Fast algorithms for linear and nonlinear microwave circuit simulation

A new method is proposed for dominant pole-zero (or pole-residue) analysis of large linear microwave circuits containing both lumped and distributed elements. This method is based on a multipoint Fade approximation. It finds a reduced order rational s-domain transfer function using a data set obtained by solving the circuit at only a few frequency points. We propose two techniques in order to obtain the coefficients of the transfer function from the data set. The proposed method provides a more efficient computation of both transient and frequency domain responses than conv'entional simulators and more accurate results than the techniques based on single-point Fade approximation such as Asymptotic Waveform Evaluation. This study also describes a new method for the transient analysis of large circuits containing weakly nonlinear elements, linear lumped components, and the linear elements specified with frequency domain parameters such as lossy multiconductor transmission lines. The method combines the Volterra-series technique with Asymptotic Waveform Evaluation approach and corresponds to recursive analysis of a linear equivalent circuit. We have also proposed a new method to find steady state responses of nonlinear microwave circuits. It is a modified and more efficient form of Newton-Raphson iteration based harmonic balance (HB) technique. It solves the convergence problems of the HB technique at high drive levels. The proposed method makes use of the parametric dependence of the circuit responses on the excitation level. It first computes the derivatives of the complex amplitudes of the harmonics with respect to the excitation level efficiently and then finds the Fade approximants for the amplitudes of the harmonics using these derivatives.