Network coordinates (NC) system is an efficient mechanism to predict Internet distance with scalable measurements. In this paper, we focus on the node churn problem the continuous process of nodes arrival and departure in distributed applications. Studies on Vivaldi, a representative distributed NC system, shows that under node churn the prediction accuracy of the NC system will be seriously im...

In this paper, the conformal finite-difference time-domain (CFDTD) method using PSO optimization is applied to design a compact directive balanced antipodal Vivaldi antenna for ultrawideband (UWB) applications. This paper demonstrates miniaturized antipodal Vivaldi antenna (32 × 35 × 1.6mm3), having low-cross polarization levels and reasonable gain from 3.1 to 10.6 GHz. The antenna peak gain is...

Phased-array feeds are possibly the best option for the 240 to 1200 MHz band on VLA antennas due to their wide bandwidth and relatively small size. One of the greatest assets of these antennas is the ability to produce a shaped beam by appropriately phasing the elements allowing in some cases nearly uniform aperture illumination with minimal ground-directed spillover. The beam-forming propertie...

In this letter, a tapered slot ultrawide band (UWB) Vivaldi antenna with enhanced gain having band notch characteristics in the WLAN/WiMAX band is presented. In this framework, a reference tapered slot Vivaldi antenna is first designed for UWB operation that is, 3.1–10.6 GHz using the standard procedure. The band-notch operation at 4.8 GHz is achieved with the help of especially designed comple...

In [2] it was conjectured that all integer sequences (ak)k∈Z satisfying 0 ≤ ak−1 + λak + ak+1 < 1 (k ∈ Z) for real λ with |λ| < 2 are periodic. This question arose in the study of shift radix systems. The conjecture is trivially true for λ = −1, 0, 1. A computer assisted proof for λ = 1− √ 5 2 was given by Lowenstein, Hatjispyros and Vivaldi [5], where also the solution for λ = 1+ √ 5 2 is ment...

Radar operation from the CReSIS Meridian UAV requires a broadband antenna array composed of lightweight, thin, end-fire antenna elements. Toward this goal four Vivaldi antenna designs were simulated, fabricated, and characterized. The final design, dubbed the CReSIS Aerial Vivaldi – Revision A (CAV-A) provides operation over a band extending from 162 MHz to 1.121 GHz. The CAV-A measures 40 cm l...

Network Coordinate System (NCS) is an efficient and scalable mechanism to predict latency between any two network hosts based on historical measurements. Most NCS models, such as metric space embedding based, like Vivaldi, and matrix factorization based, like DMF and Phoenix, use squared error measure in training which suffers from the erroneous records, i.e. the records with large noise. To ov...

Network coordinates (NC) system is an efficient mechanism for Internet distance prediction with scalable measurements. The intrinsical cause for the unsatisfactory accuracy of the simulation-based NC algorithms has been identified. Then Pharos, a fully decentralised and hierarchical scheme, is proposed to solve this problem. Pharos leverages multiple coordinate sets at different distance scales...

An ultra-wide-band (UWB), stripline-fed Vivaldi antenna is characterized both numerically and experimentally. Three-dimensional far-field measurements are conducted and accurate antenna gain and efficiency as well as gain variation versus frequency in the boresight direction are measured. Using two Vivaldi antennas, a free-space communication link is set up. The impulse response of the cascaded...

Singleand dual-polarized arrays of Vivaldi notch elements have been extensively analyzed by using efficient numerical analyses. From these analyses and from experimental studies, element designs and array configurations have been determined to provide more than two octaves of bandwidth while scanning to 45° from broadside in all directions. Parameter studies illustrating the effects of some key...