CRYOGENIC MMIC LOW NOISE AMPLIFIERS

Monolithic (MMIC) and discrete transistor (MIC) low noise amplifiers are compared on the basis of performance, cost, and reliability. The need for cryogenic LNA’s for future large microwave arrays for radio astronomy is briefly discussed and data is presented on a prototype LNA for the 1 to 10 GHz range along with a very wideband LNA for the 1 to 60 GHz range. A table of MMIC LNA and mixer designs under development for the frequencies up to 210 GHz is reported and data on cryogenic amplifiers in the 85 to 115 GHz is reviewed. The current status of the topics of transconductance fluctuations and cryogenic noise modeling will be briefly summarized. MMIC VS MIC COMPARISON As a starting point it is instructive to compare the advantages and disadvantages of monolithic microwave integrated circuit (MMIC) low noise amplifiers with microwave integrated circuit (MIC) amplifiers constructed with discrete chip transistors and passive microstrip circuit boards. A summary of this comparison on the basis of performance, frequency range, cost, and reliability follows. Transistor Performance- The discrete transistors used in the MIC case are manufactured in the same manner as the transistors built into the MMIC amplifier and to a large extent this leads to the same expected performance. Two exceptions can be argued. In the MIC case, transistors can be selected to give the lowest noise; however the MMIC'