Broadband scanning arrays require small element spacing over a broad frequency band to achieve the desired scan capabilities. Previous research has concentrated on the development of small broadband elements to meet the demands of broadband arrays. However, mutual coupling between elements in a tightly spaced array can change the operating frequency and bandwidth from that of the single isolated element. Several research efforts have focused on minimizing the mutual coupling to maintain the frequency response of the single isolated element. This dissertation focuses on using the strong coupling between Foursquare antennas to obtain the broadband frequency response while maintaining a small element spacing. The isolated Foursquare antenna was modeled using an in-house FDTD code. The modeled current distribution over the frequency band of operation revealed how the antenna achieved a broadband frequency response. Because of this understanding of the single element, the downward shift in the frequency response of the Foursquare antenna in a fully active array could be anticipated. Furthermore, the infinite array models of the Foursquare revealed an increase in bandwidth. Both are desirable characteristics for a broadband scanning array. Therefore, through this research using the Foursquare element, it has been shown that the strong mutual coupling in a tightly spaced array can have advantages if initially taken into consideration when designing the array. / Ph. D.

This thesis investigates the performance of a phased array of antenna elements conforming to a paraboloidal surface. We hypothesize that such a conformal phased array would have performance comparable to that of a correspondingly sized planar array. The performance of a paraboloidal array of antenna elements was simulated using an array program, and the resulting gains, side-lobe levels, and half-power beamwidths compared to those of a similarly sized planar array. Furthermore, we propose a beam-forming feed network for this paraboloidal phased array, and discuss the influence that coupling between the elements could have on the array performance. Lastly, we propose that such an array be used in conjunction with a parabolic reflector antenna to form a versatile hybrid antenna with several potential applications. / Master of Science

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Approved for public release; distribution is unlimited / The space environment has unique hazards that force electronic systems designers to use different techniques to build their systems. Radiation can cause Single Event Upsets (SEUs) which can cause state changes in satellite systems. Mitigation techniques have been developed to either prevent or recover from these upsets when they occur. At the same time, modifying on-orbit systems is difficult in a hardwired electronic system. Finding an alternative to either working around a mistake or having to keep the same generation of technology for years is important to the space community. Newer programmable logic devices such as Field Programmable Gate Arrays (FPGAs) allow for emulation of complex logic circuits, such as microprocessors. FPGAs can be repro-grammed as necessary, to account for errors in design, or upgrades in software logic circuits. In an effort to provide one solution for both of these issues, this research was undertaken. The Configurable Fault Tolerant Processor (CFTP) emulates three identical processors, using Triple Modular Redundancy (TMR) to mitigate SEUs on a radiation tolerant FPGA. With the reconfigurable capabilities of FPGA technology, as newer processors can be emulated, these new configurations can be uploaded to the satellite as software code, thereby actually upgrading the processor in flight. This research used a 16-bit Reduced Instruction Set Computer (RISC) processor as its cores. This thesis describes how the Harvard architecture of the processor is interfaced with the Von Neumann architecture of the memory. It also develops the process by which errors are detected and corrected, as well as recorded. The end result is a design simulation ready for implementation on an FPGA. / Lieutenant, United States Navy

Embedded below the radome of a missile, existing RF-seekers use a mechanical rotating antenna to steer the radiating beam in the direction of a target. Latest research is looking at replacing the mechanical antenna components of the RF seeker with a novel 3D conformal antenna array that can steer the beam electronically. 3D antennas may oer signicant advantages, such as faster beamsteering and better coverage but, at the same time, introduce new challenges resulting from a much more complex radiation pattern than that of 2D antennas. Thanks to the mechanical system removal, the new RF-seeker has a wider available space for the design of a new 3D conformal antenna. To take best benets of this space, dierent array shapes are studied, hence the impact of the position, orientation and conformation of the elements is assessed on the antenna performance in terms of directivity, ellipticity and polarisation. To facilitate this study of 3D conformal arrays, a Matlab program has been developed to compute the polarisation pattern of a given array in all directions. One of the task of the RF-seeker consists in estimating the position of a given target to correct the missile trajectory accordingly. Thus, the impact of the array shape on the error between the measured direction of arrival of the target echo and its true value is addressed. The Cramer-Rao lower bound is used to evaluate the theoretical minimum error. The model assumes that each element receives independently and allows therefore to analyse the potential of active 3D conformal arrays. Finally, the phase monopulse estimator is studied for 3D conformal arrays whose quadrants do not have the same characteristics. A new estimator more adapted to non-identical quadrants is also proposed.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Dennis W. Prather, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

Thesis (Ph.D.)--City University of Hong Kong, 2006. / "Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references (leaves 179-189)