Miniaturized cavity-backed slot antenna loaded with magneto-dielectric ferrite for RFID tag reader

摘要

A miniaturization microstrip-fed Cavity-backed Slot antenna for portable RFID reader at 277 MHz is presented in this paper. The proposed antenna consists of magneto-dielectric ferrite substrate, 50 Ω microstrip feeding line, radiating narrow slot, low cavity, one magneto-dielectric ferrite film and a windowed metallic superstrate. The magneto-dielectric ferrite substrate with relatively high and similar values of relative permittivity of 6.86 and relative permeability of 6.95 was loaded to reduce size without decreasing bandwidth, which has dielectric loss tangent of 0.0035 and magnetic loss tangent of 0.09. However, Ferrite material decrease the gain due to the losses of the ferrite material. Thence low cavity, windowed superstrate and ferrite film were utilized to enhance the gain of 8.9 dB than compared patch antenna. By placing the magneto-dielectric ferrite film with thickness of 1 μm beneath the cavity, a gain enhancement of 1.27 dB was obtained. The proposed antenna has an impedance bandwidth of 11.2% and gain of -3.66 dBi. The length of radiating slot is guided wavelength, which is about one sixth of free space wavelength. The depth of the cavity is only 4.6 mm and the overall size of the antenna is 220 mm χ 220 mm χ 14.3 mm. The miniaturization of one fifth free space wavelength were achieved at the operating frequency. The configuration and parameters of the proposed antenna are investigated and analyzed. The characteristics of the antenna had been simulated by Ansoft HFSS, such as radiation pattern in XOZ plane and YOZ plane, radiation efficiency, return loss, etc. There is a trade-off between miniaturization and gain. The suggested antenna can meet the need of portable RFID tag reader.