Miniaturized microstrip antenna array with ultra mutual coupling reduction for wearable MIMO systems

In this paper, a miniaturized microstrip antenna array with two patches is proposed for wearable MIMO systems. The array is designed to resonate at 4.2 GHz and 8.1 GHz for biomedical micro-sensing technology and biomedical diagnostics applications, respectively. In this paper, the use of a diagonal slot on the microstrip patch to reflect the surface current in a direction opposite to that of the neighboring patch. Moreover, the common area of the ground plane, between the two antennas, is augmented with Uniform Compact-Photonic Band Gap (UC-PBG) structures to prevent surface waves. This approach reduces the mutual coupling to -17 dB within a separation distance of 1.4 mm ≈ λ_o/51, where λ_o is the wavelength at 4.2 GHz. The microstrip antenna patch is consistent of rectangular part slotted with a diagonal trace and a meander trace which reduces the electrical size of the microstrip patch, when it is printed on substrate of ε_r = 3.5, to λ_o/18 × λ_o/5. The maximum linear dimension of the antenna array is λ_o/7.2 × λ_o/4.3 × λ_o/137. The performance of the array is characterized in terms of S-parameters, broadband gain and correlation spectra as well as the radiation patterns. The proposed antenna array provides bore-sight gain of -15.1 dBi at 4.2 GHz and -7.5 dBi at 8.1 GHz of 54.2 MHz and 81.8 MHz, respectively. The numerical model of the proposed array is simulated based on the Finite Integration Technique (FIT) using the Transient Domain (TD) solver of CST Microwave Studio.