A radiometer for a space communications receiver

By adding a square wave of noise to the input of an ultra-low-noise microwave receiver [1] via a directional coupler, see Figure 1, a radiometer with a sensitivity greater than a Dicke type can be achieved when the basic system temperature is less than
18\deg
K. A noise-adding radiometer is compatible with a communications receiver and can be used 1) to measure and monitor the system temperature and 2) to check the boresighting of a space communications antenna by detecting and tracking radio stars. The major hardware components are readily available, the excess noise temperature, mismatch, and instabilityproblemsnormallyassociated with a mechanical or ferrite switch are avoided, and the residual circuit fluctuation can be reduced to an acceptable value by using a new high-output-level square-law detector, Figure 2, and an improved noise lamp pulse circuit.