1 Capturing Asymmetrical Spectral Regrowth in RF Systems Using a Multi-Slice Behavioral Model and Enhanced Envelop Transient Analysis Wonhoon Jang, Aaron Walker, Kevin Gard, and Michael B. Steer Abstract— Nonlinear distortion in RF and microwave systems results in spectral regrowth of digitally-modulated signals. The distortion above and below the main channel can be at different levels and this is attributed to baseband effects. This paper presents a new multi-slice behavioral model architecture that captures this asymmetry and can be implemented in a variety of circuit simulators including Spice, Harmonic Balance, Envelope Transient and System Simulators. The work is experimentally validated using a HBT power amplifier at 2.5 GHz driven by a WCDMA signal. The model is used with envelope transient circuit simulation which is enhanced to accommodate an arbitrary baseband transfer function. Index Terms— Envelope transient simulation, behavioral modeling, WCDMA, spectral regrowth, baseband memory effects. This material is based upon work supported by the U.S. Army Research Office as a Multidisciplinary University Research Initiative on Multifunctional Adaptive Radio Radar and Sensors (MARRS) under grant number DAAD19-01-1-0496 W. Jang, A. Walker, K. Gard and M. B. Steer are with the Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7911, U.S.A. I. I NTRODUCTION Behavioral models are commonly used to capture the characteristics of bandlimited nonlinear radio frequency (RF) and microwave subsystems [1]–[4]. They can be used to rapidly investigate the response of the subsystem to various digitally-modulated signals, to provide insight into nonlinear operation, and as an aid in developing linearization strategies. Behavioral models should be much simpler than the underlying circuitry, should be conveniently extracted from simulation or experimental measurements, and should be compatible with the in- tended simulation scheme. Ideally a behavioral model would be compatible with all common circuit simulation strategies. The most convenient microwave measurement to perform is a single-tone test in which the power of a single RF tone applied to the input of an RF subsystem is swept from the level corresponding to linear operation up to power levels that result in a near saturated output that departs by at least several decibels from the extrapolated linear response. While harmonics will in general be generated, filtering at the output of a band-limited nonlinear system prevents their direct