RECENT ANTENNAS DEVELOPMENTS AT ALCATEL SPACE INDUSTRIES

Cyril MANGENOT, Philippe LEPELTIER, Frederic CROQ, Jacques MAUREL

Alcatel Space Industries Space Antenna Department, 26, Avenue J.F Champollion

31037 Toulouse, France Email : cyril.mangenot@space.alcatel.fr

ABSTRACT This article will gives an overview of recent space active antennas researches and developments at ALCATEL SPACE INDUSTRIES. Antenna Department activities in the field of communication satellites cover the past twenty years; they concern several national, European and international programs. The demand for continuous system improvements towards more capacity, better use of the frequency spectrum, high efficiency shaped coverage’s, high polarisation discrimination and radiated power increase, put stringent requirements on antenna performances and associated technologies. This, together with multi beam capability and reconfigurability, makes antennas R&D work a major challenge for the future. Research and development activities on active antennas at ALCATEL SPACE INDUSTRIES will be describes through some example of products recently delivered or currently under development. We have selected them to illustrate the diversity of antenna concepts and technologies for both geosynchronous and low earth orbit satellites. 1. GEOSYNCHRONOUS TELECOMMUNICATION ACTIVE ANTENNA In the frame of STENTOR the French experimental satellite, ALCATEL is now under the final test phase of an active transmit antenna able to provide 3 fully reconfigurable circular or contoured beams over Europe. The purpose of this technological program was to validate, in flight, advanced technologies and processes, as well as the overall design of the active antenna architecture and the command and calibration philosophy. The Tx antenna is based on a Direct Radiating Array of 48 controls of 4 W each implemented on the earth facing panel of the platform. The following figures represents the antenna block diagram and the radiating side of the antenna.

C.C.U

TXDRIVEASSEMBLY

U.S.O.

TXCAL

SPOT 1SPOT 2SPOT 3

CALIBRATIONCOUPLERS (x3)

RADIATING PANEL

QUADRISSPA(x12)

FILTERS(x48)

RADIATINGELEMENTS

(x48)

CALIBRATIONCOMBINERS (x4)

BFN

THERMALELEMENTS

EQUIPPEDSTRUCTURE

2. LEO SATELLITE SYNTHETIC APERTURE RADAR LARGE PLANAR ARRAY ANTENNA

To comply with mission requirements that needs electronic beam scanning in both elevation and azimuth planes, an active direct radiating array is proposed for SAR missions. Due to Figure Of Merit constraints and beam steering / shaping in elevation plane, antenna surface lies between 10 and 30 m² and is composed of nearly 1000 active controls. The antenna surface is spitted in identical tile ( typically 20 to 64) which are attached to an holding structure. This structure can be folded away under launcher fairing. ALCATEL SPACE INDUSTRIES has been responsible during the first part of the 90’s of tile activities on all studies under national contracts ( RADAR 2000, OSIRIS,…) and on ENVISAT program . Thanks to this experience concluded by successfully passed radiofrequency and environmental tests for 3 different frequency bands applications, all our R&D effort is now dedicated to cost reduction of active antenna by technological investigation ( automatic report of MMIC functions and wiring, connecting optimisation, tile integration,….) and antenna architecture command and calibration optimisation (relaxation of equipment’s requirements, block diagram optimisation,…). An example of realisation is presented with the RADAR 2000 tile made of 96*8 patches associated with 96 transmit receive active modules. This panel is 1/64 of the whole SAR for which a complete study has been made on every aspects ( mechanical, thermal, electrical, radiations,…).

3. LOW EARTH ORBIT SATELLITE MULTIMEDIA ACTIVE ANTENNA The SKYBRIDGE System developed by ALCATEL is based on a constellation of 80 operational satellites orbiting at 1469 km, each of them having 18 High Traffic Transponder Antennas (HTTA). A total of 1440 antennas with challenging and innovative requirements have to be produced within a limited time. The HTTA will operate in Ku-band and will generate beams that remain fixed on the ground as the satellite moves along its trace. The antenna will perform the beam scanning and the beam shaping necessary to cope with the cell size changes as the satellite moves along its trace. These changes in pointing angle and apparent shape, as seen from the satellite, are represented in following figure. The major constraints and design drivers on the antenna architecture were the following : • Low recurring cost for mass production , antenna design with a modular approach to ease the assembly,

integration and tests, • Drastic implementation constraints due to neighbouring of antennas (limited available stowed volume,

limited field of view constraints between antennas ) • High number of tracking/rallying cycles (40000 per year during 8 years), • Antenna pointing accuracy better than 0.14° half cone angle, • High Reliability, • Time limited to a few second for the rallying sequence. To perform this mission, the antenna architecture that has been retained is constituted by two separate Tx and Rx antennas mounted on a elevation over azimuth APM as can be seen on the figure below. The transmit antenna is made of a Variable Power Divider/Beam Forming Network (VPD/BFN) and a Direct Radiating Array (DRA), the receive antenna is constituted of a Low Noise Amplifier/Beam Forming Network (LNA/BFN) and a Direct Radiating Array (DRA). This innovative antenna architecture is an ALCATEL SPACE INDUSTRIES patent and takes all the benefits of ALCATEL activities for more than 10 years in the active antenna field..

10° elevationlimit

spot footprints

horizon

98721

Illustration of 700 Km cell apparent size change seen

from the satellite CAO figure of HTT antenna

4. LEO SATELLITE DATA TRANSMISSION CONFORMABLE ARRAY ANTENNA Current X-Band links from LEO Satellites to ground stations are limited in data rates because of their low gain, due to the global coverage by a single beam. Future needs for LEO satellite earth observation systems will require X-band high rate payload data telemetry and thus high gain on a 60° half cone coverage. ALCATEL SPACE INDUSTRIES has developed a multibeam scanning antenna to insure isoflux EIRP on the earth. A « semi-active » truncated cone direct radiating array has been selected as the best option for such a mission, because of its higher gain compared to a passive fixed beam, its electronic scanning with low amplitude and phase jumps and its capability for simultaneous links (up to three beams in three adjacent sub-bands) with several ground stations. For performance demonstration, manufacturing of equipment required for one-beam: 1:24 divider, a complete set of eight 3x3 Butler matrices and 24 subarrays (each including 6 patches) have been manufactured and assembled on a representative truncated conical structure. Complete tests (radiated patterns, track of ground station) have been performed on the whole antenna and a good accuracy has been obtained by comparing simulations to measurements. The main results can be summarized as follows: - optimisation of amplifiers efficiency, all delivering constant and uniform power. - very low amplitude and phase jumps when scanning (respectively lower than 0.3 dB and 3° measured on typical trajectories) - control unit optimised to �t=100 ms between commutations and 5 bits phase-shifters - high gain (20 dBi towards Horizon, compensating range attenuation elsewhere) - low mass (less than 8 kg for Flight Model antenna)

CHANNEL FILTERS

BEAM 1

BEAM 2

BEAM 3

RF INPUTS(from modulators)

{{{{ DIVIDER 1 / 24

BUTLER

ACTIVEMMIC MODULE

ASIC

CONTROL UNIT

POWER SUPPLY

PAYLOAD I/F

3 x 3

CONICAL ANTENNAwith 24 subarrays

PRE-AMPLIFIER

to calibration combiner

5. CONCLUSIONS This paper has provided a survey of recent and on going active antennas developments at ALCATEL SPACE INDUSTRIES and has shown the diversity of techniques and technologies available now to offer the best product in regards to mission requirements. ACKNOWLEDGMENT The authors thanks France TELECOM, CENTRE NATIONAL D’ETUDES SPATIALES and EUROPEAN SPACE AGENCY for lending their support to the ALCATEL SPACE INDUSTRIES antenna activities. The author thanks also all members of the ALCATEL SPACE INDUSTRIES Antenna Department for their contribution.