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In this paper, the room-temperature and cryogenic performance of two low-noise amplifier (LNA) modules in the frequency range from 70 to 116 GHz is presented and analyzed. The investigation is based on LNA millimeter-wave integrated circuits using 35-nm and 50-nm gate-length metamorphic high-electron-mobility transistor technologies. At room temperature, the WM-2540 waveguide modules demonstrate an average noise temperature of 214 and 247 K over the 70–116-GHz frequency range. The lowest achieved noise temperatures are 171 and 196 K. When cooling the LNA modules to an ambient temperature of 6 K, the average noise temperatures improve to 30.1 and 31 K. The lowest achieved noise temperatures are 20.7 and 19.2 K. To the best of the authors' knowledge, the demonstrated LNAs yield the lowest published average noise temperatures at room temperature over the 70–116-GHz frequency range. Furthermore, the achieved cryogenic noise performance is among the best results published so far.

MMIC Broadband Low Noise Amplifiers (LNA) for radio astronomy applications with 100 nm GaAs metamorphic High Electron Mobility Transistor (mHEMT) process have been developed. Cryogenic performance of a 4–12 GHz and a 25–34 GHz LNAs is presented. The 4–12 GHz LNA cooled at 15 K exhibits an associated gain of 31.5 dB ± 1.8 dB and average noise temperature of 5.3 K with a low power dissipation of 8 mW. Cooled to 15 K the 25–34 GHz amplifier has demonstrated a flat gain of 24.2 dB ± 0.4 dB with 15.2 K average noise temperature, and a very low power dissipation of 2.8 mW on chip. The mHEMT based LNA MMICs have demonstrated excellent noise characteristics at cryogenic temperatures for their use in radio astronomy applications.

Modern ultra low noise receivers used for Radio astronomy have evolved to provide very wide instantaneous bandwidth. Some of the configurations used in present cryogenic Front Ends, like sideband separating mixers and balanced amplifiers need 90° hybrids at the IF, typically in the 4–12GHz band. There are devices commercially available covering this band with good ambient temperature characteristics, but their cryogenic performance drops to unacceptable levels. This paper describes the design, construction and measurement of a multioctave stripline hybrid for the 4–12GHz band specially conceived to survive and perform well when cooled to 19K (−254°C). The materials and mechanical construction have been carefully selected and the result is a very compact, reliable and low thermal mass device, able to survive extreme thermal cycling. The coupling and reflection show very low temperature dependence. The comparison of the results of a typical commercial unit with the new design presented clearly shows its advantages at cryogenic temperature.

The design, fabrication and measurement of a HEMT's, ultra-low noise, microwave, cryogenically-coolable amplifier is described. The design band covers from 2.1 to 2.5 Ghz and average noise temperature under 2.5k and gain over 25 dB have been measured for a two stage amplifier when cooled under 12.5k. Microwave Design System from HP and Pospieszalski HEMT's noise model have been used to do the design and excellent agreement has been verified between theoretical model and measured parameters. The amplifier has been done to work as an RF fist stage of a radio-astronomy receiver.

A design technique for very broadband, low-noise amplifiers is described. It is based on a wideband noise model of a MODFET. The computer-aided design and realization of L-, K-, and K alpha -band and wideband 8-18-GHz cryogenically coolable amplifiers with optimal noise performance are described. The uniqueness of the results presented rests in the demonstration that a single frequency measurement of noise parameters provides sufficient information for the design of a number of wideband amplifiers in the 1-40-GHz range. >