Antennas for personal communication systems
Date
2017-06-09
Authors
Douglas, Mark Gordon
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Abstract
The worldwide demand for personal communication system (PCS) devices is motivating
the development of compact, high-performance antennas. It is also prompting a better
understanding of the effects of the user and the mobile communication environment on
the antenna performance. The objective of this dissertation is to add to the current
knowledge in both areas. Using the Finite-Difference Time-Domain (FDTD) technique,
a monopole antenna and a diversity antenna were modeled for PCS applications. Also,
techniques were developed and applied to facilitate the accurate numerical analysis of
PCS antennas and to investigate the electromagnetic interaction between PCS antennas
and the mobile communication environment.
A monopole antenna and a polarization diversity antenna (PDA) were investigated at
frequencies near 900 MHz. Antenna performance was evaluated in terms of the far-field
radiation patterns, the mean effective gain (MEG), the radiation efficiency and the
specific absorption rate (SAR) of energy in the user's body. For the diversity antenna,
the statistical independence of the two diversity branches was determined from the
correlation coefficient. The antenna modeling incorporated the antenna, a cellular
telephone handset, models of the user's head and hand, and a statistical model of the
mobile environment. Two mobile environments, an urban outdoor environment and a
suburban outdoor environment, were modeled. The results show that (i) changing the
antenna configuration from the monopole antenna to the PDA significantly affects the antenna efficiency and SAR in the user’s body; (ii) the type of mobile communication
environment chosen (urban or suburban) has a pronounced effect on the correlation
coefficient of the PDA and on the MEGs of the PDA and the monopole antenna; (iii) in
terms of the MEG, the PDA is more sensitive than the monopole antenna to the presence
of the user’s body; and (iv) overall, the PDA performs better than the monopole antenna
in terms of antenna efficiency, peak averaged SAR in the head, and MEG.
The accurate FDTD modeling of wires is crucial to the FDTD analysis of PCS antennas,
particularly as monopole antennas and other linear wire antennas are often used with
PCS devices. A study of the FDTD modeling of thin wires is included in this
dissertation. The accuracy of the wire models was determined by calculating the input
impedance of a dipole antenna over a broad range of dipole radii and comparing with the
results of a Method of Moments formulation. Two existing thin wire models were
analyzed and found to be inaccurate for some purposes. This finding led to the
development of a new model, which includes a special treatment of the field components at the wire ends and a model of the source region. The proposed wire model is more
accurate than the two existing wire models for a given spatial resolution. Thus, this new
wire model facilitates accurate computations of input impedance and resonant frequency
for linear wire antennas. The stability of the wire model was addressed, and a
formulation for the maximum stability coefficient to be used with the proposed thin wire
model was developed.
Description
Keywords
Antennas (Electronics), Mobile communication systems