Analysis of self-resonant bent antennas
Date
2018-07-19
Authors
Ali, Mohammod
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Abstract
The primary focus of this dissertation is on the analyses of self-resonant bent
antennas. The need for the accurate characterization of such antennas due to their
growing importance in present day wireless communications is the motivation for this
work. To this end, several self-resonant bent antennas are analyzed which includes
an inverted-L antenna (ILA), a meander-line dipole (MLD) antenna, a meander-line
bow-tie (MLBT) antenna, a dual meander antenna, and a printed meander antenna.
A simple analytical model, based on the induced EMF method, is presented to
compute the input impedance of the ILA. First, a sinusoidal distribution of current
on the antenna, with zero current at the end is assumed, and then an expression for
the input impedance is derived using the near-fields of the antenna. The accuracy
of the formulation is verified by comparing the results computed using it with that
from NEC [1] computation. Unlike the analytical solutions available in the literature,
our proposed solution is not restricted to antennas that are electrically small. In
addition the new formulation can be extended to treat other antennas, such as the
T-antenna, the folded unipole antenna, and the loop-loaded monopole antenna.
The input impedance, radiation pattern, and gain of the MLD and MLBT antennas
are computed and correlated with their parameters. Input impedances of both
antennas are computed using NEC. Simple analytical models are presented to compute
the radiation patterns of the MLD and the MLBT antennas. For each antenna,
a sinusoidal distribution of current is assumed and closed-form expressions for the
radiation fields are derived. The results computed using the analytical models are
verified by comparing them with the results from the NEC computation. Since in
each model the radiation pattern of an antenna is expressed in terms of ready to
evaluate algebraic expressions, the computation of such pattern is fast and easy.
The input impedance and radiation characteristics of a dual meander antenna
are computed using NEC. Similarly as before the input impedance, radiation pattern,
and gain of this antenna are also correlated with its parameters. The input
impedance and radiation pattern of a planar printed meander antenna are investigated
using the Finite-Difference Time-Domain (FDTD) technique. The antenna is modeled on a dielectric substrate both in the presence and absence of a metallic
ground plane. Characteristics of the antenna are examined as function of dielectric
constant, and substrate thickness. New results of input impedance, radiation
pattern, and gain are presented which are vital for the design of such antennas.
Several novel applications of self-resonant bent antennas are described. First, a
wide-band dual meander-sleeve antenna is designed, manufactured, and measured
for application in dual frequency vehicular personal communication. The antenna
can operate simultaneously in the 824-894 MHz and 1850-1990 MHz bands of the
PCS system. Second, an MLBT dipole is introduced as a feed for plane sheet
reflectors. Numerical results computed using NEC show that the feed when used
in front of a plane sheet reflector, results in superior radiation characteristics than
a conventional dipole feed, namely, it reduces the reflector dimension by 46% for
the same front to back ratio, beam width and gain. Finally, a compact plane sheet
reflector antenna is described that uses an MLBT monopole feed. Since the antenna uses a monopole, a balun is not required. This antenna has a gain and half-power
beam width of 8.4 dBi and 94° respectively.
Description
Keywords
Antennas (Electronics), Wireless communication, Bent antennas