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

Licentiate thesis, 2006

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.