Self-Oscillating Circularly Polarized Active Integrated Monopole Antenna Using Cross-Coupled Pair and Inverted-L Strip

A self-oscillating active integrated antenna (AIA) featuring circular polarization (CP) is presented in this letter. The oscillation is sourced by a cross-coupled pair (XCP) with negative conductance. Microstrip lines with embedded LC resonators are applied to fulfill the feedback loop between the pair of transistors, which functions as the frequency selective element with harmonic suppression capability. A monopole antenna is attached to the output of the XCP for radiating the oscillation power into space; the CP operation, meanwhile, is obtained by introducing a perturbation using an inverted-L strip protruding from the ground plane. A left-handed circularly polarized AIA (CPAIA) was designed at 916 MHz as a potential far-field wireless power charging source in the ultrahigh-frequency ISM (industrial, scientific, medical) band. The experimental validation reveals that, when compared with existing CPAIA designs, the proposed work consumes much less dc power but still keeps acceptable radiation parameters; it also features the smallest size and highest dc-to-RF conversion efficiency. The lowpower consumption makes the direct integration with a small-size solar panel become feasible.