A coaxially packaged MADT for microwave applications

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, r
b
', 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, f
T
rather than f
cα
should 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 f
T
to f
cα
, can be as low as 0.43 in graded-base transistors of this type.