By T. M. Straus and I. Rabowsky, Hughes Aircraft Company
The fade margin of any microwave path can be extended by reducing the noise figure of the receiver. Low noise Ku Band gallium arsenide FET amplifiers and image reject filters have been developed specifically for multichannel microwave receiver application in the 12.7 - 13.2 GHz band. Incorporation of the the amplifier into such receivers either as a retrofit or in new designs generally requires built-in AGC circuitry to control the signal level and optimize performance. Without AGC ahead of the LNA, the third order distortions can build up to unacceptably large levels during unfaded conditions. Performance tradeoffs of various typical system configurations are examined. These tradeoffs illustrate the regimes in which AGC utilization is required.