Antenna analysis
Author(s)
Advisor
Altıntaş, AyhanDate
2009Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Multiple-input-multiple-output (MIMO) wireless communication systems have
been attracting huge interest, since a boost in the data rate was shown to be
possible, using multiple antennas both at the transmitter and receiver. It is
obvious that the electromagnetic effects of the multiple antennas have to be
included in the wireless channel for an accurate system design, though they are
often neglected by the early studies.
In this thesis, the MIMO channel is investigated from an electromagnetics
point of view. A full-wave channel model based on the method of moments solution
of the electric field integral equation is developed and used in order to
evaluate the MIMO channel matrix accurately. The model is called the channel
model with electric fields (MEF) and it calculates the exact fields via the radiation
integrals, and hence, it is rigorous except the random scatterer environment.
The accuracy of the model is further verified by the measurement results. Thus,
it is concluded that MEF achieves the accuracy over other approaches which are
incapable of analyzing antenna effects in detail.
Making use of the presented technique, MIMO performance of printed dipole
arrays is analyzed. Effects of the electrical properties of printed dipoles on the
MIMO capacity are explored in terms of the relative permittivity and thickness
of the dielectric material. Appropriate dielectric slab configurations yielding high
capacity printed dipole arrays are presented. The numerical efficiency of the technique
(particularly for freestanding and printed dipoles) allows analyzing MIMO
performance of arrays with large number of antennas, and high performance array
design in conjunction with well-known optimization tools. Thus, MEF is
combined with particle swarm optimization (PSO) to design MIMO arrays of
dipole elements for superior capacity. Freestanding and printed dipole arrays are
analyzed and optimized, and the adaptive performance of printed dipole arrays in
the MIMO channel is investigated. Furthermore, capacity achieving input covariance
matrices for different types of arrays are obtained numerically using PSO
in conjunction with MEF. It is observed that, moderate capacity improvement is
possible for small antenna spacing values where the correlation is relatively high,
mainly utilizing nearly full or full covariance matrices. Otherwise, the selection
of the diagonal covariance is almost the optimal solution.MIMO performance of printed rectangular patch arrays is analyzed using a
modified version of MEF. Various array configurations are designed, manufactured,
and their MIMO performance is measured in an indoor environment. The
channel properties, such as the power delay profile, mean excess delay and delay
spread, are obtained via measurements and compared with MEF results. Very
good agreement is achieved.
Keywords
MIMOoptimal input covariance
indoor MIMO measurements
particle swarm optimization (PSO)
microstrip patch arrays
microstrip dipole arrays
planar printed arrays
mutual coupling
method of moments (MoM)