Overall system requirements for low noise performance

The limit of system performance with low-noise amplifiers will probably not be receiver noise, but rather the ambient noise background against which the signal is sought and the noise which is generated by the aerial, transmission lines or other components of the complete system. For a ground based system receiving signals from a satellite, considerations of galactic noise and atmospheric attenuation lead to a choice of wave length in the centimetric band, as the optimum with regard to source noise. The optimum frequency for satellite-to-satellite communication would be much higher. The practical limits which may be achieved in the various components of a microwave system are discussed and the overall performance is assessed.