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The 3-Port Scattering and Noise parameters of a GaAsFET are measured. The noise measurement method is novel and is verified by good agreement between the measured 3-Port Noise parameters of a passive network and predicted noise parameters calculated from its 3-Port S-Parameters. Circuit theory is presented for calculating the Scattering and Noise parameters of a 3-Port transistor embedded in a passive network. The circuit is represented by a signal flow graph containing partially-correlated stationary random noise sources. An algorithm is presented which uses the measured transistor data and the circuit analysis technique to design amplifiers with simultaneous input power match and optimum noise figure. Such amplifiers do not use isolators or a balanced configuration and hence are more amenable to economic MMIC implementation. The procedure is illustrated using the example of a circuit consisting of a transistor, a lossless series feedback inductor and a lossless parallel feedback capacitor.