This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonMutual Coupling (MC) is the exchange of energy between multiple antennas when placed on
the same PCB, it being one of the critical parameters and a significant issue to be considered
when designing MIMO antennas. It appears significantly where multiple antennas are placed
very close to each other, with a high coupling affecting the performance of the array, in terms
radiation patterns, the reflection coefficient, and influencing the input impedance. Moreover;
it degrades the designed efficiency and gain since part of the power that could have been
radiated becomes absorbed by other adjacent antennas’ elements. The coupling mechanism
between multiple antenna elements is identified as being mainly through three different paths
or channels: surface wave propagation, space (direct) radiation and reactive near-field
coupling.
In this thesis, various coupling reduction approaches that are commonly employed in the
literature are categorised based on these mechanisms. Furthermore, a new comparative study
involving four different array types (PIFA, patch, monopole, and slot), is explained in detail.
This thesis primarily focuses on three interconnected research topics for mutual coupling
reduction based on new isolation approaches for different wireless applications (i.e. Narrowband,
Ultra-wide-band and Multi-band).
First, a new Fractal based Electromagnetic Band Gap (FEBG) decoupling structure between
PIFAs is proposed and investigated for a narrowband application. Excellent isolation of more
than 27 dB (Z-X plane) and 40 dB (Z-Y plane) is obtained without much degradation of the
radiation characteristics. It is found that the fractal structures can provide a band-stop effect,
because of their self-similarity features for a particular frequency band.
Second, new UWB-MIMO antennas are presented with high isolation characteristics.
Wideband isolation (≥ 31 dB) is achieved through the entire UWB band (3.1-10.6 GHz) by
etching a novel compact planar decoupling structure inserted between these multiple UWB
antennas.
Finally, new planar MIMO antennas are presented for multi-band (quad bands) applications.
A significant isolation improvement over the reference (≥ 17 dB) is achieved in each band by
etching a hybrid solution.
All the designs reported in this thesis have been fabricated and measured, with the simulated
and measured results agreeing well in most cases