| 摘要 |
An antenna coupling system includes separate low-noise receiving amplifier and down converter circuits for amplifying the antenna signal above background noise and for converting it down to frequencies compatible with a suitable receiver, respectively. The system is particularly intended for microwave frequency antennas of the type used to receive satellite signals. The amplifier circuit includes at least one microwave frequency amplifier, such as a GaAs FET, with a low frequency variable feedback circuit connected across it which is arranged to self-tune the amplifier to the antenna input signal strength. The converter circuit is of the image reject single conversion and image recovery type and is arranged to split the amplifier output signal into two parts which are each combined with a local oscillator signal and then re-combined in such a way that unwanted image signals are rejected.
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