DESIGN OF A 900 MHz OSCILLATOR.

Designing a microwave transistor oscillator can be greatly simplified by using a procedure that utilises both the device line and load-pull measurement techniques. The device line technique requires an initial circuit that has a negative input resistance at the design frequency but does not oscillate when loaded by the 50 OMEGA test system. The optimum load impedance required for maximum power output can then be obtained by measuring the device line. However, if the load impedance is equal to the input impedance but differs in sign, then an initial transient oscillation will occur. This oscillation will change the transistor's S-parameters; consequently, the input impedance of the initial circuit changes, and the circuit may or may not produce steady-state oscillation. If the circuit oscillates, then the device line technique cannot be applied. With the load-pull technique, an initial circuit that is already oscillating can be characterized to obtain the load impedance needed for optimum power output at or near the initial frequency of oscillation. Thus, depending upon whether the initially designed circuit produces steady state oscillation or not, the design can be completed with either the load-pull or device line techniques. The design and performance of a 900 MHz microstrip oscillator using a silicon bipolar transistor is described to illustrate the use of this design procedure.