A coaxially packaged MADT for microwave applications

Abstract

A coaxially packaged transistor capable of delivering greater than 11 db of power gain at 1000 Mc, with a resultant maximum frequency of oscillation of 3500 Mc, has been developed. This device is a p-n-p micro-alloy diffused-base transistor (MADT). The principal difference between this device and a standard high-frequency MADT amplifier is the reduction of electrode size and use of a coaxial construction. The parasitic elements, rb', and emitter and collector transition capacities, have very striking effects. Also, the excess phase of alpha at alpha cutoff, as described by Thomas and Moll, can be very large (150° on this device); for this reason, fTrather than fcαshould be used as the figure of merit for graded-base transistors. Because of this excess phase, the value of K(0.85 for homogeneous-base transistors), which is used to relate fTto fcα, can be as low as 0.43 in graded-base transistors of this type.