This paper describes the development of a 4 GHz transmit antenna generating six shaped beams for covering main areas of Africa. Design and optimisation, hardware activities and performance data are presented. Two polarisation sensitive gridded single offset reflectors (diameter 2..15 m) are fed by two orthogonally polarised feed arrays with 16 and 20 feeds respectively. The antenna generates three independent beams for each polarisation. Frequency reuse by polarisation diversity and by space diversity between two far displaced beams allows for 30 channels in total to be transmitted. A flexible channel to beam allocation is possible (reconfiguration) with a slightly reduced channel number. The three horizontally polarised beams are partly overlappling with five of the 16 feeds to be shared. These feeds are excited via dual mode subnetworks. This feedsystem consisting of 16 compact, high efficiency SCRIMP-Horns, a dual mode beam forming network in barline technique has been manufactured and tested. Measurement results are compared with pattern predictions on the level of primary as well as secondary pattern. The correspondence is in both cases very close. Mutual, coupling between horns has been included exactly into the analysis. This is mandatory for a realistic cross-polar prediction as it is demonstrated by comparison with the measurements.
The development of a C-Band contoured beam antenna for the coverage of the People's Republic of China is described. The antenna applies two polarisation sensitive reflector shells which are mounted behind each other. The orthogonally gridded reflectos of 2 m diameter are fed by two 7-horn clusters of corresponding linear polarisations, providing both combined transmit (3.7 -4.2 GHz) and receive (5.925 -6.425 GHz) functions. Each array consists of diagonal horns followed by waveguide diplexers which are fed by two beamforming networks (Tx and Rx respectively) in coaxial technique (barline). A dual mode transmit network provides two independent input ports. The engineering model of this antenna will be completed in 1989. First breadboard results of the most critical components of the feedsystem are given. JIBQDUTflNIn March 1988 MBB was awarded a contract from the People's Republic of China for the development of some important subsystems for the Chinese communication satellite DFH-3. One of the key elements of this contract is the development of the C-band communication antenna subsystem. The combined transmit-receive antenna enables operation of 24 channels in 500 MHz bandwidth by applying polarisation diversity. Part of this work was sponsored by the European Space Agency (ESA). REQUIREMENTSThe design objective was to realise a contoured beam coverage of the People's Republic of China with maximum edge of coverage gain for both the transmit (3.7 -4.2 GHz) as well as the receive (5.925 -6.425 GHz) frequency band. A minimum gain of about 27 dBi is required in both bands for at least 90 % of the coverage area. This value has to be achieved taking into account a satellite pointing accuracy of +/-0.1 degree. Full polarisation reuse is necessary to be able to receive and transmit 24 40-MHz channels in 500 MHz bandwidth. A minimum cross-polarisation isolation of 33 dB is required in the service zone. Furthermore two independent Tx-input ports are necessary for each linear polarisation to be able to multiplex 12 40-MHz channels without having to use a contiguous output multiplexer. A minimum decoupling of 40 dB between Tx-and Rx-ports is specified and a maximum VSWR of 1.2 :1 for all input ports. Very stringent mechanical requirements are specified for the antenna subsystem. The most critical is the first Eigen-frequency specification of more then 35 Hz (folded configuration) in combination with the maximum mass requirement of 41 kg. Furthermore a maximum pointing uncertainty of 0.05 degr. for the complete antenna subsystem has to be realised.
In 1989, the iarge Compensated Compact Range (CCR) at MBB, Ottobrunn, Germany became fully operational (test zone: 5.5 x 5.0 x 6.0 m, frequency range: 2'-200 GHz).Smce that date the characteristics of the range have been extensively tested. The unique performance data of the CCR resulted in two contracts, selling copies of the MBB range.Both facilities, one at Spar Aerospace, Montreal, Canada and the other at Space Systems/Loral, Palo Alto, California, have been acceptance tested in AprilfMay 1991. The facility at SS/L will be mainly used for antenna and payload tests on spacecraft level. A special test feature of the CCR, where the feeds are defocused relative to the reflector optics, has been extensively investigated. The defocused feeds create scanned and tilted plane waves, which realize independent quiet zones separated in frequency and space. This special separation allows multiple quiet zones to be centered around the respective satellite antennas. The high quality of the scanned plane waves allows antenna pattern to be measured on the spacecraft without moving the satellite laterally.The multiple quiet zones make all kinds of link tests possible. The quality of two scanned plane waves has been tested in C-band and will be reported and the resulting possibilities for the payload tests will be discussed.
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