2010 한국초전도 공동 workshop 2010.2.22-23, 대전

An Ultra Low-noise Radio Frequency Amplifier

G. D. Hong a, H. S. Lee b, Y. S. Jangc

a Hankuk University, Seoul, Korea ( 9pt italic )

b Korea Institute for Superconductivity, Pusan, Korea

c Superconductivity Research Center, Taejeon, Korea

We have developed an extremely sensitive radio frequency amplifier based on the dc superconducting quantum interfer-ence device (dc SQUID). Unlike a conventional semiconductor amplifier, a SQUID can be cooled to ultra-low temperatures (100mK or less) and thus potentially achieve a much lower noise temperature. In a conventional SQUID amplifier, where the integrated input coil is operated as a lumped element, parasitic capacitance between the coil and the SOUID washer limits the frequency up to which a substantial gaincan be achieved to a few hundred MHz. This problem can be circumvented by operating the input coil of the SQUID as a microstrip resonator: instead of connecting the input signal between the two ends of the coil, it is connected between the SQUID washer and one end of the coil; the other end is left open. Such amplifiers have gains of 15dB or more at frequencies up to 3 GHz. If required, the resonant frequency of the microstrip can be tuned by means of a varactor diode connected across the otherwise open end of the resonator. The noise temperature of microstrip SOUID amplifiers was measured to be between 0.5K±0.3K at a frequency of 80 MHz and 1.5K±1.2K at 1.7GHz,when the SQUID was cooled to 4.2K. An even lower noise temperature can be achieved by cooling theSQUID to about  0.4K. In this case, a noise temperature of 100mK±20mK was achieved at 90 MHz, and of about 120±100mK at 440 MHz.

keywords : SQUID, rf amplifier, microstrip, low noise