High-efficiency frequency doubling by GaAs traveling-wave MESFET's

The feasibility of using a traveling-wave (TW) GaAs MESFET as a frequency doubler for high conversion efficiency (η = P out (2ω) / P dc has been experimentally demonstrated by obtaining η = 16 percent. Transistors were fabricated with large gate width (w = 1000 µm) and connecting pads, at both ends of the gate and drain electrodes. A maximum doubler power of ∼ 10 dBm was Obtained under optimum bias and circuit conditions. It is shown that the efficiency is maximum when all four ports are suitably terminated by loads for fundamental and second harmonic frequencies. For the FET's investigated, an inductor termination of 4.7 nH at the free drain end was found to produce the main improvement of the overall harmonic gain.