High-EIRP Self-Oscillating Circularly Polarized Active Integrated Crossed-Slot Antenna

A high effective isotropic radiated power (EIRP) circularly polarized active integrated antenna (CPAIA) for wireless charging Internet of Things (IoT) devices is demonstrated. The CPAIA combines a number of techniques to achieve the goal. A high-quality (Q) factor composite right-/left-handed (CRLH) resonator operated at +1 mode is adopted to excite an offset crossed-slot radiator. Together with a feedback oscillator, the high-Q resonator ensures good dc-to-RF conversion efficiency. The location for CP excitation is determined by the characteristic mode analysis, with the CRLH cell replacing an ordinary feed. To further boost the EIRP, an artificial magnetic conductor is installed on the back side of the CPAIA as a reflector. At the oscillation frequency of 927 MHz, an EIRP of 18.5 dBm and a conversion efficiency of 29% is achieved. Both results outperform existing data in the literature.