A question for the RF engineers amongst us. How important the output return loss of the antenna feed.
To my mind if you have an LNA of 75K input noise temperature, as well as adding that noise to the receive signal it will also transmit that noise back towards the antenna where it is radiated out to space. But if the feed has a poor return loss, say 6dB, one quarter of that noise (19K) will be reflected back towards the LNA together with the received signal. So instead of a nominal system noise of 75K it is actually nearer 94K. Is this true??
A second point is the LNA actually has a physical temperature nearer 290K in practice. Is it the 300K or 75K that is radiated outwards to space?
Melvyn
