1,721,087 research outputs found
Investigation, Design and Implementation of MIMO Antennas for Mobile Phones. Simulation and Measurement of MIMO Antennas for Mobile Handsets and Investigations of Channel Capacity of the Radiating Elements Using Spatial and Polarisation Diversity Strategies.
No full textThe objectives of this work were to investigate, design and implement Multiple-Input Multiple-Output (MIMO) antenna arrays for mobile phones. Several MIMO antennas were developed and tested over various wireless-communication frequency bands. The radiation performance and channel capacity of these antennas were computed and measured: the results are discussed in the context of the frequency bands of interest.
A comprehensive study of MIMO antenna configurations such as 2 × 1, 3 × 1, 2 × 2 and 3 × 3, using polarisation diversity as proposed for future mobile handsets, is presented. The channel capacity is investigated and discussed, as applying to Rayleigh fading channels with different power spectrum distributions with respect to azimuth and zenith angles. The channel capacity of 2 × 2 and 3 × 3 MIMO systems using spatial polarisation diversity is presented for different antenna designs. The presented results show that the maximum channel capacity for an antenna contained within a small volume can be reached with careful selection of the orthogonal spatial fields. The results are also compared against planar array MIMO antenna systems, in which the antenna size considered was much larger.
A 50% antenna size reduction method is explored by applying magnetic wall concept on the symmetry reference of the antenna structure. Using this method, a triple dual-band inverted-F antenna system is presented and considered for MIMO application. Means of achieving minimum coupling between the three antennas are investigated over the 2.45 GHz and 5.2 GHz bands.
A new 2 2 MIMO dual-band balanced antenna handset, intended to minimise the coupling with the handset and human body was proposed, developed and tested. The antenna coupling with the handset and human hand is reported in terms the radiation performance and the available channel capacity.
In addition, a dual-polarisation dipole antenna is proposed, intended for use as one of three collocated orthogonal antennas in a polarisation-diversity MIMO communication system. The antenna actually consists of two overlaid electric and magnetic dipoles, such that their radiation patterns are nominally identical but they are cross-polarised and hence only interact minimally
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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.
No full textThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Choosing threshold levels for electromagnetic hazards
Get PDFThe concept of electromagnetic hazards is today frequently taken to refer to direct effects on biological tissue. However, several other effects are possible and have been the subject of a substantial amount of research in earlier decades. One of these is the hazard of ignition of flammable gas/vapor mixtures due to sparks resulting from radiofrequency currents flowing in metallic structures. Although the physics of the mechanism linking power from a radio transmitter to ignition of a flammable mixture is relatively straightforward, compared with bioelectromagnetic effects, there are many uncertainties and poorly-understood steps in the process, leading to considerable difficulties for committees tasked with setting safety limits. The author has experience of such committees, notably that concerned with British Standard 6656, and the way in which these difficulties were addressed may give useful insights for the regulation of other hazards
Design and implementation of adaptive baseband predistorter for OFDM nonlinear transmitter. Simulation and measurement of OFDM transmitter in presence of RF high power amplifier nonlinear distortion and the development of adaptive digital predistorters based on Hammerstein approach.
No full textThe objective of this research work is to investigate, design and measurement of a digital
predistortion linearizer that is able to compensate the dynamic nonlinear distortion of a High
Power Amplifier (PA). The effectiveness of the proposed baseband predistorter (PD) on the
performance of a WLAN OFDM transmitter utilizing a nonlinear PA with memory effect is
observed and discussed. For this purpose, a 10W Class-A/B power amplifier with a gain of 22
dB, operated over the 3.5 GHz frequency band was designed and implemented.
The proposed baseband PD is independent of the operating RF frequency and can be used in
multiband applications. Its operation is based on the Hammerstein system, taking into account
PA memory effect compensation, and demonstrates a noticeable improvement compared to
memoryless predistorters.
Different types of modelling procedures and linearizers were introduced and investigated, in
which accurate behavioural models of Radio Frequency (RF) PAs exhibiting linear and
nonlinear memory effects were presented and considered, based on the Wiener approach
employing a linear parametric estimation technique. Three new linear methods of parameter
estimation were investigated, with the aim of reducing the complexity of the required filtering
process in linear memory compensation. Moreover, an improved wiener model is represented to
include the nonlinear memory effect in the system. The validity of the PA modelling approaches
and predistortion techniques for compensation of nonlinearities of a PA were verified by several
tests and measurements. The approaches presented, based on the Wiener system, have the
capacity to deal with the existing trade-off between accuracy and convergence speed compared
to more computationally complex behavioural modelling algorithms considering memory
effects, such as those based on Volterra series and Neural Networks.
In addition, nonlinear and linear crosstalks introduced by the power amplifier nonlinear
behaviour and antennas mutual coupling due to the compact size of a MIMO OFDM transmitter
have been investigated
Modelling and analysis of complex electromagnetic problems using FDTD subgridding in hybrid computational methods. Development of hybridised Method of Moments, Finite-Difference Time-Domain method and subgridded Finite-Difference Time-Domain method for precise computation of electromagnetic interaction with arbitrarily complex geometries
No full textThe main objective of this research is to model and analyse complex electromagnetic problems
by means of a new hybridised computational technique combining the frequency domain
Method of Moments (MoM), Finite-Difference Time-Domain (FDTD) method and a subgridded
Finite-Difference Time-Domain (SGFDTD) method. This facilitates a significant advance in the
ability to predict electromagnetic absorption in inhomogeneous, anisotropic and lossy dielectric
materials irradiated by geometrically intricate sources. The Method of Moments modelling
employed a two-dimensional electric surface patch integral formulation solved by independent
linear basis function methods in the circumferential and axial directions of the antenna wires. A
similar orthogonal basis function is used on the end surface and appropriate attachments with
the wire surface are employed to satisfy the requirements of current continuity. The surface
current distributions on structures which may include closely spaced parallel wires, such as
dipoles, loops and helical antennas are computed. The results are found to be stable and showed
good agreement with less comprehensive earlier work by others.
The work also investigated the interaction between overhead high voltage transmission lines and
underground utility pipelines using the FDTD technique for the whole structure, combined with
a subgridding method at points of interest, particularly the pipeline. The induced fields above
the pipeline are investigated and analysed.
FDTD is based on the solution of Maxwell¿s equations in differential form. It is very useful for
modelling complex, inhomogeneous structures. Problems arise when open-region geometries
are modelled. However, the Perfectly Matched Layer (PML) concept has been employed to
circumvent this difficulty. The establishment of edge elements has greatly improved the
performance of this method and the computational burden due to huge numbers of time steps, in
the order of tens of millions, has been eased to tens of thousands by employing quasi-static
methods.
This thesis also illustrates the principle of the equivalent surface boundary employed close to
the antenna for MoM-FDTD-SGFDTD hybridisation. It depicts the advantage of using hybrid
techniques due to their ability to analyse a system of multiple discrete regions by employing the
principle of equivalent sources to excite the coupling surfaces. The method has been applied for
modelling human body interaction with a short range RFID antenna to investigate and analyse
the near field and far field radiation pattern for which the cumulative distribution function of
antenna radiation efficiency is presented. The field distributions of the simulated structures
show reasonable and stable results at 900 MHz. This method facilitates deeper investigation of
the phenomena in the interaction between electromagnetic fields and human tissues.Ministry of Higher Education Malaysia and Universiti Tun Hussein Onn Malaysia
(UTHM
Design and modelling of beam steering antenna array for mobile and wireless applications using optimisation algorithms. Simulation and measrement of switch and phase shifter for beam steering antenna array by applying reactive loading and time modulated switching techniques, optimised using genetic algorithms and particle swarm methods.
No full textThe objectives of this work were to investigate, design and implement beam steering antenna arrays for
mobile and wireless applications using the genetic algorithm (GA) and particle swarm optimisation (PSO)
techniques as optimisation design tools. Several antenna designs were implemented and tested: initially, a
printed dipole antenna integrated with a duplex RF switch used for mobile base station antenna beam
steering was investigated. A coplanar waveguide (CPW) to coplanar strip (CPS) transition was adopted to
feed the printed dipole. A novel RF switch circuit, used to control the RF signal fed to the dipole antenna
and placed directly before it, was proposed. The measured performance of the RF switch was tested and
the results confirmed its viability. Then two hybrid coupled PIN diode phase shifters, using Branchline
and Rat-Race ring coupler structures, were designed and tested. The generation of four distinct phase
shifts was implemented and studied. The variations of the scattering parameters were found to be realistic,
with an acceptable ±2 phase shift tolerance.
Next, antenna beam steering was achieved by implementing RF switches with ON or OFF mode
functions to excite the radiating elements of the antenna array. The switching control process was
implemented using a genetic algorithm (GA) method, subject to scalar and binary genes. Anti-phase
feeding of radiating elements was also investigated. A ring antenna array with reflectors was modelled
and analysed. An antenna of this type for mobile base stations was designed and simulation results are
presented.
Following this, a novel concept for simple beam steering using a uniform antenna array operated at 2.4
GHz was designed using GA. The antenna is fed by a single RF input source and the steering elements
are reactively tuned by varactor diodes in series with small inductors. The beam-control procedure was
derived through the use of a genetic algorithm based on adjusting the required reactance values to obtain
the optimum solution as indicated by the cost function. The GA was also initially used as an optimisation
tool to derive the antenna design from its specification.
Finally, reactive loading and time modulated switching techniques are applied to steer the beam of a
circular uniformly spaced antenna array having a source element at its centre. Genetic algorithm (GA)
and particle swarm optimisation (PSO) processes calculate the optimal values of reactances loading the
parasitic elements, for which the gain can be optimised in a desired direction. For time modulated
switching, GA and PSO also determine the optimal on and off times of the parasitic elements for which
the difference in currents induced optimises the gain and steering of the beam in a desired direction.
These methods were demonstrated by investigating a vertically polarised antenna configuration. A
prototype antenna was constructed and experimental results compared with the simulations. Results
showed that near optimal solutions for gain optimisation, sidelobe level reduction and beam steering are
achievable by utilising these methods. In addition, a simple switching process is employed to steer the
beam of a horizontally polarised circular antenna array. A time modulated switching process is applied
through Genetic Algorithm optimisation. Several model examples illustrate the radiation beams and the
switching time process of each element in the array
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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