MIMO Antenna Design in Thin-Film Integrated Passive Device

This paper presents a novel approach to construct a multiple-input multiple-output (MIMO) antenna in a small package based on integrated passive device (IPD) manufacturing technology. Such an IPD utilizes a thin-film glass substrate that yields a low loss performance for RF components. A thin film process with limited layers available and size considerations in IPD manufacturing pose major challenges in antenna design, especially for multiple antennas. This thin-film process results in a high cavity quality factor (Q) causing a narrowband in the conventional patch antenna. To overcome this problem, this paper develops antenna elements that incorporate a T-shaped coupling fed driven strip and a loop structure. The gap between the driven strip and the loop structure functions as an internal tuning circuit, thus contributing to a lower overall Q and antenna miniaturization. The size of the proposed antenna element is only 1.8 × 0.65 mm² (0.031 λ0×0.011 λ0) in the IPD size of 4 × 4 mm² (0.068 λ0×0.068 λ0). The experimental results indicate that the antenna achieves a gain of 1.4 dBi and a radiation efficiency of 60% over the IEEE 802.11a band (5.15-5.825 GHz). In addition, the multiple antenna elements are arranged to construct a MIMO system. Furthermore, a good isolation is achieved using a space of only 0.3 mm (0.005 λ) spacing between two antennas, resulting in a compact design and small package (4 × 4 × 0.25 mm³). The parameters are also investigated in detail, with the experimental results correlating well with the simulation results.