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Antenna Shape Synthesis Using Characteristic Mode ConceptsEthier, Jonathan L. T. 26 October 2012 (has links)
Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.
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Antenna Shape Synthesis Using Characteristic Mode ConceptsEthier, Jonathan L. T. January 2012 (has links)
Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.
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High Performance RF and Basdband Analog-to-Digital Interface for Multi-standard/Wideband ApplicationsZhang, Heng 2010 December 1900 (has links)
The prevalence of wireless standards and the introduction of dynamic
standards/applications, such as software-defined radio, necessitate the next generation
wireless devices that integrate multiple standards in a single chip-set to support a variety
of services. To reduce the cost and area of such multi-standard handheld devices,
reconfigurability is desirable, and the hardware should be shared/reused as much as
possible. This research proposes several novel circuit topologies that can meet various
specifications with minimum cost, which are suited for multi-standard applications. This
doctoral study has two separate contributions: 1. The low noise amplifier (LNA) for the
RF front-end; and 2. The analog-to-digital converter (ADC).
The first part of this dissertation focuses on LNA noise reduction and linearization
techniques where two novel LNAs are designed, taped out, and measured. The first LNA,
implemented in TSMC (Taiwan Semiconductor Manufacturing Company) 0.35Cm
CMOS (Complementary metal-oxide-semiconductor) process, strategically combined an
inductor connected at the gate of the cascode transistor and the capacitive cross-coupling
to reduce the noise and nonlinearity contributions of the cascode transistors. The proposed technique reduces LNA NF by 0.35 dB at 2.2 GHz and increases its IIP3 and
voltage gain by 2.35 dBm and 2dB respectively, without a compromise on power
consumption. The second LNA, implemented in UMC (United Microelectronics
Corporation) 0.13Cm CMOS process, features a practical linearization technique for
high-frequency wideband applications using an active nonlinear resistor, which obtains a
robust linearity improvement over process and temperature variations. The proposed
linearization method is experimentally demonstrated to improve the IIP3 by 3.5 to 9 dB
over a 2.5–10 GHz frequency range. A comparison of measurement results with the prior
published state-of-art Ultra-Wideband (UWB) LNAs shows that the proposed linearized
UWB LNA achieves excellent linearity with much less power than previously published
works.
The second part of this dissertation developed a reconfigurable ADC for multistandard
receiver and video processors. Typical ADCs are power optimized for only one
operating speed, while a reconfigurable ADC can scale its power at different speeds,
enabling minimal power consumption over a broad range of sampling rates. A novel
ADC architecture is proposed for programming the sampling rate with constant biasing
current and single clock. The ADC was designed and fabricated using UMC 90nm
CMOS process and featured good power scalability and simplified system design. The
programmable speed range covers all the video formats and most of the wireless
communication standards, while achieving comparable Figure-of-Merit with customized
ADCs at each performance node. Since bias current is kept constant, the reconfigurable
ADC is more robust and reliable than the previous published works.
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