英文report怎么写 Phased Array Antennas For Mobile Earth
4.2 Satellite communications
Present and future satellite systems, will require multiple beamed antennas or phased array antennas to provide better gain, beam shaping and frequency reuse facilities depending on the requirements of the communication system.
Multiple spot beams can achieve higher EIRP and G/T than what is achievable by
an omni- directional antenna system; while at the same time employing frequency reuse techniques in order to increase the overall system throughput. By the use of frequency reuse systems, the same spectrum can then be further reused
The frequency reuse system is limited by the beam to beam level of isolation
and also the interference rejection.
MEO and LEO satellite constellations require frequency scanning capabilities, with a view up to 60Â°, by using frequency reuse schemes; the same spectrum can be reused
multiple times over the coverage area as shown in figure 4.1. However, in
practice, frequency reuse is limited by the achievable beam to beam isolation
and interference rejection. Therefore, a solution with adaptive arrays may be
considered in this case.
Figure 4.1. Satellite with frequency re-use enabled.
The possibility of a higher number of radiating elements in the GPS transmitting array is being considered to provide either high EIRP spot beams over the coverage area or adaptive nulling capabilities.
The efficiency of future satellite communications and navigation systems can
be significantly improved by the use of adaptive antenna arrays with intelligent
beam-forming and beam-steering. Degradation of the system performance caused
by multipath propagation or interferers can be reduced by limited bandwidth.
Side lobe reduction and nulling in the direction of the interferer.