A composite varactor for achieving both high power and high efficiency

Maximum power output and maximum efficiency are generally conflicting goals in the design of harmonic generator varactors. This incompatibility arises from the fact that high power requires a high reverse breakdown voltage and therefore inherently high resistivity material, whereas high efficiency requires minimization of losses and hence low resistivity material. However, both goals may be simultaneously approached by the series connection, within a single package of 2 or more appropriately chosen, low loss, lower voltage, varactor dice. In initial experiments, GaAs surface barrier dice of 30 volts breakdown have been employed, series connecting up to 4 dice in one package. Tested in a 4-to-12 Gc tripler, an 18-fold increase in output power was achieved, for the 4-dice unit as compared to a single junction. The efficiency decreased only slightly, from 72% to 65%. Further results with diffused GaAs and Si dice will be described, as well as a novel package design which affords large heat dissipation, small package dimensions, and integration of other active or passive devices.