Amplificatori M. I. C. implicanti transistori ad arseniuro di gallio

The design criteria for broad-band MESFET microwave amplifiers, that is to say the equivalent circuit of the GaAs transistors used, the matching networks and the microstrip dispersion on alumina substrates, are examined. It is found that the unilateral equivalent circuit of the MESFET is valid up to 12 GHz and the same bandwidth is confirmed by noise parameters. The amplifier design is examined, solving the matching problems with lumped networks instead of distributed networks. Nevertheless, for high values of inductance or capacitance, distributed parameter networks must be employed. Therefore, the microstrip dispersion on alumina substrates is investigated, proposing a linear relation between the effective dielectric constant and the frequency. As an example, a two-stage amplifier with three matching networks in the band 8 divided by 12 GHz, obtaining a gain near 15 db and an input and output VSWR less than 2, is analyzed