THE COUPLED MODE THEORY OF THE TRAVELLING WAVE FET INTERACTION

A new method of increasing the power capability of microwave FETs by increas-ing the electrode length is proposed. An analytical model with distributed parameters of the structure is derived. A set of equations deseribing the mutual interaetion of voltage and eurrent on the electrodes with the charge current in the active layer of FET is found. This set of basie equations is transformed into coupled mode form. When the electromagnetic coupling is weak enough and in synchronous case, the wave amplification with ultra wide bandwidth occurs. The wave amplitude along the drain electrode system increases linearly with distance, the power output is directly proportional to the active drain electrode length. A broadband power combining exists. In nonsynchronous case, wave amplification shows only a narrow bandwidth. When the electromagnetic coupling cannot be neglected, the wave amplitude grows exponentially along the electrode length, indicating a high gain characteristic. the TW FET can be realized by proper design of the electrode system, and high power output with long life operation results.