Isolation enhancement between tightly spaced compact unidirectional patch-antennas on multilayer EBG surfaces

Abstract

In this article, ultracompact unidirectional patch antennas are used in different two-antenna systems for biomedical applications at 5.2 GHz. Multilayer mushroom type electromagnetic bandgap (EBG) structures are designed as slow-wave medium to reduce the size of the individual patch antennas to 0.1λ0 by 0.18λ0. Various techniques are investigated herein to improve antenna isolation for an enhanced Multiple-Input Multiple-Output (MIMO) performance. First, the coupling between 0.3λ0-spaced antennas is verified to occur dominantly through radiation and near-field coupling between the patches rather than through substrate-bound modes. Second, various configurations are proposed to suppress antenna coupling. These approaches include reorientation of the antennas and employment of parasitic radiators between the patches. A novel design is presented in which a unidirectional parasitic slot radiator on an EBG reflector is inserted between the antennas to decouple them. Measurement results confirm efficacy of these approaches in mitigating antenna coupling by more than 11 dB in the operating bandwidth of the antennas. The compact patch antennas maintain efficiency values of higher than 70%. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:30–38, 2015.