Nonlinear analysis of a reflectarray cell based on a voltage-controlled oscillator

In this work, harmonic balance (HB) analysis combined with electromagnetic (EM) simulation is used to accurately analyze a reflectarray cell consisting of a microstrip antenna oscillator. In a more practical implementation, the antenna radiator is separated from the nonlinear circuit by considering a probe fed patch, and placing the oscillator circuit on a separate substrate connected to the patch using an SMA adaptor. The scattered wave phase variation is achieved using as the control parameter the bias voltage of a varactor forming part of the oscillator circuit. Previous works limited to linear analysis [2] are extended here by combining HB and EM simulation to first, accurately predict the free-running oscillation, and second, analyze the injection locked solutions of the system when introducing the illuminating signal. Furthermore, the limitation of this configuration to approximately 180 deg phase tuning is highlighted by performing stability analysis of the obtained solutions, not present in previous works. Measurements of the performance of a reflectarray cell based on a 4.67 GHz antenna oscillator are presented.