A Compact Cavity-Backed Slot Antenna Using Dual Mode for IoT Applications

This letter presents a compact cavity-backed slot antenna using dual mode for Internet of Things (IoT) applications. The proposed antenna has stub structures for generating additional resonant mode, by which two polarization components orthogonal to each other are realized within the impedance bandwidth. By the combination of the two modes, circularly polarized radiation is generated. The impedance bandwidth increase by the additional resonant mode, and the proposed stub structures act as a capacitive loading contributing to the miniaturization of the antenna. For validation of the proposed antenna, simulations were conducted, and the antenna was fabricated and measured. The fabricated antenna size is 0.23\lambda _{0} \times\; 0.23\lambda _{0} \times\; 0.04\lambda _{0}, showing a significantly compact size compared to the conventional structures. The measured results confirm that the antenna has a impedance bandwidth from 896 to 958 MHz, and 3 dB axial ratio (AR) bandwidth is about 5 MHz. The measured peak gain and AR at 915 MHz are 2.4 dBic and 0.6 dB, respectively.