Low noise radio frequency amplifiers based on niobium dc SQUIDs with microstrip input coupling

Abstract

Certain applications such us cmon detectors require radio frequency (rj) amplifiers uuli noisi temperatures ut// below I k litis need cannot be met with current semiconductor amph/icis which have minimum noise temperatures of 2 oi 3 K even when tooled to liquid helium temperatures or below I unci noise Icmpetalutes can be obtained by using a dc SQUID us an rf amplifier II e ha\e curried out experiments using a dc SQUID to amplify rf signals that were coupled to one end of the microstrip which is formed bv the input coil of the SQUID and the SQUID washer We achieved gams of up to 20 dl) in the fiequenes range of 100 MHz to 900 MHz With a bath temperature of 4 2 K and a loom temperature post-amplifier the system noise temperature ranged from 0 5 K ± 0 3k at <S0 \IH: to 3 0 K ± 0 7 K at 500 MHz Particularly at frequencies above 350 MHz hosvever the measured noise temperature svas determined bv the noise of the semiconductor post-amplifier (I s x SOK) rather than the SQUID When sic cooled the SQUID down to I H K and used a cooled posl-amplifiei consisting of a helero-fteld effect tiansistor (IITEl) with a noise temperature of 12 K we measured a ssstcm noise lemperaiuie of I) 3 k ± 0 15 Kat 250 MHz and 0 25 K t 0 15 k at 365 Mil: DISCLAIMER This document was prepared as an account of work sponsored by the United States Government.While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California.The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California.