An experimental study of distributed effects in a microwave bipolar transistor

The theory of distributed microwave transistor action described by A. J. Wahl has been tested by measurements made upon a microwave transistor embodying a single millimeter long emitter. The interesting effects predicted by Wahl for a transistor of this shape (high gain and stability at microwave frequencies) are expected to appear only in the presence of very low loss metallization. The required low loss metallization was in this case fabricated by sputter etching gold, using nickel as a sputter etching mask. The experimental devices measured had power gains and impedances which were in close agreement with those predicted using the theory of Wahl. In particular, power gains were obtained which were four times greater than would be expected from a conventional transistor having the same junction structure and area. This increased power gain is attributable to positive feedback due to wave reflections originating from the geometrical shape of the transistor and test circuit.