電磁最佳化實驗室EM Optimization LabYen-Sheng Research Group, Department of Electronic Engineering

Three compact antenna systems for the multiple-input-multiple-output (MIMO) small-cell base stations operating in the Long Term Evolution (LTE) standard are proposed. The operational frequency band is 698−960 MHz. The proposed antenna systems include a single-element antenna, two-element antennas, and four-element antennas, respectively, all designed in a cylinder with a diameter of 160 mm and a height of 50 mm. The single-element antenna has a size of 79 × 12 mm2, namely 0.184 × 0.028 λ02, where λ0 is the wavelength of 700 MHz; it shows a sufficient bandwidth over the desired frequency band. As for the dual-element antennas, the spacing between the two antennas (0.248 λ0) is so small that the mutual coupling between them is particularly severe; therefore, this paper uses a defected ground structure (DGS) to optimize the system performances, and the antenna efficiency is enhanced from 55% to 67%. Lastly, the four-element antennas have much more serious mutual coupling. In this case, a miniaturized DGS with three different resonant frequencies is proposed, and the proposed structure enhances the entire system performances. In comparison with the literature, this thesis provides the most compact four-element antenna systems aiming at LTE 700.