Novel Isolation Structures of MIMO Antennas for Mobile Devices

Abstract

In communication systems, multiplying the radio link capacity with the multiple transmitter and receiver antennas for carrying out multipath propagation is termed as Multiple-input-multiple-output (MIMO). It improves the data rate by reduction of channel errors. However, use of MIMO leads to high correlation factor in broadcasting of multiple signals. Moreover, mutual coupling between the antennas is increased due to less space available between the antennas especially for compact antennas used in mobile devices. Mutual coupling degrades the angle of arrival to estimate the offset of carrier frequency and signal to interference noise ratio. Major contributing factor for mutual coupling between antennas is the flow of surface current or surface waves and space radiation. In first part of the thesis, novel decoupling technique for two-element multiple-in multiple out (MIMO) antennas for smartwatch applications with floating metallic bezel have been presented. The radiating elements consist of embedded loop-type groundradiation antennas and operate at the 2.45 GHz Bluetooth/WiFi bands. An isolator, consisting of a loop-type structure with a lumped capacitor, is attached externally with the ground plane such that wideband isolation between the antennas has been achieved. It is demonstrated that the small-sized isolator is coupled with the large-sized bezel surrounding the ground plane, where the bezel operates as a low-Q decoupler between the antenna elements producing wideband isolation property. Accordingly, optimized results can be obtained by controlling the location of the isolator, the gap between the isolator and the bezel, and the loaded capacitor.