Abstract: A plurality of heterojunction bipolar transistors (HBTs), each including one or more HBT cells, are combined so as to drive all of the cells equally and involves coupling the input drive signal via a pair of microstrip transmission lines to the two farthest transistors having a first common circuit node therebetween. A third microstrip transmission line is located between the other two microstrip transmission lines and is connected from the first circuit node to a second circuit node which is common to the two nearer transistors in order to couple the drive signal in an opposite direction to the nearer transistors. In such an arrangement, a negative mutual inductance exists between the center transmission line and the two outer transmission lines. The microstrip transmission lines are designed with physical dimensions and mutual separation distances so that the total inductance of the transmission lines which exists between the circuit nodes equals the mutual inductance be therebetween.