A technique for assessing the severity of terrain shadowing in mobile satellite service

A graphical analysis technique is presented that produces an estimate of the severity of terrain shadowing of a particular geosynchronous satellite. The technique can be used to analyze the coverage provided by a new group of satellites capable of direct communication with mobile and transportable units. Application of the technique to a number of highways in Alaska is described.     

A technique for an array to generate circular polarization with linearly polarized elements

A method is presented for generating circularly polarized radiation from an array composed of linearly polarized elements having unique angular and phase arrangements. With this technique the complexity, weight, and RF loss of the array feed can be significantly reduced, especially in a large array. This uniquely formed array has the capability of generating excellent circular polarization (CP) over a relatively wide frequency bandwidth. In addition, the array is capable of scanning its main beam in the principal planes to relatively wide angles from its broadside direction without serious degradation to its CP quality. Another feature of this uniquely arranged array is a reduction in the occurrence of mutual coupling. The discussion in this paper places special emphasis on the microstrip type of radiator, although the technique presented can be adapted to most types of linearly polarized antenna elements.     

A technique for calibrating an electron-beam evaporator x-ray source

An electron-beam metal evaporator was modified to act as an x-ray source for simulating x-ray lithography induced radiation damage in semiconductor devices. Besides x-rays, such a set-up generates secondary and backscattered electrons. Simulation of radiation damage induced during a typical x-ray lithography processing step requires that secondary and backscattered electrons be removed from the incident radiation. A common method to separate the electrons and x-rays is to block the electrons with a thin beryllium film. However, thin beryllium films are expensive and are not commercially available in large sizes. Instead, a relatively inexpensive polymer pellicle was used to block the electrons. A disadvantage of the pellicle is that its x-ray transmission characteristics are unknown and must be determined experimentally. Previous works calibrated the pellicle x-ray transmission and system electron/x-ray flux ratios using the known x-ray transmission characteristics of beryllium film. To check the accuracy of the beryllium calibration results, a new calibration method employing two pellicles was developed. A comparison of the calibration data found a large discrepancy between the two calibration methods. The discrepancy was attributed to ultraviolet light absorption in the radiation dosimeters. A correction for the ultraviolet light absorption is presented for determining the true electron/x-ray flux ratios and pellicle x-ray transmission.     

A simple technique to determine barrier height change in gate oxide caused by electrical stress

Charge trapping in the gate oxide and at the interfaces caused by electrical stress may lead to changes of both the oxide field and the shape of tunneling barrier. In this study, a simple technique based on the analysis of a small change in the Fowler-Nordheim (FN) tunneling current has been developed to quantitatively examine the changes of the effective barrier height and the electric field at the tunneling interface. A power-law dependence of the changes of both the barrier height and the electric field on the stress time is observed.     

Extensions to an authentication technique proposed for the globalmobility network

We present three attacks on the authentication protocol that has been proposed for the so-called global mobility network in the October 1997 issue of the IEEE Journal on Selected Areas in Communications. We show that the attacks are feasible and propose corrections that make the protocol more robust and resistant against two of the presented attacks. The aim is to highlight some basic design principles for cryptographic protocols, the adherence to which would have prevented these attacks     

Experimental evaluation of an array technique for zenith to horizon coverage

An experimental study of a new array concept with application to providing low cost efficient antennas with hemispherical coverage for aircraft to satellite communication links is described. The combined array-surface wave antenna consists of 64 waveguide elements scanned conventionally except at endfire. At endfire the array is shorted to become a corrugated surface-wave antenna and excited by an eight-element feed to provide a directional beam near the horizon. The array is rotated to give hemispherical coverage.     

A Bayes method for assessing product-reliability during developmenttesting

A fully Bayes approach is presented for analyzing product reliability during the development phase. Based on a Bayes version of the Barlow-Scheuer reliability-growth model, it is assumed that the product goes through a series of test/modification stages, where each product test yields attribute (pass-fail) data, and failure types are classified as fixable or nonfixable. Relevant information on both the failure probabilities and the reliability-growth process is used to motivate the prior joint distribution for the probability of each failure type over the specified range of testing. Results at a particular test-stage can be used to update the knowledge about the probability of each failure type (and thus product reliability) at the current test-stage as well as at subsequent test-stages, and at the end of the development phase. A relative ease of incorporation of prior information and a tractability of the posterior analysis are accomplished by using a Dirichlet distribution as the prior distribution for a transformation of the failure probabilities     

A search strategy for assessing a business opportunity

The optimal stopping model presented here explores opportunity assessment with reference to a tradeoff between, on the one hand, reducing decision accuracy and, on the other hand, both increasing search costs and a higher probability that the opportunity is grasped by a competitor. From this model we propose a heuristic that specifies three threshold lines to define four decision areas. Decision area 1 prescribes the business opportunity be accepted, decision areas 2 and 4 prescribe that search continue, and decision area 3 prescribes that the business opportunity be rejected. We use a simulation to investigate the robustness of the heuristic beyond the model's boundary conditions     

New method for assessing EED susceptibility to electromagneticradiation

An infrared fiber optical temperature sensor (IFOTS) used for the measurement of induced electric currents caused by electromagnetic radiation in electroexplosive devices (EEDs) is presented. Features of the sensor include an infrared optical fiber that is immune to electromagnetic radiation, a probe assembly that eliminates any appreciable thermal and electrical loading of the EEDs bridgeware, a signal processing technique that enhances signals in the presence of noise, and a means of providing continuous and/or pulsed measurement of bridgeware temperature caused by induced electric currents     

A sea change for semiconductors

Skies were blue and trade winds were steady as the SS Semiconductor set sail in early 2001. The previous year's haul had set records, and forecasters were heralding yet another banner year. But powerful forces were to shake even this vessel's sturdy timbers. A low-pressure center caused by the bursting dot-com bubble and warm moist Y2K air from around the globe stirred up a storm so violent that it shredded the mainsail. Gales of corporate malfeasance from the southwest and typhoons of terrorism from the east swept wave after wave of stock-market volatility over the decks. While many of the crew were tossed overboard, cargo destined for distant ports sat idle in the holds. It was a long time before the winds grew calm enough for the crew to repair the battered boat and limp to port. But customers there, who had also been buffeted by the foul weather, were scarce. And the ship's officers were forced to sell their cargo at a fraction of its original value. Now, almost two years after the near-fatal voyage, forecasters are again predicting blue skies, and officers and crew are guardedly optimistic that good fortune awaits in the year ahead.     

A framework for process change

Forces such as technology change and increased competition provide opportunities and challenges that drive a firm to continuously evaluate and modify its resource capabilities. As a consequence, a firm's process change strategy is of paramount importance for sustained manufacturing success. However, fundamental elements of process change strategy are not well understood. Long term performance benefits associated with potential process change alternatives are often unclear. Moreover, uncertainty exists regarding the actual benefits that may be attained from various types of process change. Critical issues impacting the proper implementation of process change are frequently underestimated or largely ignored. Therefore, despite the improved performance sought, process change often leads to lower productivity, excessive equipment downtime, and deterioration in quality. As the authors review the relevant empirical and normative literature, a framework emerges that characterizes the salient features of a firm's process change strategy. The underlying dynamics of process change are explored and strategies are discussed to reduce the short-term disruption and enhance the long-term gain. In particular, the authors demonstrate the importance of creating and applying knowledge to improve the outcome of process change. They describe managerial actions that can be taken to reduce various sources of uncertainty associated with process change. Moreover, they identify key contributions as well as limitations of the existing normative literature on process change. Insights from the empirical literature are given that both support elements of the existing normative models and provide direction for future normative research. Thus, the authors seek to aid practicing managers and researchers alike to better understand the full scope and implications of process change.     

A complete methodology for assessing GaN behaviour for military applications

For military applications, due to a very long life cycle, great power requirements and numerous (>1000) HPA (High Power Amplifier) per system, GaN power devices are considered as critical components. So, an independent assessment made in a government laboratory was required by program officers in order to check all the key parameters of this new technology. The objective of this paper is to present the global methodology and analyse data obtained on GaN technologies, simultaneously taking into account process issues, reliability concerns and microwave measurements. The originality of this work is to gather all these aspects, thanks to a new RF life test bench designed especially for GaN products. We described also failure analysis results which combine classical cross-sections and delayering, STEM and TEM observations and EBIC signatures. Finally, predictive reliability calculations for a 15 W power transistor were performed thanks to the new FIDES model and compared with manufacturer data.     

A tsunami warning system using an ionospheric technique

Earthquakes generate Rayleigh waves which travel along the surface of the earth about 20 times faster than the potentially destructive tsunami (if one is also generated) and reach distant points several hours before the tsunami. The Rayleigh wave excites an upward-propagating acoustic wave which, because of the exponential decrease in air density with height, increases to a large amplitude at ionospheric heights and produces ionization density changes in the ionosphere proportional to the amplitude and form of the wave. HF radio signals reflected from the ionosphere are Doppler-shifted by these motions and can be processed to produce a record which is a faithful reproduction of the Rayleigh wave. By analyzing the ionospheric record and tracing the Rayleigh wave back to the earthquake's epicenter, the characteristics of the earthquake can be determined. This information can then be used to deduce the probability that the earthquake generated a tsunami Instrumentation for a tsunami warning system based on this method is simple and inexpensive.     

A heuristic technique for assigning frequencies to mobile radio nets

In preparing or revising an RF channel plan for a group of mobile radio nets operating in the same region, the order in which the nets are assigned channels can be crucial to success. One well-known principle for selecting such an assignment sequence is to rank the channel requirements of the various nets in descending order of "assignment difficulty." This paper describes an easily automated heuristic assignment technique in which the channel requirements that prove themselves to be "difficult," through repeated failures to be assigned channels, rise rapidly toward the top of the list of requirements. The heuristic technique is useful in solving complex frequency-assignment problems that involve cochannel, adjacent-channel, spurious and intermodulation interference; nonrepetitive zone structures; fixed pre-existing frequency assignments; and frequency-resource lists that contain gaps and vary from zone to zone.     

A distortion control technique for achieving high power efficiency in an HPA array

This paper proposes a new technique for reducing the intermodulation (IM) distortion products in a high-power amplifier (HPA) array. The proposed technique dissolves the relations between carriers and IMs by applying IM phase control. As a result, IMs are distributed to all the output ports in the array, and the carrier power to intermodulation power ratio (C/IM) of the HPA array can be increased. The improvement in CI/M is as high as 10log N dB, where N is the number of HPAs. Newly developed even-order distortion implemented intermodulation distortion controllers (EODICs) are used to achieve the IM phase control. A test carried out using a four-parallel HPA array with EODICs confirms that the technique noticeably improves C/IM and demonstrates its validity.