Development of Cryogenic Low Noise 4-8 GHz HEMT Amplifier and its Advanced Characterization

Sammanfattning: In most radio astronomy instrumentation, cryogenic low noise amplifiers (LNA) are used as intermediate frequency (IF) amplifiers. The system noise temperature is among the most important parameters of a receiver and requires state of the art components. The characterization of amplifiers requires the measurement to be carried out at cryogenic temperature, typical 4-20 Kelvin, and with noise temperatures of a few Kelvin. The accuracy of a measurement may be in the order of ±0.5 K and can thus be significant compared with the measured value. This thesis describes work done on development of a 3-stage cryogenic LNA for radio astronomy and a method for characterization of such by using a superconductor-insulator-superconductor (SIS) tunnelling junction as the source of white noise. The cryogenic LNA is designed for a band of 4-8 GHz and uses Mitsubishi MGFC4419G InGaAs pseudomorphic High Electron Mobility Transistors (p-HEMT) as active device, Indium phosphide HEMT in the 1st stage has been tested and increases performance. The idea of using a SIS tunnel junction as noise source for y-factor measurements has previously been used as a diagnostic tool for receivers where the mixer junction is the source. A tunnel junction will generate shot-noise when biased in its linear region. Here a dedicated chip with SIS junction and its associated circuitry is designed with the purpose to be used for precise y-factor measurements. To provide good coupling without the need of a matching network, the junction should be manufactured with a normal state resistance RN=50 Ω.

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