Nonlinear simulation techniques for the optimized design of push-push oscillators

In the push-push oscillator, the circuit symmetry enables, through a suitable choice of terminating impedances, an output frequency that is twice the oscillation fundamental frequency. The main difficulty is the complexity of the design, for which there is a lack of specific simulation tools. Here, a harmonic-balance technique is presented, allowing the circuit optimization for prefixed oscillation frequency and maximum output power at the second harmonic component. The oscillator dynamics is analyzed through the envelope transient approach, making use of a new initialization technique of the circuit variables. For a realistic prediction of the first-harmonic cancellation, a sensitivity analysis is performed. A continuation technique is applied to obtain the variation of the output power and frequency versus inequalities in significant circuit parameters. The circuit phase noise is analyzed through the envelope transient approach. The techniques have been applied to a 18 GHz push-push oscillator, with very good agreement with the experimental results.