Analysis of Decoupling for MIMO Antennas

Abstract

In this thesis, we analyzed the isolation, radiation efficiency and radiation pattern of MIMO antennas according to isolator type. The operating frequency of MIMO antennas is 2.4 ~ 2.5GHz (Wi-Fi and Bluetooth). The Isolator uses slot type and 3D monopole type and is located at the center of two antennas. The resonator frequency of the isolator can be easily controlled by changing the value of capacitor (Ci) and inductor (Li). In simulation, the isolation of two antennas is -7.47 dB based on 2.45 GHz for reference. When using Isolator, the isolation was improved to -18.11dB for the slot type case and -17.57dB for the 3D monopole type, respectively. When prototype is measured, isolation is -8.97 dB based on 2.45 GHz for reference. When using Isolator, the isolation was improved to -15.23 dB for the slot type case and -27.74 dB for the 3D monopole type, respectively. In simulation, the average radiation efficiency is 88.2% and 88% for antenna #1 and antenna #2, respectively. When using slot type isolator, antenna #1 and antenna #2 were 75.79% and 75.35%, respectively, lower than the reference. When using 3D monopole type isolator, antenna #1 and antenna #2 improved by 95.5% and 91.6%, respectively. When the prototype is measured, the average radiation efficiency of the reference is 54.89% and 55.25% for antenna #1 and antenna #2, respectively. When using slot type isolator, antenna #1 and antenna #2 were 44.84% and 45.75%, respectively, lower than the reference. When using 3D monopole type isolator, antenna #1 and antenna #2 are 59.94% and 56.53%, respectively. The average efficiency is improved compared to the reference. Also, it was confirmed that the 3D monopole type isolator is coupled to ground mode other than ground λ mode through radiation pattern. Therefore, when designing a MIMO antenna, it is necessary to design an isolator that couples with a ground mode that is not the same as the antenna.