Abstract: This microwave circuit incorporates a transistor structure that provides either a two port amplifier or an injection frequency locked oscillator. This circuit eliminates circulators employed with Gunn and Impatt diode amplifiers and injection frequency locked oscillators. The collector-base junction is reverse biased so that the collector region functions either in the Impatt mode or in the transferred electron mode. An RF input signal is applied across the forward biased emitter-base junction. With a load across the collector-base junction having a conductance equal to the absolute value of the negative conductance generated by the collector region, the circuit functions as an oscillator at a frequency which is injection locked to the frequency of the input signal. With a load of increased conductance to suppress oscillations, i.e. overload the collector region, the circuit functions as an amplifier.