Design considerations for resonant travelling wave IMPATT oscillators†

Abstract

It is shown theoretically that distributed IMPATT structures can be used as resonant lengths of active transmission line if particular care is taken to choose the substrate thickness and resistivity correctly in order to minimize losses. In contrast to discrete IMPATT structures, a relatively high substrate resistivity is required for the travelling wave structures. Such self-resonant oscillating structures can have an input admittance of the same order as the total depletion layer negative conductance, since the shunting effect of the depletion layer capacitance has automatically been tuned out. Thus, for a given value of circuit impedance the distributed structure can be much larger in area, and output power than the corresponding discrete IMPATT. It is shown theoretically possible to produce a 450 W pulsed device with an input impedance of −1Ω, although a 100 W device with an input impedance of −4Ω might be a more practicable objective.