coverage (EOC) gain (0.1/0.2 db, depending on coverage and frequency) but avoids strong local losses (up to 1 db) over the coverage that would have occurred, when this measure had not been taken into account within the shaping process. COI, USA) are fed by radially corrugated horns. The horn design is based on the extensive experience of Astrium GmbH gained on previous programs such as INTELSAT VIII, DFS Kopernikus, TV- SAT and AMOS). The corrugation structure has been optimised, using a software tool operating with the mode matching technique and the method of moments. The excellent comparison of the predicted co- and cross-polar radiation pattern versus measured results is exemplary shown in Figure 4. The example of a radially corrugated feed horn, designed by Astrium GmbH is shown in Figure 5. measured _ calculated 0.0 Relative Amplitude (db) Angle (degree) Figure 4 INSAT 2E Feed: Comparison between predicted and measured Feed Pattern Figure 3 INSAT 2E Satellite with Feed and Contoured Reflector The polarisation sensitive reflector as well as the CFRP reflector (manufactured by Figure 5 INSAT 2E Feed Example

4 Precautions against the generation of PIMP have been taken into account by the following reduction measures: - Surface Treatment, to avoid Corrosion - Proper Flange Design - Well-Defined Contact Pressure - Temperature Compensation of Contact Pressure - Proper Design of Reflector Grounding and Bonding - Proper Design of Sunshield Attachments and Grounding The coverage polygon in Figure 6 is the solid line and is derived from the coverage requirements plus pitch, roll an yaw errors. The shaping procedure worked very well for maximising gain over the whole coverage. This can be seen by the fact that the first contours in Figure 6 are corresponding to the 22.2 db specified values follows the coverage polygon very closely. The wide beam transmit/receive antenna assembly consists out of two single offset, shaped reflector shells (front shell gridded), arranged behind each other, each fed by a corrugated feed horn. The main geometrical data are listed in Table 1. Diameter [mm] Offset Distance [mm] Focal Length [mm] Polarisation Front Shell vertical Rear Shell horizontal Table 1 Geometrical Data of the INSAT 2E Reflector Shells The transmit antenna operates in the frequency band between 3600 and 4200 MHz and the receive antenna in the band between 5850 and 6650 MHz. The boresight of the antenna points to 100 East / 21 North on the earth. Relevant RF parameter are listed in Table 2. EOC Gain Cross-Pol. Discrimin. Return Loss Power Handling Transmit 21.7 dbi > 30 db < - 23 db 7 x 65 W Receive 22.2 dbi > 30 db < - 23 db N/A Table 2 Relevant RF Parameter of INSAT 2E Antenna System Figure 6 INSAT 2E Wide Beam Antenna, Typical Rx Co-Polar Plot The SINOSAT communication antenna subsystem makes also use of the advantaged technology to generate multiple beams on earth with a shaped and polarisation sensitive reflector [3]. The geostationary orbital position of the satellite is East to provide China with C-band transponder and wide parts of East Asia with Ku-band transponder. Within the design, a high attenuation due to rain by a 6 db increased gain over the corresponding area was taken into account. Two shaped Polarisation Sensitive Reflector (PSR) antenna systems with 1.6 m and 1.8 m in diameter were assembled on the spacecrafts East and West Panel, dedicated to the Ku-band transmit/receive functions and C-band transmission, respectively. The reception of C-band frequencies will be performed

5 via a dual-linear polarised centre-fed shaped reflector antenna with 1 m in diameter accommodated on the earth deck of the spacecraft. The spacecraft layout of SINOSAT is shown in Figure 7. The design of the SINOSAT communication antennas has been performed to achieve an optimum electrical performance, i.e. maximum gain over the required coverages, maximum cross-polar discrimination, high power handling capability and extremely low risk of passive intermodulation products (PIMPs) under the given geometrical and thermal constraints of the spacecraft layout and the launcher. For that aim, the advanced feed horn technology was combined with standard surface shaping procedures at Astrium GmbH. filter, supplied by Bosch Telecom, Germany. For design of the corrugated horns a mode matching and method of moment software tool was used, as already described at the INSAT 2E horn design. The transmit/receive antenna assemblies for C- as well as Ku-band consists out of two shaped reflector shells, arranged behind each other and fed via the corresponding corrugated horns. The main characteristics of both assemblies are given in Table 3. Diameter [mm] Offset Distance [mm] Focal Length [mm] Shell Rotation Feed Diameter [mm] Feed System Length Polarisation C-Band Front Shell vertical Rear Shell horizontal Diameter [mm] Offset Distance [mm] Focal Length [mm] Shell Rotation Feed Diameter [mm] Feed System Length Polarisation Ku-Band Front Shell vertical Rear Shell horizontal Figure 7 Layout of the SINOSAT Spacecraft For design of the polarisation sensitive and shaped reflectors, nearly the same procedures and tools were applied as for design of the already mentioned INSAT 2E satellite antennas. The reflectors for the SINOSAT satellite were manufactured by Aerospatiale/Les Mureaux, France, and are also fed by radially corrugated horns. The frequency band separation in the Ku-band is achieved by a diplexer using a cut-off high-pass filter and a corrugated low-pass Table 3 Geometrical Data of the SINOSAT C- and Ku-Band Reflector Shells and Feed The C-band antenna operates 12 channels per polarisation (36/54 MHz) in the frequency range between 3.68 GHz and 4.20 GHz. It is assembled on the spacecrafts West panel. The boresight points to East / 20.4 North on the earth. The Ku-band antenna operates 7 channels per polarisation (channel bandwidth 54 MHz) in the frequency ranges between

6 12.25 GHz and GHz (downlink) and GHz and GHz (uplink). It is assembled on the spacecrafts East panel. The boresight points to East / 29.9 North on the earth. The main interesting RF parameter of the C- and Ku-band transponders are given in Table 4.. The hardware of a SINOSAT shaped reflector with feed is shown in Figure 8. Related contour plots for the C- band and for the Ku-band in Figure 9 C-Band HP/VP EOC Gain 24.4 / 24.5 dbi* Cross-Pol. Discrimin. > 33 db* Return Loss < - 23 db Power Handling 24 x 15.2 W EOC Gain (Zone 1) EOC Gain (Zone 2) Cross-Pol. Discrimin. Return Loss Power Handling Ku-Band Transmit dbi dbi > 33 db < - 23 db 7 x 72 W * over more than 95 % of the coverage Receive dbi N/A > 33 db < - 23 db N/A Table 4 Relevant RF Parameter of the SINOSAT Antenna for C- and Ku-Band (a) (b) Figure 9 Co-Polar Antenna Pattern of SINOSAT, plotted on Earth: (a) C-Band Tx-Antenna (3.9 GHz, Horizontal Polarisation) (b) Ku-Band Tx/Rx-Antenna (12.25 GHz, Horizontal Polarisation) The newest development in shaped reflector technology at Astrium GmbH was performed for the INTELSAT X satellite. A principle sketch of the satellite is shown in Figure 10. The satellite (Version 10-01) consists out of different antennas, working in different frequency bands. The responsibility for the design and manufacturing of the large C- band reflector antennas including feeds is at Astrium GmbH. Figure 8 Hardware of SINOSAT Shaped Reflector with Feed

7 Y Y Reflector Rim for the East Antenna 1.50E E E E E E E E E E E E E E E E E+03 X Figure 12 Exemplary C-Band Reflector Rim Contour for Zones Z3 and Z4 of INTELSAT X Figure 10 Principle Sketch of INTELSAT X Satellite with The characteristic parameter of the C-band antenna are as follows: - 4 Tx and Rx Zone Beams (Z1.. Z4) - 2 deployable offset reflectors mounted on the West (Z1/Z2) and East (Z3/Z4) side walls of the spacecraft - Circular Polarisation - Coverages include parts of North America, South America and Europe Figure 13 Exemplary C-Band Reflector Surface Data for Zones Z1 and Z2 The reflector rim contours of the two shaped reflectors are shown in Figure 11 and Figure 12 and the related surface data are shown in Figure 13 and Figure 14. Reflector Rim for the West Antenna 1.50E E E E E E E E E E E E E+03 Figure 14 Exemplary C-Band Reflector Surface Data for Zones Z3 and Z4-5.00E E E+03 X Figure 11 Exemplary C-Band Reflector Rim Contour for Zones Z1 and Z2 of INTELSAT X The minimum gain requirements of the antennas is in the order of 22 to 24 dbi. The composite isolation for all zones is required to be better than 25 db, the beam

8 to beam isolation is required to be better than 27 db. For the feeds, radially corrugated horns are designed to be used. 4. Multi-feed Reflector Antennas The multi-feed reflector antenna design is most often chosen to meet contoured beam requirements when a high number of frequency reuse and high isolation between coverages are required and the coverages are close to each other. One example for multi-feed reflector antenna applications is the antenna of the Israeli communication satellite AMOS, which is operating successfully at the geostationary orbital postion 4 West [4]. The total mass of the satellite is less than 1000 kg and it offers seven Ku-band transponders of 35 Watt. Basically, the AMOS communication antenna provides services in the middle East and Eastern Europe with an EIRP of some 55 dbw. The antenna subsystem of AMOS has to perform telecommunication services in the 11/14 GHz frequency bands from the geostationary arc at 4 West. Three high gain spot beams have to be provided, one pointing to Israel/Middle East, one to East Europe/Hungary and one to Portugal. Only two beams shall be operated simultaneously, the Israel/Middle East beam and either that to Hungary or that to Portugal. The selection of the active beam shall be done by RF-switching within the antenna subsystem. Dual linear polarisation has been required. The AMOS satellite antenna with feed system and offset reflector is shown in Figure 15. The design of the combined transmit ( GHz) and receive ( GHz) antenna has been driven by the main requirements of 41.1 / 42.2 dbi (Tx and Rx) gain over Israel and 39.9 dbi (Tx and Rx) over Hungary. Therefore, an offset parabolic reflector with circular aperture of 1.70 m in diameter and 1.20 m in focal length has been chosen. The reflector is manufactured out of a thin sandwich shell stiffened by horizontal and longitudinal sandwich ribs. Both shell and ribs are made from ultrahigh modulus GY70/Epoxy skins on an aluminium honeycomb core. Figure 15 AMOS Satellite Antenna with Feed System in CCR of Astrium GmbH The feed assembly has been composed of three individual feed systems, each one consisting of a conical corrugated horn (aperture diameter 70 mm), a square to circular waveguide transition and an orthomode transducer to separate the two senses of linear polarisation. The feed systems dedicated to the Hungary and the Portugal beams can be selected via two waveguide switches (Tx and Rx). The conical corrugated horn as well as the two rectangular horns are made from aluminium using standard milling and eroding techniques. Inner and outer surfaces are alodyne treated, the flange areas are silver plated to reduce the risk of passive intermodulation products (PIMP).

9 The apertures are covered by white painted Kapton sunshields. The waveguide transition and the ortho-mode transducers are also made from aluminium, standard milling and eroding processes have been applied. A complex aluminium structure interfacing with the S/C West panel supports the three feed systems in the focal plane. Each feed system is defocused w.r.t. the reflector s focal point such that the corresponding beam meets its dedicated coverage area. The output ports of the ortho-mode transducers are connected via tailor made waveguide runs to the waveguide switches and to the repeater I/F on the spacecraft North panel, respectively. The INTELSAT-VIII hemi/zone antenna system was designed, manufactured, integrated and tested at DSS, the former Astrium GmbH, in Ottobrunn. The antenna is one of the most recent and most complex applications of the multi-feed reflector antenna design on a commercial communication satellite, until now [3]. Some attempts have been made in industry to provide hemi/zone beams with a single feed per beam combined with a shaped reflector. However, the results indicated, that for the multi-frequency reuse, required by INTELSAT, there is no viable way. Therefore, the INTELSAT VIII hemi/zone antenna was designed as a multi-feed antenna with an offset parabolic reflector. In order to achieve a lightweight structure of the feed array, the Astrium SCRIMP horn with its high aperture efficiency and excellent cross-polar performance was applied for each feed [5]. For regarding mutual coupling between the feed elements within the design of the whole feed array, certain array software was applied. The number of feeds, feed size, reflector diameter, focal length and offset height was designed to fulfil the requirements. The resulting overall antenna geometry is summarised in Table 5. The had to provide six fold frequency reuse from eight different orbital locations spread over the Atlantic, Indian and Pacific Ocean Regions (AOR, IOR, POR) with an additional ability to combine two beams to become one in the Pacific Ocean Region. The composite beam coverages that resulted after the optimisation process with the goal to achieve small composite coverages and large separations between the beams are shown in Figure 16. Reflector Aperture Offset Plane Symmetry Plane Focal Length Clearance Frequency [MHz] Table 5 Geometry Transmit Elliptical 2600 mm 2540 mm 2800 mm 1000 mm Receive Circular 1800 mm 1800 mm 1730 mm 750 mm Data of INTELSAT VIII Antenna Figure 16 Hemi/Zone Beams and Coverages of INTELSAT VIII Satellite Antenna A block diagram of the beam forming network of the INTELSAT VIII satellite antenna is shown in Figure 17.

10 Figure 17 Block Diagram of Beam Forming Network of INTELSAT VIII Satellite Antenna Additional applied RF switches are installed to provide a certain reconfigurability, as also shown in Figure 17. The re-configurability provides the possibility to combine the zone beams E and F to a combined coverage, called zone G. This type of zone beam combination required enhancements for existing design software because of the distribution of the excitation coefficients. The two separate zone beams are required to have high isolation between them as well as to all other beams. When the two hemi beams operate in one circular polarisation, the zone beams have to operate in the related orthogonal circular polarisation. For the design of the feed array, as well as for evaluation in order to calculate the primary fields in spherical modes, the software tools GRASP, SCOPE and SWEP, from TICRA, Denmark, were used. At last, an optimised design with 88 active elements resulted out of the calculations. The mapping of the element beams on the hemi and zone coverages is shown in Figure 18. Figure 18 Feed Array and Coverage Overlay of INTELSAT VIII Tx/Rx Antenna The optimisation process resulted in the calculation of the amplitude and phase excitation coefficients which have to be realised by the beamforming network (BFN). Within the BFN the TEM line technology is used whereas also dispersion effects are considered within the modelling. A three layer BFN resulted for both the transmit and the receive antenna. A section of the complex upper layer of the transmit antenna is shown in Figure 19. The related feed array during horn integration is shown in Figure 20.

11 Figure 19 Section of Upper Layer of INTELSAT VIII Transmit Antenna BFN Figure 21 Contour Plot of Co-Polar Field of INTELSAT VIII Satellite Antenna at Hot and Cold Temperature At last, the RF performance was measured with the feed array integrated with the related reflector on a spacecraft mockup in the Compensated Compact Range (CCR) of Astrium GmbH in Ottobrunn. Figure 20 Feed Array of INTELSAT VIII Transmit Antenna during Horn Integration After installation of the horns and measurement of the VSWR the feed array is subjected to a series of environmental tests including a complete characterisation of the RF performance at temperature extremes. For that aim, a special RF transparent climate-box had to be designed and the entire feed array was tested in the Cylindrical Near-Field Test Facility (CNTF) of Astrium GmbH in Ottobrunn. The temperature range for the test covered - 61 C to + 85 C. The tests exhibited a very stable performance for the co- and cross-polar antenna pattern. A comparative plot of the performance at hot and cold temperature is exemplarily shown in Figure 21 for the transmit zone F. The INTELSAT IX communication satellite antenna is also based on a multifeed technology. Compared to its predecessor, the INTELSAT VIII antenna, the feed array consists out of some more feed elements and is larger in aperture dimension for illumination of its designated coverage [6]. The geometrical data are summarised in Table 6. Reflector Aperture Offset Plane Symmetry Plane Focal Length Clearance Frequency [MHz] Table 6 Geometry Transmit Super- Elliptical 3200 mm 2800 mm 3300 mm 1275 mm Receive Circular 2300 mm 2300 mm 2262 mm 900 mm Data of INTELSAT IX Antenna

12 The feed and BFN were developed and designed equivalent as described before with the INTELSAT VIII satellite antenna. Further, also the same technology was applied. The Tx feed array during integration is shown in Figure 22 and the integrated feed with reflector and spacecraft mockup is shown in Figure 23. expected during the next decade. Since the GEO systems operate in L- or S-band, they require reflectors with diameters typically ranging between 12 m and 15 m and a corresponding feed system of more than 100 radiating elements. With respect to accommodation and mass one combined transmit / receive (Tx/Rx) antenna is preferred rather than two separate transmit and receive antennas. Another advantage of the combined antenna is the congruence between up- and downlink beams considering the narrow footprints of the beams (typical: 0.6 to 0.8 ). A technology for combined Tx/Rx RF feed systems for L-band and increased power applications have been developed and are currently being qualified at Astrium GmbH under ESA contract [7]. The design drivers are: Figure 22 Feed Array of INTELSAT IX Transmit Antenna during Integration at Astrium GmbH in Ottobrunn Figure 23 Feed Array with Reflector and Spacecraft Mockup of INTELSAT IX Transmit Antenna installed at DUT Positioner of Astrium CCR in Ottobrunn A strong increase in the demand for regional Geostationary Earth Orbit (GEO) based mobile communication services is - light weight manufacturing technology, - cable-less feed assembly integration, - high RF power - high rate and low cost manufacturing - short delivery times. The considered circular polarised feed system is composed of the radiating elements, the polarisers, the diplexers and the output networks (Butler matrices) with integrated band-pass and low-pass filters. The development of radiators and networks is a spin-off from Astrium s multifeed technology for C-band. It takes advantage of all relevant experience gained during the various applications of this technology during recent space programs (DFH-3, Intelsat VIII and IX). Since mass reduction is one of the design drivers, the components are realised in light weight silver plated magnesium technology. The block diagram of the semi-active Tx/Rx antenna subsystem is shown in Figure 24. A single offset unfurlable reflector is fed by a feed system, comprising 80 to 120 radiator elements.

13 FEED ASSY Unfurlable Reflector Horn Array Polarizer Level Diplexer Level Tx filters and LP filters. The feed and ONET assemblies are connected by cables. The major requirements for the feed assembly are summarised in Table 7. ONET ASSY ONET INET ONET INET LNA / VGA D/A-A/D Conversion Digital Signal Processing LNA / VGA Figure 24 Block Diagram of Multi-Feed Antenna Subsystem for Communication Service in L- or S-Band Item Frequency: Return loss at diplexer ports Radiator gain at Diplexer ports Polarisation Axial ration on axis Power handling Multipacting margin PIMP for two 18.5 dbw carriers Specification MHz transmit MHz receive 20 db 9.2 dbi at Tx band center 9.6 dbi at Rx band center LHC 1.0 db 19.0 dbw 9.4 db 5 th order < -145 dbm Digital Beam Forming (DBF) and digital signal processing will be used to provide the required flexibility w.r.t. service areas and channel switching. In the Tx path, the digital signal will be converted to analogue signal in base band and then up converted to the carrier frequencies at L-band. The low power signals will be distributed to the inputs of Solid State Power Amplifiers (SSPAs) by an input network (INET). The amplified signals at the output of the SSPAs will then be recombined by a Butler matrix network (ONET). Each input of the ONET is equipped with a band pass filter in order to reject any potential active intermodulation products (AIMP) generated by the SSPAs. The outputs of the ONET are connected to the polarizers of the horn radiators via the diplexers. The receive signals from each radiator element are directed through the Rx-path of the diplexers. They are amplified in the Low Noise Amplifiers (LNAs), down converted into the base band and finally converted into digital signals. The feed assembly is composed of the horn radiators, the polarisers, the diplexers with LP filters and the mechanical support structure. The ONET assembly is composed of 8x8 Butler matrices with integrated test couplers at the output ports, Table 7 Major Requirements for the L-/S- Band Feed Assembly The feed and ONET components have been developed and a representative subarray (i.e. 24 radiator elements and an ONET) has been manufactured with an Engineering Qualification Model (EQM). The hardware of the sub-array is shown in Figure 25. Figure 25 EQM Feed Array Assembly in Compact Range for Pattern Measurements The radiator element consists of a circular waveguide horn section (SCRIMP horn), a dual probe feeding section and a polarizer.

14 The radiator elements are manufactured out of magnesium. Because of the low electrical conductivity of magnesium, all magnesium parts are silver plated. A Copper undercoating provides magnesium surfaces with hermetically sealed protection against corrosion. The envelope and the mass of the L-band radiator including polarizer amount to 170 mm x 230 mm (height x diameter) and 580 g. The radiator element has been designed to operate in the frequency range MHz (i.e. Tx band of MHz and Rx band of MHz). These frequency bands are representative envelopes of potential commercial applications. Typical pattern cuts of an array element are shown in Figure 26. Figure 27 Batch of Tx-filters In Figure 28 the measured electrical performance of a batch of 8 Tx-filter assemblies (assembly of Band pass, Low pass filter and contactless transition) is shown. Figure 26 Typical pattern cut of an array element for Tx frequency, return loss at any input port (element) > 22 db For the filter and diplexer a novel design process has been developed. The design is characterised by low sensitivity with respect to manufacturing tolerances and thermal expansion and a minimum number of monolithically manufactured pieces (i.e. 2 pieces for the BP and 3 pieces for the LP filter). Therefore an efficient integration process with high reproducibility and low PIM risk no tuning screws are required is ensured. Figure 28 Measured RF performance of a batch of 8 Tx-filters (no tuning required) The EQM ONET assembly consists of 8 Tx band pass and low pass filters at the input, a 8 x 8 Butler matrix, 8 bidirectional test couplers and contactless transitions. In order to reduce the mass of the ONET assembly, all parts are manufactured out of silver plated magnesium. The envelope of the ONET assembly is: 611 x 391 x 189 mm 3 including connectors.

15 INTELSAT IX and the L-/S-band mobile communication satellite study concepts are described in detail. The feed and reflector technologies are explained and pattern measurement results are shown. 6. References Figure 29 EQM Network Assembly (ONET) The ONET is a two-layer component in Astrium s space proven bar line technology. The different inner conductors are connected between the adjacent layers by contactless transitions. The crosssection of the bar line has been optimised to fulfil the multipacting requirements. 5. Conclusion The limited frequency spectrum and place within satellite orbits require satellites, using efficiently this resources. Future communication satellites are required to provide several beams to illuminate several spots on earth. Further, in order to use the spacecrafts power resources economically, the service areas have to be illuminated efficiently by contoured beams. For that aim, the concepts of shaped reflector and multi-feed antennas were developed and applied to overcome the disadvantages of the formerly used elliptical beam antennas. Within the paper, the modern antenna concepts of different satellite programs, developed at Astrium GmbH are explained. For the formerly used elliptical antennas the antenna concept of the German TV-SAT is exemplarily described. For shaped reflector antenna applications, the INSAT 2E, SINOSAT and INTELSAT X concepts and for multi-feed antenna applications, the AMOS, INTELSAT VIII, [1] D. Fasold, M. Lieke, The Antenna Module of the Direct Broadcasting Satellite TV-SAT, IEEE AP-S International Symposium, San Jose, USA, 1989 [2] L. Jensen, R. Sekora, N. Schröder, Advanced Reflector Antennas For Geostationary Spacecraft, IETE, India, 1997 [3] C. Hunscher, L. Jensen, Advanced Spacecraft Antennas for Broadcasting and Fixed Satellite Services, IAF, Bejing, China, 1996 [4] M. Lieke, C. Hunscher, T. Kutscheid, E. Zeevi, Electrical and Mechanical Design of the AMOS Communication Antenna Subsystem, European Microwave Conference, Israel, 1995 [5] H. Wolf, B. Sauerer, D. Fasold, V. Schlesinger, "Computer Aided Optimisation of Circular Corrugated Horns", PIERS, Noordwijk, The Netherlands, 1994 [6] S. Paus, L. Jensen, N. Ratkorn, E. Sommer, H. Wolf, The INTELSAT IX C-Band Hemi/Zone Antennas, European Microwave Conference, Munich, Germany, 1999 [7] R. Gehring, E. Sommer, H.Wolf, A. Wolframm, P. Rinous, A Combined Transmit/Receive Feed System for Personal Mobile Communications in L/S-Band in Consideration of Increases Power Applications, ANTEM, Montreal, Canada, 2002