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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.