A Design of High Efficiency Distributed Amplifier Using Optimum Transmission Line

In this paper, we propose a numerical analysis on reversed current of distributed amplifier based on transmission line theory and proposed a theory to obtain optimum transmission line length to minimize the reversed currents by cancelling those components. The reversed current is analyzed as being simply absorbed into the terminal resistance in the conventional analysis. In the proposed analysis, however, they are designed to be cancelled by each other with opposite phase by the optimal length of the transmission line. Circuit simulation and implementation using pHEMT transistor were performed to validate the proposed theory with the cutoff frequency of 3.6 GHz. From the measurement, maximum gain of 14.5 dB and minimum gain of 12.8 dB were achieved in the operation band. Moreover, measured efficiency of the proposed distributed amplifier is 25.6 % at 3 GHz, which is 7.6 % higher than the conventional distributed amplifier. Measured output power is about 10.9 dBm, achieving 1.7 dB higher output power than the conventional one. Those improvement is thought to be based on the cancellation of refersed current.