| 摘要 |
<p>Apparatus for use in a communications satellite to select signals in a first frequency range from a received multiplexed signal comprises a first mixer arranged to mix the received signal with a local oscillator LO signal obtained by mixing first and second LO signals to down-convert the received signal so that a signal within the received signal at a centre frequency of the first frequency range is converted to an intermediate frequency IF, a bandpass filter arranged to filter the mixed signal such that the filter bandwidth defines the width of the first frequency range, the bandpass filter having a passband with a centre frequency at the IF, and a second mixer arranged to mix the filtered IF signal with the second LO signal to up-convert the IF signal to the output frequency range. The first and/or second LO signal is controllable to change the frequency that is converted to the intermediate frequency by the mixer, to select a different frequency range as the first frequency range. A system is also disclosed for flexibly routing signals in a communications satellite. The system comprises an input arranged to send the received signal to each one of a plurality of frequency-conversion modules comprising the apparatus, a plurality of amplifiers for amplifying converted signals outputted by the frequency-conversion modules, and an output module arranged to receive the amplified signals and form a plurality of downlink beams, each downlink beam including one or more of the amplified converted signals. The amplifiers can be variable-power amplifiers to amplify each converted signal to a transmit power according to the bandwidth occupancy. The system can be used in forward or return path payloads.</p> |
