A Noise Test-system For Cryogenic Low Noise Amplifiers

This article presents the development of a noise test-system for cryogenic low noise amplifiers (LNAs) of Shanghai Astronomical Observatory(SHAO). This noise test-system, based on the existing equipments, supports both the Variable Load Temperature (VLT) method and the Cold Attenuator (CA) method to establish a system which makes cryogenic low noise amplifiers' either precise or fast measurement realizable. The VLT method is an relatively accurate method with about 1K test uncertainty; contrarily CA method is much faster and with no more than 4K uncertainty. It is verified that the accuracy of this system is guaranteed at least in the frequency range of 10MHz to 10GHz. At present SHAO has used this system to check and accept five S-band and five X-band import LNAs and is planning to use this test-system to develop cryogenic LNAs independently.Based on the linear property of LNAs, this article compares noise measurement for room temperature LNAs and cryogenic LNAs, and presents solutions to measure cryogenic LNAs' noise. Subsequently, this article presents the hardware and software of the noise test-system. Finally, this article shows some LNAs noise results tested by this system and analyzes the system errors and assesses this system.