I.M. Angelov, I.K. Stoev, V.N. Todorov, Z.G. Ivanov, A.Y. Spasov
Institute of Electronics, Bulgarian Academy of Sciences, 72 Lenin blvd, Sofia 1784

Abstract. Results on studies of low noise FETs and transistor amplifiers, obtained in the Institute of Electronics at the Bulgarian Academy of Sciences, Sofia have been presented. The investigations were carried out in wide temperature and frequency ranges. Models of the FETs, taking into account the change in their parameters after cooling, and making possible the extrapolation with sufficient accuracy of S-parameters up to frequencies, where direct measurements are not yet possible, have been proposed. Suspended lines have been used with a view of decreasing losses and improving the technological and mechanical stability in the design of FET amplifiers. This brings about an improvement in the amplifier noise figure of about 0.15 to 0.5 dB, depending on the operating frequency. The results of the theoretical studies are illustrated with a presentation of cooled amplifiers for the 0.5-4 GHz, 3.7-4.1 GHz, 19-23 GHz and 26-28 GHz ranges, designed on the basis of the theoretically obtained parameters.

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