35 research outputs found
Wideband two-dimensional and multiple beam phased arrays and microwave applications using piezoelectric transducers
Modern satellite, wireless communication, and radar systems often demand
wideband performance for multi-channel operation and the ability to steer multiple
beams for multiple moving targets. This dissertation covers a variety of topics to design
low-cost and wideband antenna systems. The main areas of study are microwave devices
controlled piezoelectric transducers (PETs) and wideband baluns and balanced
microwave circuits using parallel-strip lines. Some focus has also been given to the
design of Rotman lens for multiple beam generation and Vivaldi antenna arrays for
wideband two-dimensional scanning.
The dielectric perturbation technique controlled by PET is introduced to design a
wideband phase shifter and a QPSK modulator, and to tune the resonant frequency of a
slot dipole. The designed PET-controlled phase shifters are used for beam steering in a
dual beam phased array using a bidirectional feeding scheme and a five-beam phased
array using a microstrip Rotman lens.
Vivaldi-type antennas are commonly used to achieve wideband performance. Very
wideband performance can be achieved using an antipodal tapered slot antenna because
of its inherent simple wideband transition from microstrip line to parallel-strip line. An
antipodal tapered slot antenna and a phased array are designed to span 10 to 35 GHz. In
addition, a 4??4 two-dimensional antenna array is designed using wideband antipodal
tapered slot antennas, and two sets of PET-controlled phase shifters for E- and H-plane
scanning are fabricated to steer the beam. As a microwave system using wideband
antenna array, a new low-cost and wideband phased array radar is developed using a
modulated pulse over 8 to 20 GHz band.
The double-sided parallel-strip line as a balanced line is presented. The parallelstrip
line offers much flexibility for microwave circuit designs. This transmission line
makes it possible to realize a low impedance line and allows the design of a compact
wideband balun and junction. Wideband transitions (or baluns) from parallel-strip line to
microstrip line, a typical unbalanced transmission line, are realized to cover several
octave bandwidth. Balanced microwave filters and a hybrid coupler are developed using
the parallel-strip line
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Balanced antennas for mobile handset applications. Simulation and Measurement of Balanced Antennas for Mobile Handsets, investigating Specific Absorption Rate when operated near the human body, and a Coplanar Waveguide alternative to the Balanced Feed.
The main objectives of this research are to investigate and design low profile antennas
for mobile handsets applications using the balanced concept. These antennas are
considered to cover a wide range of wireless standards such as: DCS (1710¿1880 MHz),
PCS (1850¿1990 MHz), UMTS (1920¿2170 MHz), WLAN (2400¿2500 MHz and 5000
¿ 5800 MHz) and UWB frequency bands. Various antennas are implemented based on
built-in planar dipole with a folded arm structure.
The performance of several designed antennas in terms of input return loss, radiation
patterns, radiation efficiency and power gain are presented and several remarkable
results are obtained. The measurements confirm the theoretical design concept and show
reasonable agreement with computations. The stability performance of the proposed
antenna is also evaluated by analysing the current distribution on the mobile phone
ground plane. The specific absorption rate (SAR) performance of the antenna is also
studied experimentally by measuring antenna near field exposure. The measurement
results are correlated with the calculated ones.
A new dual-band balanced antenna using coplanar waveguide structure is also proposed,
discussed and tested; this is intended to eliminate the balanced feed network. The
predicted and measured results show good agreement, confirming good impedance
bandwidth characteristics and excellent dual-band performance.
In addition, a hybrid method to model the human body interaction with a dual band
balanced antenna structure covering the 2.4 GHz and 5.2 GHz bands is presented.
Results for several test cases of antenna locations on the body are presented and
discussed. The near and far fields were incorporated to provide a full understanding of
the impact on human tissue. The cumulative distribution function of the radiation
efficiency and absorbed power are also evaluated.UK Engineering and Physical Sciences Research Council (EPSRC
Metamaterial
In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow