A Radiometer for a Space Communications Receiver

A noise-adding radiometer, unlike the Dicke type, does not require the input to be switched to a reference temperature. Since a typical good switch adds 7°K or more to the system temperature, it can cause a relatively large increase in the temperature of an ultra-low-noise receiver, and this in turn will cause a significant decrease in the radiometer and/or communications sensitivity. The use of an input switch can be avoided by using a noise-adding radiometer which, for an ultra-low-noise system temperature, is just as sensitive as a Dicke radiometer. A unique feature is that it can be added to an ultra-low-noise communications receiver without causing a large increase in the system temperature. Thus a sensitive tracking receiver, designed primarily to handle communications,1 can also be used to monitor, measure, and m a p the system environment temperature including radio stars. Conversely, the radio stars with known positions can be used to check the boresighting of the antenna. The major hardware components required for a noise-adding radiometer are readily available; the excess noise temperature, mismatch, and instability problems normally associated with a mechanical or ferrite switch are avoided; and the fluctuations due to imperfect circuit components can be reduced to an acceptable value by using a new high2047