Low Noise Receiving Downconverter

In microwave radio relay systems the receiver thermal noise is one of the main contributors to the total noise of the radio line which is one of the fundamental limitations on many important system parameters, such as the number of voice circuits per radio frequency channel, repeater spacing, and system length. Since in heterodyne systems the receiver noise is essentially the noise of the receiving downconverter, the noise figure of the downconverter is one of the most important factors in setting the entire system performance. In radio systems such as those described by Tillotson, low noise figures and wide bandwidths are required in conversion from the higher microwave frequencies above 10 GHz to higher than normal intermediate frequencies in the range of several hundred MHz.1 The system concept also places a premium on circuit and mechanical simplicity, low power consumption, and environmental stability. The downconverter described in this paper was designed to meet the requirements of such a system. Before the Schottky-barrier diode, noise figures below about 7 dB could only be obtained by using tunnel diodes or parametric microwave amplifiers with atendant sacrifice in receiver simplicity, stability, 1651