Array signal processing is an important branch in the field of signal processing. In recent years, it has developed dramatically. It can be applied in such fields as radio detection and ranging, communication, sonar, earthquake, exploration, astronomy and biomedicine. The field of direction of array signal processing can be classified into self-adaption array signal processing and spatial spectrum, in which spatial spectrum estimation theory and technology is still in the ascendant status, and become a main aspect in the course of array signal processing. Spatial spectrum estimation is focused on investigating the system of spatial multiple sensor arrays, with the main purpose of estimating the signal’s spatial parameters and the location of the signal source. The spatial spectrum expresses signal distribution in the space from all directions to the receiver. Hence, if one can get the signal’s spatial spectrum, then the direction of arrival (DOA) can be obtained. As thus, spatial spectrum estimation is also called DOA estimation. DOA technology research is important in array signal processing, which is an interdisciplinary technology that develops rapidly in recent years, especially the direction of arrival with multiple signal sources, the estimation of coherent signal sources, and the DOA estimation of broadband signals. DOA estimation has a wide application prospect in radar, sonar, communication, seismology measurement and biomedicine. Over the past few years, all kinds of algorithms which can be used in DOA estimation have made great achievements, the most classic algorithm among which is Multiple Signal Classification (MUSIC). In this thesis I will give an overview of the DOA estimation based on MUSIC algorithm.

<p>This thesis addresses the problem of source localization and time-varying spatial spectrum estimation with maneuverable arrays. Two applications, each having different environmental assumptions and array geometries, are considered: 1) passive broadband source localization with a rigid 2-sensor array in a shallow water, multipath environment and 2) time-varying spatial spectrum estimation with a large, flexible towed array. Although both applications differ, the processing scheme associated with each is designed to exploit array maneuverability for improved localization and detection performance.</p><p>In the first application considered, passive broadband source localization is accomplished via time delay estimation (TDE). Conventional TDE methods, such as the generalized cross-correlation (GCC) method, make the assumption of a direct-path signal model and thus suffer localization performance loss in shallow water, multipath environments. Correlated multipath returns can result in spurious peaks in GCC outputs resulting in large bearing estimate errors. A new algorithm that exploits array maneuverability is presented here. The multiple orientation geometric averaging (MOGA) technique geometrically averages cross-correlation outputs to obtain a multipath-robust TDE. A broadband multipath simulation is presented and results indicate that the MOGA effectively suppresses correlated multipath returns in the TDE.</p><p>The second application addresses the problem of field directionality mapping (FDM) or spatial spectrum estimation in dynamic environments with a maneuverable towed acoustic array. Array processing algorithms for towed arrays are typically designed assuming the array is straight, and are thus degraded during tow ship maneuvers. In this thesis, maneuvering the array is treated as a feature allowing for left and right disambiguation as well as improved resolution towards endfire. The Cramer Rao lower bound is used to motivate the improvement in source localization which can be theoretically achieved by exploiting array maneuverability. Two methods for estimating time-varying field directionality with a maneuvering array are presented: 1) maximum likelihood estimation solved using the expectation maximization (EM) algorithm and 2) a non-negative least squares (NNLS) approach. The NNLS method is designed to compute the field directionality from beamformed power outputs, while the ML algorithm uses raw sensor data. A multi-source simulation is used to illustrate both the proposed algorithms' ability to suppress ambiguous towed-array backlobes and resolve closely spaced interferers near endfire which pose challenges for conventional beamforming approaches especially during array maneuvers. Receiver operating characteristics (ROCs) are presented to evaluate the algorithms' detection performance versus SNR. Results indicate that both FDM algorithms offer the potential to provide superior detection performance in the presence of noise and interfering backlobes when compared to conventional beamforming with a maneuverable array.</p> / Dissertation

Šioje disertacijoje teoriškai ir eksperimentiškai tiriamas erdvinių šviesos darinių formavimasis didelės apertūros monolitiniuose parametriniuose šviesos generatoriuose (PŠG), nagrinėjamos fotoninių kristalų (FK) rezonatorių erdvinės dispersijos savybės. Darbas susideda iš įvado, literatūros apžvalgos ir dviejų pagrindinių dalių. Pirmoje dalyje aprašomas PŠG tyrimas didelės apertūros (5x5x1,5 mm) BBO I fazinio sinchronizmo tipo kristalo monolitiniame mini rezonatoriuje. Generatoriui kaupinti naudojami antros Nd:IAG lazerio harmonikos (532 nm) 13 ns trukmės ir 7-15 mJ energijos impulsai. Erdviniai šviesos dariniai registruojami artimajame ir tolimajame laukuose. Eksperimentiškai parodoma ir teoriškai interpretuojama, kad tokio rezonatoriaus emisija gali būti kūginė ir daugiakūgė, o signalinės ir skirtuminės bangų kryptys gali būti valdomos keičiant kampą tarp rezonatoriaus optinės ašies ir kaupinimo pluošto. Taip pat parodoma, kad dryžių erdvinio šviesos darinio formavimasis gali būti pasiekiamas injektuojant pagrindinio dažnio užkrato signalą. Antrojoje disertacijos dalyje pristatomi ir tiriami plokščiųjų veidrodžių Fabri ir Pero tipo rezonatoriai su vidine lūžio rodiklio moduliacija, atitinkančia vieną fotoninio kristalo (FK) išilginį periodą. FK rezonatoriai sukurti veidrodžių paviršiuje suformuojant 2 µm, 4 µm ir 15 µm periodinę lūžio rodiklio moduliaciją (t.y. suformuojant vienmatę arba dvimatę fazinę difrakcinę gardelę). FK rezonatorių kampinis pralaidumas matuotas... [toliau žr. visą tekstą] / This Ph.D. thesis contains experimental and theoretical analysis of nonlinear optical pattern formation in monolithic mini-cavity optical parametrical oscillators and spatial properties of linear photonic crystal resonators. The thesis consists of introduction, literature review and two chapters. In the first chapter experimental investigation of optical parametrical oscillation (OPO) in broad aperture monolithic (5x5x1.5 mm) BBO type I crystal mini-cavity is described. OPO was pumped by second harmonic (532 nm) 13 ns duration, 7 15 mJ energy pulses, of Nd:YAG laser. Optical patterns were registered in a near and far field of OPO emission. Experiments and theoretical interpretation revealed that emission of such resonator can be conical and multiconical and direction of signal and idler waves can be controlled by changing the mini-cavity orientation with respect to pump beam. It was also showed, that the stabilization of stripes (or roll) pattern can be achieved by a weak seed injection at subharmonic frequency and temporal spectrum of the stripe pattern degenerate OPO emission is 1/f – like noise spectrum . In the second chapter plane-mirror Fabry-Pérot resonators filled with a single period of photonic crystal (PhC) are introduced and analyzed. PhC resonators are realized by adding periodical 2 µm, 4 µm and 15 µm refraction index modulation on a resonator mirror surfaces (i.e. fabricating 1D or 2D phase diffraction grating). PhC resonator angular transmission measured by... [to full text]

This Ph.D. thesis contains experimental and theoretical analysis of nonlinear optical pattern formation in monolithic mini-cavity optical parametrical oscillators and spatial properties of linear photonic crystal resonators. The thesis consists of introduction, literature review and two chapters. In the first chapter experimental investigation of optical parametrical oscillation (OPO) in broad aperture monolithic (5x5x1.5 mm) BBO type I crystal mini-cavity is described. OPO was pumped by second harmonic (532 nm) 13 ns duration, 7 15 mJ energy pulses, of Nd:YAG laser. Optical patterns were registered in a near and far field of OPO emission. Experiments and theoretical interpretation revealed that emission of such resonator can be conical and multiconical and direction of signal and idler waves can be controlled by changing the mini-cavity orientation with respect to pump beam. It was also showed, that the stabilization of stripes (or roll) pattern can be achieved by a weak seed injection at subharmonic frequency and temporal spectrum of the stripe pattern degenerate OPO emission is 1/f – like noise spectrum . In the second chapter plane-mirror Fabry-Pérot resonators filled with a single period of photonic crystal (PhC) are introduced and analyzed. PhC resonators are realized by adding periodical 2 µm, 4 µm and 15 µm refraction index modulation on a resonator mirror surfaces (i.e. fabricating 1D or 2D phase diffraction grating). PhC resonator angular transmission measured by... [to full text] / Šioje disertacijoje teoriškai ir eksperimentiškai tiriamas erdvinių šviesos darinių formavimasis didelės apertūros monolitiniuose parametriniuose šviesos generatoriuose (PŠG), nagrinėjamos fotoninių kristalų (FK) rezonatorių erdvinės dispersijos savybės. Darbas susideda iš įvado, literatūros apžvalgos ir dviejų pagrindinių dalių. Pirmoje dalyje aprašomas PŠG tyrimas didelės apertūros (5x5x1,5 mm) BBO I fazinio sinchronizmo tipo kristalo monolitiniame mini rezonatoriuje. Generatoriui kaupinti naudojami antros Nd:IAG lazerio harmonikos (532 nm) 13 ns trukmės ir 7-15 mJ energijos impulsai. Erdviniai šviesos dariniai registruojami artimajame ir tolimajame laukuose. Eksperimentiškai parodoma ir teoriškai interpretuojama, kad tokio rezonatoriaus emisija gali būti kūginė ir daugiakūgė, o signalinės ir skirtuminės bangų kryptys gali būti valdomos keičiant kampą tarp rezonatoriaus optinės ašies ir kaupinimo pluošto. Taip pat parodoma, kad dryžių erdvinio šviesos darinio formavimasis gali būti pasiekiamas injektuojant pagrindinio dažnio užkrato signalą. Antrojoje disertacijos dalyje pristatomi ir tiriami plokščiųjų veidrodžių Fabri ir Pero tipo rezonatoriai su vidine lūžio rodiklio moduliacija, atitinkančia vieną fotoninio kristalo (FK) išilginį periodą. FK rezonatoriai sukurti veidrodžių paviršiuje suformuojant 2 µm, 4 µm ir 15 µm periodinę lūžio rodiklio moduliaciją (t.y. suformuojant vienmatę arba dvimatę fazinę difrakcinę gardelę). FK rezonatorių kampinis pralaidumas matuotas... [toliau žr. visą tekstą]