Simulation of Autonomous Nonlinear Microwave Circuits by Krylov-Subspace Methods

The paper discusses a novel approach to autonomous nonlinear microwave circuit simulation by the harmonic-balance (HB) technique coupled with Krylov-subspace methods. A new formulation of the nonlinear solving system for autonomous circuits is introduced. This consists of the ordinary HB system for the forced case, with the addition of one equation used to fix the arbitrary phase of the autonomous regime. In this way, the iterative solution schemes already available for the forced case can be substantially reused in the autonomous case, with a negligible over-head due to the additional equation. Further equations may be added to impose additional contraints, e.g., to hold constant the magnitude of a selected harmonic in order to suppress the degenerate solution.