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This paper presents the design of electromagnetic band gap (EBG) structure using fractals geometry and its effect on antenna performance. The EBG structure has been designed on substrate ∈r=4.3 and thickness h=1.53 mm. The 1st iterative EBG structure offers the surface wave suppression around 20 dB down from 2.94 to 4.58 GHz corresponds to 43.62% bandwidth. The experimental results of 2nd iterative EBG structure revealed the surface wave suppression in two bands from 2.45 to 3.36 GHz and from 8.52 to 11.02 GHz. The surface wave suppression bandwidth for both the bands is 31.325 and 25.59%, respectively. The antenna designed with the proposed EBG in same plane exhibits improvement in the bandwidth by 20.5%, gain by 2.44 dB and reduction in back lobe in comparison to antenna without EBG. [ABSTRACT FROM AUTHOR]

Accurate modeling of transmission lines becomes increasingly important in high-speed interconnect system design. However, it is rather difficult to obtain broadband transmission line models, in particular using frequency-domain measurements. This paper points out two potential accuracy issues. First, inaccurate DC values of the frequency-domain data cause a severe error in the time-domain simulations. Second, it is difficult to characterize the characteristic impedance over a wide frequency range due to the reflection caused by the port discontinuities. This paper proposes the combination of both time and frequency measurement data to mitigate the DC accuracy issue. For the characteristic impedance model, a new de-embedding technique is presented to mitigate the port discontinuity issue. Several numerical examples, such as MCM-L coplanar lines and package microstrip lines, are studied to validate the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Time-spreading (TS) phase encoding optical code division multiplexing access (OCDMA) systems with pulse-position modulation (PPM) signalling are investigated, the multiple access interference, optical beat noise and bandwidth limitation of receiver are considered. The authors also compare the performance of the PPM system with that of the conventional on-off keying (OOK) system with optimum threshold detection. Numerical results show that there exists an optimum pulse-position multiplicity for the PPM OCDMA system, and the corresponding PPM scheme is superior to OOK scheme in the coherent bandwidth-limited TS OCDMA system under the chip time constraint. [ABSTRACT FROM AUTHOR]

In the nVoD (near video-on-demand) paradigm, video is distributed through broadcast channels with constrained bandwidth, so that at reception there is a bounded playback start time that is independent of the number of users. In other words, there is unlimited scalability for low bandwidth cost, at the expense of a bounded start time. Thus, regarding bandwidth, nVoD schemas are well suited for satellite channels, so packet losses have not been considered in their context for a long time. Recent research based on digital fountains and intrinsic redundancy of nVoD transmissions has produced nVoD protocols with correction capabilities, which have little or zero impact on bandwidth usage. The authors analyse the most recent proposals using satellite channel models and compare them in terms of error correction performance and client and server resources. [ABSTRACT FROM AUTHOR]

As an efficient distribution mechanism, Peer-to-Peer (P2P) technology has become a tremendously attractive solution to offload servers in large-scale video streaming applications. However, in providing on-demand asynchronous streaming services, P2P streaming design faces two major challenges: how to schedule efficient video sharing between peers with asynchronous playback progresses? how to provide incentives for peers to contribute their resources to achieve a high level of system-wide Quality-of-Experience (QoE)? In this paper, we present iPASS, a novel mesh-based P2P VoD system, to address these challenges. Specifically, iPASS adopts a dynamic buffering-progress-based peering strategy to achieve high peer bandwidth utilization with low system maintenance cost. To provide incentives for peer uploading, iPASS employs a differentiated prefetching design that enables peers with higher contribution prefetch content at higher speed. A distributed adaptive taxation algorithm is developed to balance the system-wide QoE and service differentiations among heterogeneous peers. To assess the performance of iPASS, we built a detailed packet-level P2P VoD simulator and conducted extensive simulations. It was demonstrated that iPASS can completely offload server when the average peer upload bandwidth is more than 1.2 times the streaming rate. Furthermore, we showed that the distributed incentive algorithm motivates peers to contribute and collaboratively achieve a high level of system wide QoE. [ABSTRACT FROM AUTHOR]

In this paper the optimized structure of divider for digital predistortion algorithm is implemented. The divider is a core element of the algorithm. Its implementation has to face several conditions: due to the required high bandwidth, the design should fulfill the requirements for a high clock rate. Thus, a very short critical path is necessary and therefore a pipelined structure is chosen. Although the insertion of pipeline steps shortens the critical path, it enlarges the latency, which has to be avoided. Therefore, a trade-off between the hardware effort and the latency has to be found. Due to the fact that the divider is instantiated three times in this design, the hardware effort is a critical parameter and should be reduced as much as possible. [ABSTRACT FROM AUTHOR]

Abstract: Nowadays control systems are mostly implemented on digital platforms and, increasingly, over shared communication networks. Reducing resources (processor utilization, network bandwidth, etc.) in such implementations increases the potential to run more applications on the same hardware. We present a self-triggered implementation of linear controllers that reduces the amount of controller updates necessary to retain stability of the closed-loop system. Furthermore, we show that the proposed self-triggered implementation is robust against additive disturbances and provide explicit guarantees of performance. The proposed technique exhibits an inherent trade-off between computation and potential savings on actuation. [ABSTRACT FROM AUTHOR]

The convergence behavior of a convolution representation of stable linear time-invariant (LTI) systems operating on the Zakai class of bandlimited signals is analyzed. It is shown that there are signals in the Zakai class for which the convolution integral diverges if the system is the Hilbert transform or the ideal low-pass filter with bandwidth less than or equal to the signal bandwidth. Moreover, using a previously obtained result of Habib, it is proved that the class of stable LTI systems that map the Zakai class into itself does not include the Hilbert transform and the ideal low-pass filter with bandwidth less than or equal to the signal bandwidth. Finally, it is shown that the concept of the analytical signal, which is used in communications, is problematic for the signal space Zπ, because the operator for its computation is unbounded and discontinuous. [ABSTRACT FROM AUTHOR]

For cavity-assisted optomechanical cooling experiments, in order to achieve the quantum ground state of the mechanical oscillator, the cavity bandwidth needs to be smaller than the mechanical frequency. In the literature, this is the so-called resolved-sideband or good-cavity limit, and this is based on an understanding of optomechanical dynamics. We provide a different but physically equivalent explanation of such a limit: that is, information loss due to finite cavity bandwidth. With an optimal feedback control to recover the information in the cavity output, we can surpass the resolved-sideband limit and achieve the quantum ground state. In addition, recovering this information can also significantly enhance the entanglement between the cavity mode and the mechanical oscillator. Especially when the environmental temperature is high, such optomechanical entanglement will either exist or vanish critically depending on whether information is recovered or not. This provides a vivid example of a quantum eraser in the optomechanical system. [ABSTRACT FROM AUTHOR]

A new dual-fed microstrip patch antenna, which provides both radiating and power dividing/combining functions, is proposed. Distorting the normal patch mode (TM01 mode) makes the two feeding port possess very good isolation so that they can be employed as a power divider/combiner as well. A single-layer design with 0.5% impedance bandwidth, more than 22 dB port-to-port isolation and 7 dBi antenna gain at the centre frequency of 5.8 GHz was measured. Its percentage bandwidth is less than that of the conventional patch because of the increased quality factor at the distorted patch mode resonance. To improve the impedance bandwidth of the antenna, a multilayered design achieves broader impedance bandwidth and higher antenna gain than that of single-layer design. A 12.5% impedance bandwidth is achieved and the average antenna gain is measured at about 11.2 dBi. Bandwidth enhancement is achieved by introducing one more resonance near the operating frequency, whereas antenna gain is enhanced because of the increase in effective antenna volume. Within the operating frequency band, more than 23 dB measured port-to-port isolation is achieved. [ABSTRACT FROM AUTHOR]

Design and realisation of a novel substrate integrated waveguide (SIW) power splitter with high isolation is presented. The configuration of the proposed splitter is similar to a conventional four-port waveguide magic Tee whose E-plane arm is matched. To implement the matched E-plane arm in the SIW technology, a slot on the upper conductor of the SIW along with a number of terminating resistors is used. The designed SIW splitter is then fabricated and measured on the coaxial ports of three coaxial-to-SIW transitions. Measured results on the coaxial ports indicate that the fabricated power splitter features more than 10 dB of input and output return loss across a 42% bandwidth from 9.6 to 14.8 GHz. The isolation between output ports is better than 10 dB within a wider frequency range from 8.7 to 15.5 GHz. [ABSTRACT FROM AUTHOR]

This study demonstrates the feasibility of using microstrip L-shaped stepped impedance resonators in a dual-band filter, in conjunction with one of two coupled fed structures. Traditional single-band coupled filter design theory is used and each design parameter of the filter is controlled by two suitable physical parameters. Thus, the specifications, such as the central frequencies and the bandwidth of the two bands, can be fulfilled simultaneously. The filter maintains the geometry of the resonators without the need for additional matching networks. Design curves are constructed systematically, and used to obtain an appropriate pair of physical parameters that meet the desired specifications without trial and error. The L-shaped resonator makes the required values of the physical parameters possible to be found. Two dual-band filters operated at 2.4/5.2 GHz bands are fabricated and measured to verify the design concept. [ABSTRACT FROM AUTHOR]

An effective method is introduced to improve the stopband performance of microstrip parallel-coupled line bandpass filters. The proposed filter is constructed by adding several partially coupled resonators close to each trace in the conventional microstrip parallel-coupled line bandpass filter. The lengths of the coupled section and the stub section in each partially coupled resonator are selected such that the desired transmission zero is obtained. Proper selection of the number and the frequency of each transmission zero eventually makes it possible to suppress the unwanted spurious responses. In order to demonstrate the characteristics of the proposed filter, a third-order bandpass filter, which is centred at the operating frequency of 1 GHz with 10% fractional bandwidth, is designed, tuned, fabricated and tested. Measurement and simulation results show that the proposed prototype has a broad upper stopband performance, whereas it keeps the desired passband loss and shape almost equal to that of the conventional ones. [ABSTRACT FROM AUTHOR]

This study presents a novel approach for designing broadband single layer printed log-periodic dipole array (PLPDA) antenna fed by substrate integrated waveguide (SIW). The PLPDA antenna has the merits of wide bandwidth, low profile and light weight, which should be fed by the balanced line. The balanced line, created by the geometric features of the SIW, provides a balun with a considerably wide bandwidth with low profile, broad dominant mode bandwidth, low insertion loss and so on. Prototype of the proposed substrate integrated printed log-periodic dipole array (SIPLPDA) antenna and 1×4 antenna array at Ka band are designed and fabricated; the measured data are in good agreement with the simulated results. [ABSTRACT FROM AUTHOR]

In this study, a novel compact microstrip antenna with an ultra wide bandwidth is presented. The proposed antenna is a U-shaped square patch combined with two parasitic tuning stubs which is fed by a coplanar waveguide (CPW). The total size of the fabricated antenna is 24×28×0.787 mm3. The dimensional parameters for the antenna are introduced and their effects on the frequency characteristic have been investigated through a parametric study. Simulated and experimental results indicate that the antenna achieved an ultra wideband impedance bandwidth (S11 < -10 dB) as high as 129%. The radiation patterns of the antenna are measured and presented. The simulated results show good agreement with the measured results. The measured gains range from 1.6 to 5.3 dBi against frequency. These characteristics make the antenna suitable for UWB applications. [ABSTRACT FROM AUTHOR]

An attractive gyromagnetic resonator for the design of communication circulators is one for which the shape of the centre conductor between the top and bottom ferrite disks and ground plates incorporates a triplet of short metal strips or U.E.'s at the junction of a circular one. The complex gyrator circuit of one such geometry has recently been experimentally characterised in the literature. The introduction of U.E.'s in the resonator circuit provides a means of decoupling the coupling angle at the terminals of the circular plate from any external networks and a means of adjusting the susceptance slope parameter of the complex gyrator circuit of the junction. The study includes the practical design of one device at 2.0 GHz with a 23 dB return loss over a 30% bandwidth. [ABSTRACT FROM AUTHOR]

A novel ultrawideband (UWB) antenna referred to as the inverted-hat antenna (IHA) is described. Specifically, the paper provides a systematic approach to generate a frequency-scaled IHA structure subject to aperture width and height constraints. An experimental verification is also given. The proposed compact wideband antenna exhibits frequency-independent behavior by introducing a moderate number of appropriately scaled elliptical segments and by controlling the outer surface growth profile. A modified seven-ellipse IHA is demonstrated in this paper to provide a 10:1 impedance bandwidth with satisfactory radiation properties. The simulation and measurement results are in reasonably good agreement. [ABSTRACT FROM AUTHOR]

An output-threshold multiple-relay-selection (OT-MRS) scheme for dual-hop multibranch cooperative wireless networks is proposed. In this scheme, the first Lc (nonordered) relays are sequentially selected out of L relays such that the SNR of the maximal ratio combined Lc relayed paths and the direct path exceeds a preset threshold. Analytical results for the performance bounds are derived. The numerical results verify the analyses and show that OT-MRS outperforms optimal single-relay selection and generalized-selection-combining-based multiple relay-selection for low to moderately high SNRs. The proposed scheme provides more flexibility in utilizing bandwidth and spatial diversity in cooperative wireless networks. [ABSTRACT FROM AUTHOR]

The combination of digital media, personal computing, and global networking is creating a radical shift in the telecom industry. However, the transport backbone, which was built on 10G wavelengths, is nearing capacity and is driving the need for upgrades to 40G and 100G. 100G Ethernet and OTU4 bring new fundamental concepts, which require new training and new testing. 100G Ethernet and OTU4 equipment is currently in development or in trial, and the next phase is to deploy this equipment in the field. This article is mostly based on the work done by IEEE P802.3ba and ITU-T Study Group 15 to provide an overview of how 100G Ethernet and OTU4 are different from previous technologies, and includes guidance on which tests need to be performed with these emerging technologies. 112G line side testing is also briefly discussed. [ABSTRACT FROM AUTHOR]

Abstract: We propose “ICDC – InterContinental Disk Copy”, a data sharing facility between distant places. ICDC aims to transfer huge amount of data files easily on Long Fat-pipe Networks with some background traffic. ICDC consists of commodity PCs and Solid State Drives and we apply Inter Packet Gap tuning technique to it. Using “ICDC-1Gbps model”, we transferred data between Tokyo and Cadarache via New York. We attained about 860Mbps, i.e., 86% usage of the network bottleneck bandwidth. [ABSTRACT FROM AUTHOR]

Abstract: For the fast feedback plasma controllers, ITER''s Control, Data Access and Communication system (CODAC) will need to provide a mechanism for hard real-time communication between its distributed nodes. In particular, the ITER CODAC team identified four types of high-performance communication applications. Synchronous Databus Network (SDN) is to provide an ability to distribute parameters of plasma (estimated to about 5000 double-valued signals) across the system to allow for 1ms control cycles. Event Distribution Network (EDN) and Time Communication Network (TCN) are to allow synchronization of node I/O operations to 10ns. Finally, the Audio–Video Network (AVN) is to provide sufficient bandwidth for streaming of surveillance and diagnostics video at a high resolution (1024×1024) and frame rate (30Hz). In this article, we present some combinations of common-off-the-shelf (COTS) technologies that allow the above requirements to be met. Also, we present the performances achieved in a practical (though small scale) technology demonstrator, which involved a real-time Linux operating running on National Instruments’ PXI platform, UDP communication implemented directly atop the Ethernet network adapter, CISCO switches, Micro Research Finland''s timing and event solution, and GigE audio–video streaming. [Copyright &y& Elsevier]

In fixed worldwide interoperability for microwave access (WiMAX), radio and network planning can be optimised by tuning a cost/revenue function which incorporates the cost of building and maintaining the infrastructure and the effect of the available resources on revenues. Supported throughput typically decreases with larger cells because of the implied greater average distance of users from the base station, although the use of sub-channelisation can keep throughput steady up to a larger radius. Sectorisation can improve the throughput of the cell by facilitating the use of higher order modulation and coding schemes; besides, sectorisation equipment is more expensive, and there is the need for three times more spectrum bandwidth, increasing costs while increasing system capacity by a factor of 3. On a multi-cell level, system capacity is determined by the chosen frequency reuse pattern, K. In this study, under the assumption of a revenue per Mbyte of information transfer somewhere between 0.0025 € and 0.010 €, the choice of K=3 or 4 with sectorial cells is preferable to the use of omnidirectional cells with K=7. This study also concludes that a cell radius in the range 1000–1500 m is preferable, corresponding to profit in percentage terms of near the achievable maximum, while keeping costs acceptable. [ABSTRACT FROM AUTHOR]

Increasing the number of cores in a multi-core processor can only be achieved by reducing the resources available in each core, and hence sacrificing the per-core performance. Furthermore, having a large number of homogeneous cores may not be effective for all the applications. For instance, threads with high instruction level parallelism will under-perform considerably in the resource-constrained cores. In this paper, we propose a core architecture that can be adapted to improve a single thread’s performance or to execute multiple threads. In particular, we integrate Reconfigurable Hardware Unit (RHU) in the resource-constrained cores of a many-core processor. The RHU can be reconfigured to execute the frequently encountered instructions from a thread in order to increase the core’s overall execution bandwidth, thus improving its performance. On the other hand, if the core’s resources are sufficient for a thread, then the RHU can be configured to executed instructions from a different thread to increase the thread level parallelism. The RHU has low area overhead, and hence has minimal impact on scalability of the number of cores. To further limit the area overhead of this mechanism, generation of the reconfiguration bits for the RHUs of multiple cores is delegated to a single core. In this paper, we present the results for using the RHU to improve a single thread’s performance. Our experiments show that the proposed architecture improves the per-core performance by an average of about 23% across a wide range of applications. [ABSTRACT FROM AUTHOR]

The article discusses the effectiveness of reflectarray antenna on lumped components. It focuses on the characterization of loss and bandwidth performance of a reflectarray antenna. It describes the device as a combination of an array of microstrip patch elements and flat reflector printed on a thin dielectric substrate.

A cavity-backed bow-tie dipole antenna is presented as base station antenna for wide band American and European cellular communication systems (1.7–2.17 GHz). A beam widening of the horizontal plane is achieved by the cavity aperture reduction and the inclusion of a metallic support between the cavity floor and the antenna reflector plane. The structure design procedure is exposed, and a reasonable agreement between simulations and measurements is obtained. Single antenna and medium gain array prototypes have been manufactured and tested. A 35% reflection bandwidth and an 85° to 95° sector coverage is achieved in the desired operation band. [ABSTRACT FROM AUTHOR]

In many diagnostics and imaging applications intensity only measurements of the diffracted field are available. Hence, it is of interest to develop procedures able to solve the underlying inverse scattering problem under these conditions. In this paper, we introduce an approach in which the geometrical and electromagnetic properties of unknown complex targets are reconstructed from the squared amplitudes of the diffracted fields. The approach relies on some preliminary considerations on the spatial bandwidth of the diffracted intensities which allow one to fix rules to effectively measure the data and on an alternative formulation of the electromagnetic scattering that lowers the 'degree of non-linearity' of the relationship among the electric features of the targets and the fields. The proposed procedure is tested against benchmark experimental data in the microwave frequency range and the obtained results confirm the possibility of achieving faithful quantitative images of unknown targets from phaseless data without making approximations in the inverse scattering problem. [ABSTRACT FROM AUTHOR]

Efficient spectrum-sharing mechanisms are crucial to alleviate the bandwidth limitation in wireless networks. In this paper, we consider the following question: can free spectrum be shared efficiently? We study this problem in the context of 802.11 or WiFi networks. Each access point (AP) in a WiFi network must be assigned a channel for it to service users. There are only finitely many possible channels that can be assigned. Moreover, neighboring access points must use different channels so as to avoid interference. Currently these channels are assigned by administrators who carefully consider channel conflicts and network loads. Channel conflicts among APs operated by different entities are currently resolved in an ad hoc manner (i.e., not in a coordinated way) or not resolved at all. We view the channel assignment problem as a game, where the players are the service providers and APs are acquired sequentially. We consider the price of anarchy of this game, which is the ratio between the total coverage of the APs in the worst Nash equilibrium of the game and what the total coverage of the APs would be if the channel assignment were done optimally by a central authority. We provide bounds on the price of anarchy depending on assumptions on the underlying network and the type of bargaining allowed between service providers. The key tool in the analysis is the identification of the Nash equilibria with the solutions to a maximal coloring problem in an appropriate graph. We relate the price of anarchy of these games to the approximation factor of local optimization algorithms for the maximum k-colorable subgraph problem. We also study the speed of convergence in these games. [ABSTRACT FROM AUTHOR]

This study constructs stepped-impedance-stub lines for a dual-band branch-line coupler design with improved design flexibility. The proposed structure demonstrates dual-band performance and a compact size due to additional stepped-impedance stubs to branches. The developed synthesis method has two degrees of freedom which can be exploited to miniaturize circuit size and/or replace impractical impedances with more realizable ones. Observations also show the advantage of a wide-range realizable frequency ratio of dual bands. The current work fabricates three experimental dual-band branch-line couplers, including a two-section coupler, and achieves a size reduction up to 21.7%, compared with conventional structures. The measured results validate good dual-band performance at 2.4/5.8 GHz with enhanced bandwidths up to 21% and 12%, respectively. This research also successfully applies the proposed circuit to synthesize a dual-band rat-race coupler. [ABSTRACT FROM AUTHOR]

This paper presents a detailed study of the IF properties of phonon-cooled NbN hot electron bolometer (HEB) terahertz mixers and receivers, performed over the widest intermediate frequency range reported so far. First, a broadband technique is used to obtain the IF small-signal output impedance of HEB mixers using network analyzer measurements. The impedance is measured over an IF range of 300 kHz to 8.5 GHz under the presence of dc bias and local oscillator (LO) illumination. The LO frequencies (fLO) used in this investigation range from 694 GHz to nearly 2 THz, covering frequencies below and above the superconducting bandgap frequency of the NbN film for the first time. The impedance (real and imaginary parts) can be fitted to the Standard model for HEB devices over almost the entire range of frequencies measured. The impedance data are then used in conjunction with a computer-aided design model for the monolithic micorwave integrated circuit IF amplifier to design and analyze the performance of integrated receivers (mixer/IF amplifier combinations). The measured and predicted variations of the receiver noise, mixer gain, and mixer output noise with IF are in good agreement. A record IF noise bandwidth of 8 GHz (obtained for fLO = 694 GHz) is demonstrated for a receiver designed using the technique described in this paper. [ABSTRACT FROM AUTHOR]

This letter presents a hybrid error control and artifact detection (HECAD) mechanism which can be used to enhance the error resilient capabilities of the standard H.264/advanced video coding (AVC) codec. The proposed solution first exploits the residual source redundancy to recover the most likelihood H.264/AVC bitstream. If error recovery is unsuccessful, the residual corrupted slices are then passed through a pixel-level artifact detection mechanism to detect the visually impaired macroblocks to be concealed. The proposed HECAD algorithm achieves overall peak signal-to-noise ratio gains between 0.4 dB and 4.5 dB relative to the standard with no additional bandwidth requirement. The cost of this solution translates in a marginal increase in the complexity of the decoder. In addition, this method can be applied in conjunction with other error resilient strategies and scales well with different encoding configurations. [ABSTRACT FROM AUTHOR]

A novel miniature balanced mobile handset antenna is presented in this study, which covers digital communication system (DCS) (1710–1880 MHz), personal communication system (PCS) (1850–1990 MHz), universal mobile telecommunications system (UMTS) (1920–2170 MHz) and wireless local area network (WLAN) (2400–2484 MHz) frequency bands. The antenna is a built-in planar dipole with folded structure and with the addition of a dual arm on each half of the dipole. The performance of the antenna is analysed and optimised under certain design constraints. The stability performance of the proposed antenna against proximity effects is evaluated. The effects of the phone user's hand on the return loss and radiation patterns have been characterised by simulation with a simple hand model. A prototype of the proposed antenna is fabricated and tested. A wide bandwidth planar balun is used to feed the wideband balanced antenna from an unbalanced source. The calculated and measured results show good agreement and confirm good wideband characteristics with multiband operation. The specific absorption rate (SAR) performance of the antenna is also studied experimentally by measuring near field exposure. The measured results have shown low induced current in the ground plane and thus confirm minimisation of performance variations and SAR. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a 2 x 4 T-type folded substrate integrated waveguide (TFSIW) slot array antenna. Each linear array is fed through a microstrip line and a TFSIW Y-junction. The size of the proposed antenna is reduced by 40% and the impedance bandwidth (-- 10 dB) is 5.6%. The dimensions of the structure are presented and the proposed array antenna is fabricated in a two-layer substrate. Simulation and measurement of the proposed antenna are compared. [ABSTRACT FROM AUTHOR]

A four-layer transmitarray operating at 30 GHz is designed using a dual-resonant double square ring as the unit cell element. The two resonances of the double ring are used to increase the per-layer phase variation while maintaining a wide transmission magnitude bandwidth of the unit cell. The design procedure for both the single-layer unit cell and the cascaded connection of four layers is described and it leads to a 50% increase in the -1 dB gain bandwidth over that of previous transmitarrays. Results of a 7.5% -1 dB gain bandwidth and 47% radiation efficiency are reported. [ABSTRACT FROM AUTHOR]

In order to reduce the thickness of a steerable beam square loop antenna, the effects of combining it with various periodic high impedance surfaces (HISs) are investigated. When a via-less HIS is used, the radiation pattern has high side lobes, which are shown to be due to surface waves propagating in the HIS lattice. Using a HIS with vias between the plates and ground removes the surface waves, but the beam is distorted due to strong coupling between the HIS's vias and the antenna element. Consequently a hybrid HIS is designed. This uses a via-less lattice beneath the loop, with vias at the edge of the HIS to suppress surface wave propagation. Consequently, a square loop antenna with four feeds on a hybrid HIS substrate is proposed for beam steering applications. This antenna has a low-profile with a total thickness of 4.69 mm for a test frequency band of 4.3 GHz to 5.0 GHz. It exhibits a gain of 8.65 dB at the test frequency (4.7 GHz). Compared to the earlier reported steerable square loop antenna, the new antenna achieves a 61% reduction in substrate thickness, a bandwidth enhancement by 150 MHz and an increase in gain by 1.95 dB. [ABSTRACT FROM AUTHOR]

The design is described of a planar dual-arm equiangular spiral antenna incorporated with chip resistors inside the substrate. The chip resistors were applied to this equiangular spiral antenna to achieve 9:1 impedance bandwidth (2 to 18 GHz) with an extremely low profile structure. The simulated and measured magnitude of the reflection coefficient (S11) gain, and measured radiation patterns are presented. [ABSTRACT FROM AUTHOR]

The digital divide is conventionally measured in terms of information and communication technology (ICT) equipment diffusion, which comes down to counting the number of computers or phones, among other devices. This article fine-tunes these approximations by estimating the amount of digital information that is stored, communicated, and computed by these devices. The installed stock of ICT equipment in the consumer segment is multiplied with its corresponding technological performance, resulting in the “installed technological capacity” for storage (in bits), bandwidth (in bits per second), and computational power (in computations per second). This leads to new insights. Despite the rapidly decreasing digital equipment divide, there is an increasing gap in terms of information-processing capacity. It is shown that in 1996 the average inhabitant of the industrialized countries of the Organization for Economic Cooperation and Development (OECD) had a capacity of 49 kibps more than its counterpart from Latin America and the Caribbean. Ten years later, this gap widened to 577 kibps per inhabitant. This innovative approach toward the quantification of the digital divide leads to numerous new challenges for the research agenda. [ABSTRACT FROM AUTHOR]

In this article, a compact and wideband planar inverted-F antenna is introduced.The bandwidths for s11 < -10 dB are up to 790 MHz (a fractional bandwidth of 38.2%) with bending a part of metal radiator down and notching a rectangle slot. Measured results show that the designed antenna can meet the requirements of the DCS/PCS/UMTS/WLAN communication system. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1097–1100, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25138 [ABSTRACT FROM AUTHOR]

FAST TCP is a promising new transfer control protocol developed for high-speed long-latency networks, whose performance has previously only been studied for data traffic sent in one direction. In this study, the authors propose a mathematical model for bi-directional connections using the FAST TCP protocol, which captures the asymmetric bandwidth dynamics in duplex dumbbell networks, prevalent in ADSL, satellite and other high-speed technologies. Using this model, the authors obtain a powerful result that the queue delays observed by opposite FAST TCP flows only have a time difference in a dumbbell network. Furthermore, the authors establish the conditions under which the bi-directional FAST TCP flows achieve stability, and on this basis the throughput rates of the forward and backward flows at steady-state are deduced. The authors find that, in the case of bandwidth asymmetry and one flow in each direction, in equilibrium the throughput of the bi-directional FAST TCP flows can only achieve the smaller link capacity of the duplex links, and the link with larger capacity is not fully occupied. These theoretical findings are corroborated by NS2 simulations. [ABSTRACT FROM AUTHOR]

This paper introduces two alternative algorithms for efficient data transfer in the Grid environment. For data transfer from a source node to the destination node, the algorithms can construct multiple dynamic paths by selecting some other nodes as data relays. The bandwidth available in different paths can be aggregated thus to significantly speed up the data transfer process. The proposed algorithms differ from each other in whether the global networking information should be considered. Experimental results indicate that both algorithms can provide efficient data transfer under various circumstances. [ABSTRACT FROM AUTHOR]

Network coding has gained significant attention in recent years as a means to improve throughput, especially in multicast scenarios. These capacity gains are achieved by combining packets algebraically at various points in the network, thereby alleviating local congestion at the nodes. The benefits of network coding are greatest when the network is heavily utilized or, equivalently, when the sources are saturated so that there is data to send at every scheduling opportunity. Yet, when a network supports delay-sensitive applications, traffic is often bursty and congestion becomes undesirable. The lighter loads typical of real-time traffic with variable sources tend to reduce the returns of network coding. This work seeks to identify the potential benefits of network coding in the context of delay-sensitive applications. As a secondary objective, this paper also studies the cost of establishing network coding in wireless environments. For a network topology to be suitable for coding, links need to possess a proper structure. The cost of establishing this structure may require excessive radio resources in terms of bandwidth and transmit power. Bursty traffic together with structural cost tend to decrease the potential benefits of network coding. This paper describes how, for real-time applications over wireless networks, there exist network topologies for which it may be best not to establish a network structure tailored to network coding. [ABSTRACT FROM AUTHOR]

Totally asynchronous code-division multiple-access (CDMA) systems are addressed. In Part I, the fundamental limits of asynchronous CDMA systems are analyzed in terms of spectral efficiency and SINR at the output of the optimum linear detector. The focus of Part II is the design of low-complexity implementations of linear multiuser detectors in systems with many users that admit a multistage representation, e.g., reduced rank multistage Wiener filters, polynomial expansion detectors, weighted linear parallel interference cancellers. The effects of excess bandwidth, chip-pulse shaping, and time delay distribution on CDMA with suboptimum linear receiver structures are investigated. Recursive expressions for universal weight design are given. The performance in terms of SINR is derived in the large-system limit and the performance improvement over synchronous systems is quantified. The considerations distinguish between two ways of forming discrete-time statistics: chip-matched filtering and oversampling. [ABSTRACT FROM AUTHOR]

A compact differential dual-frequency antenna with stacked configuration is described. Compared with the conventional stacked dual-frequency antenna, the radiating element with a half guided wavelength is distributed on two layers and connected through via holes, thus the dimension of the antenna is reduced effectively. In order to improve the bandwidth at the first resonant frequency (f1), a reflecting board is introduced and connected with the ground plane through three via holes. As a result, a new resonant frequency closing to f1 can be excited and the bandwidth at f1 is enhanced. Both differential antennas with and without the reflecting board are fabricated and measured. The realized antennas have a compact size of 15 mm × 15 mm, which equals to 0.23λ1 × 0.23λ1 (λ1 , the guided wavelength at f1). Experimental results show that the proposed antenna can operate at 2.4 GHz and 5.2 GHz bands. Good agreement between the simulated and measured results is obtained. [ABSTRACT FROM AUTHOR]

Active rectifiers using pulsewidth-modulation voltage-source converters are popular choices for adjustable-speed drives to provide high input power quality. However, input current harmonics are often generated as a result of input voltage source disturbances. Since the frequencies of the fifth-,seventh-, and higher-order harmonics can easily exceed the current controller bandwidth in high-power applications, the elimination of these harmonic disturbances imposes difficult control challenges. Cost-effective observer-based harmonic estimation and mitigation methods are introduced in this paper that compensate delay effects caused by the digital signal processing. These delays can significantly limit the current controller bandwidth if not compensated. Analytical, simulation, and experimental results are developed to illustrate the effectiveness of the new harmonic estimation and control techniques. [ABSTRACT FROM AUTHOR]

A technique to develop all-fiber devices based on the customization of Brillouin gain spectrum is proposed in this article. It is based on the proper concatenation and elongation of optical fibers. To check experimentally the proposed technique, an optical device with a “like W” stimulated Brillouin scattering shape was implemented. Our experiment shows a 3-dB bandwidth of 219 MHz with two reject bands placed at 10.7855 and 10.876 GHz, respectively, from the pump wavelength. Optical devices such as Brillouin amplifiers or Brillouin filters can be developed using the proposed technique. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:787–790, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25033 [ABSTRACT FROM AUTHOR]

This article presents a new method to realize sectoral antennas for base station by incorporating metallic partially reflecting surface (M-PRS).The main idea consists in inserting simple radiating elements, as patches, inside a Fabry-Perot cavity resonator. This consists of a ground plane, where the feeding system rests covered by a rectangular M-PRS. A patch array is used as a feeding structure to enhance directivity and radiation bandwidth. A rectangular M-PRS antenna for the uplink UMTS frequency band [1.92–1.98 GHz] working in vertical polarization is designed, and its performances are disclosed. Finally, a prototype is realized and the experimental measurements are compared to the simulated ones. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:990–994, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25044 [ABSTRACT FROM AUTHOR]

We proposed a compact microstrip band-pass filter with wide stopband in this article.Microstrip gap and interdigital capacitor combine with stub inductors shorted to the ground plane by via were used to take advantage of different aspects of left-handed behavior to achieve compact size and wide stopband characteristics. The designed filter has a compact structure with overall dimensions of 20 mm by 17.05 mm, a 3-dB bandwidth of 25.2% at 1.19 GHz, insertion loss of -3 dB, attenuation greater that 60 dB in the lower stopband and greater that 27 dB up to 5.2 times the centre frequency. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:830–833, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25061 [ABSTRACT FROM AUTHOR]

Wave concept iterative procedure (WCIP) is used to analyze dual-band and enhanced band frequency selective surfaces (FSS). In the metallic U-shaped simple FSS, a fine-tune of the two rejected bands is insured by varying independently the length of the two parallel U-shaped FSS strips. The dual band response can also be obtained from the two-level rectangular conducting patches FSS. An enhanced rejecting bandwidth is observed for FSS with two square ring printed on each substrate side. The WCIP results are successfully compared with measurements and HFSS results. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:836–839, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25073 [ABSTRACT FROM AUTHOR]

In this article, novel metamaterial transmission lines exhibiting right-handed wave propagation at low frequencies and left-handed wave transmission at high frequencies are presented. The unconventional dispersion characteristics of these composite right/left-handed transmission lines is obtained by parallel connecting left-handed and right-handed unit cells, both implemented by using complementary split-ring resonators. Thanks to the diplexer action of the structure, either the right-handed (tuned at the lower frequency band) or the left-handed (tuned at the upper frequency band) unit cell transmits the injected power, thus achieving the unconventional dispersion of the structure. It is also shown in this article that these artificial lines are of interest for the design of certain microwave components exhibiting dual-band characteristics. Examples are provided including design and characterization. The measurements are indicative of good device performance at the two operating bands and wide bandwidths. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:904–909, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25077 [ABSTRACT FROM AUTHOR]

A band-rejection type RF switch, which has very high off-state isolation, low on-state insertion loss, and adjustable bandwidth, is proposed using a dual-mode ring resonator and two PIN diodes. To enable sharp band stop and dual-mode transmission, the ring resonator is directly fed using nonorthogonal feeding. Two PIN diodes are mounted in shunt after a quarter-wavelength transmission line from each feeding point, to turn the switch on and off and to reduce the size of the ring resonator. To estimate the practicable transmission characteristics of the proposed switch in relation to the angle of feeding and the wire-bonded PIN diodes, a lossy transmission-line equivalent circuit model is proposed, and even–odd mode analysis is carried out. The calculated frequency response shows good agreement with the measurement. The fabricated switch exhibits off-state isolation of 43.08 dB, and on-state insertion loss of 0.74 dB, within the range of 2.298–2.401 GHz. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:947–950, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25080 [ABSTRACT FROM AUTHOR]

A reconfigurable printed log periodic dipole array (LPDA) is presented.It is shown that several frequency bands across a wide frequency range can be selected by switching the printed dipoles of the LPDA. In comparison with the reconfigurable printed dipole antenna introduced by the present authors before, the significant advantage of the reconfigurable LPDA lies in its flexibility in selecting the frequency bands with different bandwidths. The measurement results show that the reconfigurable LPDA operates over a frequency range of 3:1. The characteristics of the wideband reconfigurable LPDA is suitable for frequency switching in FCC ultra wideband allocation. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:861–864, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25040 [ABSTRACT FROM AUTHOR]