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Abstract:
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Phased array antenna (PAA ) is a key component in many of the modern military and commercial radar and communication systems requiring highly directional beams with narrow beam widths . One of the advantages that this technology offers is a physical movement -free beam steering . Radar and communication technologies also require the PAA systems to be compact , light weight , demonstrate high bandwidth and electromagnetic interference (EMI ) free performance . Conventional electrical phase shifters are inherently narrowband . This calls for technologies that have a larger bandwidth and high immunity to electromagnetic interference . Optical true -time -delay (TTD ) technique is an emerging technology that is capable of providing these features along with the ability to provide frequency independent beam steering . Photonic crystal fiber (PCF ) based optical TTD lines are capable of providing precise and continuous time delays required for PAA systems . Photonic crystal fibers are a new class of optical fibers with a periodic arrangement of air -holes around a core that can be designed to provide extraordinary optical characteristics which are unrealizable using conventional optical fibers . In this dissertation , highly dispersive photonic crystal fiber structures based on index -guidance and bandgap -guidance were designed . Designs exhibiting dispersion coefficients as large as -9500ps /nm /km and 4000ps /nm /km at 1550nm were presented . A TTD module utilizing a fabricated highly dispersive PCF with a dispersion coefficient of -600ps /nm /km at 1550nm was formed and characterized . The module consisted of 4 delay lines employing highly dispersive PCFs connected with various lengths of non -zero dispersion shifted fibers . By employing PCFs with enhanced dispersion coefficients , the TTD module size can be proportionally reduced . A 4 -element linear X -band PAA system using the PCF -TTD module was formed and characterized to provide continuous time delays to steer radiofrequency (RF ) beams from -41 degrees to 46 degrees by tuning the wavelength from 1530nm to 1560nm . Using the PCF -TTD based X -Band PAA system , single and simultaneous multiple beam transmission and reception capabilities were demonstrated . Noise and distortion performance characteristics of the entire PAA system were also evaluated and device control parameters were optimized to provide maximum spurious -free -dynamic range . In order to alleviate computational and weight requirements of practical large PAA systems , a sparse array instead of a standard array needs to be used . X -Band sparse array systems using PCF and dispersive fiber TTD technique were formed and RF beam steering was demonstrated . As an important achievement during the research work , the design and fabricated structure of a PCF currently reported to have the highest dispersion coefficient of -5400ps /nm /km at 1549nm , along with its limitations was also presented . Finally , other interesting applications of highly dispersive PCFs in the areas of pulse compression and soliton propagation were explored . |