Low-noise `circulator-coupled¿ amplifier for unattended small earth terminals

The design of a low-noise `circulator-coupled¿ amplifier for unattended small earth terminals is described in this paper. The amplifier uses a circulator-coupled active-bypass circuit with two transistors in the first stage, and a passive bypass circuit with one transistor in the subsequent stages. This configuration presents a unique low-cost approach to the design of high-gain amplifiers in a redundant fashion and can be very useful for those particular earth terminals in which `acceptance degradation¿ can be tolerated. The scattering matrix and noise formula of the amplifier configuration are derived, as well as the flat-gain criterion for broadband applications. The experimental results of a 3.7¿4.2 GHz two-stage amplifier which utilises gallium arsenide field-effect transistors are presented in this paper.