Microwave structuring of MESFET electrodes for increased power and efficiency

It is shown by theoretical and experimental results that proper electrode design leads to broad banding, or increased output power and efficiency, and a control of harmonic contents of MESFET amplifiers and oscillators. A travelling-wave MESFET model is developed with the drifting space-charge, and wave propagation characteristics along the transverse dimension of suitably structured transistor electrodes together with electro-magnetic coupling between the closely spaced electrodes. A hybrid power-FET structure has been fabricated for frequencies around 100 MHz. It consists of 6 FETs, nominally rated for 100 mW each, giving together a reliable cw 1 W for class A and, at lower power levels, efficiencies of 40 and 50 % together with a gain of 13 db for class B and C respectively.