Decoupling techniques for multiple-input multiple-output antenna systems

Abstract

For multiple-input multiple-output (MIMO) antenna systems, the antenna coupling always diminishes the channel capacity. Tremendous efforts have been devoted to the coupling suppression and various decoupling techniques (DTs) have been presented. In this thesis, a systematic study on the DT and its application to the MIMO antenna systems is presented. The unifying goal is to enrich the decoupling solutions for MIMO antennas. Firstly, an efficient parasitic DT (PDT) is proposed. Firstly, the PDT is applied to two antennas. The decoupling theory and design procedure are validated by two benchmarks. Secondly, the PDT is extended to the multiple-element MIMO (M-MIMO) antennas. The decoupling theory is rigorously derived, based on which the design procedure is further described with two practical examples. The results demonstrate that high antenna isolations and low envelop correlation coefficients (ECCs) can be attained by using the proposed PDT. Secondly, an efficient parasitic decoupling network (PDN) for closely coupled antennas is proposed, which provides a new perspective and approach to design the DN based on parasitic decoupling concept. The decoupling theory and design procedure are validated by two benchmarks of the two- and three-element monopole arrays. The isolations of more than 25 dB and ECCs of less than 0.07 are achieved for both examples, which verifies the decoupling theory and proves the PDN concept. Thirdly, an efficient and systematic method to design the neutralization line (NL) DT is proposed. A general network model that leads to a general design procedure of NL is developed to satisfy the criteria derived from antenna impedances for the perfect isolation. The NL DT is validated by three practical examples. The high isolations and low ECCs are attained simultaneously. The NL can be implemented in different forms to satisfy each design specification. The NL DT helps to keep the immunity of antenna radiations. Fourthly, a novel DT for closely packed MIMO patch antennas using near-field resonator (NFR) as the coupling-mode transducer is proposed. The decoupling mechanism is illustrated by investigating the electric-field (E-field) and magnetic-field (H-field) distributions. Three practical decoupling examples are demonstrated and the high antenna isolations are achieved. Good radiation performances are reserved with no reduction in gain, front-to-back ratio (FBR) or polarization purity. Finally, two antenna designs for use in base stations with high antenna isolations are presented. The first design presents a low-profile dual-polarized dipole antenna using artificial magnetic conductor (AMC) reflector. Two perpendicularly crossed-dipoles are employed to achieve the dual polarizations with high port isolation. The second design presents a novel miniaturized dual-band dipole array-antenna consisting of two parallel 1×4 subarrays. Using the band notch dipole (BND) of high radiation suppression at desired notch frequencies, the radiation from each subarray is mutually suppressed. High isolation between the subarrays, therefore, is achieved while reducing the subarray separation. In summary, this thesis contributes to 1) the development of novel DTs and their relevant theory, 2) addressing features and issues for each DT by analyzing its effects in antenna radiations and 3) providing new decoupling concepts for the MIMO antenna designs.