Cryogenically-cooled, HFET amplifiers and receivers: state-of-the-art and future trends

Recent progress in the development of ultra-low-noise, cryogenically coolable, HFET (heterostructure field-effect transistor) amplifiers and receivers for radio astronomy applications is reported. Examples of state-of-the-art receivers at frequencies from L- to Q-band are discussed. A model-based prediction of future performance demonstrates that HFET receivers should soon be competitive with SIS (superconductor-insulator-superconductor) mixer receivers at W-band frequencies. It is noted that the trade-off in low-noise amplifier design (bandwidth, input voltage standing wave ratio, stability, gain) can be reliably investigated in a computer model leading to a design with an optimal noise bandwidth performance. The bandwidth of a receiver is no longer limited by the amplifier bandwidth. In many receiving systems, the noise of a HFET amplifier is no longer a dominant contribution to the system noise.<>