Circularly Polarized Self-oscillating Active Integrated Slot-Loop Antenna Using Cross-Coupled Pair

A circularly-polarized self-oscillating active integrated slot antenna, rarely discussed in literature, is proposed and demonstrated in this paper. The proposed design simply consists of a cross-coupled pair oscillator and a slot-loop antenna. The circular polarization characteristics of the antenna were fulfilled by using spatially dual-feed technique with a quadrature phase difference. The fabricated antenna shows a stable oscillation at 920 MHz for UHF RFID applications with an equivalent isotropic radiated power (EIRP) of 8.1 dBm. The polarization characteristics of the proposed antenna were verified by a simple polarization sensing system capable of capturing the amplitude ratio and phase difference between two orthogonal field components simultaneously. Good agreement between the simulated and measured results is observed.