Wireless Injection Locking of Zero-IF Self-Oscillating Mixers

The recently introduced Zero-IF self-oscillating mixers (SOMs) enable a direct frequency conversion, of interest for the implementation of compact and low consumption radio frequency identification (RFID) tags, among other applications. In previous works, the Zero-IF SOM is placed in only one of the terminals of the wireless link, the other one being based on a conventional scheme. In this article, a system made up of two wirelessly locked Zero-IF SOMs, operating as a frequency upconverter and downconverter, will be analyzed to evaluate its potential for low-cost short-range communications. A complete formulation describing the system under antenna and propagation effects will be presented, which, as a particular case, is able to predict the behavior of the previously proposed Zero-IF SOM, locked by an independent signal. The formulation based on oscillator models extracted from harmonic balance allows deriving design criteria for an optimum and robust performance and can predict the maximum communication range, as well as the stability properties and phase-noise behavior. The operation under modulated conditions is analyzed with a novel envelope-transient formulation, accounting for the time differentiation caused by the propagation effects. The methods have been applied to a system of two Zero-IF SOMs operating at 900 MHz.