Linear microwave amplification using impatt diodes

Impatt diode amplifiers are candidates for use in super high frequency (s.h.f.) systems as broadband,intermediate power amplifiers, but their poor linearity makes them unattractive for some systems.The linearity of some X¿band impatt diode amplifiers is considered in this paper. The amplifiers are of the circulator coupled, reflexion type, where p +nn + silicon diodes of various doping levels are operated in the impatt mode.The impatt class of diodes shows a r.f.negative resistance that depends on the r.f. voltage, so that the design of linear amplifiers using passive circuitry is empirical. The structure of the diode chip determines the spatial distribution of the electric field which, in turn, determines the value of the negative resistanceand its dependence on r.f. power. A range of theoretical? W mesa structures has been investigated to get a computed, optimum, linear amplifier at a frequency of 12 GHz, where the optimizingparameter is the choice of passive stepped impedance transformer. The computations show that somewhat better linearity can be obtained with lower-doped diodes than with the higher¿doped diodes used in the design of impatt oscillators. The characteristics of experimental amplifiers using relatively highly¿doped diodes are presented and show good qualitative agreement with the computed responses.