Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 14 of 14 for “"Theory of Diffraction"”.
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Image formation using geometrical theory of diffraction and its applications to lithography
… DIFFRACTED RAYS POSTULATED IN GEOMETRICAL THEORY OF DIFFRACTION THROUGH</P><P>THE OPTICAL SYSTEM AND COLLECTING THEM IN IMAGE SPACE, IT IS DISCOVERED THAT, IF THE</P><P>DIFFRACTED RAY FIELDS ARE SAMPLED ABOUT THE PENUMBRA REGIONS ABOVE SOME THRESHOLD</P><P>VALUE, 1D AND 2D IMAGE …
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Evaluation of the uniform theory of diffraction for edge diffraction at low frequency
This thesis examines the UTD diffraction coefficient's limitations in accuracy for a half plane and a wedge at low frequency. The UTD solutions are developed for scattering by a strip and a square cylinder with diffraction considered as a local phenomenon. Single and multiple diffractions are …
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Radijo bangų difrakcijos ir spindulių trasavimo metodų palyginimas urbanizuotose vietovėse /
Telecommunication is a key element of modern civilization, and we can find applications of it in every sphere. Most of the world has and uses a mobile telecommunication device, for example a smartphone, which can send and receive information packets through radio waves. Telecommunication systems …
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Computer-aided design-based high-frequency electromagnetic wave scattering from complex bodies
This work investigates the use of high frequency electromagnetic scattering techniques, such as the physical theory of diffraction (PTD) and the geometrical theory of diffraction (GTD) and the shooting and bouncing rays (SBR) method combined with computer aided design (CAD) compatible geometries, …
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Analysis and Optimization of Reflector Antenna Systems (Pattern Calculation, Optimum Directivity, Sidelobe Reduction)
This thesis studies the secondary pattern of a perfectly conducting reflector antenna system being illuminated by an array feed with arbitrary location, polarization, and orientation. The methods of analysis used are physical optics (PO) and the application of the Fast Fourier Transform (FFT) to …
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Finite difference techniques for body of revolution radar cross section
Although a number of radar cross section prediction techniques have been developed which exploit body of revolution symmetry, the use of finite-difference techniques with these geometries has not been throughly explored. This thesis investigates several finite-difference approaches which vary both …
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Theoretical Study of Laser Beam Quality and Pulse Shaping by Volume Bragg Gratings
The theory of stretching and compressing of short light pulses by the chirped volume Bragg gratings (CBG) is reviewed based on spectral decomposition of short pulses and on the wavelength-dependent coupled wave equations. The analytic theory of diffraction efficiency of a CBG with constant chirp …
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Prediction of low-frequency sound-pressure fields in fitted rooms for active noise control
… for workers in industrial workshops; rooms of highly varying size and dimensions, usually containing obstacles (the ‘fittings’). Low-frequency noise can be generated from sources such as reciprocating or rotating machinery, or ventilation systems. As the exposure time to the noise lengthens, …
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Non-Line-of-Sight localisation of a sound source
… techniques that are accurate in Non-Line-of-Sight (NLoS) conditions and system implementation of the proposed techniques. Such conditions can cause positive bias errors, namely NLoS errors, in the measured Time-of-Arrivals (ToAs) of first-arrival signals received by microphones and thus …
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Modification of Large Reflector Antennas for Low Frequency Operation
Modifications of large reflector antennas, such that their observing capabilities are enhanced in the range of about 10-500~MHz without affecting operation of the pre-existing higher-frequency systems, are addressed in this dissertation. The major contributions of this dissertation can be divided …
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Design and Analysis of Quasioptical Components for use in Terahertz Optics and Future CMB Missions
The main topic of this thesis concerns itself with the development and analysis of optical components used in CMB (Cosmic Microwave Background) missions in the terahertz frequency spectrum. In particular, the optical performance of PRISTINE, a mission proposal for the ESA fast (F) mission call and …
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Quasi-Optical Modelling of Telescope Systems for Planck and STEAMR
… with the high-frequency quasi-optical modelling of telescope systems, with special attention paid to the Planck satellite, but further work is also performed on the Stratosphere-Troposphere Exchange And climate Monitor Radiome- ter (STEAMR) and the Far Infrared Instrument (FIRI). The primary work …
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Numerische Berechnung elektromagnetischer Felder - Erweiterung einer Hybridmethode aus Momentenmethode und Einheitlicher Geometrischer Beugungstheorie um die Verallgemeinerte Multipoltechnik
Drei numerische Feldberechnungsverfahren - die Momentenmehtode, die Einheitliche Geometrische Beugungstheorie und die Verallgemeinerte Multipoltechnik - werden schrittweise zu einer Erweiterten Hybridmethode (EHM) kombiniert. Dabei wird jeder einzelne Kombinationsschritt anschaulich anhand von …
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Waveform design and processing techniques in OFDM radar
With the advent of powerful digital hardware, software defined radio and radar have become an active area of research and development. This in turn has given rise to many new research directions in the radar community, which were previously not comprehensible. One such direction is the recently …