Multimode Decoupling Technique With Independent Tuning Characteristic for Mobile Terminals

The isolation between antenna elements is a key metric in some promising fifth generation technologies such as beamforming and in-band full-duplex. However, the multimode decoupling technology remains a great challenge, especially for mobile terminals. One difficulty in achieving multidecoupling modes is that the operating modes of closely packed decoupling elements have very strong mutual effect, which makes the tuning complicated and even unfeasible. Thus, in physical principle, a novel idea of achieving the stability of the boundary conditions of decoupling elements is proposed to solve the mutual effect problem; in physical structure, a metal boundary is adopted to realize the stability. One distinguished feature of the proposed technique is that the independent tuning characteristic can be maintained even if the number of decoupling elements increases. Therefore, wideband/multiband high isolation can be achieved by using multidecoupling elements. To validate the concept, two case studies are given. In a quad-mode decoupling design, the isolation is enhanced from 12.7 to >21 dB within 22% bandwidth by using a 0.295 lambda(0) x 0.059 lambda(0) x 0.007 lambda(0) decoupling structure. The mechanism of the decoupling technique and the mutual effect between decoupling elements are investigated.