Non-LTI Antenna Design and Modeling Techniques

Abstract

Nearly all contemporary antenna systems are Linear Time-Invariant (LTI) devices, and allow for assumptions of frequency independence and reciprocity, but are governed by strict bounds on their performance. Recently, nonlinear and time-varying (non-LTI) antennas have become a common path of research in an attempt to break the LTI assumption and improve antenna performance beyond these limits, but lack a general modeling technique to develop fundamental equations for antenna design. The adaptability of the established method of moments (MoM) allows for a complete model of virtually any structure. Conversely, the conversion matrix method allows the expansion of circuit and network parameters to model time-varying structures. The combination of the two methods allows for a generalized model of a time-varying antenna while granting insight into their design. In a similar way, MoM can be combined with the harmonic balance method and allow for the accurate simulation of nonlinear components and pumped nonlinearities on antennas of arbitrary structure. These aspects of MoM, conversion matrices, and harmonic balance are leveraged in this work to provide a better understanding of non-LTI antennas and develop several models for achieving better performance or different capabilities.