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Cryogenically cooled K‐band high electron mobility transistor receiver for radio astronomical observation

A K‐band receiver using cooled high‐electron mobility‐transistor (HEMT) amplifiers was developed at the Nobeyama Radio Observatory (NRO). Remarkable reduction of receiver noise temperature Trec was obtained when it was cooled down to cryogenic temperature. The lowest Trec of 75 K was obtained at 23.4 GHz. This low noise characteristic reveals that the cooled HEMT amplifier is promising as a sensitive receiver for radio astronomical observations.