A Highly Compact Active Wideband Balun With Impedance Transformation in SiGe BiCMOS

A new conveyor-based single-ended to differential balun is proposed. Thanks to the quasi-absence of passive components, this is an extremely size-efficient balun (0.036 ). The use of a new impedance-matching technique makes this balun the first transistor-based solution with controllable port impedances. Fabricated in a 0.35-mum SiGe BiCMOS technology with f_T=45 GHz, the balun shows the following performance: wideband impedance matching at all three ports, good balance between the two outputs (better than 3 dB in amplitude and 13deg in phase) over frequency bands extending from 0 to 3 GHz, linear operation for powers up to input powers of -2 dBm, and stability against temperature and process variations.     

Carotid-jugular arteriovenous fistula: a case report of an iatrogenic complication following internal jugular vein catheterization for hemodialysis access

We report a case of diabetic end-stage renal disease patient who presented with a right common carotid artery jugular arteriovenous fistula as a complication of the insertion of a polyurethane double-lumen hemodialysis catheter into the right internal jugular vein .On physical examination of the neck, a pulsating mass with a palpable thrill and a bruit was noted in the right subclavicular region. The diagnosis was confirmed by color doppler ultrasonography of the neck and carotid angiography. The review of the literature suggests the occurrence of this complication as rather rare. The fistula was successfully repaired surgically. It is emphasized that while securing the access, a thorough physical examination with a special emphasis on seeking any neck swellings, thrill, and bruit along with routine use of vascular doppler for securing dialysis access is recommended.     

A tunable and reconfigurable MMIC active filter in GaAs technology

The filter presented in this article is an active band-pass filter whose center frequency and bandwidth can be tuned. It is composed of channels inserted into a distributed structure, and the frequency agility is obtained by activating one or more of them. The concept is validated with measurements realized on a 3-channel prototype structure implemented in the United Monolithic Semiconductors (UMS) PPH25 GaAs technology from UMS. This filter is tunable throughout the X and Ku bands. This first prototype yields encouraging results: the center frequency can be tuned between 9.7 and 14 GHz, with an average gain of 10 dB throughout this range and a noise figure between 7 and 11 dB. The filter occupies 13.5 mm² of area and consumes 10.5 mA per active stage from a 4 V supplying voltage. It is designed for wideband and agile receivers.     

Application of antenna arrays to mobile communications. II.Beam-forming and direction-of-arrival considerations

Array processing involves manipulation of signals induced on various antenna elements. Its capabilities of steering nulls to reduce cochannel interferences and pointing independent beams toward various mobiles, as well as its ability to provide estimates of directions of radiating sources, make it attractive to a mobile communications system designer. Array processing is expected to play an important role in fulfilling the increased demands of various mobile communications services. Part I of this paper showed how an array could be utilized in different configurations to improve the performance of mobile communications systems, with references to various studies where feasibility of apt array system for mobile communications is considered. This paper provides a comprehensive and detailed treatment of different beam-forming schemes, adaptive algorithms to adjust the required weighting on antennas, direction-of-arrival estimation methods-including their performance comparison-and effects of errors on the performance of an array system, as well as schemes to alleviate them. This paper brings together almost all aspects of array signal processing     

Improved LMS algorithm for adaptive beamforming

Two adaptive algorithms which make use of all the available samples to estimate the required gradient are proposed and studied. The first algorithm is referred to as the recursive LMS (least mean squares) and is applicable for a general array. The second algorithm is referred to as the improved LMS algorithm and exploits the Toeplitz structure of the array correlation matrix and can be used only for an equispaced linear array     

Interfacial shear strength of a glass fiber/epoxy bonding in composites modified with carbon nanotubes

In recent years, carbon nanotubes (CNTs) grown on fibers have attracted a lot of interest as an additional reinforcing component in conventional fiber-reinforced composites to improve the properties of the fiber/matrix interface. Due to harsh growth conditions, the CNT-grafted fibers often exhibit degraded tensile properties. In the current study we explore an alternative approach to deliver CNTs to the fiber surface by dispersing CNTs in the fiber sizing formulation. This route takes advantage of the developed techniques for CNT dispersion in resins and introduces no damage to the fibers. We focus on unidirectional glass fiber/epoxy macro-composites where CNTs are introduced in three ways: (1) in the fiber sizing, (2) in the matrix and (3) in the fiber sizing and matrix simultaneously. Interfacial shear strength (IFSS) is investigated using single-fiber push-out microindentation. The results of the test reveal an increase of IFSS in all three cases. The maximum gain (over 90%) is achieved in the composite where CNTs are introduced solely in the fiber sizing.     

Impedance-controlled wideband active balun based on current conveyors

The first active power-split balun with controllable output impedance is proposed. Its operation is wideband, with good balance characteristics from DC to 3 GHz. It takes up 0.036 mm in a 0.35 mum SiGe BiCMOS technology and is the smallest balun ever observed. Its additional properties are: excellent and wideband overall S-parameter performance; highest linearity observed for a balun; and stability against temperature and process variations.     

Applications of antenna arrays to mobile communications. I.Performance improvement, feasibility, and system considerations

The demand for wireless mobile communications services is growing at an explosive rate, with the anticipation that communication to a mobile device anywhere on the globe at all times will be available in the near future. An array of antennas mounted on vehicles, ships, aircraft, satellites, and base stations is expected to play an important role in fulfilling the increased demand of channel requirement for these services, as well as for the realization of the dream that a portable communications device the size of a wristwatch be available at an affordable cost for such services. This paper is the first of a two-part study. It provides a comprehensive treatment, at a level appropriate to nonspecialists, of the use of an antenna array to enhance the efficiency of mobile communications systems. It presents an overview of mobile communications as well as details of how an array may be used in various mobile communications systems, including land-mobile, indoor-radio, and satellite-based systems. It discusses advantages of an array of antennas in a mobile communications system, highlights improvements that are possible by using multiple antennas compared to a single antenna in a system, and provides details on the feasibility of antenna arrays for mobile communications applications     

Third generation mobile communication systems: overview and modelling considerations

Satellite and terrestrial cellular communication systems currently exist as two independent environments. In third generation systems these will complement each other and the cooperation between the two will allow for flexible and optimal radio resource allocation resulting in a reduction of some cost. However, the success of third generation systems will largely be dependent on their ability to provide improved quality of service over existing first and second generation systems, global coverage and an increased subscriber population. This paper reviews key features of the third generation systems, describes a teletraffic model suitable for such a multi-layer system, determines the benefits associated with a multilayer topology by studying the effect of the number of layers and the number of channels that can be supported by each layer and studies their effects on the performance parameters that determine the quality of service.