Abstract:
Multiple-Input-Multiple-Output (MIMO) systems are being used extensively
in modern communication systems. They address the needs of high data
rates and ensure a reliable communication without increasing the transmitted power or using additional frequency spectrum. They are integral part of
current 4G/LTE communication standard and will also be an enabling technology for future 5G standard. To provide with their full benefits MIMO
systems rely on multiple uncorrelated propagation channels. This correla tion is function of physical channel between transmitter and receiver as well
as the radiation pattern of antenna itself. It is difficult to cater for correla tion caused by the antenna itself because of small form factors of practical
antennas. In literature, correlation coefficient has been reduced by increas ing port isolation among antenna elements. However, this method does not
directly target the radiation patterns of antenna elements which need to
be decorrelated. Recently multiple works have reported that this technique
does not guarantee correlation coefficient reduction. Hence a method was
proposed to deliberately decorrelate radiation patterns of individual antenna
element. This was done using a partially reflected surface placed over the
MIMO antenna essentially forming a Fabry-Perot cavity. Through this technique ultra-low correlation was achieved. However, the height of designed
cavity was λ/4. This height is quite high for design to be used in sub-6GHz
frequency range applications. This thesis presents a compact design with
reduced cavity height which achieves same ultra-low correlation between an tenna elements. General guidelines have been developed for the design of
low-profile cavity for MIMO antennas. Based upon presented guidelines, a
partially reflected surface is designed. Working of this surface is validated
by decorrelating the fields of two element MIMO patch antenna radiating
at 5.36 GHz. During this 95% reduction in correlation coefficient has been
achieved with a cavity height of λ/10. Presented design is also fabricated
and results are compared with the software-based simulation results. The
design can be used for W-LAN applications where compact size is required
such as tablet PCs or access points etc.
