Beschreibung
To date, the temperature resolution of radio telescopes is the driving cost factor in radioastronomy and is mainly determined by the noise performance of the low noise amplifier in the first stage of the receiver. To reduce the effect of thermal noise sources these receivers are cooled during operation. In this work the low-cost metamorphic HEMT process of the Fraunhofer Institute for Applied Solid State Physics (IAF) is investigated for applications at low temperatures. Low noise amplifiers, dedicated to frequency regimes of interest to radio astronomers, have been designed and demonstrated in the course of this work. In a discipline of engineering, where the noise quantities to be derived are often as low as the measurement uncertainty, comparison of amplifier performance is extremely difficult. This work focuses on a novel approach allowing for convenient and highly accurate in-situ noise figure and noise parameter measurements. Building blocks - like noise source, impedance tuner and single pole double throw (SPDT) switch, required for noise figure and noise parameter measurements at cryogenic temperatures have been developed and are discussed.
