An evaluation of the broadband direction finding capabilities of array signal processing techniques

The objective of this study was to determine and compare the direction finding capabilities of high resolution spectral analysis techniques applied to the signals from an antenna array. The maintenance of acceptable resolution over a broad operating frequency range was of particular concern. The comparison was accomplished by computer simulation of the performance of a linear array of eleven isotropic elements, spaced 15 cm apart, over the frequency range from 100 MHz to 1.0 GHz;The two-signal resolution of three linear prediction based algorithms was compared. The variation in performance with signal-to-noise ratio, frequency, and center angle of arrival was also evaluated;An algorithm due to Tufts and Kumaresan which reduces the effects of noise by replacing the noisy signal correlation matrix by a smoothed, least-squares fit to it gave the best performance at the cost of the highest computational complexity. A special case of this method which is easy to compute exhibited blind angles, where performance was severely degraded in spite of wide spacing of the sources;The ratio of the physical length of the array to the length of the modulation envelope set up by the interference of the two incoming signals was found to be a constant at the point of resolution. This led to an expression for the two-signal resolution as a function of look angle, array length, frequency, and this algorithm dependent constant

Calculations of precursor propagation in dispersive dielectrics.

The present study is a numerical investigation of the propagation of electromagnetic transients in dispersive media. It considers propagation in water using Debye and composite Rocard-Powles-Lorentz models for the complex permittivity. The study addresses this question: For practical transmitted spectra, does precursor propagation provide any features that can be used to advantage over conventional signal propagation in models of dispersive media of interest? A companion experimental study is currently in progress that will attempt to measure the effects studied here

Issues in RF propagation modeling in an urban environment using the Extended Air Defense Simulation (EADSIM) mission level model.

As military operations in urban environments become more numerous, the ability of combat units to communicate, jam enemy communications, or employ RF weapons within this environment must be evaluated. To perform this evaluation in a mission level model requires a capability to evaluate the contributions of both terrain and man-made structures (interior and exterior) to RF propagation. The present study is an analysis of the adequacy of a mission level model (EADSIM) to perform these RF propagation calculations in an urban environment. Three basic environments must be assessed. The first environment consists entirely of terrain, with no man-made features impacting propagation values. The second environment includes terrain, but also includes the contribution of solid structures with abrupt edges, which may obstruct/influence LOS paths. The third environment includes not only terrain and structures, but also contains structures with interior features which must be evaluated to determine the propagation levels within and around these structures. EADSIM was used as the model for evaluation in view of its suite of propagation tools which can be used for analysis of RF propagation between transmitters and receivers including terrain. To assess EADSIM's capability to perform in these environments, flat terrain maps with an obstruction were created to permit comparison of EADSIM's propagation models with analytical calculations and with measurements. Calculations from the Terrain Integrated Rough Earth Model (TIREM) and the Spherical Earth Knife Edge (SEKE) propagation models included within EADSIM showed that the ability of the models to calculate knife-edge diffraction agreed favorably with analytical values. The representation of multipath effects was less encouraging. SEKE only models multipath when Fresnel clearance exists. TIREM models multipath, but the cyclical characteristics of multipath are not represented, and only subtractive path loss is considered. Multipath is only evaluated along a 2-D path in the vertical orientation. This precludes modeling propagation in the urban canyons of metropolitan areas, where horizontal paths are dominant. It also precludes modeling exterior to interior propagation. In view of the apparent inadequacy of urban propagation within mission level models, as evidenced by EADSIM, the study also attempts to address possible solutions to the problem. Correction of the sparsing techniques in both TIREM and SEKE models is recommended. Both SEKE and TIREM are optimized for DTED level 1 data, sparsed at 3 arc seconds resolution. This led to significant errors when map data was sparsed at higher or lower resolution. TIREM's errors would be significantly reduced if the 999 point array limit was eliminated. This would permit using interval sizes equal to the map resolution for larger areas. This same problem could be fixed in SEKE by changing the interval spacing from a fixed 3 arc second resolution ({approx}93 meters) to an interval which is set at the map resolution. Additionally, the cell elevation interpolation method which TIREM uses is inappropriate for the man-made structures encountered in urban environments. Turning this method of determining height off, or providing a selectable switch is desired. In the near term, it appears that further research into ray-tracing models is appropriate. Codes such as RF-ProTEC, which can be dynamically linked to mission level models such as EADSIM, can provide the higher fidelity propagation calculations required, and still permit the dynamic interactions required of the mission level model. Additional research should also be conducted on the best methods of representing man-made structures to determine whether codes other than ray-trace can be used

Extremely high frequency RF effects on electronics.

The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit board traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings

Loop-to-loop coupling.

This report estimates inductively-coupled energy to a low-impedance load in a loop-to-loop arrangement. Both analytical models and full-wave numerical simulations are used and the resulting fields, coupled powers and energies are compared. The energies are simply estimated from the coupled powers through approximations to the energy theorem. The transmitter loop is taken to be either a circular geometry or a rectangular-loop (stripline-type) geometry that was used in an experimental setup. Simple magnetic field models are constructed and used to estimate the mutual inductance to the receiving loop, which is taken to be circular with one or several turns. Circuit elements are estimated and used to determine the coupled current and power (an equivalent antenna picture is also given). These results are compared to an electromagnetic simulation of the transmitter geometry. Simple approximate relations are also given to estimate coupled energy from the power. The effect of additional loads in the form of attached leads, forming transmission lines, are considered. The results are summarized in a set of susceptibility-type curves. Finally, we also consider drives to the cables themselves and the resulting common-to-differential mode currents in the load

Loop-to-loop coupling.

This report estimates inductively-coupled energy to a low-impedance load in a loop-to-loop arrangement. Both analytical models and full-wave numerical simulations are used and the resulting fields, coupled powers and energies are compared. The energies are simply estimated from the coupled powers through approximations to the energy theorem. The transmitter loop is taken to be either a circular geometry or a rectangular-loop (stripline-type) geometry that was used in an experimental setup. Simple magnetic field models are constructed and used to estimate the mutual inductance to the receiving loop, which is taken to be circular with one or several turns. Circuit elements are estimated and used to determine the coupled current and power (an equivalent antenna picture is also given). These results are compared to an electromagnetic simulation of the transmitter geometry. Simple approximate relations are also given to estimate coupled energy from the power. The effect of additional loads in the form of attached leads, forming transmission lines, are considered. The results are summarized in a set of susceptibility-type curves. Finally, we also consider drives to the cables themselves and the resulting common-to-differential mode currents in the load

New mechanism for upset of electronics.

For many decades, engineers and scientists have studied the effects of high power microwaves (HPM) on electronics. These studies usually focus on means of delivering energy to upset electronic equipment and ways to protect equipment from HPM. The motivation for these studies is to develop the knowledge necessary either to cause disruption or to protect electronics from disruption. Since electronic circuits must absorb sufficient energy to fail and the source used to deliver this energy is far away from the electronic circuit, the source must emit a large quantity of energy. In free space, for example, as the distance between the source and the target increases, the source energy must increase by the square of distance. The HPM community has dedicated substantial resources to the development of higher energy sources as a result. Recently, members of the HPM community suggested a new disruption mechanism that could potentially cause system disruptions at much lower energy levels. The new mechanism, based on nonlinear dynamics, requires an expanded theory of circuit operation. This report summarizes an investigation of electronic circuit nonlinear behavior as it applies to inductor-resistor-diode circuits (known as the Linsay circuit) and phased-locked-loops. With the improvement in computing power and the need to model circuit behavior with greater precision, the nonlinear effects of circuit has become very important. In addition, every integrated circuit has as part of its design a protective circuit. These protective circuits use some variation of semiconductor junctions that can interact with parasitic components, present in every real system. Hence, the protective circuit can behave as a Linsay circuit. Although the nonlinear behavior is understandable, it is difficult to model accurately. Many researchers have used classical diode models successfully to show nonlinear effects within predicted regions of operation. However, these models do not accurately predict measured results. This study shows that models based on SPICE, although they exhibit chaotic behavior, do not properly reproduce circuit behavior without modifying diode parameters. This report describes the models and considerations used to model circuit behavior in the nonlinear range of operation. Further, it describes how a modified SPICE diode model improves the simulation results. We also studied the nonlinear behavior of a phased-locked-loop. Phased-locked loops are fundamental building block to many major systems (aileron, seeker heads, etc). We showed that an injected RF signal could drive the phased-locked-loop into chaos. During these chaotic episodes, the frequency of the phased-locked-loop takes excursion outside its normal range of operation. In addition to these excursions, the phased-locked-loop and the system it is controlling requires some time to get back into normal operation. The phased-locked-loop only needs to be upset enough long enough to keep it off balance

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Extremely high frequency RF effects on electronics.

The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit board traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings