Coupled nonlinear/electromagnetic CAD of injection-locked self-oscillating microstrip antennas

Abstract

This article presents a systematic approach to the simulation and design of self-oscillating integrated antennas, based on the combination of state-of-the-art nonlinear and electromagnetic (EM) CAD techniques. The linear subnetwork, including the oscillator circuit and the antenna, is treated as a whole and its admittance matrix is computed at all frequencies of interest (including harmonics) by EM analysis. The oscillating subsystem is then analysed by harmonic balance (HB) for autonomous circuits. The design problem is turned into the solution of a nonlinear system, with a significant reduction in the overall number of EM analyses with respect to a conventional optimization. A simple linear model of the radiated far field in terms of the exciting voltages is generated by inexpensive post-processing of the data generated by EM analysis. This allows the far-field properties to be directly specified during the design step. The conditions for stable injection locking are then determined by nonlinear methods based on the numerical implementation of bifurcation theory. Finally, when the antenna is injection-locked by a digitally modulated RF/microwave carrier, the system response in terms of radiated far-field is efficiently computed by envelope-oriented HB analysis. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 398–414, 2003.