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.
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Showing 1 to 20 of 56 for “"beamwidth"”.
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Comparison of the Role of Beamwidth in Biological and Engineered Sonar
… work, the key sonar design characteristic of beamwidth is examined in technical and biosonar. To this end, beamwidth data has been obtained for 23 engineered sonar systems and from numerical beampattern predictions for 151 emission and reception elements (noseleaves and pinnae) from bat …
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An Automated Ultrasound Calibration Framework Incorporating Elevation Beamwidth for Tracked Ultrasound Interventions
… quality is further reduced by the "elevation beamwidth" or "slice thickness", a unique feature of the ultrasound beam pattern that gives rise to localization errors and imaging uncertainties. In this thesis, we aim to provide an automated, pure-computation-based, intraoperative calibration …
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Orientation dependence of the acoustic backscatter for elongated zooplankton
… width) is computed. The relationship between beamwidth and acoustic frequency is presented in plots of beamwidth versus ka and L/λ. The model is adapted to experimental limitations of animal motion, discrete sampling and observed side lobe levels. The backscatter directivity patterns of live …
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Design And Analysis Of Adaptive And Reconfigurable Antennas For Wireless Communication
… very good performance with respect to the 3dB beamwidth and directivity. However the reconfigurable rectangular-spiral antenna is the most compact in size among all four antennas. It is (20 mm x 20 mm) in size. At 2.45 GHz it has a 3dB beamwidth of 87° and directivity of 6.47dB. As for the …
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Passive monitoring of high-intensity focused ultrasound
… and to the field characterized by a wire. The beamwidth at the focus of the reconstructed intensity field was estimated to be 1.7 mm. The nominal estimate of the beamwidth was approximately 1.4 mm (-6 dB) and the beamwidth estimated from the wire target mapping was 1.5 mm. Therefore, the novel …
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Spherical antenna array
… has been analyzed using Poisson's Sum Formula. Beamwidth expressions of both element distributions are found in various planes. All numerical results are given only for the case of 21 rings"--Abstract, page ii.
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Reconfigurable microstrip antennas with tunable radiation pattern characteristics
… real time, such as beam direction, beam shape, beamwidth, etc. Such antenna system is desired for various wireless applications because of many reasons among them; it helps to enhance signal strength received from an intended target, mitigates interference, and accommodates sudden changes in …
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Nonlinear optics for frequency-doubling in nanosatellite laser communication
… is largely driven by the reduction in beamwidth that comes with the higher frequency, and is not substantially greater than the improvement that comes with using the same narrower beamwidth at 1550 nm, although SHG would allow a diffraction-limited system to use different beamwidths for …
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Interference aware wireless networks with point to point beamforming
… delve into the physical antenna parameters like beamwidth, main lobe gain, and we see how it affects the network capacity. We intend to investigate power calculations around a transceiver and build a model that will provide an estimate of interference severity for medium access purposes. We then …
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Helical Antennas with Truncated Spherical Geometry
… the hemispherical helix is its broad half-power beamwidth. Furthermore, this antenna provides circular polarization and relatively high gain over a narrow frequency range. The results of this research show that, for example, a 4.5-turn hemispherical helix with a radius of 0.02 meter designed for …
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Null subtraction imaging technique for biomedical ultrasound imaging
… estimation of lateral resolution (-6-dB receive beamwidth), the mainlobe to sidelobe ratio (MSR) in dB and estimation of the contrast-to-noise ratio (CNR). At f/# = 2 focusing with NSI, the -6-dB beamwidth on receive as measured from a small wire target in the ATS phantom was 0.12lambda. …
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Airborne protected military satellite communications : analysis of open-loop pointing and closed-loop tracking with noisy platform attitude information
… biases less than or equal to 0.5 the half-power beamwidth, the step-tracking algorithm reduces the pointing error to within 0.1 the half-power beamwidth of the boresight, for all tested configurations. The overall system performance is bounded by the open-loop pointing solution, which is based on …
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Strategies for limiting interference and interception of free space optical communications
… possible to suppress the signal intensity in a 1 beamwidth region located 0.2 beamwidths from the intended user down to one tenth of the intensity at the intended receiver. For a two dimensional array, we show that we can similarly suppress a !!!!! beamwidth region as close as 0.2333 beamwidths to …
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Optimization of Aperiodically Spaced Antenna Arrays for Wideband Applications
… array element to obtain the required half power beamwidth and bandwidth. The final optimized aperiodic array is compared to a traditional periodic array and conclusions are made.
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Development and Optimization of Airborne FMCW Radars for High-Resolution Snow Depth Measurements
… systems to obtain a narrow transmit-receive beamwidth. Finally, we must demonstrate that we can provide near-real-time operational data products in the field with the improved UWB radar.We performed careful design, simulations, and optimization to reduce the effects of system non-linearities, …
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New Designs for Wideband Hemispherical Helical Antennas
… while maintaining the directivity and half-power beamwidth of the basic design. In the basic design, a simple wire of circular cross section is wound on the surface of a hemisphere, whereas in the proposed new designs a metallic strip forms the radiating element. Furthermore, the metallic strip …
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Evaluation of null subtraction imaging and interpolation techniques for ultrasound B-mode
… by a reduction in contrast, and while the -6 dB beamwidth calculated from the point-spread function may be much smaller than that of conventional techniques, these methods often do not perform as well on the Sparrow test for resolution. Another challenge presented by high-resolution techniques is …
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Directive antenna using metamaterial substrates
… such a way that it improves in radiation power, beamwidth, and bandwidth.
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Direction of arrival estimation for spinning antenna based electronic intelligence systems
… received signals, provided that: the antenna's beamwidth is narrow; the received data is fully spread across the antenna mainlobe; the number of data samples is large; the signal to disturbance ratio (SDR) is large. However, the antenna's beamwidth may be wide due to the wide operating RF range …
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Sensor Package Analysis and Simulation for Direct Sensor-to-Satellite Links
… circular microstrip patch element with a wide beamwidth or a miniature phased array antenna that continuously scans to access the satellite(s). The array beam is controlled with a beam-forming network (BFN), which contains 3 or 4-bit phase shifters, which can be made in micro-electro-mechanical …
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