93 research outputs found
Recent Progress in the Design of 4G/5G Reconfigurable Filters
YesCurrently, several microwave filter designs contend for use in wireless communications.
Among various microstrip filter designs, the reconfigurable planar filter presents more advantages
and better prospects for communication applications, being compact in size, light-weight and
cost-effective. Tuneable microwave filters can reduce the number of switches between electronic
components. This paper presents a review of recent reconfigurable microwave filter designs,
specifically on current advances in tuneable filters that involve high-quality factor resonator filters to
control frequency, bandwidth and selectivity. The most important materials required for this field
are also highlighted and surveyed. In addition, the main references for several types of tuneable
microstrip filters are reported, especially related to new design technologies. Topics surveyed include
microwave and millimetre wave designs for 4G and 5G applications, which use varactors and
MEMSs technologies.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424
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Design, Modelling and Implementation of Several Multi-Standard High Performance Single-Wideband and Multi-Wideband Microwave Planar Filters
The objectives of this work are to review, investigate and model the microwave planar filters of the modern wireless communication system. The recent main stream of microwave filters are classified and discussed separately. Various microwave filters with detailed applications are investigated in terms of their geometrical structures and operational performances. A comprehensive theoretical study of microwave filters is presented. The main types of microwave filters including the basic low-pass filters such as Butterworth and Chebyshev filters are fully analysed and described in detail. The transformation from low-pass prototype filters to high-pass filters, band-pass filters and band-stop filters are illustrated and introduced. Research work on stepped impedance resonator (SIR) and asymmetric stepped impedance resonator (ASIR) structure is presented. The characteristics of λg/4, λg/2 and λg (λg is the guided wavelength of the fundamental frequency in the free space) type SIR resonators, and the characteristic of asymmetric SIR resonator are categorized and investigated. Based on the content mentioned above, novel multi-standard high performance asymmetric stepped impedance resonator single-wideband and dual-wideband filters with wide stopbands are proposed. The methodologies to realize wide passband and wide stop-band filters are detailed. In addition, multi-standard high performance triplewideband, quadruple-wideband and quint-wideband filters are suggested and studied. The measurement results for all prototype filters agree well with the theoretical predictions and simulated results from Ansoft HFSS software. The featured broad bandwidths over single/multiple applicable frequency bands and the high performances of the proposed filters make them very promising for applications in future multistandard wireless communication
Compact UHF-band antennas for mobile terminals : focus on modelling, implementation, and user interaction
The background of this thesis is the trend of ever decreasing space available for antennas embedded within mobile terminals. At the same time the antennas are increasingly required to cover a large number of separate frequency bands and/or have wideband operation. In addition, those antennas should perform sufficiently well in the vicinity of the user. This forms the motivation for the novel compact coupling-based antennas introduced and studied in this thesis.
The operation of the compact coupling antennas is based on exploiting the separate wavemodes supported by the chassis of the mobile terminal. The antenna element itself functions mainly as a coupler which couples to those chassis wavemodes. That is the reason why they are called coupling-based antennas. This work concentrates on the modelling, implementation and design of such antennas in free space, and the effect of the user on the operation of the antenna. The understanding gained in this thesis can be exploited in the development of the antennas for mobile terminals of the future.
In the first part of the thesis, an equivalent circuit model is derived for a capacitive coupling-based antenna. This model gives a helpful physical explanation for the operation of this type of antennas. Broadband small antennas operating in the lower part of the UHF band are also implemented and analysed in detail. These kinds of antennas could find applications, for example, in digital television reception, low-band LTE, or the spectrum sensing of cognitive radios. Furthermore, it is shown that very low-profile antennas can be implemented by exciting the chassis wavemodes galvanically with a direct feed. The implementation of frequency-tuneable antennas is also studied in order to cover broad virtual bandwidth or several separate non-simultaneous frequency bands. The second part of this thesis discusses issues concerning user interaction with the coupling-based antennas. The antenna-user interaction is first modelled with an equivalent circuit which provides an improved understanding of the phenomenon. Then, the effects of the user's hands on the operation of the broadband lower UHF-band antenna is studied in detail. In the end of the thesis, a method for reshaping the near fields of the mobile terminal antenna is also proposed, for example, for improved hearing-aid compatibility
Novel e-band reflection-type phase shifter - theory, design, and fabrication
This dissertation reports on the development of the E-band reflection-type phase shifters (RTPS), for applications in phased array systems. A novel 3-bit phase shifter is proposed consisting of a broadside coupled quadrature coupler and two reflective loads. This design utilizes a differential configuration providing the following benefits: 1. the easy accessibility of the on-chip short-circuit; 2. the reduction of electromagnetic interference; 3. the potential for expanding the 180° designed phase shift range to 360°, with the use of a phase inverter.
Based on the fundamentals of microwave and millimetre-wave (mm-wave) circuits, theories and design methodologies of RTPS designs are discussed. Two metal layers realizing the coupler body and two extra metal layers for bridging connections of the differential microstrip lines are utilized in this design. At the reflective loads, radio frequency (RF) microelectromechanical system (MEMS) switch-controlled short-circuited microstrip lines with variable length are employed to achieve reduced loss and a large tuneable range. The phase shifter is fabricated with complex customized fabrication processes on 100 μm thick fused silica substrates.
The 3-bit (9 states) differential RTPS was successfully fabricated and measured. Typically, a probe-based set-up with a 4-port vector network analyser (VNA) has to be used to measure a 4-port device; in our case, a new calibration method using differential probes with a 2-port VNA was proposed and validated. With a further characterization, by removing the measurement pads, using the distributed open-short de-embedding techniques, excellent RF performance was achieved for a tuneable phase range of 195.6° at 78 GHz. The measured reflection coefficients are below -18 dB, with an insertion loss error of less than 0.7 dB and a phase error of less than 8.6°, over the range of 70-86 GHz. At 74 GHz, the measured insertion loss varies from 3.9 dB to 4.9 dB, regarding all 9 phase states
Investigation of high bandwith biodevices for transcutaneous wireless telemetry
PhD ThesisBIODEVICE implants for telemetry are increasingly applied today in various areas
applications. There are many examples such as; telemedicine, biotelemetry, health care,
treatments for chronic diseases, epilepsy and blindness, all of which are using a wireless
infrastructure environment. They use microelectronics technology for diagnostics or monitoring
signals such as Electroencephalography or Electromyography. Conceptually the biodevices are
defined as one of these technologies combined with transcutaneous wireless implant telemetry
(TWIT). A wireless inductive coupling link is a common way for transferring the RF power and
data, to communicate between a reader and a battery-less implant. Demand for higher data rate
for the acquisition data returned from the body is increasing, and requires an efficient modulator
to achieve high transfer rate and low power consumption. In such applications, Quadrature Phase
Shift Keying (QPSK) modulation has advantages over other schemes, and double the symbol rate
with respect to Binary Phase Shift Keying (BPSK) over the same spectrum band. In contrast to
analogue modulators for generating QPSK signals, where the circuit complexity and power
dissipation are unsuitable for medical purposes, a digital approach has advantages. Eventually a
simple design can be achieved by mixing the hardware and software to minimize size and power
consumption for implantable telemetry applications. This work proposes a new approach to
digital modulator techniques, applied to transcutaneous implantable telemetry applications;
inherently increasing the data rate and simplifying the hardware design. A novel design for a
QPSK VHDL modulator to convey a high data rate is demonstrated. Essentially, CPLD/FPGA
technology is used to generate hardware from VHDL code, and implement the device which
performs the modulation. This improves the data transmission rate between the reader and
biodevice. This type of modulator provides digital synthesis and the flexibility to reconfigure and
upgrade with the two most often languages used being VHDL and Verilog (IEEE Standard)
being used as hardware structure description languages. The second objective of this thesis is to
improve the wireless coupling power (WCP). An efficient power amplifier was developed and a
new algorithm developed for auto-power control design at the reader unit, which monitors the
implant device and keeps the device working within the safety regulation power limits (SAR). The proposed system design has also been modeled and simulated with MATLAB/Simulink to
validate the modulator and examine the performance of the proposed modulator in relation to its
specifications.Higher Education Ministry in Liby
Silicon carbide technology for extreme environments
PhD ThesisWith mankind’s ever increasing curiosity to explore the unknown, including a variety of
hostile environments where we cannot tread, there exists a need for machines to do
work on our behalf. For applications in the most extreme environments and applications
silicon based electronics cannot function, and there is a requirement for circuits and
sensors to be built from wide band gap materials capable of operation in these domains.
This work addresses the initial development of silicon carbide circuits to monitor
conditions and transmit information from such hostile environments. The
characterisation, simulation and implementation of silicon carbide based circuits
utilising proprietary high temperature passives is explored.
Silicon carbide is a wide band gap semiconductor material with highly suitable
properties for high-power, high frequency and high temperature applications. The
bandgap varies depending on polytype, but the most commonly used polytype 4H, has a
value of 3.265 eV at room temperature, which reduces as the thermal ionization of
electrons from the valence band to the conduction band increases, allowing operation in
ambient up to 600°C.
Whilst silicon carbide allows for the growth of a native oxide, the quality has limitations
and therefore junction field effect transistors (JFETs) have been utilised as the switch in
this work. The characteristics of JFET devices are similar to those of early thermionic
valve technology and their use in circuits is well known. In conjunction with JFETs,
Schottky barrier diodes (SBDs) have been used as both varactors and rectifiers.
Simulation models for high temperature components have been created through their
characterisation of their electrical parameters at elevated temperatures.
The JFETs were characterised at temperatures up to 573K, and values for TO V , β , λ ,
IS , RS and junction capacitances were extracted and then used to mathematically
describe the operation of circuits using SPICE. The transconductance of SiC JFETs at
high temperatures has been shown to decrease quadratically indicating a strong
dependence upon carrier mobility in the channel. The channel resistance also decreased
quadratically as a direct result of both electric field and temperature enhanced trap
emission. The JFETs were tested to be operational up to 775K, where they failed due to
delamination of an external passivation layer.
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Schottky diodes were characterised up to 573K, across the temperature range and values
for ideality factor, capacitance, series resistance and forward voltage drop were
extracted to mathematically model the devices. The series resistance of a SiC SBD
exhibited a quadratic relationship with temperature indicating that it is dominated by
optical phonon scattering of charge carriers. The observed deviation from a temperature
independent ideality factor is due to the recombination of carriers in the depletion
region affected by both traps and the formation of an interfacial layer at the SiC/metal
interface.
To compliment the silicon carbide active devices utilised in this work, high temperature
passive devices and packaging/circuit boards were developed. Both HfO2 and AlN
materials were investigated for use as potential high temperature capacitor dielectrics in
metal-insulator-metal (MIM) capacitor structures. The different thicknesses of HfO2
(60nm and 90nm) and 300nm for AlN and the relevance to fabrication techniques are
examined and their effective capacitor behaviour at high temperature explored. The
HfO2 based capacitor structures exhibited high levels of leakage current at temperatures
above 100°C. Along with elevated leakage when subjected to higher electric fields. This
current leakage is due to the thin dielectric and high defect density and essentially turns
the capacitors into high value resistors in the order of MΩ. This renders the devices
unsuitable as capacitors in hostile environments at the scales tested. To address this
issue AlN capacitors with a greater dielectric film thickness were fabricated with
reduced leakage currents in comparison even at an electric field of 50MV/cm at 600K.
The work demonstrated the world’s first high temperature wireless sensor node powered
using energy harvesting technology, capable of operation at 573K. The module
demonstrated the world’s first amplitude modulation (AM) and frequency modulation
(FM) communication techniques at high temperature. It also demonstrated a novel high
temperature self oscillating boost converter cable of boosting voltages from a
thermoelectric generator also operating at this temperature.
The AM oscillator operated at a maximum temperature of 553K and at a frequency of
19.4MHz with a signal amplitude 65dB above background noise. Realised from JFETs
and HfO2 capacitors, modulation of the output signal was achieved by varying the load
resistance by use of a second SiC JFET. By applying a negative signal voltage of
between -2.5 and -3V, a 50% reduction in the signal amplitude and therefore Amplitude
Modulation was achieved by modulating the power within the oscillator through the use
of this secondary JFET. Temperature drift in the characteristics were also observed,
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with a decrease in oscillation frequency of almost 200 kHz when the temperature
changed from 300K to 573K. This decrease is due to the increase in capacitance density
of the HfO2 MIM capacitors and increasing junction capacitances of the JFET used as
the amplifier within the oscillator circuit.
Direct frequency modulation of a SiC Voltage Controlled Oscillator was demonstrated
at a temperature of 573K with a oscillation frequency of 17MHz. Realised from an SiC
JFET, AlN capacitors and a SiC SBD used as a varactor. It was possible to vary the
frequency of oscillations by 100 kHz with an input signal no greater than 1.5V being
applied to the SiC SBD. The effects of temperature drift were more dramatic in
comparison to the AM circuit at 400 kHz over the entire temperature range, a result of
the properties of the AlN film which causes the capacitors to increase in capacitance
density by 10%.
A novel self oscillating boost converter was commissioned using a counter wound
transformer on high temperature ferrite, a SiC JFET and a SiC SBD. Based upon the
operation of a free running blocking oscillator, oscillatory behaviour is a result of the
electric and magnetic variations in the winding of the transformer and the amplification
characteristics of a JFET. It demonstrated the ability to boost an input voltage of 1.3
volts to 3.9 volts at 573K and exhibited an efficiency of 30% at room temperature. The
frequency of operation was highly dependent upon the input voltage due to the
increased current flow through the primary coil portion of the transformer and the
ambient temperature causing an increase in permeability of the ferrite, thus altering the
inductance of both primary and secondary windings. However due its simplicity and its
ability to boost the input voltage by 250% meant it was capable of powering the
transmitters and in conjunction with a Themoelectric Generator so formed the basis for
a self powered high temperature silicon carbide sensor node.
The demonstration of these high temperature circuits provide the initial stages of being
able to produce a high temperature wireless sensor node capable of operation in hostile
environments. Utilising the self oscillating boost converter and a high temperature
Thermoelectric Generator these prototype circuits were showed the ability to harvest
energy from the high temperature ambient and power the silicon carbide circuitry.
Along with appropriate sensor technology it demonstrated the feasibility of being able
to monitor and transmit information from hazardous locations which is currently
unachievable
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